Download - No-tillage Seeding in Conservation AgricultureNo-tillage farming in Asia 213 Summary of No-tillage Drill and Planter Design – Small-scale Machines 225 15 Managing a No-tillage Seeding

2nd Edition

C. J. Baker, K. E. Saxton, W. R. Ritchie, W. C. T. Chamen,D. C. Reicosky, F. Ribeiro, S. E. Justice and P. R. Hobbs

No-tillage Seeding in Conservation Agriculture


Second Edition

This book is dedicated to the scientists and students whose work is reviewed, together withtheir long-suffering families. Such people were driven by a desire to make no-tillage as sus-tainable and risk-free as possible, and in the process to make food production itself sustain-able for the first time in history. The odds were great but the results have been significantand will have far-reaching consequences.

No-tillage Seeding in ConservationAgriculture

Second Edition

C.J. Baker, K.E. Saxton, W.R. Ritchie, W.C.T. Chamen,D.C. Reicosky, M.F.S. Ribeiro, S.E. Justice and P.R. Hobbs

Edited by

C.J. Baker and K.E. Saxton

Published byFood and Agriculture Organization of the United Nations

CABI is a trading name of CAB International

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Library of Congress Cataloging-in-Publication Data

No-tillage seeding in conservation agriculture/C.J. Baker . . . [et al.] edited byC.J. Baker and K.E. Saxton.-- 2nd ed.

p. cm.Rev. ed. of: No-tillage seeding/C.J. Baker. 1996.Includes bibliographical references and index.ISBN 1-84593-116-5 (alk. paper)1. No-tillage. I. Baker, C.J. (C. John) II. Saxton, Keith E., 1937- III. Baker, C.J.(C. John). No-tillage seeding. IV. Food and Agriculture Organization of theUnited Nations. V. Title.

S604.B36 2006631.5′31--dc22

2005035401

Published jointly by CAB International and FAO.Food and Agriculture Organization of the United Nations (FAO)Viale delle Terme di Caracalla, 00100 Rome, ItalyWebsite: www.fao.org

ISBN-10: 1-84593-116-5 (CABI)ISBN-13: 978-1-84593-116-2 (CABI)ISBN: 92-5-105389-8 (FAO)

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Contents

Contributors xi

Foreword to the Second Edition xiiShivaji Pandey and Theodor Friedrich

Preface xiii

1 The ‘What’ and ‘Why’ of No-tillage Farming 1C. John Baker and Keith E. Saxton

What is No-tillage? 3Why No-tillage? 5

Advantages 6Disadvantages 7

Summary of the 'What' and 'Why' of No-tillage 10

2 The Benefits of No-tillage 11Don C. Reicosky and Keith E. Saxton

Introduction 11Principles of Conservation Agriculture 12Crop Production Benefits 13

Increased organic matter 14Increased available soil water 15Reduced soil erosion 15Enhanced soil quality 16Improved nutrient cycles 17Reduced energy requirements 17

Carbon Emissions and Sequestration 19Summary of the Benefits of No-tillage 20

v

3 The Nature of Risk in No-tillage 21C. John Baker, W. (Bill) R. Ritchie and Keith E. Saxton

What is the Nature of Risk in No-tillage? 21Biological risks 21Physical risks 24Chemical risks 27Economic risk 29Conclusions 32

Summary of the Nature of Risk in No-tillage 33

4 Seeding Openers and Slot Shape 34C. John Baker

Vertical Slots 35V-shaped slots 35Slanted V-shaped slots 40U-shaped slots 40Vibrating openers 50

Horizontal Slots 51Inverted T-shaped slots 51

Punch Planting 56Surface Broadcasting 57Summary of Seeding Openers and Slot Shape 58

5 The Role of Slot Cover 60C. John Baker

The Role of Soil Humidity 63Methods of Covering Seed Slots 65

Squeezing 67Rolling 67Pressing 68Scuffing 69Deflecting 69Tilling 71Folding 71

Summary of the Role of Slot Cover 72

6 Drilling into Dry Soils 74C. John Baker

How Soils Lose Moisture 74The Role of Vapour-phase Soil Water 75Germination 76Subsurface Survival 77Seedling Emergence 80The Effects of Pressing 83Field Experience 84Summary of Drilling into Dry Soils 84

vi Contents

7 Drilling into Wet Soils 85C. John Baker

Drilling Wet Soils 85Vertical double (or triple) disc openers (V-shaped slots) 86Slanted double (or triple) disc openers (slanted V-shaped slots) 86Vertical angled flat (or dished) disc openers (U-shaped slots) 86Hoe-type openers (U-shaped slots) 86Power till openers (U-shaped slots) 87Winged openers (inverted-T-shaped slots) 87

Drilled Dry Soils that Become Wet 89Opener performance 93

Summary of Drilling into Wet Soils 98

8 Seed Depth, Placement and Metering 99C. John Baker and Keith E. Saxton

Seeding Depth and Seedling Emergence 100Maintaining Consistent Opener Depth 101

Surface following 101Depth-gauging devices 101The value of semi-pneumatic tyres 103Walking beams 104Disc seed flick 105Soil disturbance 105Residue hairpinning or tucking 105Opener bounce 105Seed bounce 106Slot closure 106

Drill and Planter Functions 106Downforce mechanisms 106Seed metering and delivery 113

Summary of Seed Depth, Placement and Metering 116

9 Fertilizer Placement 118C. John Baker

Toxicity 119Banded fertilizer 120Vertical banding versus horizontal banding 121Retention of gaseous fertilizers 126

Crop Yield 126Banding options 128How close should banded fertilizer be to the seed? 131

Conclusion 132Summary of Fertilizer Placement 133

10 Residue Handling 134C. John Baker, Fatima Ribeiro and Keith E. Saxton

The Forms that Residues can Take 134Short root-anchored standing vegetation 134Tall root-anchored standing vegetation 136Lying straw or stover 136

Contents vii

Management of Residues on a Field Scale 138Large field-scale no-tillage 138Small-scale no-tillage 140

Management of Residues by Openers, Drills and Planters: Micro-management ofCrop Residues 145

Opener handling of residues 145Row cleaners 147Chopping of straw into short lengths 147Random cutting of straw in place 149Wet versus dry straw 155The case for and against scrapers 156Clearance between openers 156

Summary of Residue Handling 158

11 Comparing Surface Disturbance and Low-disturbance Disc Openers 159C. John Baker

Minimum versus Maximum Slot Disturbance – How MuchDisturbance is Too Much? 159

Disturbance effects 160Disc opener feature comparisons 163

Summary of Comparing Surface Disturbance andLow-disturbance Disc Openers 163

12 No-tillage for Forage Production 168C. John Baker and W. (Bill) R. Ritchie

Forage Species 168Integrated Systems 169No-tillage of Pasture Species 171

Pasture renewal 171Pasture renovation 175Seed metering 183

Summary of No-tillage for Forage Production 183

13 No-tillage Drill and Planter Design – Large-scale Machines 185C. John Baker

Operating Width 185Surface Smoothing 186Power Requirements 189Weight and Opener Forces 190Re-establishing Downforce 194Wheel and Towing Configurations 195

End wheels 196Fore-and-aft wheels 196

Matching Tractors to Drills and Planters 198Product Storage and Metering 200Summary of No-tillage Drill and Planter Design – Large-scale Machines 202

viii Contents

14 No-tillage Drill and Planter Design – Small-scale Machines 204Fatima Ribeiro, Scott E. Justice, Peter R. Hobbs and C. John Baker

Characteristics 204Range of Equipment 204

Hand-jab planters (dibblers) 205Row-type planters (animal-drawn and tractor-mounted) 206Animal-drawn planters 212Planters adapted from power tillers 212Tractor-drawn planters 213No-tillage farming in Asia 213

Summary of No-tillage Drill and Planter Design – Small-scale Machines 225

15 Managing a No-tillage Seeding System 226W. (Bill) R. Ritchie and C. John Baker

Site Selection and Preparation 226Weed Competition 227Pest and Disease Control 228Managing Soil Fertility 228Seeding Rates and Seed Quality 228Operator Skills 229Post-seeding Management 230Planning – the Ultimate Management Tool 230Cost Comparisons 234Summary of Managing a No-tillage Seeding System 235

16 Controlled-traffic Farming as a Complementary Practice to No-tillage 236W.C. Tim Chamen

What is Controlled-traffic Farming? 236Why Adopt a CTF Regime within a No-tillage Farming System? 236

The benefits of CTF 236The effects of CTF on soil conditions 237

Making CTF Happen 245Basic principles 245Forward planning and machinery matching 245The width-matching process 245Field layout and system management 248Orientation of permanent wheel ways 249Wheel-way management 249Guidance systems 251

Economics 251Transition costs and timescale for change to CTF 252Fixed and variable costs 253Change in output 253In-field management costs 254Summary of costs and returns 254

Summary of Controlled-traffic Farming as a ComplementaryPractice to No-tillage 254

Contents ix

17 Reduced Environmental Emissions and Carbon Sequestration 257Don C. Reicosky and Keith E. Saxton

Introduction 257Tillage-induced Carbon Dioxide Emissions 257

Emission measurements 258Tillage and residue effects 258Strip tillage and no-tillage effects on CO2 loss 260

Carbon Sequestration Using No-tillage 262Nitrogen Emissions 263Policy of Carbon Credits 265Summary of Reduced Environmental Emissions andCarbon Sequestration 267

18 Some Economic Comparisons 268C. John Baker

New Zealand Comparisons 269Assumptions 269General conclusions 274

European Comparisons 275Summary of Some Economic Comparisons 276

19 Procedures for Development and Technology Transfer 277C. John Baker

Plant Responses to No-tillage Openers in Controlled Conditions 278The micro-environment within and surrounding no-tillage seed slots 281

Soil Compaction and Disturbance by No-tillage Openers 284Soil strength 284Instantaneous soil pressure (stress) 286Instantaneous and permanent soil displacement 287Soil bulk density 287Smearing and compaction 287

Locating Seeds in the Soil 287Seed spacing 287Seed depth 287Lateral positioning of seeds relative to the centre line of the slot 288

Seed Travel within No-tillage Openers 289Drag on a Disc Opener 291Accelerated Wear Tests of No-tillage Openers 292Effects of Fertilizer Banding in the Slot 292Prototype Drills and Management Strategies 294

Single-row test drills 294Simultaneous field testing of several opener designs 295Plot-sized field drills and planters 297Field-scale prototype drills and a drilling service for farmers 297

Summary of Drill Development and Technology Transfer 299

References 301

Index 317

x Contents

Contributors

C.J. Baker, Centre for International No-tillage Research and Engineering (CINTRE),Feilding, New Zealand

W.C.T. Chamen, 4Ceasons Agriculture and Environment, Maulden, Bedfordshire, UKP.R. Hobbs, Department of Crops and Soil Science, Cornell University, Ithaca, New York,

USAS.E. Justice, National Agriculture and Environment Forum (NAEF), Kathmandu, NepalD.C. Reicosky, United States Department of Agriculture, Agricultural Research Service,

Morris, Minnesota, USAM.F.S. Ribeiro, Instituto Agronômico do Paraná (IAPAR), Ponta Grossa, Parana, BrazilW.R. Ritchie, Centre for International No-tillage Research and Engineering (CINTRE),

Feilding, New ZealandK.E. Saxton, Retired, formerly United States Department of Agriculture, Agricultural

Research Service, Pullman, Washington, USA

xi

xii

Foreword to the Second Edition

The Food and Agriculture Organization (FAO) has a history of supporting the developmentand extension of conservation agriculture cropping systems. No-tillage seeding is one ofthe key operations of conservation agriculture; no-till seeding, together with the principlesof cover crops and crop rotation, constitute conservation agriculture. The availability ofsuitable technology and equipment is a necessary precondition for making conservationagriculture work. Special equipment is required not only for direct seeding and planting,but also for the management of crop residues and cover crops.

The earlier book, entitled No-tillage Seeding: Science and Practice, by Baker, Saxtonand Ritchie, was, at the time of its publication, one of the most comprehensive publicationscovering the engineering aspects of no-tillage seeding as well as the agronomic and envi-ronmental background for no-tillage farming. It has been valuable as a reference for scien-tists and students, and also as a guide for practitioners. A case was reported where a farmerafter reading this book bought a no-till planter and converted his farm to no-till.

This new book, No-tillage Seeding in Conservation Agriculture, provides a broader pictureof the equipment used in conservation agriculture cropping systems. It includes chapters onmaterial not previously covered, for example, the management of crop residues and covercrops, preparation for the no-tillage seeding operation, and controlled-traffic farming as a com-plementary technology. There are also new chapters describing no-tillage seeding technologiesfor small-scale farmers. Technology developments from South America and South Asia aredescribed, including manual equipment, draught-animal equipment and equipment for powertillers. The subject of greenhouse gases as driving forces for climate change is also discussed ina chapter on carbon sequestration under no-tillage farming systems.

We hope that this book contributes to a better understanding of the engineering compo-nents of conservation agriculture. It is also our wish that it helps with the introduction andexpanded application of this technology. Conservation agriculture is a valuable approach tocropping that can lead to more productive, competitive and sustainable agricultural systemswith parallel benefits to the environment and to farmers and their families.

Shivaji PandeyDirector

Theodor FriedrichSenior Agricultural Engineer

Agricultural Support Systems DivisionFAO

Rome, November 2005

Preface

And he gave for his opinion, that whoever could make two ears of corn ortwo blades of grass to grow upon a spot of ground where only one grew before,

would deserve better of mankind, and do more essential service tohis country than the whole race of politicians put together.

Jonathan Swift, Gulliver’s Travels (1726)‘A Voyage to Brobdingnag’

The authors of this book describe and analyse no-tillage technologies, particularly thoserelated to no-tillage seed drilling, from a variety of accumulated experiences over the past40 years. Most of us set out to discover why no-tillage did not always work and how toovercome these obstacles. The more we learned the more appealing no-tillage farmingbecame. The understanding and system science have now been acquired and tested to thepoint where we are ever more confident it represents the future of farming.

Some of the reported research started from knowledge that none of the traditionaldrills, planters or opener technologies used for tillage farming then provided a fail-safemethodology for untilled, residue-covered soils. Inevitably that resulted in new machinedesigns and evaluations, and combined associated technologies. The guiding premise wasthat every functional part of any new design had to have a verifiable scientific reason andperformance, which often resulted in a long evolution.

No functional assumptions were made. All commonly held ideas about what seedsrequired were challenged or discarded and new experiments set up to determine theirrequirements specifically in untilled soils. This new knowledge was combined with what-ever existing knowledge proved still to be applicable. In other cases the rules for tilled soilssimply did not apply, or were proved wrong, when applied to untilled soils. Undisturbedsoils were found to provide different resources and challenges from those of tilled soils,thus requiring different approaches to seed sowing.

Other authors report what happened to soil when ploughing ceases. Everyone by nowknows that no-tillage is good and ploughing is bad for the soil, but what are the causalmechanisms and can the improvements or damage be quantified? Can the gains be furtherimproved by techniques such as controlled-traffic farming? Still other authors studiedavailable equipment and management methods and relate these to no-tillage systems and

xiii

applications, large and small. Only when the capabilities of modern no-tillage equipmentare understood and fully integrated into a crop production enterprise can it be fully quanti-fied and realistic local recommendations made.

Collectively these authors have provided a comprehensive overview of what makes asuccessful no-tillage enterprise work. This includes machinery design and operating prin-ciples, the interactions of machines with the soil, the importance of parallel inputs, such asherbicides, pesticides and controlled traffic, and the management of the system as a whole,including quantifying the importance of soil carbon and tracking carbon dioxide emissionsas a function of soil disturbance. They have also provided a guide to experimentalprocedures for evaluation of variables.

The book is not intended to be a blueprint on how to design any one style of no-tillagemachine, component or system. It is a record of the comparative performances of severaldifferent machine design options and management practices, tested under controlled sci-entific conditions, and how these have been found to integrate into a whole no-tillage sys-tem. Much of the information is about the biological performance of machines and soils,since both primarily perform biological functions. But mechanical performance is notignored either. The interface between the two is particularly important.

The reader is invited to place his or her own value on the relevance of the data pre-sented. The relevance some of the authors placed on the data led to the design of the discversion of a winged opener, called Cross Slot®. Others will see different things in the data.However, independent research and field experience have increasingly shown that thedata and the conclusions drawn from them have been remarkably accurate and prophetic.

The relevance of the book is that it illustrates that there are now ways and means tomake no-tillage more fail-safe than tillage and to obtain crop yields not only equal to thosefrom tillage but, in many cases, superior. Untilled soils contain greater potential to germi-nate, establish and grow plants than tilled soils ever did. And, of course, they are muchmore environmentally friendly. The problem for humankind has been to learn and under-stand how to harness that potential. We hope this book goes some way towards achievingthat objective.

The book expands on the first edition, entitled No-tillage Seeding: Science and Prac-tice (Baker, Saxton and Ritchie, ISBN 0 85199 103 3, first published by CAB Internationalin 1996 and reprinted in 2002).

xiv Preface

1 The ‘What’ and ‘Why’ ofNo-tillage Farming

C. John Baker and Keith E. Saxton

No farming technique yet devised byhumankind has been anywhere near as

effective as no-tillage at halting soil erosionand making food production truly

sustainable.

Since the early 1960s farmers have beenurged to adopt some form of conservationtillage to save the planet’s soil, to reduce theamount of fossil fuels burnt in growingfood, to reduce runoff pollution of our water-ways, to reduce wind erosion and air qua-lity degradation and a host of other nobleand genuine causes. Charles Little in GreenFields Forever (1987) epitomized the gen-uine enthusiasm most conservationists havefor the technique. But early farmer experi-ence, especially with no-tillage, suggestedthat adopting such techniques would resultin greater short-term risk of reduced seed-ling emergence, crop yield or, worse, cropfailure, which they were being asked toaccept for the long-term gains outlined above.

Farmers of today were unlikely to seemany short-term benefits of their conser-vation practices. Leaving a legacy of betterland for future generations was one thing,but the short-term reality of feeding thepresent generation and making a livingwas quite another. Not unreasonably, short-term expediency often took priority.Although some countries already produce

50% or more of their food by no-tillage (e.g.Brazil, Argentina and Paraguay), it is esti-mated that, worldwide, no-tillage currentlyaccounts for only some 5–10% of foodproduction. We still have a long way to go.Certainly there have been good, and evenexcellent, no-tillage crops, but there havealso been failures. And it is the failures thattake prime position in the minds of allbut the most forward-looking or innovativefarmers.

Tillage has been fundamental to cropproduction for centuries to clear and softenseedbeds and control weeds. So now we arechanging history, not always totally omit-ting tillage (although that is certainly alaudable objective) but significantly alter-ing the reasons and processes involved.Most people understand tillage to be a pro-cess of physically manipulating the soil toachieve weed control, fineness of tilth,smoothness, aeration, artificial porosity, fri-ability and optimum moisture content so asto facilitate the subsequent sowing and cov-ering of the seed. In the process, the undis-turbed soil is cut, accelerated, impacted,inverted, squeezed, burst and thrown, in aneffort to break the soil physically and buryweeds, expose their roots to drying or tophysically destroy them by cutting. Theobjective of tillage is to create a weed-free,smooth, friable soil material through which

© FAO and CAB International 2007. No-tillage Seeding in ConservationAgriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton) 1

relatively unsophisticated seed drill openerscan travel freely.

During no-tillage, few, if any, of theprocesses listed above take place. Underno-tillage, other weed-control measures,e.g. chemicals, must substitute for the phys-ical disturbance during tillage to dislodge,bury or expose existing weeds. But part ofthe tillage objective is also to stimulate newweed seed germination so that fresh weedsget an ‘even start’ and can therefore beeasily killed in their juvenile stages by asingle subsequent tillage operation. No-tillage, therefore, must either find anotherway of stimulating an ‘even start’ for newweeds, which would then require a subse-quent application of herbicide or avoidstimulating new weed growth in the firstplace.

In his keynote address to the 1994World Congress of Soil Science, NobelPrize-winner Norman Borlaug estimatedthat world cereal production (which acc-ounts for 69% of world food supply) wouldneed to be raised by 24% by the year 2000and doubled by the year 2025. More impor-tantly, Borlaug estimated that grain yieldswould need to increase by 80% over thesame time span because creating new arableland is severely limited throughout theworld. Until now, yield increases havecome largely from increased fertilizer andpesticide use and genetic improvement tothe species grown. The challenge is forno-tillage to contribute to future increases,while simultaneously achieving resourcepreservation and environmental goals. Butthis is only going to happen if no-tillage ispractised at advanced technology levels.

The notion of sowing seeds into untilledsoils is very old. The ancient Egyptians prac-tised it by creating a hole in untilled soilwith a stick, dropping seeds into the holeand then closing it again by pressing thesides together with their feet. But it wasnot until the 1960s, when the herbicidesparaquat and diquat were released by thethen Imperial Chemical Industries Ltd (nowSyngenta) in England, that the modernconcept of no-tillage was born becausenow weeds could be effectively controlledwithout tillage.

For the preceding decade it had beenrecognized that, for no-tillage to be viable,weeds had to be controlled by some othermethod than tillage. But the range of agri-cultural chemicals then available was limi-ted because of their residual effects in thesoil. A delay of several weeks was necessaryafter spraying before the new crop could besafely sown, which partly negated saving oftime, one of the more noteworthy advant-ages of no-tillage compared with tillage.Paraquat and diquat are almost instantlydeactivated upon contact with soil. Whensprayed onto susceptible living weeds, thesoil beneath is almost instantly ready toaccept new seeds, without the risk of injury.

This breakthrough in chemical weedcontrol spawned the birth of true no-tillage.Since then, there have been other broader-spectrum translocated non-residual chemi-cals, such as glyphosate, which was firstintroduced as Roundup by Monsanto. Othergeneric compounds, such as glyphosatetrimesium (Touchdown) and glufosinateammonium (Buster), were later marketed byother companies, which have expanded theconcept even further.

In other circumstances non-chemicalweed control measures have been used.These include flame weeding, steam weed-ing, knife rolling and mechanical handweeding. None of the alternative measureshas yet proved as effective as spraying with atranslocated non-residual herbicide. Thesechemicals are translocated to the roots of theplant thereby affecting a total kill of the plant.Killing the aerial parts alone often allowsregeneration of non-affected plant parts.

The application of any chemicalswithin agricultural food production cor-rectly raises the question of human andbiological safety. Indeed, many chemicalsmust be very carefully applied under veryspecific conditions for specific results, justlike any of the modern pharmaceuticals thatassist in cures and controls. Through care-ful science, and perhaps some good fortune,glyphosate has been found to be non-toxicto any biological species other than greenplants and has been safely used for manyyears with virtually no known effects otherthan the control of undesired plants.

2 C.J. Baker and K.E. Saxton

An even more recent developmentusing genetic modification of the cropsthemselves has made selected plant variet-ies immune to very specific herbicides suchas glyphosate. This unique trait permitsplanting the crop without weed concernsuntil the crop is well established and thenspraying both the crop and the weeds with asingle pass. The susceptible weeds are elimi-nated and the immune crop thrives, makinga full canopy that competes with anysubsequent weed growth, usually throughto harvest. Only selected crops such asmaize and soybean are currently commonlyused in this fashion, but they have alreadyattained a very significant percentage of theworld’s acreage. With this success, otherimportant food and fibre crops are beingmodified for this capability.

What is No-tillage?

As soon as the modern concept of no-tillagebased on non-residual (and mostly trans-located) herbicides was recognized, every-one, it seems, invented a new name todescribe the process. ‘No-tillage’, ‘direct drill-ing’ or ‘direct seeding’ are all terms describ-ing the sowing of seeds into soil that has notbeen previously tilled in any way to form a‘seedbed’. ‘Direct drilling’ was the first termused, mainly in England, where the modernconcept of the technique originated in the1960s. The term ‘no-tillage’ began in NorthAmerica soon after, but there has been recentsupport for the term ‘direct seeding’ becauseof the apparent ambiguity that a negativeword like ‘no’ causes when it is used todescribe a positive process. The terms areused synonymously in most parts of theworld, as we do in this book.

Some of these names are listed belowwith their rationales, some only for histori-cal interest. After all, it’s the process, notthe name, that’s important.

Chemical fallow, or chem-fallow, describesa field currently not cropped in whichthe weeds have been suppressed bychemical means.

Chemical ploughing attempted to indicatethat the weed control function usuallyattributed to ploughing was being doneby chemicals. The anti-chemical lobbysoon de-popularized such a restrictivename, which is little used today.

Conservation tillage and conservation agri-culture are the collective umbrella termscommonly given to no-tillage, minimumtillage and/or ridge tillage, to denote thatthe inclusive practices have a conserva-tion goal of some nature. Usually, theretention of at least 30% ground cover byresidues after seeding characterizes thelower limit of classification for conserva-tion tillage or conservation agriculture,but other conservation objectives includeconservation of money, labour, time,fuel, earthworms, soil water, soil struc-ture and nutrients. Thus, residue levelsalone do not adequately describe all con-servation tillage or conservation agricul-tural practices and benefits.

Disc-drilling reflects the early perceptionthat no-tillage or direct drilling couldonly be achieved with disc drills (a per-ception that proved to be erroneous);thus some started referring to the prac-tice as disc-drilling. Fortunately theterm has not persisted. Besides, discdrills are also used in tilled soils.

Drillage was a play on words that suggestedthat under no-tillage the seed drill wasin fact tilling the soil and drilling theseed at the same time. It is not com-monly used.

Minimum tillage, min-till and reduced tillageall describe the practice of restrictingthe amount of general tillage of thesoil to the minimum possible to estab-lish a new crop and/or effect weed con-trol or fertilization. The practice liessomewhere between no-tillage andconventional tillage. Modern practiceemphasizes the amount of surface resi-due retention as an important aim ofminimum or reduced tillage.

No-till is a shortening of no-tillage and isnot encouraged by purists, for gramma-tical reasons.

Residue farming describes conservation till-age practices in which residue retention

‘What’ and ‘Why’ of No-tillage 3

is the primary objective, even thoughmany of the ‘conservation tillage’ bene-fits previously mentioned may alsoaccrue.

Ridge tillage, or ridge-till, describes thepractice of forming ridges from tilledsoil into which widely spaced row cropsare drilled. Such ridges may remain inplace for several seasons while succes-sive crops are no-tilled into the ridges,or they might be re-formed annually.

Sod-seeding, undersowing, oversowing,overdrilling and underdrilling all referto the specific no-tillage practice ofdrilling new pasture seeds into existingpasture swards, collectively referred toas pasture renovation. The correct useof the term oversowing does not involvedrilling at all, but rather is the broad-casting of seed on to the surface of theground. Each of the other listed termsinvolves drilling of the seed.

Stale seedbed describes an untilled seedbedthat has undergone a period of fallow,usually (but not exclusively) withperiodic chemical weed control.

Strip tillage, or zone tillage, refers to thepractice of tilling a narrow strip aheadof (or with) the drill openers, so theseed is sown into a strip of tilled soilbut the soil between the sown rowsremains undisturbed. ‘Strip tillage’ alsorefers to the general tilling of muchwider strips of land (100 or moremetres wide) on the contour, separatedby wide fallowed strips, as an erosion-control measure based on tillage.

Sustainable farming is the end product ofapplying no-tillage practices continu-ously. Continuous cropping based ontillage is now considered to be unsus-tainable because of resource degrada-tion and farming inefficiencies, whilecontinuous cropping based on no-tillageis much more likely to be sustainableon a long-term basis under most agri-cultural conditions. Some discussions of‘sustainability’ include broader consi-derations beyond the preservation ofnatural resources and food production,such as economics, energy and qualityof life.

Zero-tillage was synonymous with no-tillage and is still used to a limitedextent today.

The most commonly identified featureof no-tillage is that as much as possible ofthe surface residue from the previous cropis left intact on the surface of the ground,whether this be the flattened or standingstubble of an arable crop that has beenharvested or a sprayed dense sward of grass.In the USA, where the broad category ofconservation tillage is generally practisedas an erosion-control measure, the acceptedminimum amount of surface covered byresidue after passage of the drill is 30%.Most practitioners of the more demandingoption of no-tillage or direct seeding aim forresidue-coverage levels of at least 70%.

Of course, some crops, such as cotton,soybean and lupin, leave so little residueafter harvest that less than 70% of theground is likely to be covered by residueeven before drilling. Such a soil, however,can be equally well direct drilled as a fullyresidue-covered soil in the course of estab-lishing the next crop. Thus it is alsoregarded as true no-tillage. What is no-tillageto one observer may not be no-tillage toanother, depending upon the terms of refer-ence and expectations of each observer.

The most fundamental criterion com-mon to all no-tillage is not the amount ofresidue remaining on the soil after drilling,but whether or not that soil has beendisturbed in any way prior to drilling. Eventhen, during drilling, as will be explainedlater, such a seemingly unambiguous defi-nition becomes confused when you con-sider the actions of different drills andopeners in the soil. Some literally till a stripas they go, while others leave all of the soilalmost undisturbed. So the untilled soilprior to drilling might well become some-thing quite different after drilling.

This book is focused on the subject of‘no-tillage’ in which no prior disturbanceor manipulation of the soil has occurredother than possibly minimal disturbance byoperations such as shallow weed control,fertilization or loosening of subsurface com-pacted layers. Such objectives are entirely


compatible with true no-tillage. Any distur-bance before seeding is expected to havehad very minimal surface disturbance ofsoil or residues.

Depending on the field cropping historyand the available seeding machine capabil-ity, it may be necessary to perform one ormore very minimal-disturbance functionsfor best crop performance. The most com-mon of these needs is the application of fer-tilizer when that function can not be madepart of the seeding operation. Early no-tillageseeding trials often simply broadcast the fer-tilizer over the soil surface expecting it to becarried into the soil profile by precipitation,but two things became readily apparent.First, only the nitrogen component wasmoved by water, leaving the remainingforms, such as phosphorus and potassium,on or near the soil surface. And even thenpreferential flow of soluble nitrogen downearthworm and old root channels oftenmeant that much of it bypassed the juvenileroots of the newly sown crop (see Chapter 9).

Secondly, emerging weeds between thecrop plants readily helped themselves asthe first consumers of this fertilizer and‘outgrew’ the crop. Subsurface placement isnow the only recommended procedure,often banded near the seeding furrow oremerging crop row.

Where herbicides are less available, itmay prove more economical to perform aweeding pass prior to seeding to reducethe weed pressures on the emerging crop.If used in conservation agriculture, thisoperation must be very shallow and leavethe soil surface and residues nearly intactready for the seeding operation. Typicalimplements that can achieve this quality ofweed control are shallow-running V-shapedchisels or careful hand hoeing.

Historical compaction arising frommany years of repetitive tillage often cannotbe undone ‘overnight’ by switching tono-tillage. While soil microbes are rebuild-ing their numbers and improving soil struc-ture, a process that may take several yearseven in the most favourable of climates,historical compaction may still exist. Tem-porary relief can often be achieved by usinga subsoiling machine that cracks and bursts

subsurface zones while causing only minordisturbance at the surface.

But sometimes overly aggressive sub-soilers cause so much surface disturbancethat full tillage is then required to smooththe surface again. This seemingly endlessnegative spiral must be broken if the bene-fits of no-tillage are to be gained. All thatis required is a less aggressive or shallow-acting subsoiler that allows no-tillage totake place after its passage without anyfurther ‘working’ of the soil surface layer.

Another effective method is to sow agrass or pasture species in the compactedfield and either graze this with light stock-ing or leave it ungrazed as a ‘set-aside’ areafor a number of years before embarking on ano-tillage programme thereafter withouttillage. A rule of thumb for how many yearsof pasture are required to restore soilorganic carbon (SOC) and ultimately thestructural damage done by tillage was estab-lished by Shepherd et al. (2006) for a gleysoil (Kairanga silty clay loam) under maizein New Zealand soils as:

Where tillage has been undertaken for up to4 consecutive years, it takes approximately11 years of pasture to restore SOC levelsfor each year of tillage.

Where tillage has been undertaken formore than 4 consecutive years, it takes upto 3 years of pasture to restore SOC levelsfor each year of tillage.

The rate of recovery of soil structure lagsbehind the recovery rate of SOC. The moredegraded the soil, the greater the lag time.

Why No-tillage?

It is not the purpose of this book to explorein detail the advantages and disadvantagesof either no-tillage or conservation tillage.Numerous authors have undertaken thistask since Edward Faulkner and AlsiterBevin questioned the wisdom of ploughingin Ploughman’s Folly (Faulkner, 1943) andThe Awakening (Bevin, 1944). Althoughneither of these authors actually advocatedno-tillage, it is interesting to note thatFaulkner made the now prophetic observa-tion that ‘no one has ever advanced a


scientific reason for ploughing’. In fact, longbefore Faulkner’s and Bevin’s time, theancient Peruvians, Scots, North AmericanIndians and Pacific Polynesians are allreported to have practised a form of conser-vation tillage (Graves, 1994).

None the less, to realistically focuson the methods and mechanization of no-tillage technologies, it is useful to com-pare the advantages and disadvantages ofthe technique in general as measuredagainst commonly practised tillage farming.The more common of these are summarizedbelow with no particular order or priority.Those followed by an ∗ can be either anadvantage or a disadvantage in differingcircumstances.

In Chapter 2 we shall expand on theadvantages (benefits) of no-tillage, particu-larly those derived either directly or indi-rectly from enhancement of SOC levels, andin Chapter 3 we shall examine the risks ofno-tillage in more detail.

Advantages

Fuel conservation. Up to 80% of fuel usedto establish a crop is conserved by con-verting from tillage to no-tillage.

Time conservation. The one to three tripsover a field with no-tillage (spraying,drilling and perhaps subsoiling) resultsin a huge saving in time to establish acrop compared with the five to ten tripsfor tillage plus fallow periods duringthe tillage process.

Labour conservation. Up to 60% fewerperson-hours are used per hectare com-pared with tillage.

Time flexibility. No-tillage allows late deci-sions to be made about growing cropsin a given field and/or season.

Increased soil organic matter. By leavingthe previous crop residues on the soilsurface to decay, soil organic matternear the surface is increased, which inturn provides food for the soil microbesthat are the builders of soil structure.Tillage oxidizes organic matter, result-ing in a cumulative reduction, oftenmore than is gained from incorporation.

Increased soil nitrogen. All tillage mineral-izes soil nitrogen, which may provide ashort-term boost to plant growth, butsuch nitrogen is ‘mined’ from the soilorganic matter, further reducing totalsoil organic matter levels.

Preservation of soil structure. All tillagedestroys natural soil structure whileno-tillage minimizes structural break-down and increases organic matter andhumus to begin the rebuilding process.

Preservation of earthworms and other soilfauna. As with soil structure, tillagedestroys humans’ most valuable soil-borne ally, earthworms, while no-tillageencourages their multiplication.

Improved aeration. Contrary to early predic-tions, the improvement in earthwormnumbers, organic matter and soil struc-ture usually result in improved soilaeration and porosity over time. Soils donot become progressively harder andmore compact. Quite the reverse occurs,usually after 2–4 years of no-tillage.

Improved infiltration. The same factors thataerate the soil result in improved infiltra-tion into the soil. Plus residues reducesurface sealing by raindrop impact andslow down the velocity of runoff water.

Preventing soil erosion. The sum of preserv-ing soil structure, earthworms andorganic matter, together with leavingthe surface residues to protect the soilsurface and increase infiltration, is toreduce wind and water soil erosionmore than any other crop-productiontechnique yet devised by humans.

Soil moisture conservation. Every physicaldisturbance of the soil exposes it to dry-ing, whereas no-tillage and surface resi-dues greatly reduce drying. In addition,accumulation of soil organic mattergreatly improves the water-holdingcapacity of soils.

Reduced irrigation requirements. Improvedwater-holding capacity and reducedevaporation from soils lessen the needfor irrigation, especially at early stagesof growth when irrigation efficiency isat its lowest.

Moderating soil temperatures.* Under no-tillage soil temperatures in summer


stay lower than under tillage. Wintertemperatures are higher where snowretention by residue is a factor, butspring temperatures may rise moreslowly.

Reduced germination of weeds. The absenceof physical soil disturbance under no-tillage reduces stimulation of newweed seed germination, but the in-roweffect of this factor is highly dependenton the amount of disturbance caused bythe no-tillage openers themselves.

Improved internal drainage. Improvedstructure, organic matter, aeration andearthworm activity increase naturaldrainage within most soils.

Reduced pollution of waterways. Thedecreased runoff of water from soil andthe chemicals it transports reducespollution of streams and rivers.

Improved trafficability. Untilled soils arecapable of withstanding vehicle andanimal traffic with less compaction andstructural damage than tilled soils.

Lower costs. The total capital and/or operat-ing costs of all machinery required toestablish tillage crops are reduced byup to 50% when no-tillage substitutesfor tillage.

Longer replacement intervals for machi-nery.* Because of reduced hours perhectare per year, tractors and advancedno-tillage drills are replaced less oftenand reduce capital costs over time.Some lighter no-tillage drills, however,may wear out more quickly than theirtillage counterparts because of thegreater stresses involved in operatingthem in untilled soils.

Reduced skills level.* While achieving suc-cessful no-tillage is a skilful task initself, the total range of skills requiredis smaller than the many sequential tasksneeded to complete successful tillage.

Natural mixing of soil potassium and phos-phorus. Earthworms mix large quantitiesof soil potassium and phosphorus inthe root zone, which favours no-tillagebecause it sustains earthworm numbersand increases plant nutrient availability.

Less damage of new pastures. The morestable soil structure of untilled soils

allows quicker utilization of newpastures by stock with less plant dis-ruption during early grazing thanwhere tillage has been employed.

More recreation and management time. Thetime otherwise devoted to tillage can beused to advantage for further manage-ment inputs (including the farming ofmore land) or for family and recreation.

Increased crop yields. All of the above fac-tors are capable of improving crop yieldsto levels well above those attained bytillage – but only if the no-tillage systemand processes are fully practised withoutshort cuts or deficiencies.

Future improvements expected. Modernadvanced no-tillage systems and equip-ment have removed earlier expecta-tions of depressed crop yields in theshort term to gain the longer-term bene-fits of no-tillage. Ongoing research andexperience have developed systems thateliminate short-term depressed yieldswhile at the same time raising theexpectation and magnitudes of yieldincreases in the medium to longer term.

Disadvantages

Risk of crop failure.* Where inappropriateno-tillage tools and weed- or pest-control measures are used, there will bea greater risk of crop yield reductionsor failure than for tillage. But wheremore sophisticated no-tillage tools andcorrect weed- and pest-control measuresare used, the risks will be less than fortillage.

Larger tractors required.* Although the totalenergy input is significantly reducedby changing to no-tillage, most of thatinput is applied in one single opera-tion, drilling, which may require alarger tractor or more animal power, orconversely a narrower drill.

New machinery required. Because no-tillageis a relatively new technique, new anddifferent equipment has to be purcha-sed, leased or hired.

New pest and disease problems.* Theabsence of physical disturbance and


retention of surface residues encouragessome pests and diseases and changesthe habitats of others. But such condi-tions also encourage their predators. Todate, no pest or disease problems haveproved to be insurmountable or untreat-able in long-term no-tillage systems.

Fields are not smoothed. The absence ofphysical disturbance prevents soilmovement by machines for smoothingand levelling purposes. This puts pres-sure on no-tillage drill designers to cre-ate machines that can cope withuneven soil surfaces. Some do thisbetter than others.

Soil strength may vary across fields. Tillageserves to create a consistently low soilstrength across each field. Long-termno-tillage requires machines to be capa-ble of adjusting to natural variations insoil strength that occur across everyfield. Since soil strength dictates thepenetration forces required to be app-lied to each no-tillage opener, variablesoil strength places particular demandson drill designs if consistent seedingdepths and seed coverage are to beattained.

Fertilizers are more difficult to incorpo-rate.* General incorporation of fertili-zers is more difficult in the absence ofphysical burial by machines, but spe-cific incorporation at the time of drill-ing is possible and desirable, usingspecial designs of no-tillage openers.

Pesticides are more difficult to incorporate.As with fertilizers, general incorpora-tion of pesticides (especially those thatrequire pre-plant soil incorporation) isnot readily possible with no-tillage,requiring different pest-control strate-gies and formulations.

Altered root systems.* The root systems ofno-tillage crops may occupy smallervolumes of soil than under tillage,but the total biomass and function ofthe roots are seldom different andanchorage may in fact be improved.

Altered availability of nitrogen.* There arethree factors that affect nitrogen avail-ability during early plant developmentunder no-tillage:

The decomposition of organic mat-ter by soil microbes often temporarily‘locks up’ nitrogen, making it less plant-available under no-tillage.

No-tillage reduces mineralizationof soil organic nitrogen that tillage oth-erwise releases.

The development of bio-channelsin the soil from earthworms and rootscauses preferential flow of surface-applied nitrogenous fertilizers into thesoil, which may bypass shallow, youngcrop roots.

Each (or all) of these factors may createa nitrogen deficiency for seedlings,which encourages placing nitrogen withdrilling. Fortunately some advancedno-tillage drills have separate nitrogenbanding capabilities that overcome thisproblem.

Use of agricultural chemicals.* The relianceof no-tillage on herbicides for weedcontrol is a cost and environmentalnegative but is offset by the reductionin surface runoff of other chemical pol-lutants (including surface-applied fer-tilizers) and the fact that most of theprimary chemicals used in no-tillageare ‘environmentally friendly’. Small-scale agriculture may require morehand weeding, but with greater easethan with tilled soils.

Shift in dominant weed species.* Chemicalweed control tends to be selectivetowards weeds that are resistant to therange of available formulations, requir-ing more diligent use of crop rotationsby farmers and commitment by the agri-cultural chemical industry to research-ing new formulations.

Restricted distribution of soil phosphorus.*Relatively immobile soil phosphorustends to become distributed in a nar-rower band within the upper soil layersunder no-tillage because of the absenceof physical mixing. Improved earth-worm populations help reduce thiseffect and also cycle nutrient sourcessituated below normal tillage levels.

New skills are required.* No-tillage is amore exacting farming method, requiring


the learning and implementation ofnew skills, and these are not alwayscompatible with existing tillage-relatedskills or attitudes.

Increased management and machine per-formance. There is only one opportu-nity with each crop to ‘get it right’ undera no-tillage regime. Because no-tillagedrilling is literally a once-over opera-tion, there is less room for error com-pared with the sequential operationsinvolved in tillage. This places empha-sis on the tolerance of no-tillage drillsto varying operator skill levels andtheir ability to function effectively insuboptimal conditions.

No-tillage drill selection is critical.* Fewfarmers can afford to own several dif-ferent no-tillage drills awaiting themost suitable conditions before select-ing which one to use. Fortunately moreadvanced no-tillage drills are capableof functioning consistently in a widerrange of conditions than most tillagetools, making reliance on a single no-tillage drill for widely varying condi-tions both feasible and a practicalreality.

Availability of expertise. Until the many spe-cific requirements of successful no-tillageare fully understood by ‘experts’, thequality of advice to practitioners fromconsultants will remain, at best, vari-able. Local, successful no-tillage farmersoften become the best advisers.

Untidy field appearance.* Farmers whohave become used to the appearance ofneat, ‘clean’, tilled seedbeds often findthe retention of surface residues (‘trash’)‘untidy’. But, as they come to appreciatethe economic advantages of true no-tillage, many such farmers graduallycome to see residues as an importantresource rather than ‘trash’ requiringdisposal.

Elimination of ‘recreational tillage’.* Somefarmers find driving big tractors andtilling on a large scale to be recre-ational. Others regard it as a chore andhealth-damaging. Farmers in develop-ing countries regard tillage as burden-some or impossible.

Figure 1.1 shows some of the likely short-and long-term trends that might arise as aresult of converting from tillage to no-tillage.


Fig. 1.1. The likely short- and long-term trends that might arise as a result of converting from tillage tono-tillage (from Carter, 1994).

Each identified item or process progressesover the years from stopping tillage as theeffects of no-tillage take precedent. Therealization is that the effects of no-tillageare developed as the soil and its physicaland biological characteristics change.The result of these combined processes hasbeen observed and documented in nearlyevery soil and climate worldwide, to thepoint of becoming common knowledge. It isin this transition stage that many who con-vert to no-tillage farming become disillu-sioned and sceptical that the benefits willin fact occur.

Summary of the ‘What’ and ‘Why’of No-tillage

No-tillage farming is a significant methodo-logy shift in production farming as performedover the past 100 years of mechanized agri-culture. It intuitively requires new thinkingby the producers of the ‘what’ and ‘why’to change the processes. Only by encom-passing the full scope of ‘why’ we shouldchange from an enormously successfulfood production system shall we move for-ward with confidence to develop ‘what’a modern no-tillage farming system shouldincorporate. The short-term advantagesfar outweigh the disadvantages, and in thelonger term it involves no less than makingworld food production sustainable for thefirst time in history.


2 The Benefits of No-tillage

Don C. Reicosky and Keith E. Saxton

Intensive tillage farming reduces soil organicmatter and degrades soil quality – no-tillagefarming enhances soil quality and sustains

long-term agriculture.

Introduction

Sustainable food and fibre production ofany given field and region requires that thefarming methods be economically competi-tive and environmentally friendly. To achievethis result requires adopting a farming tech-nology that not only benefits productionbut provides an environmental benefit tothe long-term maintenance of the soil andwater resources upon which it is based. Wemust reduce pollution and use our resourcesin line with the earth’s carrying capacity forsustainable production of food and fibre.

The responsibility of sustainable agri-culture lies on the shoulders of farmers tomaintain a delicate balance between theeconomic implications of farming practicesand the environmental consequences ofusing the wrong practices. This responsibi-lity entails producing food and fibre to meetthe increasing population while maintainingthe environment for a sustained high qua-lity of life. The social value of an agricul-tural community is not just in production,but in producing in harmony with nature

for improved soil, water and air quality andbiological diversity.

Sustainable agriculture is a broad con-cept that requires interpretation at the regionaland local level. The principles are capturedin the definition reported by El-Swaify(1999) as: ‘Sustainable agriculture involvesthe successful management of resources foragriculture to satisfy changing human needs,while maintaining or enhancing the qualityof the environment and conserving naturalresources.’

Conservation agriculture, especiallyno-tillage (direct seeding), has been provedto provide sustainable farming in manyagricultural environments virtually aroundthe world. The conditions and farming scalesvary from humid to arid and vegetable plotsto large prairie enterprises. All employ andadapt very similar principles but with awide variety of machines, methods andeconomics.

The benefits of performing crop pro-duction with a no-tillage farming system aremanyfold. Broad subjects discussed hereonly begin to provide the science and resultslearned over recent decades of exploringand developing this farming method. Inaddition to improved production and soiland water resource protection, many otherbenefits accrue. For example, it saves timeand money, improves timing of planting


and harvesting, increases the potential fordouble cropping, conserves soil water thro-ugh decreased evaporation and increasedinfiltration, reduces fuel, labour and machi-nery requirements and enhances the globalenvironment.

Principles of ConservationAgriculture

Conservation agriculture requires imple-menting three principles, or pillars, as illus-trated in Fig. 2.1. These are: (i) minimumsoil tillage disturbance; (ii) diverse croprotations and cover crops; and (iii) continu-ous plant residue cover. The main directbenefit of conservation agriculture and directseeding is increased soil organic matter andits impact on the many processes that deter-mine soil quality. The foundation underlyingthe three principles is their contributionand interactions with soil carbon, the pri-mary determinant of long-term sustainablesoil quality and crop production.

Conservation tillage includes the con-cepts of no-tillage, zero-tillage and directseeding as the ultimate form of conserva-tion agriculture. These terms are often usedinterchangeably to denote minimum soildisturbance. Reduced tillage methods, some-times referred to as conservation tillage,such as strip tillage, ridge tillage and mulchtillage, disturb a small volume of soil andpartially mix the residue with the soil andare intermediate in their soil quality effects.These terms define the tillage equipmentand operation characteristics as they relateto the soil volume disturbed and the degreeof soil–residue mixing. Intensive inversiontillage, such as that from mouldboard-ploughing, disc-harrowing and certain typesof powered rotary tillage, is not a form ofconservation tillage. No-tillage and directseeding are the primary methods of conser-vation tillage to apply the three pillars ofconservation agriculture for enhanced soilcarbon and its associated environmentalbenefits.

True soil conservation is largely relatedto organic matter, i.e. carbon, management.

12 D.C. Reicosky and K.E. Saxton

Fig. 2.1. Schematic representation of the three pillars or principles of conservation agriculturesupported by a foundation of soil carbon.

By nothing more than properly managingthe carbon in our agricultural ecosystems,we can have less erosion, less pollution,clean water, fresh air, healthy soil, naturalfertility, higher productivity, carbon cre-dits, beautiful landscapes and sustainability.Dynamic soil quality encompasses thoseproperties that can change over relativelyshort time periods, such as soil organicmatter, soil structure and macroporosity.These can readily be influenced by theactions of human use and managementwithin the chosen agronomic practices.Soil organic matter is particularly dynamic,with inputs of plant materials and losses bydecomposition.

Crop Production Benefits

Producing a crop and making an economicprofit are universal goals of global farming.Production by applying no-tillage methodsis no different in these goals, but there aredefinite benefits for the achievement, whichwe outline in this chapter. But these benefitsonly occur with fully successful no-tillagefarming. There are certainly obstacles andrisks in moving from traditional tillagefarming, which has been the foundationtechnology for centuries, as outlined inChapter 3.

Acceptable crop production requiresan adequate plant stand, good nutrition andmoisture with proper protection from weed,insect or disease competition. Achievingthe plant stand in untilled, residue-coveredsoils is the first major obstacle, a particularchallenge in modern mechanized agriculture,but certainly surmountable, as explainedin the core of this text. Providing adequatenutrition and water for full crop potentialsis readily achieved with the benefits ofno-tillage, as discussed below.

Weed-control methods, by necessity,shift to dependence on chemicals, flame-weeding, mechanical crushing or handpicking for full no-tillage farming to staywithin the goal of minimum soil distur-bance. Chemical developments in recentdecades have made great strides in theireffectiveness, environmental friendliness

and economic feasibility. Supplemental tech-niques of mowing, rolling and crushingwithout soil disturbance are showing signi-ficant promise to reduce weed presence andincrease the benefit of cover crops and resi-dues. Experience has shown that control-ling insects and diseases has generally beenless of a problem with no-tillage, even thoughthere are often dire predictions about thepotential impact of surface residues har-bouring undesirables. As with weeds, crophealth and pest problems are not likely tobe avoided but may well shift to new varie-ties and species with the change in the fieldenvironment.

As a result of these developments andskilled applications, it has been repeatedlyshown that crop production can be equalledand exceeded by no-tillage farming comparedwith traditional tillage methods. Becausemany soils have been tilled for many years,it is not uncommon to experience some yieldreduction in the first few no-tillage years,largely because, as discussed later, it takestime for the soil to rebuild into a higher qua-lity. This ‘transition period reduction’ canoften be overcome or even averted withincreased fertility, strategic fertilizer band-ing with drill openers and careful cropselection.

The full benefit of no-tillage comes inthe reduced inputs. Most notable are thereduced inputs by minimizing labour andmachine hours spent establishing and main-taining the crop. Reduced machine costsalone are significant, since all tillage equip-ment is dispensable. True no-tillage farmingrequires only an effective chemical sprayer,seeding–fertilizing drill and harvester.

With no seedbed preparation of thesoil by tillage, seed drilling has become themajor limitation to many efforts to success-fully change to no-tillage farming. Modifyingdrills used in tillage farming has gener-ally not been very successful, resulting inundesirable crop stands for optimum pro-duction. Many were not equipped to pro-vide simultaneous fertilizer banding; thusit had to be provided by a supplementalminimum-tillage machine or, in the worstcase, surface-applied, where it was veryineffective and stimulated weed growth.

Benefits of No-tillage 13

Fortunately, drill development has pro-gressed to now provide acceptable seedingin many cases, but, as described in laterchapters, many still do not fully meet alldesirable attributes, especially in relation tothe amount of soil disturbance they create.

As a result of science and techniquedevelopments of recent years, no-tillagecrop production now not only is feasiblebut has significant economic benefits. Com-bining and multiplying this result by thefurther benefits of soil and environmentalqualities make no-tillage farming a highlydesirable method of crop production.Further, many are now finding personaland social benefits from the reducedlabour inputs, which remove much of thedemanded time and drudgery often associ-ated with traditional farm life. A commonremark by successful no-tillage farmers is ‘Ithas brought back the fun of farming.’

Increased organic matter

Understanding the role of soil organic matterand biodiversity in agricultural ecosystemshas highlighted the value and importanceof a range of processes that maintain andfulfil human needs. Soil organic matter is sovaluable for its influence on soil organismsand properties that it can be referred toas ‘black gold’ because of its vital role inphysical, chemical and biological proper-ties and processes within the soil system.

The changes of these basic soil proper-ties, called ‘ecosystem services’, are the pro-cesses by which the environment producesresources that sustain life and which weoften take for granted. An ecosystem is a com-munity of animals and plants interactingwith one another within their physicalenvironment. Ecosystems include physical,chemical and biological components suchas soils, water and nutrients that support thebiological organisms living within them,including people. Agricultural ecosystemservices include production of food, fibreand biological fuels, provision of clean airand water, natural fertilization, nutrientcycling in soils and many other fundamen-tal life support services. These services may

be enhanced by increasing the amount ofcarbon stored in soils.

Conservation agriculture through itsimpact on soil carbon is the best way toenhance ecosystem services. Recent analyseshave estimated national and global economicbenefits from ecosystem services of soil for-mation, nitrogen fixation, organic matterdecomposition, pest biocontrol, pollinationand many others. Intensive agriculturalmanagement practices cause damage or lossof ecosystem services, by changing suchprocesses as nutrient cycling, productivityand species diversity (Smith et al., 2000).Soil carbon plays a critical role in the harmonyof our ecosystems providing these services.

Soil carbon is a principal factor in main-taining a balance between economic andenvironmental factors. Its importance canbe represented by the central hub of a wagonwheel, a symbol of strength, unity and pro-gress (Reicosky, 2001a). The ‘spokes’ of thiswheel in Fig. 2.2 represent incrementallinks to soil carbon that lead to the environ-mental improvement that supports total soilresource sustainability. Many spokes makea strong wheel. Each of the secondarybenefits that emanate from soil carboncontributes to environmental enhancementthrough improved soil carbon management.Soane (1990) discussed several practicalaspects of soil carbon important in soilmanagement. Some of the ‘spokes’ of theenvironmental sustainability wheel aredescribed in the following paragraphs.

Based on soil carbon losses with inten-sive agriculture, reversing the decreasingsoil carbon trend with less tillage intensitybenefits a sustainable agriculture and theglobal population by gaining better controlof the global carbon balance. The literatureholds considerable evidence that intensivetillage decreases soil carbon and supportsincreased adoption of new and improvedforms of no-tillage to preserve or increasestorage of soil organic matter (Paustianet al., 1997a, b; Lal et al., 1998). The environ-mental and economic benefits of conserva-tion agriculture and no-tillage demand theirconsideration in the development ofimproved soil carbon storage practices forsustainable production.


Increased available soil water

Increased soil organic matter has a significanteffect on soil water management because ofincreased infiltration and water-holdingcapacity. Enhanced soil water-holding capac-ity is a result of increased soil organic matter,which more readily absorbs water andreleases it slowly over the season to minimizethe impacts of short-term drought. Hudson(1994) showed that, for some soil textures, foreach 1% weight increase in soil organic mat-ter, the available water-holding capacity inthe soil increased by 3.7% volume. Otherfactors being equal, soils containing moreorganic matter can retain more water fromeach rainfall event and make more of it avail-able to plants. This factor and the increasedinfiltration with higher organic matter andthe decreased evaporation with crop residueson the soil surface all contribute to improvedwater use efficiency.

Increased organic matter is known toincrease soil infiltration and water-holdingcapacity, which significantly affect soil watermanagement. Under these situations, cropresidues slow runoff water and increase infil-tration by earthworm channels, macroporesand plant root holes (Edwards et al., 1988).

Water infiltration is two to ten times fasterin soils with earthworms than in soils with-out earthworms (Lee, 1985).

Soil organic matter contributes to soilparticle aggregation, which makes it easierfor water to move through the soil andenables plants to use less energy to establishroot systems (Chaney and Swift, 1984).Intensive tillage breaks up soil structure andresults in a dense soil, making it more diffi-cult for plants to fully access the nutrientsand water required for their growth andproduction. No-tillage and minimum-tillagefarming allows the soil to restructure andaccumulate organic matter for improvedplant water and nutrient availability.

Reduced soil erosion

Crop residue management practices haveincluded many agricultural practices toreduce soil erosion runoff and off-site sedi-mentation. Soils relatively high in C, parti-cularly with crop residues on the soil surface,very effectively increase soil organic matterand reduce soil erosion loss. The primaryrole of soil organic matter to reduce soil ero-dibility is to stabilize the surface aggregates


Fig. 2.2. Environmental sustainability wheel with benefits emanating from the soil carbon hub.

through reduced crust formation and sur-face sealing, resulting in less runoff (LeBissonnais, 1990). Reducing or eliminatingrunoff that carries sediment from fields torivers and streams is a major enhancementof environmental quality. Under these situ-ations, crop residues act as tiny dams thatslow down water runoff from fields, allow-ing the water more time to soak into the soil.

Crop residues on the surface not onlyhelp hold soil particles in place but keepassociated nutrients and pesticides on thefield. The surface layer of organic matterminimizes herbicide runoff and, with con-servation tillage, herbicide leaching can bereduced by as much as half (Bravermanet al., 1990).

Increased soil organic matter and cropresidues on the surface will significantlyreduce wind erosion (Skidmore et al., 1979).Depending on the amount of crop residuesleft on the soil surface, soil erosion can bereduced to near zero as compared with thatfrom an unprotected, intensively tilled field.Wind or water soil erosion causes soil deg-radation and variability to the extent of aresulting crop yield decline.

Papendick et al. (1983) reported that theoriginal topsoil on most hilltops had beenremoved by tillage erosion in the Palouseregion of the Pacific Northwest of the USA.Mouldboard ploughs were identified as theprimary cause, but all tillage implementswill contribute to this problem (Groveset al., 1994; Lobb and Kachanoski, 1999).Soil translocation from mouldboard plough-based tillage can be greater than soil losstolerance levels (Lindstrom et al., 1992;Groves et al., 1994; Lobb et al., 1995, 2000;Poesen et al., 1997). Soil is not directly lostfrom the fields by tillage translocation; rather,it is moved away from the convex slopesand deposited on concave slope positions.

Lindstrom et al. (1992) showed thatsoil movement on a convex slope in south-western Minnesota, USA, could result in asustained soil loss level of approximately30 t/ha/year from annual mouldboard-ploughing. Lobb et al. (1995) estimated soilloss in southwestern Ontario, Canada, froma shoulder position to be 54 t/ha/year from atillage sequence of mouldboard-ploughing,

tandem-discing and C-tine cultivating. Inthis case, tillage erosion, as estimated throughresident caesium-137, accounted for at least70% of the total soil loss. The net effect ofsoil translocation from the combined effectsof tillage and water erosion is an increase inspatial variability of crop yield and a likelydecline in soil carbon, related to lower soilproductivity (Schumacher et al., 1999).

Enhanced soil quality

Soil quality is the fundamental foundationof environmental quality. Soil quality islargely governed by soil organic matter (SOM)content, which is dynamic and respondseffectively to changes in soil management,tillage and plant production. Maintainingsoil quality can reduce the problems of landdegradation, decreasing soil fertility andrapidly declining production levels thatoccur in large parts of the world needing thebasic principles of good farming practice.

Soil compaction in conservation tillagefarming is significantly reduced by the reduc-tion of traffic and increased SOM (Angersand Simard, 1986; Avnimelech and Cohen,1988). Soane (1990) presented several mech-anisms by which soil ‘compactibility’ can beaffected by SOM:

1. Improved internal and external bindingof soil aggregates.2. Increased soil elasticity and reboundingcapabilities.3. Reduced bulk density due to mixingorganic residues with the soil matrix.4. Temporary or permanent existence ofroot networks.5. Localized change of electrical charge ofsoil particle surfaces.6. Change in soil internal friction.

While most soil compaction occursduring the first vehicle trip over the tilledfield, reduced weight and horsepowerrequirements associated with no-tillage canalso help minimize compaction. Additionalfield traffic required by intensive tillagecompounds the problem by breaking downsoil structure. Maintenance of SOM


contributes to the formation and stabiliza-tion of soil structure. The combined phy-sical and biological benefits of SOM canminimize the effect of traffic compactionand result in improved soil tilth.

While it is commonly known that tillageproduces a well-fractured soil, sometimesrequiring several tillage passes, it is a mis-conception that this is a well-aggregated,healthy soil. These soils never fare wellwhen judged against modern knowledge ofhigh ‘soil quality’. A tilled soil is poorlystructured, is void of many microorganismsand has poor water characteristics, just toname a few characteristics. As soils are farmedwithout tillage and supplied with residues,they naturally improve in overall quality,again support many microorganisms andbecome ‘mellow’ to the point of being easilypenetrated by roots and earthworms. Thistransition takes several years to accomplishbut invariably occurs given the opportunity.

Many traditional experienced farmerswill often ask, ‘How many years of no-tillageare possible before the soil becomes so com-pact as to require tillage?’ No-tillage experi-ence has shown exactly the opposite effect:once a no-tilled soil has regained its quality,it will continue to resist compaction andany subsequent tillage will cause unduedamage. Most soils will continue to buildorganic matter and improve in quality crite-ria for years into the practice of no-tillagefarming if the sequence is not broken by thethunderous effect of tillage.

Improved nutrient cycles

Improved soil tilth, structure and aggregatestability enhance the gas exchange and aer-ation required for nutrient cycling (Chaneyand Swift, 1984). Critical management ofsoil airflow, with improved soil tilth andstructure, is required for optimum plantfunction. It is the combination of manyfactors that results in comprehensive envi-ronmental benefits from SOM manage-ment. The many attributes suggest newconcepts on how we should manage thesoil for long-term aggregate stability andsustainability.

Ion adsorption or exchange is one of themost significant nutrient cycling functionsof soils. Cation exchange capacity (CEC) isthe quantity of exchange sites that can absorband release nutrient cations. SOM canincrease this capacity of the soil from 20 to70% over that of the clay minerals and metaloxides present. In fact, Crovetto (1996)showed that the contribution of organicmatter to the cation exchange capacityexceeded that of the kaolinite clay mineralin the surface 5 cm of his soils. Robert (1996)showed that there was a strong linear rela-tionship between organic carbon and thecation exchange capacity of his experimen-tal soil. The capacity was increased fourfoldwith an organic carbon increase from 1 to4%. The toxicity of other elements can beinhibited by SOM, which has the ability toadsorb soluble chemicals. Adsorption byclay minerals and SOM is an importantmeans by which plant nutrients are retainedin crop rooting zones.

Increased infiltration and concerns overthe use of nitrogen in no-tillage agriculturerequire an understanding of the biological,chemical and physical factors controllingnitrogen losses and the relative impactsof contrasting crop production practiceson nitrate leaching from agroecosystems.Domínguez et al. (2004) evaluated theleaching of water and nitrogen in plots withvarying earthworm populations in a maizesystem. They found that the total flux ofnitrogen in soil leachates was 2.5-fold greaterin plots with increased earthworm popula-tions than in those with lower populations.Their results are dependent on rainfallamounts, but do indicate that earthwormscan increase the leaching of water and inor-ganic nitrogen to greater depths in the pro-file, potentially increasing nitrogen leachingfrom the system. Leaching losses were loweron the organically fertilized plots, attribu-ted to higher immobilization potential.

Reduced energy requirements

Energy is required for all agricultural opera-tions. Modern, intensive agriculture requiresmuch more energy input than traditional


farming methods since it relies on the use offossil fuels for tillage, transportation, graindrying and the manufacture of fertilizers,pesticides and equipment used to applyagricultural inputs and for generating elec-tricity used on farms (Frye, 1984). Reducedlabour and machinery costs are economicconsiderations that are frequently givenas additional reasons to use conservationtillage practices.

Practices that require lower energyinputs, such as no-tillage versus conventionaltillage, generally result in lower inputs offuel and a consequent decreases of CO2-carbon emissions into the atmosphere perunit of land area under cultivation. Emissionsof CO2 from agriculture are generated fromfour primary sources: manufacture and useof machinery for cultivation, productionand application of fertilizers and pesticides,the soil organic carbon that is oxidizedfollowing soil disturbance (which is largelydependent on tillage practices) and energyrequired for irrigation and grain drying.

A dynamic part of soil carbon cycling inconservation agriculture is directly related tothe ‘biological carbon’ cycle, which is dif-ferentiated from the ‘fossil carbon’ cycle.Fossil carbon sequestration entails the cap-ture and storage of fossil-fuel carbon priorto its release to the atmosphere. Biologicalcarbon sequestration entails the capture ofcarbon from the atmosphere by plants. Fossilfuels (fossil carbon) are very old geologi-cally, as much as 200 million years. Biofuels(bio-carbon) are very young geologicallyand can vary from 1 to 10 years in age andas a result can be effectively managed forimproved carbon cycling. One example ofbiological carbon cycling is the agriculturalproduction of biomass for fuel. The majorstrength of biofuels is the potential to reducenet CO2 emissions to the atmosphere.Enhanced carbon management in conser-vation agriculture may make it possible totake CO2 released from the fossil carboncycle and transfer it to the biological carboncycle to enhance food, fibre and biofuelproduction, for example, using natural gasfertilizer for plant production.

West and Marland (2002) conducted acarbon and energy analysis for agricultural

inputs, resulting in estimates of net carbonflux for three crop types across three tillageintensities. The analysis included estimatesof energy use and carbon emissions forprimary fuels, electricity, fertilizers, lime,pesticides, irrigation, seed production andfarm machinery. They estimated that netCO2-carbon emissions for crop productionwith conservation, reduced and no-tillagepractices were 72, 45 and 23 kg carbon/ha/year, respectively.

Total carbon emission values were usedin conjunction with carbon sequestrationestimates to model net carbon flux to theatmosphere over time. Based on US averagecrop inputs, no-tillage emitted less CO2

from agricultural operations than did con-ventional tillage, with 137 and 168 kg ofcarbon/ha/year, respectively. The effect ofchanges in fossil-fuel use was the dominantfactor 40 years after conversion to no-tillage.

This analysis of US data suggests that,on average, a change from conventional till-age to no-tillage will result in carbon seques-tration in soil, plus a saving in CO2

emissions from energy use in agriculture.While the enhanced carbon sequestrationwill continue for a finite time until a newequilibrium is reached, the reduction in netCO2 flux to the atmosphere, caused by thereduced fossil-fuel use, can continue indefi-nitely, as long as the alternative practicesare continued.

Lal (2004) recently provided a synthesisof energy use in farm operations and itsconversion into carbon equivalents (CE).The principal advantage of expressing energyuse in terms of carbon emission as kg CE liesin its direct relation to the rate of enrich-ment of atmospheric CO2 concentration. Theoperations analysed were carbon-intensiveagricultural practices that included tillage,spraying chemicals, seeding, harvesting,fertilizer nutrients, lime, pesticide manufac-ture and irrigation. The emissions for differenttillage methods were 35.3, 7.9 and 5.8 kgCE/ha for conventional tillage, chisel tillageor minimum tillage and no-tillage methodsof seedbed preparation, respectively.

Tillage and harvest operations accountfor the greatest proportion of fuel consump-tion within intensive agricultural systems.


Frye (1984) found fuel requirements usingreduced tillage or no-tillage systems were55 and 78%, respectively, of those usedfor conventional systems that includedmouldboard-ploughing. On an area basis,savings of 23 kg/ha/year in energy carbonresulted from the conversion of conventionaltillage to no-tillage. For the 186 million ha ofcropland in the USA, this translates to apotential reduction in carbon emissions of4.3 million metric tonnes carbon equivalent(MMTCE)/year.

These results further support the energyefficiencies and benefits of no-tillage. Con-version of ploughed tillage to no-tillage,using integrated nutrient management andpest management practices, and enhancingwater use efficiency can save carbon emis-sions and at the same time increase the soilcarbon pool. Thus, adopting conservationagriculture techniques is a holistic approachto management of soil and water resources.Conservation agriculture improves efficiencyand enhances productivity per unit ofcarbon-based energy consumed and is asustainable strategy.

Carbon Emissions and Sequestration

Tillage or soil preparation has been an inte-gral part of traditional agricultural produc-tion. Tillage fragments the soil, triggers therelease of soil nutrients for crop growth,kills weeds and modifies the circulation ofwater and air within the soil. Intensive till-age accelerates soil carbon loss and green-house gas emissions, which have an impacton environmental quality.

By minimizing soil tillage and its asso-ciated (CO2) emissions, global increases ofatmospheric carbon dioxide can be reducedwhile at the same time increasing soil car-bon deposits (sequestration) and enhancingsoil quality. The best soil management sys-tems involve minimal soil disturbance andfocus on residue management appropriateto the geographical location, given the eco-nomic and environmental considerations.Experiments and field trials are required foreach region to develop proper knowledge

and methods for optimum application ofconservation agriculture.

Since CO2 is the final decomposi-tion product of SOM, intensive tillage,particularly the mouldboard plough, re-leases large amounts of CO2 as a resultof physical disruption and enhanced bio-logical oxidation (Reicosky et al., 1995).With conservation tillage, crop residues areleft more naturally on the surface to pro-tect the soil and control the conversion ofplant carbon to SOM and humus. Intensivetillage releases soil carbon to the atmos-phere as CO2, where it can combine withother gases to contribute to the greenhouseeffect.

Soils store carbon for long periods oftime as stable organic matter. Natural systemsreach an equilibrium carbon level deter-mined by climate, soil texture and vege-tation. When native soils are disturbed byagricultural tillage, fallow or residue burn-ing, large amounts of carbon are oxidizedand released as CO2 (Allmaras et al., 2000).Duxbury et al. (1993) estimated that agricul-ture has contributed 25% of the historicalhuman-made emissions of CO2 during thepast two centuries. However, a significantportion of this carbon can be stored, or sequ-estered, by soils managed with no-tillageand other low-disturbance techniques. Incre-ased plant production greater than thatof native soil levels by the addition offertilizers or irrigation can enhance carbonsequestration.

Carbon is a valuable environmentalnatural resource throughout the world’sindustrial applications of production andfossil energy consumption. Releasing carbonto the atmosphere by energy processes maybe offset by capturing carbon with plantbiomass and subsequently soil carbonsequestration in the form of organic matter.Energy consumers may at some time berequired to compensate for their atmosphericcarbon emissions by contracting with thosewho can sequester atmospheric carbon. Con-servation agriculture may be able to providethis sequestration benefit and thus be com-pensated for its role in maintaining low netcarbon emissions. While this ‘carbon trad-ing’ mechanism is still in the discussion


stage, it provides an important potentialbenefit.

A more detailed explanation of carbondioxide emissions and sequestration is givenin Chapter 17, together with comments onhow these interact with nitrous oxide andmethane emissions and the potential forcarbon trading.

Summary of the Benefits ofNo-tillage

Conservation tillage, and particularlyno-tillage, agriculture has universal appealbecause of numerous benefits. Improvedproduction with fewer inputs and reducedtime and energy are often cited as the high-lights. Conservation agriculture techniquesbenefit the farmers and the whole of soci-ety, and can be viewed as both ‘feeding and

greening the world’ for global sustain-ability. Agricultural policies are needed toencourage farmers to improve soil qualityby storing carbon as SOM, which will alsolead to enhanced air quality, water qualityand productivity and help to mitigate thegreenhouse effect.

Some of the more important benefits ofconservation tillage farming are:

1. Improved crop production economics.2. Increased SOM.3. Improved soil quality.4. Reduced labour requirements.5. Reduced machinery costs.6. Reduced fossil-fuel inputs.7. Less runoff and increased availableplant water.8. Reduced soil erosion.9. Increased available plant nutrients.10. Improved global environment.


3 The Nature of Risk in No-tillage

C. John Baker, W. (Bill) R. Ritchie and Keith E. Saxton

The ultimate decision to adopt a no-tillagesystem will have more to do with how farmers

perceive it altering their business risksthan anything else.

The risks associated with no-tillage are thosethat result in reduced income to the farmerthrough impaired crop performance and/orincreased costs. To be a sustainable techni-que, the failure rate for no-tillage must beno more, and preferably less, than that fortillage (Baker, 1995).

While early sceptics of the no-tillageconcept forecast many and varied problemsthat would ultimately lead to the downfallof the practice, experience has shown thatthere are no insurmountable obstacles inmost circumstances. The fact remains, how-ever, that many farmers are still reluctant toattempt the new technique, fearing that itmay increase their risks of crop failure orreduced yield.

The perception of risk is probably thesingle biggest factor governing the rate ofadoption of no-tillage, and it is likely toremain so for a long time. Only educationand personal experiences will finally putrisk into perspective. Recent results con-vincingly show that no-tillage is not inher-ently more risky than conventional tillage,even in the short term. Indeed, it can reducethe risk factor during crop establishmentif it is undertaken and managed correctly.

Of course, tillage is also subject to increasedrisk under poor management. It is thereforepertinent to explore the concept of risk dur-ing crop establishment and growth, and toexplain how this is affected by soundno-tillage practices.

What is the Nature of Risk inNo-tillage?

To plant and grow a crop with no-tillage, afarmer undertakes an economic risk that isaffected by three functional risk categories:(i) biological; (ii) physical; and (iii) chemi-cal. These risks are comparable betweentillage and no-tillage systems becausealmost all of them are the everyday risksof cropping either way. Only their relativelevels and remedies differ between the twotechniques. The combined effects of thefunctional risks result in economic risks.The results and associated implications aresometimes surprising and are examined atthe end of this chapter.

Biological risks

Biological risks arise from pests, toxins,diseases, seed vigour, seedling vigour,nutrient stress and, ultimately, crop yield.


The change to residue farming in general,which is the cornerstone of no-tillage, canhave a marked effect on the incidence ofdiseases and pests, both positively and nega-tively. Seed placement and soil and residuedisturbance by various drill or openerdesigns can influence all of these factors.

Pests

The change in earthworm and slug popula-tions creates the most common pest pro-blems in no-tillage. Slugs are particularlyprone to proliferate in residue in high-humidity climates and must often be con-trolled by chemical means. Earthworms, onthe other hand, can be either beneficial ordamaging, depending on type. Earthwormsgenerally provide positive effects that helpaerate, drain and cycle nutrients. All of theeffects of earthworms are not yet known butsome of their benefits in wet soils areexplained in detail in Chapter 7. Whiletillage destroys earthworms, no-tilled soilnearly always has a significant and import-ant increase in populations, and they are agreat ‘indicator’ organism for other bene-ficial biota developments. Other damagingworms, such as wireworms, are generallynot different regarding crop risks.

Slugs (Deroceras reticulatum) (Follas,1981, 1982) find shelter beneath the soil inmany types of seed slots and feed on sownseeds and establishing seedlings. Clearly,slugs increase the biological risks of no-tillage.But they are relatively cheaply countered bythe application of a suitable molluscicide.

Other pests can increase their damagerisk because of increased surface residuesor decreased physical destruction by tillagemachines. But then so too do many of theirpredators.

An example of pest–drill interaction isthat experienced with inverted T-shapedslots (see Chapter 4), which create sub-surface soil-slot environments that arehigher in soil humidity than either tilledsoils or other no-tillage slots. Soil faunathat are sensitive to soil humidity, such asslugs and earthworms, tend to congregatein such slots. These may have both posi-tive and negative effects for the sown crop

(Carpenter et al., 1978; Chaudhry, 1985;Baker et al., 1987; Basker et al., 1993).

Diseases

The most common soil disease that no-tillageappears to encourage is Rhizoctonia. Distur-bance of the soil during tillage appears topartly destroy the fungal mycelia. Otherfungal diseases are carried over in cerealresidue and decaying organic matter in rootchannels, requiring diligent use of croprotations or application of appropriatefungicides. On the other hand, the soil dis-ease take-all (Gaeumannomyces graminis)appears to become more confined underno-tillage because of reduced soil movement.

A concept called ‘green bridge’ wasidentified by Cook and Veseth (1993), inwhich certain root bacteria from recentchemically killed plants can readily trans-fer to new seedlings if no-tillage seeding isundertaken within 14–21 days after thegreen crop begins dying. The specificpathogen has not yet been identified, butsome delay after spraying and before no-tillage seeding appears to be an advantagewhere these bacteria exist, particularly ininstances of continuous cereal cropping.

Toxins

The risks arising from toxins relate mainlyto contact between seeds and decaying resi-due within the sown slot under persistentlywet conditions (see Chapter 7). This risk,which is peculiar to no-tillage in cold wetsoils, is eliminated by the use of no-tillageopeners that effectively separate seed fromthe residues (Chaudhry, 1985) or the use ofneutralizing agents sown with the seed(Lynch, 1977, 1978; Lynch et al., 1980).

The most common occurrence of residueeffects has been experienced with double-disc drills seeding into wet, soft soils withsurface residues. The residues tend to befolded and ‘tucked’ or ‘hairpinned’ into theseed slot with the seed dropped in the samelocation, which results in both the seed andresidue experiencing decaying conditionsand poor plant stands.

22 C.J. Baker et al.

Some explanations for early no-tillagefailures assumed that allelopathic exudatesfrom dying plants may have killed newlysown seeds. But later detailed explanationsfor the causes of seedling emergence fail-ures pointed to other (largely physical) fac-tors and it has been hard to find anyconfirmed cases of allelopathy having playedany role at all.

Nutrient stress

Without soil tillage to stir and mix appliedfertilizer applications, careful attentionmust be paid to placing the fertilizer inuntilled soils to optimize crop uptake andyield. Bands of fertilizer to the side andbelow the seed have proved to be very effec-tive, sometimes utilizing one fertilizer bandfor each pair of seed rows. While it isimportant to place fertilizers far enoughaway from seeds and seedlings to avoidtoxicity problems (see ‘Chemical Risks’), italso appears that separation distances can(and indeed should) be much closer thanthose commonly accepted for tilled soils(see Chapter 9). Fertilizer banding has beenfound to be optimally accomplished bysimultaneously seeding and fertilizing witha combination direct seed drill and ferti-lizer dispenser, and which is now commonpractice.

Again, the risk under no-tillage increasesonly if inappropriate equipment is used. Onthe other hand, there is voluminous evi-dence to show that, when fertilizers areplaced correctly, no-tillage crop yields maybe greater than those obtained from tilledsoils (see Chapter 9). Thus, while the risk ofnutrient stress under no-tillage may increasewith inappropriate equipment, it maydecrease compared with tillage if improveddesigns of no-tillage drills and planters areutilized.

Physiological stress

It has been stated that untilled seedbeds arenot as ‘forgiving’ as their tilled counterparts(Baker, 1976a). This is often true becauseseedlings have to emerge through coveringmaterial that is physically more resistant

than friable tilled soils. If the seeds are sowninto mellow soils that have been no-tilledfor several years or with scientificallydesigned furrow openers, such as inverted-T-shaped slots, the micro-environment ofthe slots will actually place less physiologi-cal stress on the seedlings than will a tilledsoil. Thus physiological stress at the time ofseedling emergence need not increase thebiological risks. It may actually decreasethe risk (see Chapter 5). Figure 3.1 showsthe difference in growth between seedlingsestablished within contrasting no-tillageslots resulting from physiological stress.

Seed quality

International seed testing authoritiesthroughout the world test mainly for purityand optimally wetted germination as themain indicators of seed quality. But thereare also agreed voluntary tests that describeother aspects of seed quality. One such test,the ‘accelerated ageing’ or ‘vigour’ test,examines a seed’s ability to germinate afterexperiencing a period of stress (usuallyhigh or low temperature). It is possible for agiven seed line to record a high-percentagegermination but a low-percentage vigour.Therefore final germinations counts give noreal indication of the vigour of a seed linealthough interim counts might be helpful inthis respect.

There is an important interaction betweenseed vigour and drill opener designs, whichcan have important impacts on biologicalrisk, and operators need to understand thisinteraction. No-tillage openers that createinverted-T-shaped slots produce about asfavourable a micro-environment as it ispossible to create for seeds, in either tilledor untilled soils. The main attribute is theavailability of both vapour-phase andliquid-phase water. This ensures that evenlow-vigour seeds will germinate, almostregardless of the soil conditions.

In contrast, seeds sown into tilled soilsor less favourable no-tillage slots that onlyprovide liquid-phase water for germinationof seeds are less likely to germinate. Farm-ers usually attribute such failures to a vari-ety of reasons, but seldom test the vigour of

Risk in No-tillage 23

the seed they had sown. When germinationof low-vigour seeds does occur in tilledsoils and open no-tillage slots, emergence ofthe seedlings is seldom restricted becauseof the friable nature of tilled soils and theopen nature of vertical no-tillage slots. Butthe ensuing crop is likely to perform poorly.

Extensive field experience withinverted-T-shaped no-tillage slots, whereeven low-vigour seeds will often germinateunder unfavourable conditions, have shownthat the seedlings often did not have thevigour to emerge and were instead foundtwisted, weak and un-emerged beneath thesoil surface. Observers at first attributedsuch twisting to fertilizer burn, but it is nowknown that fertilizer burn causes shrivel-ling and premature death of seedlings, nottwisting. When vigour tests were carriedout over a 3-year period on some 40 lines ofseeds that had shown symptoms of sub-surface seedling twisting in inverted-Tno-tillage slots, all seed lines were found tobe of low vigour (some as low as 18%).

The question is: What can be doneabout the problem? The responsibility restswith both the seed industry and individualno-tillage farmers. The seed industry needsto improve the quality of the seeds it offers

for sale or at least be prepared to discloseinformation on seed vigour to farmers. Somecompanies already do this. No-tillage far-mers, for their part, need to seek informa-tion from the seed industry about the vigourof particular seed lines and to be preparedto pay more for high-vigour lines. Those drillmanufacturers that market advanced no-tillage seed drills need to advise purchasersthat the weakest part of the system may nowbe seed quality, whereas previously it hadbeen drill quality.

Physical risks

Weather

Weather is likely to be the most variableand uncontrollable element in farming, andperforming no-tillage won’t change that.However, no-tillage does have the oppor-tunity to significantly modify the impact byseveral means, some already mentioned orobvious. Increased available plant water isoften the first noticeable effect, since resi-dues and minimal soil disturbance reduceevaporation and increase infiltration.

Improved trafficability in wet soil isoften a surprising no-tillage effect. With only


Fig. 3.1. Growth responses of wheat seedlings as a result of physiological stress when sown by awinged opener (left) and double disc (right) no-tillage openers.

one or two no-tillage crop years, the ‘fabric’of the soil strengthens (mainly throughimproved soil structure) and animal ormachine treading causes much less com-paction with fewer surface depressions. It iscommon knowledge that no-tilled fields areaccessible for seeding or spraying severaldays sooner following rainfall than tilledsoils, with less damage by surface compac-tion. No-tilled soils are not more dense orcompact than tilled soils; they just havemore resistance to down pressures as aresult of the increased organic matter andstructure.

No-tillage also moderates excessiveweather effects, such as extreme rainfalls andtemperatures. With the surface residues pro-tecting the surface against raindrop impact,runoff and erosion, rills and gullies don’tform. Residues minimize the high wind pro-files from having an impact on the soil sur-face and significantly reduce wind erosion.And very subtle dampening of soil tempera-ture variations often prevents freezing ofoverwintering plants. No-tillage seeding intostanding residues has allowed successfulwinter wheat crops in far more northerlyclimates in the northern hemisphere thanpreviously possible, with increased yieldscompared with spring-seeded crops.

Young et al. (1994) showed how sea-sonal weather variations could affect therisk of altering the profitability of conserva-tion tillage (which includes a component ofno-tillage) compared with conventional till-age (Fig. 3.2). They pointed out that theperiod 1986 to 1988 was particularly dry inthe Palouse area of Washington State, whichfavoured the profitability of conservationtillage. The 1990/91 winter was particularlycold, which also favoured conservation till-age. At other times (1989 and 1990) theweather did not favour either technique. Inthis manner the relative risks of changingprofitability are clearly illustrated. Suchrisks cannot be predicted with any accu-racy, but they can be minimized by select-ing conservation tillage techniques and/ormachines with the widest possible toleranceof changing weather patterns.

It is obvious that no-tillage machinescannot control the weather. But it has beenrepeatedly noted that when no-tillage isundertaken with appropriate residue mani-pulation and seeding machines designedwith proper seeding slots, seeds and seed-lings have considerably better protectionfrom weather variations (e.g. too hot, cold,dry, windy or wet) than when that soil iseither tilled or drilled with inappropriate


Fig. 3.2. The relative profitability of two crop establishment systems in Washington State over 5 years(from Young et al., 1994).

no-tillage equipment. Thus, risks arisingfrom inclement weather have the potentialto be reduced under no-tillage if appropri-ate methods and equipment are used.

Machine function

Many of the physical risks arise from howwell no-tillage machines perform theirintended functions. The machine's designersmust understand and incorporate therequired capabilities to perform its intendedfunctions in a wide variety of soil types, resi-dues and weather conditions. These varia-tions can change widely even within a singlefield or on a single day. There is much riskinserted into the farming system from amachine that operates at different levels ofperformance on different days in differentparts of a field. A successful no-tillage drillmust have a wide tolerance of changing,sometimes even hostile, conditions.

There are few more important physicalfunctions than creating the correct micro-environment for the seeds within the soil.Different drill openers differ markedly intheir abilities to do this (see Chapter 4) andthis affects the level of risk associated withdifferent machines. To reduce machine-related risks, the openers of no-tillage drillsmust follow ground surface variations andmove through significant surface residueswithout blockage. Seeding depth can onlybe maintained by careful tracking of the soilsurface by the seed opener.

Maintaining surface residues is themain long-term benefit from no-tillage,especially for reducing erosion and tempe-rature fluctuations and increasing soil faunaand infiltration. Residues are an equallyimportant ingredient in short-term biologi-cal performance of seedling emergenceand vigour. No-tillage does not offer theoption to ‘till out’ last season’s mistakes ofvehicle ruts, animal paths, washed gullies,hardpans, etc. It is critically important toavoid creating field surfaces that are notmechanically manageable the followingcropping season.

No-tillage seeding machines not onlymust physically handle residues consis-tently without blockage but must also have

the ability to micro-manage those residuesclose to the slot and to utilize them for thebenefit of the sown seeds and plants (Bakerand Choudhary, 1988). Conversely, theinability of any opener to do these thingssignificantly increases the risks from no-tillage, since the residues themselves are animportant ingredient in creating a favour-able habitat for seeds and seedlings. A posi-tive utilization of crop residues in no-tillageis considerably different from tillage farm-ing in that residues are seen as beneficialrather than a hindrance to machine perfor-mance. Since tilled soils, almost by defini-tion, have minimal surface residues, theydo not benefit in comparison with goodutilization of residues by no-tillage openers,but they may compare well with no-tillagewhere residues are not utilized.

Similarly, the ability to uniformly trackthe untilled soil surface for uniform seedingby no-tillage drills will greatly determinethe biological risks associated with poorseedling stands and vigour. These aspectsare discussed in greater detail in Chapter 8,but in summary it should be acknowledgedthat there is a need for no-tillage openers tofollow the surface better than their tillagecounterparts, or the risk of poor crop standswill increase.

No-tillage drills encounter much higherforces and wear of components than theirtillage counterparts. Since some of the criti-cal functions, such as residue handling andslot formation, are often dependent on themechanical wear remaining within narrowlimits, maintenance of no-tillage machinesis more important than for conventionaldrills. To put it another way, the absenceof adequate maintenance on no-tillagedrills may increase the risk of malfunctiondisproportionately.

None of the physical functions describedabove, however, has any relevance to riskunless its successful implementation has anidentifiable biological function with regardto the sown seeds and emerging plants.Somewhat surprisingly, many of the early‘desirable functions’ listed for no-tillageopeners (e.g. Karonka, 1973) failed to defineany biological objectives at all. Failureto recognize these biological-engineering


linkages alone probably increased the levelof risk of early no-tillage and accounted formuch of the ‘hit-and-miss’ reputation thetechnique acquired in its early days.

Ritchie et al. (2000) summarized thebiological risks associated with six criticalfunctions that no-tillage drill openers mustperform. Their modified chart is shown inFig. 3.3. Each criterion was assigned a riskrating of 1 to 10 (1 being low-risk and 10being high-risk) according to publishedscientific data and engineering principles.

Several commonly used drill openerswere ranked using the criteria of Fig. 3.3 andare shown in Table 3.1. The risk-assessmentof the disc version of winged openers closelymatches actual field surveys of users inNew Zealand, which have consistently founda 90–95% success rate over several yearsand hundreds of thousands of hectares offield drilling (Baker et al., 2001). But themost commonly used opener throughout theworld (vertical double disc) ranks poorly.This helps explain the many no-tillagefailures associated with this opener.

Chemical risks

Chemical risks have many of the sameimplications as physical risks. They arelinked to the resultant biological risks thatarise from them. Two stand-alone chemicalrisks are the effectiveness of weed controlby herbicide application and the risk oftoxicity or ‘seed burn’ from inappropriateplacement of fertilizer in the seed slot rela-tive to the seed placement.

Weed control

Weed control with herbicides must be aseffective as that with mechanical means orthe risk of impaired crop performance willincrease. The principal variables determin-ing herbicide effectiveness are as follows.

APPLICATION OF ACTIVE INGREDIENT. The abilityof operators to properly interpret the labelsand literature supplied with various herbi-cides and pesticides has much to do with

the success of applications. In addition,operators need to be able to recognize weedspecies and to be able to reliably calibratetheir spraying machines. All of these opera-tor choices are more risky than correspond-ing tillage operations. Nor are sprayingmistakes as forgiving as tillage mistakes,which can often be ‘repaired’ the next day.

SELECTION OF APPROPRIATE CHEMICAL. Theselection of tillage tools can follow a trial-and-error routine where: (i) the non-performance of one implement becomesobvious within a short time; (ii) the conse-quences are seldom of great magnitude; and(iii) rectification using an alternative imple-ment is accomplished quickly. Few, if any,of these flexibilities are available whenchoosing appropriate chemicals for a givenweed or pest situation. Occasionally a mis-taken choice can be rectified by the applica-tion of another chemical, but the optionsare fewer than with tillage and the risks aretherefore greater.

WEATHER. Some chemicals require severalhours without rain to be fully effective,while others are virtually ‘rain-fast’. Sincemost chemicals involve a significant outlayof cash and, unlike tillage tools, are notreusable, the risk from untimely rain andwind is greater than with tillage.

WATER QUALITY. Some foliage-applied herbi-cides, especially those that are inactivatedupon contact with soil, such as glyphosate,have their efficacy altered by impurities inthe mixing water. Of particular concern iswater derived from storage dams or under-ground bores that is contaminated with par-ticles or iron and carbonates. Some chemicaleffectiveness is quite variable with wateracidity levels. Similarly, impurities on theleaves of target foliage, such as mud anddust from stock or vehicle traffic or recentlyapplied lime, may inactivate some herbicides.

VIGOUR OF WEEDS. The vigour of the targetweeds at application time is important.Some herbicides (e.g. glyphosate) work bestwhen sprayed on to healthy, actively grow-ing plants. Others (e.g. paraquat) work best



Fig

.3.3

.A

biol

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alris

k-as

sess

men

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drill

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when the target plants are already stressed.Knowledge of these requirements is essen-tial if effective weed control is to take place.

OPERATOR ERROR. During tillage, drivingerrors by an operator are seen immediatelybut they are seldom sufficiently serious toshow up in the subsequent crop as an areaof impaired yield. With once-over spraying,errors do not show up immediately.Paraquat is the most rapid to take effect buteven then it is days before mistakes becomevisible. Most other herbicides take at least aweek to show any visible effect, by whichtime the crop may have been sown, makingremedial action virtually impossible with-out adversely affecting the sown crop.

Toxicity of fertilizers

There are two risks from inappropriate fer-tilizer placement at sowing. If fertilizer is

broadcast on to the ground surface ratherthan placed in the soil at the time of drill-ing, there is a serious risk of impaired cropperformance and yield as a result of limitedplant availability (see Chapter 9). On theother hand, when fertilizer is sown with theseed there is a danger of the fertilizer dam-aging or ‘burning’ the seed under no-tillageunless the two are effectively separatedin the soil. The latter risk increases withincreased soil dryness. Separation is moredifficult to achieve in no-tillage than intilled soils, but it has been shown to bequite possible with the correct equipmentwithout increased risk.

Economic risk

All forms of risk during no-tillage are finallymeasured as economic risk. But economic


Disc versionof winged

opener

Verticalangled

discSlanted

angled disc

Shank andsweep

openersVertical

double disc

Simplewinged

tinea

Slot micro-environment

1 4 4 3 7 2

Slot covering 1 3 2 2 7 4Fertilizer

placement1 3 3 2 7 7

Seed depthcontrol

2 1 1 9 3 8

Surface following 1 4 4 9 5 9Residue handling 1 3 3 7 3 10Total out of

max. 607 18 17 32 32 40

Chance ofimpaired biologicalperformanceb

11% 30% 28% 53% 53% 67%

aSimple winged tine openers are designed to be used predominantly in smooth pasture. Comparingthese openers for all no-tillage (including arable) penalizes them unfairly but they are neverthelessincluded here to illustrate how Fig. 3.3 exposes the limitations of such openers.bThe figures represent the chances of obtaining an impaired biological performance from using any ofthese openers. For example, the table suggests that use of the disc version of winged openers will resultin an 11% chance of a poor crop, whereas use of shank and sweep openers will result in a 53% chanceof a poor crop unless there is little residue present and the fields are smooth and flat.

Put another way, the table suggests that in heavy residues on less-than-smooth ground there would beabout five times as much chance of getting an impaired crop using shank and sweep type openers ascompared with the disc version of winged openers.

Table 3.1. Examples of how some common no-tillage openers rank in terms of biological risk.

risk should not be centred on cost savingsalone. Indeed, focusing on cost savings mayincrease rather than decrease both real andimagined economic risks. This is for tworeasons:

1. Where farmers already own tillageequipment, they see the acquisition ofno-tillage equipment or even the use of con-tractors (custom drillers) – no matter howcheap – as duplication of an existing cost.2. Purchasing inferior no-tillage equipmentfor cost savings may well result in loweredcrop yields, even if only temporarily. Sucha result may indeed be less cost-effectivethan either tillage or no-tillage undertakenwith more expensive (and probably supe-rior) equipment that maintains or evenimproves crop yields.

We shall examine both scenarios below.

The costs of tillage versus no-tillage

The costs of several alternatives for adopt-ing no-tillage under a double cropping sys-tem (two crops per year, e.g. wheat followedby a winter forage crop for animal con-sumption) in New Zealand were analysedand compared with the costs of tillage(C.J. Baker, 2001, unpublished data).

These were:

1. Engaging a tillage contractor (customdriller) versus engaging a no-tillage contractor.2. Purchasing new tillage equipment ver-sus purchasing new no-tillage equipment.3. Retaining ownership of used tillageequipment versus purchasing used no-tillageequipment.4. Retaining ownership of used tillageequipment versus purchasing new no-tillageequipment.5. Retaining ownership of used tillageequipment versus engaging a no-tillagecontractor.

Fixed costs were included, such asinterest on the investment, depreciation,insurance and housing, and expressed as aper-hour cost of annual machine use. Drillsand planters are used for a shorter periodeach year to plant the same area under no-tillage than under a tillage regime. Thus the

per-hour costs increase even though theper-hectare and per-year costs decrease.The analysis also assumed that a singlelarge tractor and driver would be requiredfor no-tillage compared with two or moresmaller tractors and drivers for tillage.

For simplicity, the study assumed thatthe no-tillage drill being compared was ofan advanced design, which ensured that cropyields would remain unchanged regardlessof which option was chosen. Such anassumption is reasonable when applied toadvanced no-tillage drills (which cost moreanyway) but is unrealistic for inferior drills(see below).

The cost analysis did not account fortaxation issues, subsidies or other purchaseincentives of any nature. These could other-wise be expected to favour no-tillage sincemany countries have incentives to encour-age the practice because of its conservationvalue. Thus the results could be consideredconservative in terms of the benefitsrecorded for no-tillage.

A more detailed account of the eco-nomic analysis is given in Chapter 18.

Operating costs strongly favoured no-tillage. In all of the above options (1) to (5),the costs favoured no-tillage by betweenUS$16 and US$40/ha/year.

The greatest advantage (US$40/ha/year)was shown by option (2) – purchasing newtillage equipment versus purchasing newno-tillage equipment. This was mainlybecause of reduced running costs of theno-tillage equipment since the total capitaloutlays in each case were very similar.

The least advantage (US$16/ha/year)was shown by option (4) – retaining owner-ship of used tillage equipment versus pur-chasing new no-tillage equipment. Clearlythe advantage would increase for thisoption when and if a decision was even-tually taken to sell the existing tillageequipment, provided that a market for suchequipment still existed. But realistically,the costs of purchasing no-tillage equip-ment would probably remain additional tothe costs of retaining ownership of existingtillage equipment for a period.

Farmers often see retention of theirexisting tillage equipment as ‘insurance’


while they gain the knowledge and skillsnecessary to master the new no-tillage tech-nique to a stage where they can abandontillage altogether. Other farmers claim thatby going ‘cold turkey’ (i.e. selling the tillageequipment at the same time as they pur-chase the no-tillage equipment) the learningprocess is achieved faster and more effec-tively. This study took the conservativeapproach.

The advantage for no-tillage fromoption 1 – engaging a no-tillage versus till-age contractor – was US$36/ha/year. Theadvantage for no-tillage from option 3 –retaining ownership of used tillage equip-ment versus purchasing used no-tillageequipment – was US$30/ha/year and foroption 5 – retaining ownership of used till-age equipment versus engaging a no-tillagecontractor – was US$34/ha/year. Costadvantages for no-tillage would be expectedto increase when sale of the existing tillageequipment became feasible.

Machine impacts on crop yields andeconomic risk

The effect of any one no-tillage drill designon crop yield and risk (and therefore eco-nomic returns) will be more important thanits initial cost, when compared with eithertillage or cheaper no-tillage alternatives.This belief has caused the research anddevelopment of improved no-tillage machinesand systems as a means to reduce the risksassociated with the practice, almost regard-less of cost. The following analyses ofmachine capability versus expected cropyields and the resulting economics clarifiesthis belief.

The per-hectare charges that no-tillagecontractors (custom drillers) make for theirservices are a good barometer of the relativecosts associated with different no-tillagemachines and systems. If we take NewZealand contractors as an example, wefind that those with advanced (expensive)no-tillage drills in 2004 charged betweenUS$72 and US$96/ha for their services,whereas those with lesser (cheaper) drillscharged between US$36 and US$60/ha.

Differences between the ranges ofcharges are attributable mainly to differ-ences in the initial costs of the two classesof machines and the different sizes of trac-tors needed to operate them. Differenceswithin both ranges of costs reflect differ-ences in the costs of competing options(such as tillage) together with differencesin work rates and maintenance costsbrought about by different field sizes,shapes, topographies and soil types (includ-ing abrasiveness).

Taking the midpoint of each scale,the premium a farmer therefore paid inNew Zealand in 2004 for access to a moreadvanced drill was about US$36/ha. Actualcontractor charges in other countries willdiffer from these figures but the relativitybetween the costs associated with advancedmachines and lesser machines is likely tobe similar.

So a key question is: How much doesan advanced no-tillage drill have toincrease crop yields in order to justify theUS$36/ha premium paid for the better tech-nology under 2004 price conditions?

Wheat sold in New Zealand in 2004 forapproximately US$170/t. The average yieldof spring-sown wheat in New Zealand in2004 was 5.7 t/ha and the average autumn-sown wheat yield was 7.4 t/ha (N. Pyke,Foundation for Arable Research, 2004, per-sonal communication). Gross returns foraverage spring- and autumn-sown wheatcrops in 2004 were therefore US$969/haand US$1258/ha, respectively.

To recover an additional US$36/ha inthe costs of no-tillage drilling would requirean increase in yield of 0.21 t/ha (or210 kg/ha). This represented a 3.7% increasein yield of a spring-sown wheat crop or a2.9% increase in an autumn-sown wheat crop.

Such yield increases have been com-mon. For example, the US Department ofAgriculture obtained an average of 13% wheatyield increase in seven separate experi-ments over a 3-year period in WashingtonState by switching to a more advanced no-tillage drill compared with the best ‘other’no-tillage drill that was then available(Saxton and Baker, 1990). Similarly, theNew South Wales Department of Agriculture


(Australia) recorded an 11-year average of27% yield advantage from soybean sownannually after oats using the same advancedno-tillage openers, compared with tillage(Grabski et al., 1995).

Commercial field experience over a9-year period in New Zealand, the USA andAustralia suggests that such research-plotmeasurements have been a realistic reflec-tion of field expectations. Wheat and othercrop yields approaching twice the nationalaverages have become common from no-tillage practised at its most advanced level.

Conclusions

It can be said that, when comparing theeconomic risks of tillage and no-tillage,more management and more sophisticatedmachinery are needed to undertake no-tillage correctly and successfully. But, if theappropriate management and machineryare used and the reasons for these choices

are understood, there will be no more andoften less economic risk with no-tillagethan with tillage. All of the various formsof risk come together in the multiple-yearrotations required of modern farming in anintegrated management system. Figure 3.4illustrates the results of a comprehensiveassessment of financial risk made during 6consecutive years of experiments by Younget al. (1994) in Washington State, USA.

These experiments compared the com-bined results of conservation tillage, whichincluded several consecutive years ofno-tillage, versus conventional tillage, theeffects of maximum, moderate and mini-mum weed control and crop rotations, allunder a high level of agronomic manage-ment. Considering all treatments and 6years of variable weather factors, conserva-tion tillage had the smallest economic riskdue to conserved moisture, good yields andlow inputs. They concluded that the winterwheat–spring barley–spring peas rotation atmaximum or moderate weed management


Fig. 3.4. Profit and risk analyses for 12 cropping systems in the Palouse area, Washington, 1986–1991(from Young et al., 1994). WWW, wheat, wheat, wheat rotation; WBP, wheat, barley, peas rotation.

levels (RM3 or RM2) dominated all othersystems in profitability (profit of $30–40/ha)and had the lowest economic risk or ‘profitvariability’.

Summary of the Nature of Risk inNo-tillage

1. The perception that no-tillage involvesgreater risk than tillage is one of the greatestimpediments to its more widespreadadoption.2. The combination of all the componentsof risk manifests them as economic risk.3. The components of risks in no-tillageare biological, physical and chemical.4. Biological risks relate to pests, toxins,nutrient stress, seed vigour, seedling vig-our, disease and impaired crop yield.5. Physical risks relate to weather, slotmicro-environment and machine perfor-mance and reliability.

6. Chemical risks relate to the supply andavailability of plant nutrients, seed ‘burn’from fertilizers and the effectiveness ofapplication of chemical herbicides andpesticides.7. The function and design of no-tillageseed drills can have an influence on pests,toxins, nutrient stress, diseases, fertilizer‘burn’, slot micro-environment, machineperformance and durability and the supplyand availability of plant nutrients.8. Performed correctly with appropriateequipment, no-tillage has no more, andoften less, total risk than tillage, even in theshort term.9. Performed incorrectly with inappro-priate equipment, no-tillage has greaterassociated risk than tillage.10. It is often ‘false economy’ to cut costs inno-tillage, particularly in machine effec-tiveness, as the savings in cost may be muchless than the reductions in crop yield thatare likely to result.


4 Seeding Openers and Slot Shape

C. John Baker

Very few no-tillage openers were originallydesigned for untilled soils. Most are adaptations

of conventional openers for tilled soils.

A seeding opener is the soil-engagingmachine component that creates a ‘slot’,‘furrow’ or ‘opening’ in the soil into whichseed and perhaps fertilizer and insecticideare placed. Different shapes of soil slots maybe created by conventional and no-tillageopeners. The most important feature is thecross-sectional shape, as if you had cutacross the opener path after its passage witha knife and were looking at the verticalexposed face.

Openers are the only components of ano-tillage drill or planter that actually breakthe soil surface. In no-tillage seeding, theyare required to perform all of the functionsnecessary to physically prepare a seedbedas well as sow the seed and perhaps ferti-lizer. In contrast, in conventional tillage asuccession of separate tillage tools are usedto prepare the seedbed, and the seed drillthen only has the relatively simple task ofimplanting the seed and perhaps fertilizerinto a pre-prepared medium.

A large amount of scientific evidenceshows that the most important aspect ofthe mechanics of different no-tillage openerdesigns is the shape of the slots they createin the soil and their interaction with seed

placement and seedling emergence andgrowth. Generally, there are three basic slotshapes created by no-tillage openers andtwo other ways of sowing seed that do notinvolve creating a continuous soil slot atall: (i) V-shaped slots; (ii) U-shaped slots;(iii) inverted-T-shaped slots; (iv) punchplanting (making discrete holes in theground and sowing one or more seeds perhole); and (v) surface broadcasting (seedsrandomly scattered). Only one slot shape,the inverted-T slot, is used in no-tillage thathas not been an adaptation of a slot shapealready used for tilled soils.

Figure 4.1 is a diagrammatic represen-tation of slot shapes i–iii as created in a siltloam soil at three different moisture con-tents (Dixon, 1972). The mechanics of eachof these seeding methods and the resultingcharacteristics will be further discussed indetail in the following sections.

Several authors (e.g. Morrison et al.,1988; Bligh, 1991) have compiled lists anddiagrams of openers and in some casescompared observations of field perfor-mance. But few detailed scientific studieshave been made in which all but theimportant variables being studied havebeen controlled or accurately monitored.Such studies (which also included somenew and innovative designs) are reportedbelow.

© FAO and CAB International 2007. No-tillage Seeding and Conservation34 Agriculture, 2nd edn. (eds C.J. Baker and K.E. Saxton)

Vertical Slots

V-shaped slots

In untilled soils, V-shaped slots are almostinvariably created by two discs that touch(either at their bases or behind this posi-tion) and are angled outwards towards theirtops. The two discs are not always of equaldiameter. The included angle (the angle ofthe V) is usually about 10°, but this is notcritical. Seed is delivered into the gapbetween the two discs, preferably rearwardsof the centre ‘pinch point’, so as to preventthe seed from being crushed as the discscome together.

When arranged so that both discs areat the same angle to the vertical, the slothas a vertical V shape and is created byeach of the angled discs pushing roughlyequal amounts of soil sideways. Thefront edges of the two discs at the ground-surface level are apart from one another,

which can cause a problem if residuesenter the gap. To avoid this they are usu-ally configured in one of the followingthree forms.

Double disc: offset (Fig. 4.2)

In this form one of the two angled discs(there is no third leading disc) is positionedforward of the other so as to present a singleleading cutting edge and deflect residue.The second disc still forms the other side ofa vertical V but its leading edge is nestledbehind that of the first disc, thus avoidingresidue blockage and reducing the magni-tude of downforce required for penetration.

Double disc: unequal size (Fig. 4.3)

By placing the smaller of the two discsalongside its larger neighbour, the leadingedge of the larger disc becomes the leadingedge of the whole assembly in much the

Seeding Openers and Slot Shape 35

Fig. 4.1. Typical profiles ofvertical V- (left), U- (centre)and inverted-T- (right) shapedno-tillage seed slots in a siltloam soil at 15%, 20% and27% moisture contents (fromDixon, 1972).

36 C.J. Baker

Fig. 4.2. Typical offset double disc no-tillage openers that create vertical V-shaped slots.

Fig. 4.3. Typical unequal-sized double disc no-tillage openers that create vertical V-shaped slots.

same way as for the offset design. Often, thesmaller disc is also offset.

Triple disc (Fig. 4.4)

In this form a third vertical disc is placedahead of, or between, the two angled discs.This additional disc cuts the residue suffi-ciently for the two following discs to deflectit sideways. The third disc, however, addsto the amount of downforce required forpenetration.

All forms of double disc and tripledisc openers create vertical V-shaped slotssince the actual slot shape is created by thetwo angled discs, regardless of their sizesor offsets. The third (leading) disc in thetriple disc configuration mainly cuts theresidue and influences the slot in a minorway. The triple disc design with the lead-ing disc operating slightly below the basesof the two angled discs reduces some of thedetrimental effects of ‘hairpinning’ (seeChapter 7, ‘Drilling into Wet Soils’) androot penetration problems common to bothdouble and triple disc configurations. Sim-ilarly, by using a wavy-edged leading disc(sometimes referred to as a ‘turbo disc’), a

degree of soil loosening will usually beachieved ahead of the two angled discs andthis helps offset the compacting tendenciesof the following double discs.

The action of vertical double disc open-ers in the soil is to wedge the soil sidewaysand downwards in a V formation. They donot normally heave or raise the soil upwards.In some very sticky soils that cling to theoutsides of the discs, some of that soil willbe torn away and carried upwards, leaving adisrupted slot (Fig. 4.5).

Figure 4.6 shows the zones of compac-tion created by a vertical triple disc openeroperating in a normal manner in a silt-loamsoil (Mitchell, 1983).

From a dry soil perspective, the mostdistinguishing feature of the slot is the neat-ness of the vertical V-shaped cut, unless thesoil is friable, in which case this neat cutmay collapse. But even friable soils progres-sively become more structured and less fri-able (as organic matter levels and microbialaction increase under no-tillage). Thus, withtime, most vertical V-shaped slots becomemore clearly defined and less likely tocollapse of their own accord after passage ofthe opener.


Fig. 4.4. A typical triple disc no-tillage opener that forms a V-shaped slot (from Baker, 1976b).

Because of its wedging action, there isoften little or no covering material availableto cover seeds placed into the bottom of theV slot. This is even more of a problem when

the opener is used in a moist, non-friablesoil. Figure 5.1 illustrates such a situation.The plastic nature of the moist soil preventsthe formation of loose soil crumbs, which

38 C.J. Baker

Fig. 4.5. A slot created by a vertical double disc opener in wet sticky soil in which the soil has stuck tothe outside of the disc and been pulled up from the slot zone.

Fig. 4.6. The pattern of soil strength around a vertical V-shaped no-tillage slot as created by a tripledisc opener in a damp silt loam soil (from Baker et al., 1996).

might otherwise fall back over the seed ascovering material (see Chapter 5).

The usual recourse is to follow verticaldouble disc openers with some configura-tion of V-shaped press wheels arranged sothat they squeeze the soil in the oppositedirection to the discs after the seed has beendeposited (Fig. 4.7). Unfortunately, thisaction is also one of compaction, albeit inthe opposite direction to the original forces.In an untilled soil, the wedging action ofvertical double disc openers does little, ifanything, to create a favourable environ-ment for seeds.

The greatest advantages of vertical dou-ble disc openers are: (i) their construction isrelatively simple and maintenance-free,although the latter attribute depends on theuse of good bearings and seals; and (ii) theirability to pass through surface residueswithout blockage.

The most important disadvantagesare: (i) the high penetration forces required;(ii) their poor performance in suboptimalsoil conditions; (iii) their tendency to tuck(or ‘hairpin’) residue into the slot, which indry soils interferes with seed–soil contactand in wet soils results in fatty acid

fermentation that kills germinating seeds(Lynch, 1977); and (iv) the inability of indi-vidual openers to separate seed from fertil-izer in the slot. Indeed, due to the shape ofthe slot, vertical double disc openers tendto concentrate the seed and fertilizertogether at the base of the slot more thanother openers (Baker and Saxton, 1988;Baker, 1993a, b).

Despite these shortcomings, verticaldouble disc openers have been included onmore no-tillage drill designs than anyother opener design to date. Unfortunately,however, because of their dependence onfavourable soil conditions to achieve accept-able seeding results (or, more correctly,their intolerance of unfavourable condi-tions), they have also been responsible formuch of the perception that risk increaseswith the practice of no-tillage.

It is important to emphasize the dis-tinction between tilled and untilled soilsand to illustrate the dangers inherent inderiving designs of no-tillage machinesfrom those that had been successful in tilledsoils. Tilled soils are naturally soft beforeseeding and the wedging action of verticaldouble disc openers is generally beneficial,


Fig. 4.7. Press wheels arranged in a V configuration for closing no-tillage slots created by verticaldouble disc openers (from Baker, 1981a, b).

especially when the soil is dry. It conso-lidates the soil alongside and beneath theseed, which results in increased capillarymovement of water to the seed zone. Cover-ing is seldom a problem in tilled soils,because the entire seedbed is comprisedof loosened soil. Thus, in many ways,V-shaped openers are an advantage in tilledsoils, whereas they have serious short-comings in untilled soils.

Other mechanical forms of verticalV-shaped openers for tilled soils simply donot work in untilled soils because they willnot penetrate in the less friable conditions.These include sliding shoe-type openersand V-ring roller openers (Baker, 1969b).Further consideration of these designs isnot justified since they simply cannot effec-tively seed no-tilled soils.

Slanted V-shaped slots

To reduce the compaction tendencies ofvertical V-shaped slots, some designershave slanted double or triple disc openersat an angle to the vertical, and sometimesalso angled to the direction of travel. Whenthey are slanted vertically, the uppermostdisc pushes the soil partially upwards, thusreducing the compaction that otherwiseresults from the soil being displaced onlysideways by vertical double disc openers.The lowermost disc on slanted double discopeners, however, is then forced to displacesoil in a more downward direction, addingto its compaction tendency. Since rootsmainly travel in a downward direction, it isdebatable whether or not the slanting ofdouble or triple disc openers overcomes thedisadvantages inherent from their tendencyto compact the slot in the root zone. On theother hand, slanting of V-shaped slotsundoubtedly makes them easier to cover,since a near-vertical press wheel is requiredto shift soil more in a downward directionthan sideways.

Two slanting double discs can be com-bined in such a way that the front pair ofdiscs (which are angled vertically in onedirection) sow fertilizer and the rear pair ofdiscs (which are angled vertically in the

opposite direction) sow seed at a shall-ower depth. Not only does this effectivelyseparate seed and fertilizer in the verticalplane, but additionally the zone that wouldnormally be compacted below the seed bythe lowermost disc of the rear opener ispre-loosened by the uppermost disc of thefront opener, thus partly negating the unde-sirable compaction effect of the seedingopener. Figure 4.8 shows a pair of slanteddouble disc openers.

Single discs that are angled in relationto the direction of travel (and sometimesalso slanted vertically) are discussed below.

U-shaped slots

There is a wide range of opener designs thatform U-shaped slots (Baker, 1981a, b):(i) angled disc-type openers; (ii) hoe openers;(iii) power till openers; and (iv) furrowers.

The slots made by all of these designsare distinguishable from V-shaped slots bythe slot bases being broad rather thanpointed like a V. The slot-making action of

40 C.J. Baker

Fig. 4.8. A pair of slanted discs at opposingangles. The front discs place fertilizer and the reardiscs place seed at a shallower depth. (FromBaker et al., 1996.)

each of these openers is quite different,even though they all result in a similarlyshaped slot, but none of the openers has thedownward wedging action of double discopeners. Thus there is less soil compactionassociated with all U-shaped slots thanwith V-shaped slots.

Angled disc-type openers mostly scrapesoil away from the centre of the slot; hoe-and furrow-type openers burst the soilupwards and outwards; power till openerschop the soil with a set of rotating blades;and furrow-type openers scoop the soil outfrom the slot zone. Further, all of thedesigns produce some loose soil on the sur-face near the slot, which can be used tocover the slot again, although in all casesthis usually requires a separate operationto drag this soil back over the slot (seeChapter 5) and its effectiveness is soil-moisture-dependent.

Angled disc-type openers

The action of angled discs is mostly(although not entirely) one of scuffing. Ver-tical angled discs are angled slightly to thedirection of travel (normally about 5–10degrees). Seed is delivered to a boot located

at or below ground level, close to the rear(lee) side of the discs where it is largely pro-tected from blockage by residue because ofthe angle of the disc. There are two forms ofangled vertical disc opener.

ANGLED FLAT DISCS (FIG. 4.9). This type uses avertical flat disc (i.e. it has no undercuttingaction) angled to the direction of travel. Thedisc and supporting bearings need to haveconsiderable inherent strength since theside forces are quite large, especially whenoperating at some speed and/or in plasticsoils that resist sideways movement. Becausethe discs continually have a sideways force,they are often configured in pairs with eachpair of discs at opposite angles so that theside forces of the entire machine cancel(see Fig. 4.9).

Where the discs are not arranged inpairs, difficulty is sometimes experiencedin turning corners in one direction with thedrill, while turning in the other directionposes no problem. This is another examplein which the requirements of no-tillage aredifferent from tillage, since the soil forcesin tilled soils are sufficiently low to notcause problems when cornering with angleddisc-type openers.


Fig. 4.9. A pair of angled flat disc no-tillage openers (from Baker et al., 1996).

Relatively steep side-slope drillingcauses machine ‘tailing’, in which the wholemachine pulls at an angle to the direction oftravel because of gravity pulling the drillsideways. This poses a problem for drillsarranged with half of the openers angled ineach direction. That part of the drill inwhich the openers are caused to travel withno angle creates very small, ineffective seedslots, while the other openers double theirangle and create extra wide slots that aredifficult to cover.

ANGLED CONCAVE DISCS. This type uses aslightly concave, near-vertical disc set at anangle to the direction of travel (Fig. 4.10).The strength derived from the curvature ofthe disc allows thinner steel to be used inits construction, assisting in soil penetra-tion. The axle of angled dished discs can beeither horizontal or slightly tilted from thehorizontal in either direction.

If the axle is tilted downwards on theconvex (back) side of the disc, the action ofthe disc will be to undercut the soil like adisc plough. The benefits of this action arethat the displaced soil is not thrown to oneside where it is otherwise often difficult to

retrieve again for covering purposes, as it islifted, hinged and inverted. The disadvant-ages are that, in soils that are held togetherby plant roots (e.g. pasture), a soil flap isproduced, which falls back over the seed.Since the seed is placed under the ‘hinged’end of this flap, this can restrict seedlingemergence. Figure 4.11 shows an angleddished disc that has had a small scraperadded to attempt to slice this flap off.

If the axle is tilted upwards on the con-vex (back) side of the disc, it has the effectof confining the disc action to one of scuff-ing only, with little or no undercutting.Because of the disadvantages of under-cutting, this has become the most com-monly preferred option with concave discopeners for no-tillage, along with arrangingthem with the disc axle horizontal.

TILTED AND ANGLED FLAT DISCS. Some designershave tilted as well as angled the flat discson their openers (Fig. 4.11). This has mainlybeen to reduce the throwing action ofangled discs so that there is less soil distur-bance and also to provide more of a mulchcover than where the discs stand verticallyupright. Tilting the discs may also help

42 C.J. Baker

Fig. 4.10. An angled dished disc no-tillage opener (from Baker et al., 1996).

penetration and reduce the hillside opera-tion problem discussed above. But it doesnothing to reduce the tendency of suchopeners to hairpin residues into the slot,which interferes with seed germination and/or seedling emergence. Nor do such openerssolve the problem of fertilizer placement,since no more opportunity exists to sepa-rate fertilizer from seed than with any otherconfiguration of angled disc.

The actions of all angled discs (flat orconcave, upright or tilted) are very muchdependent on their operating speed.Because all variations depend on at leastangulation to the direction of travel (if notalso angulation to the vertical) for much oftheir slot-creating actions, the speed withwhich they approach the soil has a markedeffect on the amount of soil throw andtherefore the width and shape of the result-ing slot. At higher speeds, the slots tend tobe wider and shallower than at slowerspeeds and the loose soil available for cov-ering tends to be thrown further to one side,where it is more difficult to retrieve. Incommon with discs that travel straightahead, the penetration of angled discs isalso reduced with increasing speed, but this

can be countered by simply increasing thedownforce to achieve penetration.

The two biggest advantages of allangled discs are their ability to handle sur-face residues without blockage and theiravoidance of compaction or smearing of theslot at the base and on at least one side wall.They are also relatively cheap, simple andmaintenance-free.

The biggest disadvantages of angleddisc openers are: (i) they tuck or hairpinresidues into the slot in a similar mannerto double disc openers; (ii) they makeU-shaped slots, which, especially if wideat the top, dry easily despite the presenceof loose soil; (iii) they are often difficultto set for correct operation; (iv) they mayangle and operate poorly on hillsides;(v) they are not able to separate seed fromfertilizer in the slot; (vi) they are affectedby the speed of travel; and (vii) they wearrapidly.

Hoe- or shank-type openers

The term hoe or shank describes any shapedtine or near-vertical leg that is designed topenetrate the soil. Seed is delivered either


Fig. 4.11. An angled dished disc no-tillage opener with both vertical and horizontal angle. This openeralso features a scraper to cut and remove the turf slice. (From Baker et al., 1996.)

down the inside of the hollow tine itself ordown a tube attached to its back.

The shapes of hoe or shank openersrange from winged (Fig. 4.26, p. 54), whichare often also designed to separate seed andfertilizer simultaneously in the slot, through

blunt bursting openers (Fig. 4.12) to sharpundercut points, which are designed tomake a relatively narrow slot and penetratethe soil easily (Fig. 4.13). Sometimesa pair of narrow shanks is arranged withhorizontal offset to separately place seed

44 C.J. Baker

Fig. 4.12. A blunt hoe-type no-tillage opener (from Baker et al., 1996).

Fig. 4.13. A sharp hoe-type no-tillage opener (from Baker, 1976b).

and fertilizer (Fig. 4.14). One of the problemswith hoe-type openers is that they wear rap-idly; thus, the original shape seldom lastslong. Because of this they may take on sev-eral new shapes during their lifetime, mak-ing it difficult to generalize on the basis ofslot shape.

Generally, all hoes scrape out a roughlyU-shaped slot by bursting the soil upwardsfrom beneath. In moist conditions they tendto smear the base and sometimes the sidewalls of the slot, but this only affects seed-ling root systems if the soil is allowed todry and thus become an internal crust (seeChapter 5).

The bursting action produces consider-able loose soil alongside the slot, whichmay be helpful when covering but can alsoleave severe ridging between rows. Becauseof this latter problem most shank-typeopeners are operated at low speeds (maxi-mum 6–9 kph, 4–6 mph).

The nature and extent of the loose soilalongside the slot is also dependent on soilmoisture content. Often, in damp plasticsoils, no loose soil will be produced at all,while at other times a few hours of dryingafter drilling will produce crusty edges tothe slots, which can then be brushed with asuitable harrow or dragged to at least

partially fill the slot with loose soil. Themost appropriate covering action after pas-sage of hoe-type openers is therefore a mat-ter of judgement at the time, which is one oftheir inherent disadvantages.

The biggest disadvantage of hoe or shankopeners, however, is the fact that they canonly handle modest levels of residues with-out blockage (also see Chapter 10), espe-cially when arranged in narrow rows. Theplacement of a leading disc ahead of a hoe orshank opener, regardless of how or in whatposition it is placed relative to the hoe, can-not make a group of such openers arrangedin narrow rows able to handle residuessatisfactorily.

The most successful hoe or shank drillconfigurations for residue clearance havebeen to space the openers widely apart inmultiple rows (ranks) in the direction oftravel. This is based on the observation that,unless the residue is particularly heavy ordamp or becomes wedged between adjacentopeners, the inevitable accumulation ofresidue on each tine will usually fall offto one side, as a function of its own weight.If sufficient clearance is built into the spac-ing between adjacent tines, the falling offof clumps of residue will not block themachine – at least, not as often. These


Fig. 4.14. A pair of shank openers with horizontal offset. The front shank applies fertilizerwhile the rear shank applies seed offset to one side and sometimes shallower.

clumps of residue can cause problems forseedling emergence and later at harvesting,so it is questionable whether this action canbe described as handling residue at all.Unfortunately, wide spacing demands unde-sirable dimensions from the whole drill,which compromises other functions such asthe ability to follow the ground surface andseed delivery. Figure 4.15 shows a shank-type no-tillage drill with widely spacedopeners.

Hoe or shank openers have severaladvantages: (i) they are relatively inexpen-sive; (ii) they can be made to ‘double-shoot’seed and fertilizer relatively simply; (iii)they do not tuck (or hairpin) residues intothe slot; in fact, they brush the residueaside, although this is a disadvantage forcontrolling the microclimate within thesown slot, as described in Chapter 5.

Their major disadvantages are: (i) ahigh wear rate; (ii) their poor residue handl-ing ability; and (iii) their inability to sepa-rate seed from fertilizer in the slot (seeChapter 9).

Power till openers

Power till openers are an enigma in no-tillage.Because most people had become accustomed

to tilling the soil before planting seeds, itseemed natural to till the soil in strips forno-tillage. Thus, power till openers consistof miniature rotary cultivators that arepower-driven from a common source andliterally till a series of narrow strips forthe seed. While the tillage ensures thatseeds will become well covered with loosesoil, it has long been known that rotarytillage is one of the least desirable ways oftilling soil. Its main disadvantages, whenapplied either to general seedbed prepara-tion or discretely in strips, is that it stimu-lates weed seed germination, is verydestructive of soil structure and is power-demanding (Hughes, 1975; Hughes andBaker, 1977).

The actual placement of seed varieswith design. With some, the seed is scat-tered into the pathway of the rotating bladesand thus becomes thoroughly mixed withthe soil, but depth of placement becomesrandom. With others, separate conventionalopeners for tilled soils (shoe, hoe or disctype) operate behind the rotating blades asif they were drilling into a fully tilledseedbed.

The advantages of power till openersare that the downforces required for pene-tration are little more than those commonly

46 C.J. Baker

Fig. 4.15. A no-tillage drill with widely spaced shank-type openers designed to ‘clear’ residues.

required for tilled soils. Power till openerssubstitute power applied through the trac-tor power take-off (PTO) shaft to the rotorsfor the downforces and draft forces morecommon to other non-rotating types ofno-tillage openers. They create U-shapedslots, they do not tuck residue into the slot,they generally cover the seed well and, incold climates, where there might otherwisebe a disadvantage from the slow decompo-sition of surface residues, they chop up thisresidue and incorporate it into the soil.

On the other hand, because they physi-cally dispose of the surface residues in thismanner, power till openers do little tomicro-manage the residues close to theseed, which is one of the most importantfunctions that successful no-tillage openersshould perform. Further, few of them sepa-rate the seed from the fertilizer in the slot,although, because of the amount of loosesoil in the slot, there is more mixing of fer-tilizer with soil, which provides partialseparation from the seed.

Power till openers are relatively com-plex mechanical devices when comparedwith other opener designs. They have aparticular problem with wear, surface

following and damage from stones andother obstructions.

Early designs were adaptations of con-ventional field rotary cultivators. The normalwide L-shaped blades, which were mountedon a common axle driven by the tractor PTO,were replaced with sets of narrow L bladescorresponding to the desired row width andspacing. These created the discrete rows oftilled soil. The width of the tilled strips var-ied from about 20 mm to 200 mm, dependingon the objectives. Figure 4.16 shows theeffects from a narrow set of blades, whileFig. 4.17 shows wider tilled strips.

In early designs each set of blades wasmounted on a common axle, so it wasimpossible for each tilled strip to maintain aconstant depth while traversing the normalundulations of the ground. Even the use ofindependently articulated seed-depositingopeners, which followed in the tilled strips,could not fully compensate for areas ofsoil that had missed being tilled altogetherbecause the machine had traversed asmall hollow, for example. Figure 4.16 showsa common-axle-type power till drill withindependently mounted seed-depositingopeners.


Fig. 4.16. Narrow tilled strips left by a power till ‘no-tillage’ opener (from Baker et al., 1996).

Later designs attempted to mount eachrotating set of blades independently so thatthey were capable of following the soil sur-face. This proved to be inordinately expen-sive, because, while each set of bladesrequired its own flexible drive train, it alsohad to offer some protection from stone

damage. Belt drives allowed slippage inthese circumstances.

Some designs compromised by mount-ing blade sets in pairs. Figure 4.18 showsthe head of a twin rotor model in whichthe rotors are able to articulate up anddown. Other designs attempted to power

48 C.J. Baker

Fig. 4.17. Wide tilled strips left by a strip-tillage machine (from Baker et al., 1996).

Fig. 4.18. Power till no-tillage openers arranged in pairs (from Baker, 1981a, b).

each rotor individually through a chaindriven by a wavy-edged ground-engagingdisc ahead of the rotor in the hope that thedisc would slip in the soil when a stone wasencountered by the rotor. Figure 4.19 showssuch a device.

Although power till openers have beenan obvious design route for many engineers,with a number of models released for com-mercial production around the world, veryfew have been commercially successfuldue to the disadvantages mentioned above.Perhaps their greatest use is where otheropeners cannot function. An example of sucha condition is the revegetation of high-altitude pastures where ambient tempera-tures remain sufficiently low to discouragecomplete decomposition of organic matter.The result is a build-up, over centuries, of amat of undecomposed vegetation, whichcan be several centimetres thick (Fig. 4.20)and which simply resists the operation ofany other no-tillage opener except designsthat physically chop it up and mix it withsoil. In these conditions, the objective is todrill improved pasture species by no-tillageto increase animal carrying capacity onotherwise low-producing fragile farmland.

Power till openers in general createmore short-term mechanical aeration withinthe slot than any other type of opener,although the benefits of this are usuallytemporary in comparison with openers thatencourage natural aeration by earthworms(see Chapter 7). They have a tendency tocompact the base of the slot, but, unlikedouble disc openers, this does not seem tocause difficulties for seedling roots.

Furrowers

One opener, designed in England espe-cially for pasture renovation, consisted oftwo vertical discs, spaced laterally severalcentimetres apart, which cut two verticalslits. The discs were followed by a minia-ture mouldboard-plough, which scoopedout the soil between the slits at the sametime as it created a small track in the baseof the broad U-shaped slot, where seed wasdeposited (Haggar, 1977; Choudhary et al.,1985). The function of scooping was toeliminate weed competition in the seedzone without spraying and to allow earlyseedling development to take place in asunken zone physically protected from


Fig. 4.19. A power till no-tillage opener driven by a ground-engaging wavy disc (from Baker et al., 1996).

treading by cattle (Fig. 4.21). Seed cover inthe damp English climate is not a highpriority, but such openers are regarded asspecialist tools designed solely for oneintended purpose.

Vibrating openers

Several designers have attempted to reducethe downforces required to push the discsand other components of no-tillage openers

50 C.J. Baker

Fig. 4.20. Undecomposed sod in the Scottish Highlands (from Baker, 1981a, b).

Fig. 4.21. A furrowing no-tillage opener (from Choudhary et al., 1985).

into the ground by causing the openers tovibrate. Such a task has been particularlydemanding when applied to a disc since thevibration mechanism needs to operate onthe disc hub as it rotates, as well as movingup and down in response to natural undula-tions in the ground surface. Individualvibrating hydraulic motors have been usedon individual openers, which increase thecost, complexity and power requirementconsiderably. Very slow operating speedsand difficulty in keeping all bolts and nutstight because of the general vibrations gen-erated throughout the machine have alsobeen disadvantages.

In the end, it is the shape and action ofthe soil-engaging components that deter-mine the biological success or otherwise ofno-tillage openers more than the forcesrequired for penetration of draught. Vibrat-ing openers do nothing to improve biologi-cal reliability. Most designers have found itcheaper to add weight and/or use a largertractor to overcome penetration and draughtforces than to engage relatively complexvibrating devices.

Horizontal Slots

Inverted-T-shaped slots

All of the openers discussed so far havebeen adaptations of openers designed origi-nally for tilled soils (with the exception ofthe specialized furrow and vibrating open-ers). The modifications to such openers,when employed for no-tillage, have mostlyconsisted of increased robustness, withonly minor changes in function.

The inverted-T-shaped slot is the onlyknown horizontal no-tillage slot shape andis one of very few slot shapes that havebeen developed specifically for no-tillagepurposes, with few functions applicable totilled soils.

The inverted-T principle was devel-oped when researchers explored geometri-cal alternatives to the more common V andU slot shapes to overcome several oftheir inherent disadvantages (Baker, 1976a).The researchers reasoned that the most

radically different shape would be to invertthe wide-top narrow-base V shape and tocreate instead a narrow-top, wide-base slot.Practicality dictated that the simplest wayto achieve this was to construct an openerconsisting of a vertical shank with sub-surface wings that were horizontal in thelateral plane but inclined downwardstowards the front in the longitudinal plane.

The other reasoning behind the wingedconcept was that the designers wanted to beable to fold the residue-covered soil back overthe slot for moisture conservation and seed-ling protection. Since wings tended to under-cut the surface layer of soil with a horizontalslicing action, this would allow the formationof horizontal shelves on either side of a ver-tical slit. In most conditions the wing actionalso created horizontal flaps of residue-covered soil with which to cover the shelves.It was a major objective of the inverted-T con-cept to create horizontal slots with a highdegree of control and predictability.

Two winged opener concepts weredeveloped, both of which created essen-tially the same inverted-T-shaped slots.

Simple winged opener

The first simple winged opener design con-sisted of a vertical shank attached to thebottom of a hollow tine (Baker, 1976a, b).Figure 4.22 shows the original wingedopener design. The opener was hollow, toallow passage of seed, and open at the back.The shank curved out at its base on bothsides to form a pair of symmetrical wings,which were downwardly inclined towardstheir fronts by 10° and projected laterallyapproximately 20 mm either side.

A leading vertical flat disc was usedahead of the shank to provide a neat verticalcut through pasture. The leading disc wasnot expected to give the opener an ability toclear lying surface residue (see Chapter 10),but to ensure passage of the opener throughstanding pasture (sod) with minimal tearingand disruption to the soil surface.

A commercial company in New Zealandsuccessfully adapted the winged openerconcept for pasture renovation purposes.This market opportunity was based on


knowledge that there is six times as mucharea of the world’s surface under grazingland as there is under arable crop produc-tion (Kim, 1971; Brougham and Hodgson,1992), although, of course, not all of theworld’s grasslands are accessible to tractors.

The design was simplified by fashion-ing the shank from plate steel and welding avertical flat plate to its rear edge so as toentrap a wedge of soil ahead of this zone.Seed delivery was altered from the hol-lowed opener itself to a permanent tubepositioned behind the vertical flat plate.The reasoning had been that, as the openerbecame worn and was eventually dis-carded, the modified design would allowthe seed tube component to remain andonly the minimum possible amount ofreplacement component would be dis-carded, thus reducing the cost. It was alsoreasoned that the soil wedge trapped aheadof the flat plate would reduce wear of the

opener in that zone. Later, other designsalso provided reversible and replaceableleading edges and tungsten overlays on theopener in an attempt to further reduce theeffects of wear. Figure 4.23 illustrates anumber of versions of the same modifiedopener, which eventually became knowngenerically as the ‘Baker boot’, after theoriginator of the inverted-T principle.

Unfortunately, some of these benefits inthe modified designs were achieved at thecost of retaining control over the exact shapeof the slot. The thickness of the soil wedgethat is retained by the vertical flat plate is afunction of soil type, stickiness and moisturecontent. As a result, in sticky soils it is com-mon for this soil wedge to become widerthan the wings beneath it, with the resultthat the intended function for the wings toundercut the surface layer of soil is lost andthe opener at times functions more as awedge, creating a U-shaped slot.

52 C.J. Baker

Fig. 4.22. The originalinverted-T-shaped no-tillageopener (from Baker, 1976b).

Although several manufacturers pro-duced almost identical versions of themodified opener, not all of them provideda leading disc as originally envisaged, withthe result that the slot edges were oftentorn and inconsistent, making controlledclosure of the slot difficult, if not impossi-ble. Since low cost was a primary objectivewith this simple opener, most designsattached the opener to very simple drillsthat had limited depth control (Fig. 4.24).One design provided a vertical pivot aheadof each opener to assist with cornering(Fig. 4.25).

Despite these shortcomings, the modi-fied version of the simple inverted-T-shaped opener succeeded in its intendedpurpose of pasture renovation. Its principaladvantage has been that the inverted-T-shaped slot, however poorly made, isdemonstrably more tolerant of dry and wetsoil conditions (see Chapters 6 and 7) thannearly all other opener designs, with theresult that the success of the pasture reno-vation process improved noticeably.

The largest disadvantages of this openerhave been that, by being a rigid shank, it haspoor residue-handling qualities and speed ofoperation is limited. Where it is incorpo-rated on simple drills, surface-followingability is limited.

Other designers have utilized the win-ged opener concept to separate the dischargeof seed and fertilizer into two or morehorizontal bands (double or triple shoot).

Figure 4.26 shows a double-shoot wingedopener.

Winged opener based on a central disc

Given the superior biological results obtainedwith the inverted-T-shaped slot conceptfrom numerous experiments conducted in


Fig. 4.23. Several versions of the ‘Baker boot’ inverted-T-shaped no-tillage opener (from Baker et al.,1996).

Fig. 4.24. A simple drill featuring ‘Baker boot’inverted-T-shaped no-tillage openers (fromBaker et al., 1996).

New Zealand, Canada, Australia, Peru andthe USA, it became imperative that theshortcomings of the simple opener shouldbe overcome by designing a version thatwould suit arable agriculture as well aspasture-land. After all, it is the repeated till-age of arable land that has damaged theworld’s most productive soils. The potential

of no-tillage to reverse this process is funda-mental to the long-term sustainability ofworld food production.

A number of functional principleswere considered essential if such an openerwere to become fully capable of such anassignment:

1. The most important aspect was tomaintain the inverted-T shape of the slotitself, even at high forward speeds andshallow seeding depths.2. Ability to reposition loose residue ontop of loose soil to cover the horizontalslot, as well as to fold back more structured,previously untilled material such as flapsof turf.3. Effective separation of seed and ferti-lizer in the slot with a single opener, and toperform this function reliably over a widerange of soil type, moisture contents andforward speeds.4. Handling without blockage of surfaceresidue, even when configured in narrow(150 mm, 6 inch) rows, in difficult condi-tions ranging from dry or wet crop stubbleto tangled, well-rooted sod, on soils rangingfrom soft and wet to hard and dry.

54 C.J. Baker

Fig. 4.25. A simple drill featuring a self-steering version of the ‘Baker boot’ inverted-T-shapedno-tillage opener.

Fig. 4.26. Two versions of double-shoot wingedopeners.

5. Self-closure of the slot without unduesoil compaction for seedling emergence.6. Capability to maintain a constant seed-ing depth by consistently following theground surface.7. Replacement parts to be inexpensive andeasily removed and replaced in the field.

The resulting design, shown in Fig. 4.27,has working principles quite unlike otheropeners designed for either tilled oruntilled soils (Baker et al., 1979c). Essen-tially, the disc version of the winged openerarose from splitting the simpler wingedopener both vertically and longitudinallyand rubbing the insides of the leading edgesof the two sides against a central disc. It iscentred on a single flat vertical disc (smoothor notched) running straight ahead to cutthe residue and the vertical portion of thesoil slot. Two winged side blades are posi-tioned so that the interior of their leadingedges rubs on either side of the centraldisc. This patented principle effectivelysheds residue from the side blades withoutblockage.

The winged side blades cut horizontalslots on either side of the disc at seedingdepth by partially lifting the soil. Seed andfertilizer flow down special channelsbetween the side blades and the disc oneither side, respectively, and are placed onthe horizontal soil shelf. To achieve this,the side blades are held sufficiently clear ofthe disc at their rear edges to form a pas-sageway for seed or fertilizer. Such a gap isnarrow in comparison with other openerdesigns but movement of even large seeds isfacilitated by the fact that one side of thepassageway comprises the moving face ofthe revolving disc.

The fertilizer blade can be made slightlylonger than the seed blade so that the ferti-lizer can be separated vertically from theseed as well as horizontally, i.e. diagonally,although in most circumstances horizontalseparation has proved to be sufficient, if notpreferable (Fick, 2000).

Two angled semi-pneumatic wheelsfollow the blades to reset the raised soiland residue, thereby positively closing theslot. They also regulate the depth of eachopener independently for excellent soilsurface tracking and thus precise seeddepth control. Each opener is mounted onparallel arms necessary to maintain theshallow wing angle at seeding depth fortracking the soil surface.

Figure 4.28 is a diagrammatic represen-tation of the horizontal seed and fertilizerseparation (double shoot) with the disc ver-sion of a winged opener. Separating seedand fertilizer and sowing both with thesame opener greatly simplify the design ofno-tillage drills and reduce power demand.Fertilizer banding has become an essentialfunction of successful no-tillage seeding formost crops (see Chapter 9). Few, if any,other no-tillage openers effectively andsimultaneously achieve these importantfunctions in a wide range of soils and atrealistic forward speeds.

The opener is designed especially forno-tillage into heavy surface residues andgrass sod where simultaneous sowing ofseed and fertilizer is a priority. Becausethe incline on the wings is set at only 5° tothe horizontal (compared with 10° for the


Fig. 4.27. A disc version of the winged openerfor creating inverted-T slots.

simple inverted-T version), it is capableof drilling at depths as shallow as 15 mm. Itfunctions equally well, without modifica-tion, in heavy crop residues, pastures andsports turf (Ritchie, 1988), and can be usedunmodified to sow the full range of fieldcrops and pasture seeds, as well as for pre-cision drilling of vegetables (Ritchie andCox, 1981), maize and horticultural crops. Itcommonly retains 70–95%, of surface resi-dues intact. Figure 4.29 shows 95% residueretention after passage of a disc-versioninverted-T opener.

The main advantages of the disc ver-sion of the inverted-T-shaped opener arethat it fulfils all of the design objectiveslisted above, without compromise. The sameopener can be used unmodified for precisionseeders, as well as grain drills and pasturerenovation machines, in tilled and no-tillagefarming.

Its disadvantages are that it has a slightlyhigher draught requirement, is relatively exp-ensive to construct and requires a heavy drillframe design to ensure proper functioning.The relatively high cost can be weighedagainst its ability to maximize and evenimprove crop yields beyond those commonlyexperienced with other no-tillage openersand even tillage (Saxton and Baker, 1990). Anapparent economic disadvantage when put inthe fuller context becomes very cost-effective.

Punch Planting

Punch planters make discrete holes intowhich one or more seeds are placed beforemoving on to the next hole. Ancient farmersused pointed sticks to make the holesbecause there was insufficient energy tomake continuous slots and utilize the con-venience of continuous flow of seed andfertilizer into them.

Modern engineering has attempted tomechanize punch planting so that it can beperformed with less human labour and withgreater accuracy and speed. The devicescreated have mostly consisted of steel wheelswith split spikes attached to their rims. Thesplit spikes are hinged at their bases so thatthey can be forced to open in much the sameway as a bird’s beak. Figure 4.30 shows anexample of a prototype mechanized punchplanter.

In operation, the opening and closingfunctions are actuated by an internal camand synchronized with a seed dispenser.

56 C.J. Baker

Fig. 4.28. Horizontal separation of seed andfertilizer by the disc version of a winged opener.

Fig. 4.29. Almost complete replacement ofresidues over the slot created by a disc version ofan inverted-T-shaped opener (Class IV cover).

After each spike has become fully embeddedin the soil, a single seed or small group ofseeds is directed from the dispenser tube,located in the centre of the wheel, through ahole in the rim of the wheel into the openedspike and deposited in the soil at a controlleddepth and spacing from its neighbours.

Mechanized punch planters were seenas sensible solutions to mechanizing anancient practice. Their relative mechanicalcomplexity, however, has prevented theirwidespread adoption to date. The creationof V-shaped holes has all of the biologicaldisadvantages of continuous V-shaped slots.This includes the tucking (hairpinning) ofresidues into the holes, difficulty in closingthe holes and the wedging action of thespikes, which compacts soil under andalongside the seed zone.

Surface Broadcasting

There is little need to elaborate on the prac-tice of surface broadcasting. Again, it isderived from an ancient practice broughtabout by the absence of energy sourcesfor more mechanized solutions. Certainly,

modern machinery is capable of mechaniz-ing the broadcasting process with muchincreased speed and accuracy, but the abs-ence of positive placement of seed beneaththe soil significantly increases the biologi-cal risks from desiccation and bird, insectand rodent damage.

Broadcasting is not a recommendedpractice except in low-energy situations, andonly then where local rainfall and humidityare so predictable and reliable that germina-tion and rooting are assured. One thing infavour of no-tillage is that the retention ofdead surface residues provides a protectivecanopy beneath which the humidity is likelyto be higher than the surrounding ambientair (see Chapter 6). Research for many yearshas shown that effective seed and fertilizerplacement beneath the soil produces cropyield advantages that surface broadcastingcannot duplicate.

One solution to broadcasting that red-uces risk is ‘auto-casting’ in which seed isbroadcast mechanically behind the pickuptable of a combine harvester. The objectiveis to allow the straw and chaff to fall ontop of the seed at the rear of the machine.This in turn ensures that there is a degree of


Fig. 4.30. A prototype mechanized punch planter (from Baker, 1981a, b).

cover over the seed, but success with thismethod is still very weather-dependent andthere is no opportunity to strategicallyplace fertilizers at the time of seeding. A dryperiod following harvest increases the risksof failure. Figure 4.31 shows an auto-castingsystem attached to the rear of a combineharvester table.

Summary of Seeding Openers andSlot Shape

The important functions of seeding openersare their abilities to:

1. Create a suitable seed/seedling micro-environment.2. Avoid compacting and smearing of theslot walls.3. Handle surface residues without block-age.4. Micro-manage the surface residues sothat they are positioned where they are ofmost advantage to the sown seeds/seedlingsas well as the field in general.5. Band seed and fertilizer simulta-neously in the slot but separate them so asto avoid ‘seed burn’.6. Either avoid hairpinning altogetheror avoid hairpinned residues affecting seedgermination.

7. Self-close the slot.8. Accurately control the depth of seeding.9. Faithfully follow surface undulationsthat occur naturally in no-tillage.

The variety of slot shapes made byno-tillage seeding openers can be summa-rized as:

1. Vertical or horizontal.2. Vertical slots are either V- or U-shaped.3. Horizontal slots are usually inverted-T-shaped.4. V- and U-shaped slots may also beslanted as well as vertical.5. Compared with continuous slots, seedscan be sown in discrete holes (punch plant-ing) or by surface broadcasting, mostly usedwhere energy is limiting.6. Most vertical and some slanted V- andU-shaped slots are adaptations of slots ori-ginally designed for tilled soils.7. Most horizontal inverted-T-shaped slotswere designed specifically for no-tillageseeding.8. V-shaped slots are mainly created bydouble or triple disc openers.9. U-shaped slots may be created by hoe,angled flat disc, angled dished disc, powertill or furrow openers.10. Inverted-T-shaped slots are created bywinged openers.

58 C.J. Baker

Fig. 4.31. ‘Auto-casting’ of seed behind the pickup table of a combine harvester.

11. The practices of punch planting andbroadcasting have ancient origins but havealso been mechanized.12. There are higher risks of poor plantestablishment associated with surface broad-casting than where seed is sown beneaththe soil by openers.

The action of openers on the soil variesby the opener design as:

1. Vertical double disc openers in the soilpredominantly cut, wedge and compact.2. Slanted double disc openers cut andheave on the uppermost side and compacton the lowermost side.3. Punch planters wedge and compact.4. Hoe openers mostly heave and burst,plus cut if preceded by a disc.5. Power till openers cut, mix and pul-verize.6. Vertical angled flat disc openers cut,scuff and throw.7. Angled dished disc openers andslanted angled flat disc openers cut, scuff,fold and/or throw.8. Winged openers heave and fold, pluscut if associated with a disc.

The advantages and disadvantages ofvarious openers by design are:

1. Double and triple disc openers arelow-maintenance and have good residuehandling. Their disadvantages are V-shapedslots, especially when configured verti-cally; unreliable seedling establishment;high penetration forces; compaction andsmearing of soil; difficulty in covering; noseparation of seed and fertilizer (unlessdoubled up); seed implantation intohairpinned residue.2. Punch planter openers are low-energyand maintenance. Their disadvantages aremechanical complexity, slowness, holecompaction, difficulty in covering and noseparation of seed and fertilizer.3. Hoe openers are low-cost, nohairpinning of residue and reasonable pen-etration forces. Their disadvantages arepoor residue handling, high wear rates,

smearing in wet soils and no separation ofseed and fertilizer unless doubled up.4. Power till openers mix undecomposedorganic matter with soil, do not hairpin res-idue, low penetration forces, burial of seedand dilution of fertilizer with soil. Theirdisadvantages are poor residue handling,residue destruction, tillage, slot-base com-paction, difficulty in handling stones andsticky soils, cost, mechanical complexity,weed seed stimulation, high mainte-nance and no ability to separate seed andfertilizer.5. Vertical angled flat disc openers havereasonable penetration forces, scuffingaction, residue handling and no smearing orcompaction. Their disadvantages are seed-ing into hairpinned residue, no separationof seed and fertilizer (unless doubled up)and affected by forward speed.6. Angled dished disc openers andslanted angled flat disc openers have scuff-ing action, residue handling and no smear-ing or compaction. Their disadvantages arehigh penetration forces, seed implantationin hairpinned residue, no separation of seedand fertilizer (unless doubled up) andaffected by forward speed.7. Simple winged openers provide hori-zontal inverted-T-shaped slots that are eas-ily closed, reliable seedling emergence, nocompaction, reasonable penetration forcesand do not hairpin residues. Their dis-advantages are poor residue handling, highwear rates and no separation of seed andfertilizer.8. Disc versions of winged openers (cen-tred on a vertical disc) provide horizontalinverted-T-shaped slots, self-cover slots,reliable seedling emergence, horizontal ordiagonal separation of seed and ferti-lizer, good residue handling and micro-management, no seed implantation inhairpinned residue, capable of high forwardspeeds, low compaction, low weed seedstimulation, good depth control and lowmaintenance. Their disadvantages are highinitial costs, high penetration forces, andhigh draught.


5 The Role of Slot Cover

C. John Baker

In no-tillage, nothing influences the reliabilityof seedling emergence more than the nature

of the slot cover.

If you stand on the ground and look downon a seeded soil slot (‘furrow’ or ‘groove’),after passage of a no-tillage drill or planter,you will see varying types of seed and slotcoverage, which we have described in five‘classes’ (Baker et al., 1996):

1. Class I: visible seed (Fig. 5.1). Little orno loose soil covering the seed.2. Class II: loose soil (Fig. 5.2). Loose soiland perhaps a small amount (less than 30%)of surface residue or mulch that has beeninduced back into the slot to cover the seed.3. Class IIIa: intermittent mulch and soil(Fig. 5.3). There is a variable amount (30%or more) of residue or mulch on top of theloose soil covering the seed.

Class IIIb: a mixture of residue and soil(Fig. 4.17). Thirty per cent or more of resi-dues or mulch is mixed in with, rather thanon top of, the loose soil covering the slot.4. Class IV: complete mulch and soil(Figs 5.4 and 5.5). Soil and a covering of atleast 70% of residue or mulch has beeninduced back over the slot in roughly thesame layering positions as they were priorto drilling, i.e. with the mulch covering thesoil, which in turn covers the seed.

The basis of these classificationswas described by Baker (1976a, b, c) andBaker et al. (1996), who observed that,where an intermittent mulch/soil cover


Fig. 5.1. Visible seed in Class I no-tillage slotcover (from Baker et al., 1996).

(Class IIIa) occurred under dry conditions,seedlings were seen to emerge from undera flap of dead turf (mulch) or even a pieceof random residue and soil, but hadnot emerged from where the seed cover

was confined to loose soil alone or wherethere was no cover at all. This suggestedthat loose soil may not have been the ulti-mate seed cover as had been previouslyassumed.

Role of Slot Cover 61

Fig. 5.2. An example of Class II no-tillage slot cover (from Baker et al., 1996).

Fig. 5.3. An example of Class IIIa no-tillage slot cover (from Baker et al., 1996).

In fact, some engineers and agrono-mists continue to mistakenly assume, eventoday, that the best cover for seeds is loosesoil (Class II). This assumption comes from

what has been provided in a tilled seedbedfor centuries. Residues do not exist to anydegree on well-tilled soils. Generally, theyhave been buried or burnt prior to tillage.

62 C.J. Baker

Fig. 5.4. An example of Class IV no-tillage slot cover in heavy standing wheat stubble and scatteredstraw (from Baker et al., 1996).

Fig. 5.5. An example of Class IV no-tillage slot cover in sparse close-growing weeds. Note thereplacement and layering of whatever residue is available in its original position and the absence of soilinversion after passage of the drill. (From Baker et al., 1996.)

The only other resource available for cover-ing in addition to clean, loose soil is per-haps a press-wheel effect to provide slightlycompacted soil, but even the benefits ofthat are dubious. So loose soil has beenregarded as the ‘ultimate cover’, at least in atilled soil.

Based on the ‘loose-soil-is-best’ assump-tion, some engineers therefore postulatedthat all that was needed for no-tillage was totill the soil in a series of strips and sow seedinto the tilled strips as you would in a gen-erally tilled soil, but, in this case, leavingthe rest of the seedbed untilled betweenthe strips. This is one form of strip (or zone)tillage, which has been described previouslyin Chapter 4.

Unfortunately, this simplistic view hasno scientific basis and it is now known thatit destroys several of the very specialresources close to the seed that most until-led soils have, such as a mulch covering, anunbroken macropore system within theseed zone and an equilibrium soil humiditynear 100%.

The Role of Soil Humidity

The atmosphere in the macropores withinan untilled residue-covered soil has anequilibrium humidity of very near 100%(Scotter, 1976) at almost all moisture levelsdown to ‘permanent wilting point’, whichis when a soil is too dry for plants to sur-vive. In fact, it is 99.8% even at wiltingpoint (1500 kPa tension). In no-tilled seed-ing, the soil is only broken at the surface by

strips (slots) where the drill or planteropeners have travelled. The greatest loss ofhumidity from the soil to the atmosphereoccurs at these broken strips (slots). Theaim, therefore, of drilling into dry soilsshould be to create slots that do not encour-age loss of humidity from these zones, sincethey are also the zones where the seeds areplaced, which require moisture to initiateplant growth.

The classification of covers listedabove is arranged in order of ascendinghumidity retention. A ‘complete’ (70% orgreater) mulch/soil cover (Class IV) retainsmore humidity than an intermittent mulchand soil cover (30 to 70% residue – ClassIII), which is better than loose soil (less than30% – Class II), which itself is better thanno cover at all (Class I).

Choudhary (1979) and Choudhary andBaker (1981b) measured the daily loss ofrelative humidity (RH) from a range of dif-ferent slot shapes under controlled dry con-ditions with constant temperature. Theyused the average daily RH loss for the first3 days following seeding to compute anindex value for the ability of a slot to retainhumidity, moisture vapour potential cap-tivity (MVPC).

MVPC = 1/(average 3-day RH% loss)

Table 5.1 lists results from two separateexperiments in which Choudhary placed asmall humidity probe in positions that wouldnormally be occupied by the seeds withindrilled slots in a dry soil. Undisturbedsoil bins (weighing 0.5 t each) wereplaced within climate-controlled rooms at a


V-shaped slot(Class I cover)

U-shaped slot(Class II cover)

Inverted-T-shapedslot (Class IV cover)

Daily lossof RH% MVPC



Experiment 1 4.23% 0.24 2.78% 0.36 2.34% 0.43Experiment 2 3.13% 0.32 2.03% 0.49 1.02% 0.98Mean 3.68% 0.28 2.41% 0.43 1.68% 0.71

MVPC, moisture vapour potential captivity = 1/(average 3-day RH% loss).

Table 5.1. Effect of no-tillage slot shape and cover on slot drying rates and MVPC.

constant ambient temperature and constantRH of 60%.

Relative humidity is a measure of theamount of water vapour in the soil atmo-sphere at any one temperature. The sourceof supply of water vapour in the drilledslots is from the surrounding soil since itsequilibrium relative humidity is alwaysnear 100%, but the rate of escape of watervapour to the atmosphere outside the soil(which is usually less than 100% RH unlessit is raining or there is thick fog) is con-trolled by the diffusion-resistance to gasespassing through the covering medium in oron the slot. For at least a few days after drill-ing, the soil temperatures (even in the slot)can be expected to remain at reasonablyconstant levels (Baker, 1976a). Therefore,measurements of relative humidity in theslots at these constant temperatures closelyreflect the amount of water vapour (or thewater vapour pressure) in the slot at thetime.

The higher MVPC values (or lowerdaily losses of RH%) for Class IV coversindicate that such a slot had a higher poten-tial to retain in-slot water vapour thanClass II cover, for example, which itself hada higher water vapour retention and lowerdaily loss of RH% than Class I cover. TheClass IV cover in these experiments was, infact, 65% better than Class II and 154%better than Class I in retaining in-slothumidity. No Class III cover was includedin this experiment.

The effects of moisture transfer fromthe slot micro-environments was also stu-died by varying the overlying air humidityat a constant temperature (Choudhary,1979; Choudhary and Baker, 1980, 1981b).The humidity within the slots increaseddifferently as the ambient RH was raisedfrom 60% to 90%. Those slot shapes thatincreased most rapidly with a rise in ambi-ent humidity will obviously decrease (dry)most quickly after sowing and be lessfavourable to seed germination and plantestablishment. The most rapid change wasin the open V-shaped slots (Class I cover),which increased at the rate of 8% RH perday, followed by the U-shaped slot (Class IIcover), followed by the inverted-T-shaped

slot (Class IV cover), which increased byonly 1% RH per day.

For the inverted-T-shaped slot (ClassIV cover), the rate of re-moistening wasabout the same as its rate of drying (i.e.approximately 1% RH per day), but for theV-shaped slot (Class I cover) the rate ofre-moistening was about twice that of itsdrying. This confirmed that Class I coverhad done little to isolate the slot micro-environment from changing ambient condi-tions, while Class IV cover had effectivelyisolated the slot from such climatic changesand retained a highly humid slot atmo-sphere throughout.

From a practical point of view, if seedsare sown into a favourable soil and the fol-lowing week is dominated by hot drywinds, a slot that might have presented anideal habitat for the seeds at the time ofsowing can soon turn into a hostile environ-ment unless the slot is protected from suchclimatic changes by adequate slot cover.Choudhary and Baker (1982) showed thatno-tillage slots with Class IV cover allowedseed germination and seedling emergencefrom soils that were otherwise too dry togerminate seeds sown by either conven-tional tillage or with other no-tillage openersand slots.

A field experiment in Manawatu,New Zealand, before Class IV cover had beenfully evaluated (Baker, 1976a, c) illustratedthat loose soil (Classes II and III cover)is much better than no cover at all (Class Icover). In this experiment, a barley (Hordeumvulgare) crop was sown in late spring usinghoe openers (U-shaped slot) in a silt loamsoil with adequate moisture. One half of thesown rows was covered by pulling a barharrow over the slots (Class IIIa cover)and the other half was left as the drill hadcreated the slots (essentially uncovered,Class I). The period after drilling was hot,dry and windy. Eight days after sowing theClass IIIa covering had 205 plants/squaremetre, compared with the Class I cover,which had only 22 plants per square metre.

An experiment conducted at the sametime and in the same soil showed thatincreased seed size did not compensate forpoor covering. Where larger seeds might have

64 C.J. Baker

been expected to have more vigour andtherefore be able to compensate for emer-gence difficulties, the opposite seemed tohave happened under no-tillage. In thisexperiment a small-seeded species, lucerne(Medicago sativa), and a large-seededspecies, maize (Zea mays), were substitutedfor barley and no-tilled in exactly the samemanner. After 10 days, the small-seededlucerne had 118 plants per m2 under ClassIIIa cover and 87 under the Class I cover.After a similar length of time the maize had4.6 and 0.3 plants per m2, respectively, forthe two classes of cover.

While Class IIIa cover still increasedseedling emergence with both the larger andsmaller seeds, the increase was less withlucerne than with either maize or barley.The smaller lucerne seeds apparently had abetter chance of finding themselves coveredwith a small piece of soil or mulch, whichproduced a favourable micro-environmentfor them, even in a Class I situation, thandid the larger barley seeds, which werebetter placed than the even larger maizeseeds in this respect.

A few days after the measurements ofthis experiment, rain ensured that all seedsgerminated in all three of the experimentsand the differences between treatments dis-appeared. Thus, the effects of cover wereonly important when the soil was dry ordrying, although, as described in Chapter 7,cover is also important in wet conditionsfor other reasons.

As further evidence of the importanceof cover in both wet and dry soils, Table 5.2summarizes the ‘best’ and ‘worst’ treatmentsof 30 experiments conducted in New Zealandbetween 1971 and 1985. Each experiment,amongst other things, compared the effectsof different openers and classes of coverunder different soil moisture conditions onseedling emergence of a range of crops(Baker, 1979, 1994).

There are several clear trends to be seenin the Table 5.2 data, and the experimentsare grouped accordingly. The first is a ten-dency towards improving seedling emer-gence with Classes III and IV covers, wheresurface residues were present and the soilswere either very dry (experiments 1–12)

or very wet (experiments 25–30). As themoisture conditions became more optimal(experiments 13–18) and/or when surfaceresidues were not present (experiments19–24), the difference between the classes ofcover generally became less or non-existent.

Perhaps just as important was the mag-nitude of some of the differences. Two- to14-fold differences are rare in agriculturalexperimentation, suggesting that slot shapeand cover have a major influence on thereliability and success of no-tillage practices,a fact not formerly recognized or reported.Even a ratio of 1.2 : 1 represents a 20%advantage for the ‘best’ treatment.

It is also notable that, where Classes Iand II covers were included in the compari-sons, they were almost invariably classedeither as the ‘worst’ treatment or as ‘nobetter than’ the other treatments. Theyseldom outperformed any other treatment,the exceptions being in two very wet soilswithout residue, where seedling emergencewas low with all of the openers compared.On the other hand, Classes III and IV coverwere never bettered by any other treatmentin the presence of surface residues in wet,optimum or dry soils.

The Table 5.2 data include only the‘best’ and ‘worst’ treatments for simplicity.Comparisons of other intermediate treat-ments between these two extremes are notshown. Almost invariably, however, ClassIV cover produced greater seedling emer-gence than Class III cover, which in turnoutperformed Class II cover, especially indry conditions. More detailed descriptionsof these comparisons are given in Chapters6 and 7.

Methods of Covering Seed Slots

There are several principles involved incovering slots after the passage of no-tillageopeners, and these are often combined withpressing to obtain soil–seed contact. Thesemethods are:

1. Squeezing – attempting to move soilsideways into the slot by a wedging actionto cover and to obtain soil–seed contact.


66 C.J. Baker

Year Soila Crop

Soil moistureand residuestatusb

Best and worst treatmentsand classes of cover(best) : (worst)c

Ratio of seedlingemergence counts(best) : (worst)

1 1979 S/L Wheat V. dry (R) inv. T/C (IV) : t.d. V/C (I) 14 : 12 1971 S/L Maize Dry (R) hoe U/C (III) : hoe U (I) 14 : 13 1971 S/L Barley V. dry (R) hoe U/C (lll) : hoe U (I) 9.5 : 14 1972 S/L Barley V. dry (R) inv. T/C (IV) : hoe U/C (II) 6 : 15 1979 FS/L Wheat V. dry (R) inv. T/C (IV) : t.d. V/C (I) 5.5 : 16 1976 FS/L Wheat Dry (R) inv. T/C (IV) : t.d. V/C (I) 3 : 17 1971 S/L Kale Dry (R) hoe U/C (III) : hoe U (I) 2 : 18 1979 S/L Wheat V. dry (R) inv. T/C (IV) : t.d. V/C (I) 1.7 : 19 1979 FS/L Wheat Adeq. (R) inv. T/C (IV) : t.d. V/C (I) 1.6 : 110 1979 S/L Lucerne V. dry (R) hoe U/C (III) : hoe U (I) 1.4 : 111 1979 S/L Wheat V. dry (R) inv. T/C (IV) : t.d. V/C (I) 1.3 : 112 1979 S/L Wheat Dry (R) inv. T/C (IV) : t.d. V/C (I) 1.2 : 113 1978 S/L Wheat Adeq. (R) inv. T/C (IV) : t.d. V/C (I) no diff.14 1978 S/L Lupin Adeq. (R) inv. T/C (IV) : t.d. V/C (I) no diff.15 1979 S/L Wheat Adeq. (R) inv. T/C (IV) : t.d. VN (I) no diff.16 1979 S/L Wheat Dry (R) inv. T/C (IV) : t.d. V/C (I) no diff.17 1979 S/L Wheat Adeq. (R) inv. T/C (IV) : t.d. V/C (I) no diff.18 1979 S/L Wheat Adeq. (R) inv. T/C (IV) : t.d. V/C (I) no diff.19 1985 S/L Barley Adeq. (NR) inv. T/C (IV) : t.d. V/C (I) no diff.20 1985 S/L Barley Adeq. (NR) inv. T/C (IV) : t.d. V/C (I) no diff.21 1985 S/L Barley V. wet (NR) p.t. U/C (III) : p.p. U/C (I) 4.2 : 122 1985 S/L Barley V. wet (NR) inv. T/C (IV) : t.d. V/C (I) 1.7 : 123 1985 S/L Barley V. wet (NR) t.d. V/C (I) : inv. T/C (IV) 1.6 : 124 1985 S/L Barley V. wet (NR) t.d. V/C (I) : inv. T/C (IV) 1.2 : 125 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 4.4 : 126 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 2.9 : 127 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 2.7 : 128 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 2.5 : 129 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 1.5 : 130 1985 S/L Barley V. wet (R) inv. T/C (IV) : t.d. V/C (I) 1.4 : 1

aSoil types: S/L = silt loam; FS/L = fine sandy loam.bSoil moisture and residue status: V. dry = Very dry; Adeq. = Adequate: V. wet = Very wet.c(R) = surface residues present; (NR) = no surface residues present; (I), (II), (III) and (IV) = the classes ofcover in each experiment. Drilling and covering treatments: t.d. V = triple disc opener, vertical V-shapedslot, not covered; t.d. V/C = triple disc opener, vertical V-shaped slot, covered; hoe U = hoe opener,U-shaped slot, not covered; hoe U/C = hoe opener, U-shaped slot, covered; inv. T = winged opener,inverted-T-shaped slot, not covered; inv. T/C = winged opener, inverted-T-shaped slot, covered;p.t. U = power till opener, U-shaped slot, not covered; p.t. U/C = power till opener, U-shaped slot,covered; p.p. U = simulated punch planter, U-shaped holes, not covered; p.p. U/C = simulated punchplanter, U-shaped holes, covered.Sources: Experiments 1, 5, 8, 9, 11, 12, 15, 16, 17 and 18 (Choudhary, 1979); Experiments 2, 3, 4 and10 (Baker, 1976a); Experiment 6 (Baker, 1976b); Experiment 7 (Baker, 1971), Experiments 13 and 14(Mai, 1978); Experiments 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30 (Chaudhry, 1985).Note: In all experiments where the slots were covered, the covering material was the best available asprovided by the shape of the slot and opener action.

Table 5.2. Effects of slot cover on seedling emergence in 30 experiments.

2. Rolling – pressing vertically on the soilalongside the slot with a roller of somedescription.3. Pressing – selectively pressing on or inthe slot zone itself, including non-verticalrolling or pressing mainly to obtain seed–soilcontact, but can also include an element ofcovering.4. Scuffing – scraping up loose surfacematerial from the slot zone and directing itto fall back into the slot, solely for covering.5. Deflecting – discretely deflecting soilfrom a particular part of the slot, solely forcovering.6. Tilling – loosening the ground behindthe opener, usually so that it can be moreeasily manipulated by one of the otherdevices previously listed.7. Folding – folding soil and/or residue backfrom whence it came, solely for covering.

Often two or more of these actions arecombined in one covering/pressing deviceor system.

To a casual observer, there might notseem to be much difference between thevarious actions described above. However,a description of the advantages and dis-advantages of each principle will illustratewhy cover and, to a lesser extent, pressingare such an important factor in reducing therisks associated with no-tillage.

Squeezing

Squeezing is the principle applied by manymanufacturers of vertical double disc openers(see Chapter 4). It usually involves pressingdown with a V-shaped wheel alongside theslot after its formation in such a manner thatthe mass of soil is pushed bodily sidewayswithout actually loosening it. The aim is tosqueeze the slot closed by moving the soilback from whence it came. Figure 4.7 illus-trates squeezing wheels behind double discopeners. The advantages are that such wheelsare simple, require little adjustment and arenot inclined to block with residue.

The disadvantages are that there isalmost as much downforce required on thepressing wheels as was needed on theopener to create the slot in the first place,

adding to the weight requirements of thedrill; the pressing action further compactsthe soil next to the seed; its ability to closethe slot is highly dependent on soil plasti-city and moisture content; any useful effectmay be undone quickly if the soil dries andshrinks after pressing. Slots made in soilsthat do not squeeze easily might not be ade-quately closed, although with soils of thisnature there is little else that can be done toremedy the situation. With soils in whichthe slot can be squeezed back together,there is a risk of so tightly trapping theseeds with compacted soil that emergenceof seedling shoots is restricted.

Rolling

General rolling of a field after drilling is oftenundertaken in an attempt to produce some ofthe squeezing action described above in arandom manner, without directing the actionto any specific zone. It works best where slotformation results in considerable hingedupheaval of the soil such as with hoe openersand some simple inverted-T-shaped openers.The vertical forces from the roller tend tosquash any raised ridges of soil downwardsand, to a limited extent, sideways. Since mostof the raised portions of soil will be alongsidethe slots, a degree of covering often results,although, as with squeezing, the final result ishighly dependent on soil moisture contentand plasticity.

Both flat and ringed (‘Cambridge’) roll-ers are used. The problem with ringed roll-ers is that the points of the rings apply morepressure than the shoulders. If the point of aring happens to coincide with the centre ofa sown row it may help to bury the seed toodeeply or at least it may seal the exit zone sotightly as to restrict seedling emergence. Forthese reasons flat rollers are preferred to‘Cambridge’ rollers.

The main advantage of rollers is thatthey are generally readily available imple-ments and easy to use, and their down-forces are derived from their own weightrather than the drill. They also leave a rela-tively flat finish to the field, which might beimportant at harvesting.


The disadvantages are that coveringmust be done as a separate operation andthat much of the loose soil and debris is notadequately moved sideways into the slotzone but is instead ‘trampled’ down whereit lies, in which case it might not contributeto covering at all. This latter disadvantage ismore of a problem with hoe openers thanwith simple inverted-T-shaped openers,because the latter hinge up a flap of soilrather than bursting it out bodily sidewaysin the manner of hoe openers.

Pressing

Pressing is really rolling in a discrete zoneand perhaps at a discrete angle in or on topof the slot. The slot can be pressed eitherafter it has been covered by some othermeans (e.g. scuffing) or prior to the coveringaction. The object of pressing alone is toeffect the covering action and it is particu-larly useful with slanted double disc open-ers. Pressing in association with anothercovering device improves soil–seed con-tact, but there is little scientific evidence toshow that this results in an improvement in

seedling emergence under no-tillage exceptperhaps by improving the consistency ofseeding depth (Choudhary, 1979; Choudharyand Baker, 1981a).

Pressing before covering, on the otherhand, has been shown to be of major benefitwith some openers such as hoe and verticaldouble discs. Few manufacturers, however,have seen fit to provide press devices thatact on the seed before covering of the slot.Figure 5.6 illustrates a ribbed press wheeldesigned to press in the base of the slotwhile simultaneously rolling on the undis-turbed soil alongside. Figure 5.7 shows apacking device designed to firm the seedinto the base of the slot at the same time thatcovering takes place.

The advantages of pressing are that itusually involves a wheel (or pair of wheels)that can double as a depth-control device.This double function, however, is not easy toachieve if the press wheel operates in thebase of a slot, since the wheel then registerson a soil surface that has already been cre-ated by the opener and thus may have littlereference to the true surface of the soil. Onthe other hand, pressing before coveringdoes more to counteract the disadvantages

68 C.J. Baker

Fig. 5.6. A press wheel with central rib, which is designed to press in the base of the slot at the sametime as it locates on the soil surface (from Baker et al., 1996).

of U- and vertical V-shaped slots than anyother known method (Choudhary, 1979;Choudhary and Baker, 1981a). The effectseems to be to press the seeds into the undis-turbed soil at the base of the slot so that theiremerging roots do not need to negotiate theslot wall in order access soil water.

The disadvantages are that pressingalone is not always a covering action at all.It is usually done after or before coveringis achieved by some other means, so twoseparate mechanisms are necessary. Also,because pressing after covering is easier toachieve and the press wheels are able to rollon the undisturbed soil alongside the slotand thereby achieve depth control at thesame time, this has become the preferredoption. It does not, however, achieve asmuch biologically as pressing before cover-ing (see also Chapter 6).

Scuffing

Scuffing is probably the easiest and mosteffective general slot covering option that canbe performed by a separate machine afterdrilling, regardless of the type of drill openerused. It usually involves a heavy, wide, flexi-ble harrow of some nature, which is pulledacross the ground, preferably parallel to thedrill slots. The harrow scrapes up the generalloose soil spilled from the slots and other

debris, and pushes this material back over theslots in a random manner. Its action dependson the untilled ground between the rowsbeing able to support the weight of the deviceso that it does not cut into the soil andthereby accumulate excess soil and debris.Some of the heavy harrows used in no-tillageare therefore not applicable to tilled soils.

Various harrows have been used, rang-ing from chain harrows with the points fac-ing upwards to avoid gouging seed out ofthe slots, truck tyres that have been splitlongitudinally with the cut surfaces facingdownwards, oyster nets, heavy chains andshort lengths of railway iron chainedtogether. Figure 5.8 shows a bar harrowmade of railway iron operating in a friablesoil after a drill with hoe openers (Baker,1970). Figure 5.9 is a plan of such a harrow,suitable for a 2.4 m wide drill.

The advantages of harrows are that theyare virtually foolproof to operate, simple andinexpensive. For many slot shapes createdin damp soils, harrowing is best delayed afew hours to allow some dry crumbs todevelop, which can then be scraped up asfriable covering material. A separate harrowis ideal for such situations.

The disadvantages are that if no crumbis formed when drilling, for example, withvertical double disc openers operating in adamp soil, even harrows will be ineffectiveto provide cover. Their use constitutesanother operation, although, if a time delayis not appropriate, they can be attachedbehind the drill; and with severe residuethey can become blocked.

A variation of scuffing and rolling is pro-vided by spiral-caged rollers, as shown inFig. 5.10. These devices combine the pressingeffect of a roller with the scuffing effect of aharrow, since the spiral nature of the rollingribs ensures that some sideways scuffingtakes place as the roller rotates. They are easyand convenient to use but do not move asmuch debris and soil as a true harrow.

Deflecting

With some hoe openers, small deflectingdevices are incorporated on the rear of the


Fig. 5.7. A shank-type opener with packingdevice to firm seeds into the base of the slot at thesame time as covering takes place.

opener so as to scrape a small slice of soilfrom the slot wall and allow it to fall on to theseed and/or fertilizer. One of the purposes ofdoing this has been to attempt to get a soil

covering over a deposit of fertilizer in thebase of the slot before seed is deposited ontop of the soil, thus separating them verticallywithin the slot (Hyde et al., 1979, 1987).

70 C.J. Baker

Fig. 5.8. A simple bar harrow for covering no-tillage slots (from Baker et al., 1996).

Fig. 5.9. Plan for a simplebar covering harrow (fromBaker, 1970).

Unfortunately, the function of any fixeddevice, such as an internal scraper of thisnature, is highly dependent on the positionof the scraper relative to the slot walls.Since the slot walls themselves are never inexactly the same place in two differentsoils, or even in the same soil at differentmoisture contents or operating speeds,either the scrapers have to be manuallyadjusted for each new soil condition or thefunctional ability of the device will varyquite widely with the conditions. Whilesuccessful deflectors facilitate verticalseparation of seed and fertilizer in the slot,stationary scrapers often collect residue andcause blockages.

Tilling

Because of the difficulty of moving soil thathas been squeezed sideways back in theopposite direction, some openers attemptto loosen the soil alongside the slot withthe aid of spiked wheels or discs. Often,spiked discs are arranged alongside angledpress wheels so that the loosening and

reverse-squeezing actions are combinedinto one, such as those shown in Fig. 5.11.

The advantages are that the soil is moreeasily moved, and, because it is in a loosenedstate, the risk of further compaction, parti-cularly over the seedling emergence zone, isreduced. The disadvantage is that any distur-bance of this nature partly destroys the inte-grity of the residue and soil layering, and atbest results in a random mixture of soil andresidue as the covering medium.

Folding

Folding of material back over a slot pre-supposes that a horizontal slot has beencreated in a manner that hinged the originalcovering material up in the first place.Alternatively, the slot may have been cre-ated so that the original covering materialhas been displaced bodily sideways with-out inversion and mixing, in a manner thatallows it to be retrieved and replaced as if ithad not been moved in the first place.

Realistically, this applies only toinverted-T-shaped horizontal slots, slanted


Fig. 5.10. A spiral-caged roller for covering no-tillage slots.

double disc openers and perhaps thoseangled dished disc openers that have apositive tilt angle. Even with inverted-Topeners, the folding feature is more a func-tion of how the slot is created than theaction of the covering device. For example,the uplifted flaps of most inverted-T-shaped slots, when created in pasture,can be folded down again either by a scuff-ing harrow or by press wheels. Press wheelsare more tolerant of different soil and pas-ture conditions, and are more predictablethan scuffing harrows, but they need to beangled to combine the folding and pressingfunctions.

In non-pasture soils such as arable soilswith loose or lying residue, the foldingfunction can only be realistically performedby press wheels. It is even possible to refinethe folding function sufficiently to allowstratified soil layers, e.g. a thin dry dustmulch that overlies more moist soil, tobe replaced more or less in the same orderthat they were in before passage of theopener. Figure 4.27 and 4.29 show a pair offolding wheels, which also function asdepth-gauging wheels, on a disc version of awinged opener.

The advantages of folding are that thecovering function is predictable and reliableand usually does not require adjustment ofopener components to cope with differentsoil or residue conditions. It can also resultin complete mulch and soil cover (Class IV),so long as there was a mulch covering thesoil in the first place.

The disadvantages are that excess pres-sure from press wheels on a damp pastureflap might close the slot so tightly as to makeit difficult for seedlings to emerge. Sincethis is a function of the downforce appliedto the openers, it is easily adjusted in thenormal course of setting up a no-tillage drill.

Summary of the Role of Slot Cover

1. There are four distinguishable classesof slot covers, ranging from no cover (ClassI), loose soil (Class II), soil and a smallamount of mulch or residue (Class III), tocomplete (greater than 70%) soil and mulch(Class IV).2. In Class III, the small amount of mulchor residue in the covering medium may be

72 C.J. Baker

Fig. 5.11. A pair of combined spiked discs and angled press wheels for covering no-tillage slots(from Baker et al., 1996).

either in intermittent clumps (Class IIIa) ora thoroughly mixed combination of residueand soil (Class IIIb).3. Class I–IV covers are ranked in ascend-ing order of their abilities to retain slotwater vapour.4. The benefits of covering in terms ofseedling emergence are ranked in ascendingorder of Classes I–IV.5. Principles of covering slots and/orobtaining soil–seed contact involve squeez-ing, rolling, pressing, scuffing, deflectingand/or folding soil and/or mulch.6. Some covering methods involve sepa-rate operations and machines that are usedafter drilling, in which case the weatherand soil plasticity after seeding becomeimportant.7. Other covering methods involve simulta-neous functions by the openers themselves,

in which case the nature and speed of slotformation become important.8. Vertical double disc and triple disc fur-row openers and punch planters usuallyproduce Class I or II cover.9. Slanted double and single disc openersand winged openers are capable of produc-ing Class IV cover.10. Hoe, angled vertical flat disc and angledvertical dished disc openers tend to pro-duce Class II or IIIa cover, depending on thespeed of travel.11. Power till openers tend to produceClass IIIb cover, regardless of speed.12. Angled dished disc openers sometimesproduce Class IV cover at slow speeds.13. The disc versions of winged openersare designed to produce Class IV coverregardless of speed, soil moisture condi-tions or residue conditions.


6 Drilling into Dry Soils

C. John Baker

A dry untilled soil has more potential togerminate seeds and allow seedlings to emerge

than a dry tilled soil; but very few no-tillageopeners are capable of harnessing that potential.

Most of the world’s agriculture involvesgrowing plants in soils that become dry atsome point in their growing cycles. If farm-ers could predict exactly when the soilwas going to become dry, they would planaccordingly. In many climates an approxi-mate idea of the onset of rain allows farmersto match the planting of crops to expectedweather patterns. These matchups, how-ever, are seldom accurate to better than afew weeks, if that.

When sowing seeds into untilled soils,a matter of a few days either way may makethe difference between successful cropestablishment or failure. This is not to saythat untilled soils are less forgiving thantilled soils; indeed, most have the potentialto be more forgiving. The problem is thatmost people have not yet learned how toharness that tolerance to their advantage.

With little guarantee that it will rain ona particular day after drilling, farmers areunlikely to attempt to drill seed into analready dry soil. On the other hand, if afarmer drills seed into a soil that appearsto have adequate moisture but then findsthe next week dominated by hot dry winds,

what had been an optimum environmentfor seeds may soon become a hostileenvironment.

None the less, so long as there is suffi-cient weight for penetration of the drillopeners and sufficient energy to pull themachine through the soil, it is possible tooperate a no-tillage drill in a dry soil. Thiscontrasts with wet soils (see Chapter 7),where operation of machinery is oftensimply not possible.

How Soils Lose Moisture

To understand the tolerance of untilledsoils to dry weather, it is necessary to dis-tinguish between an untilled soil that iscovered with a mulch and an untilled soilthat has a bare surface. It is also importantto compare the ways in which tilled anduntilled soils transport water to the surfacefor evaporation.

A tilled soil will lose moisture morerapidly than an untilled soil, at least ini-tially. But because of the increased porosityof tilled soils, the loss of moisture from theupper zones will not be quickly replenishedfrom deeper zones. The capillary rise ofwater is poor through the large voids andpores that result from tillage.


Because of this, a dry layer may beformed at the top of tilled soils. In some cli-mates a dry dust mulch layer is deliberatelyformed by repeatedly tilling the surfacelayer of soil until it becomes a super-drydust with very low moisture and thermalconductivities. The rationale behind such apractice is that, in the absence of any otherform of surface mulch, there is a net savingin moisture loss by sacrificing a smallamount of water to form a ‘dust mulch’ in theinterest of conserving the greater amount ofwater lying beneath it.

An untilled soil, on the other hand,will usually have a well-developed capill-ary system from the surface to some signifi-cant depth, which acts as a continuous‘wick’, transporting water upwards duringperiods of drying at the surface. This inter-nal transport system will become moreeffective with time as soil structure improves.Thus, while the initial loss of moisture willbe slower from the surface of a bare untilledsoil than from a tilled soil because thesurface is smoother and therefore does notcreate as much air turbulence or allow air toenter as easily, it may continue supplyingwater to the surface for evaporation for amuch longer time than a tilled soil that iscovered with a dust mulch. This, then, iswhere the presence of an organic residuemulch and the action of the drill openersthat operate in an untilled soil becomeimportant.

The Role of Vapour-phase Soil Water

All soils contain both liquid-phase waterand vapour-phase water in the form ofhumidity. The equilibrium relative humi-dity of the pore spaces between the parti-cles of undisturbed soil is virtually 100% atall liquid moisture levels down to perma-nent wilting point (Scotter, 1976). The per-manent wilting point (PWP) is the pointwhere the soil is considered too dry to sus-tain most plant life. The status of liquid soilwater is often expressed as the tensionby which water films are held by the soilparticles. At PWP this tension is –15 bar.

The important point is that plants wilt anddie at PWP and will not recover if wateredagain. However, it is important to rememberthat, even at that moisture content, the soilmacropores contain 99.8% relative humidity.

Like hair on the skin of an animal, anorganic mulch traps a layer of still air closeto the soil surface, which slows down theexchange of water vapour between the soiland the atmosphere. Most importantly, thehumidity within that mulch layer will remainmuch higher than the atmosphere above it,unless, of course, it is raining or the atmos-phere is at a high humidity anyway.

On a hot, dry day, for example, if onewere to take a rapid-response humidityprobe and carefully slide the probe under asingle large leaf lying on bare untilled soilwithout moving the leaf, there would be anoticeable rise in the humidity reading asthe probe moved under the leaf and then adrop when it was removed. The same thingwould happen under a piece of plastic orpaper. This demonstrates that a localizedhigh-humidity zone is possible under amulch at the soil surface. This mulch zonecan be quite small in area and unaffected byanother un-mulched zone nearby that has amuch lower humidity. This is a very import-ant phenomenon and is one of the majordifferences between no-tillage openers.

Every farmer in the world can recog-nize whether or not a tilled soil has suffi-cient liquid-phase water for germination.The judgement is usually made on the basisof the colour of the soil – darker-colouredsoil is wetter – or the temperature of thesoil – colder soil is wetter.

Soil humidity is rarely accounted for ina tilled soil. Nor should it be. Unless thesoil humidity is at least 90%, germinationwill mainly occur through uptake (imbibi-tion) of liquid-phase water from the soil bythe seed (Martin and Thrailkill, 1993;Wuest, 2002). The humidity in the surfacelayers of a tilled soil is likely to approach90% only on a very humid day or imme-diately after rain. As will be explainedbelow, the humidity in the drilled slot of anuntilled soil is even more important than inthe general soil matrix (Choudhary, 1979;Choudhary and Baker, 1981a, b).

Drilling into Dry Soils 75

Figure 6.1 illustrates what generallyoccurs when seeds are drilled into dry until-led soils with vertical double disc openers(V-shaped slot, Class I cover); hoe openers(U-shaped slot, Class II or III cover); andwinged openers (inverted-T-shaped slot,Class IV cover). The following explanationsare relevant for each line on Fig. 6.1.

Germination

Germination can occur from uptake ofeither liquid-phase water or vapour-phasewater (humidity), or both. For liquid-phasewater uptake to occur the seed must havephysical contact with water-bearing soil byadequate soil–seed contact.

When seed is wedged in the base of aV-shaped slot (vertical or slanted) in a drysoil, the transfer of water from the soil to theseed is generally adequate, even though thecontact zones with each wall of the slot maybe relatively small (Fig. 6.2). The smooth,and often compacted, slot walls are a readysource of liquid-phase water, which is other-wise scarce in a dry soil. Thus germinationwithin a V-shaped slot in a dry soil (Class Icover) can be ‘good’.

With U-shaped slots, there is usuallymore loose soil within the slot, which alsohas a broader base for the seed to lie upon(Fig. 6.3). These two factors cause poortransfer of scarce liquid-phase moisture tothe seed. Even when loose soil covers theslot and seed, there is little liquid-phasemoisture in this covering medium becauseof its loose nature. It remains dry and acts in

76 C.J. Baker

Fig. 6.1. Summary of the responses ofcontrasting no-tillage slot shapes to drysoil conditions. (✓ = good, X = poor.)

Fig. 6.2. The position a seed takes in a verticalV-shaped no-tillage slot.

Fig. 6.3. The position a seed takes in aU-shaped no-tillage slot.

a similar manner to a dust mulch, as des-cribed above. Thus germination within aU-shaped slot in a dry soil (Class II or IIIcover) is often ‘poor’.

With inverted-T-shaped slots, thesupply of liquid-phase water to the seed islittle different from that with U-shapedslots (Fig. 6.4). The Class IV cover, however,results in the seed being surrounded byvapour-phase water of 90–100% humidity(see Chapter 4). The seeds take a little lon-ger to germinate than where liquid-phasewater is available, but eventually a highgermination count results. Thus germina-tion within an inverted-T-shaped slot in adry soil (Class IV cover) is usually ‘good’.

Subsurface Survival

The most overlooked and under-studiedstage of development of no-tilled seedlingsis the time between germination and whenthe juvenile plants finally emerge from thesoil. All of this period is spent beneath thesoil. To remain alive the seedlings derivenutrients from their seed reserves and mois-ture through the embryonic roots, whichappear at the time of germination.

These pre-emerged plants will not havedeveloped the ability to photosynthesizefood and energy from the sun’s rays. Thereis only a limited need for them to drawwater from the dry soil while they arebeneath the surface, because it is mainly thesun that stimulates transpiration from plants.The subsurface seedlings, however, dorespire (breathe), consuming moisture, andthere may be subsurface water loss wherethe soil humidity, and therefore water vapourpressure, is lower than the correspondingwater vapour pressure within the embryo-nic plants, which results in a diffusion lossthrough the cell walls.

Together with respiration, the end resultis a tendency for subsurface seedlings todesiccate (dry out) unless they have anavailable source of soil water. With verticalV-shaped slots (Class I cover), many of thenew seedlings become desiccated and die.Often they see sunlight very soon after ger-mination because of the absence of coveringmaterial in the slot. But, even with Class IIcover (loose soil), they may still die. Thereason often is that the embryonic roots haveto negotiate and penetrate the compactedslot walls before they can access liquid-phase water from the surrounding soil.

Since the slot walls are nearly verticaland there is little resistance against whichthe roots can base penetration forces, otherthan the weight of the seed, the roots tend tohave difficulty penetrating the slot wallsand instead spread sideways along the slot.The result is that seedlings after germina-tion receive a poor water supply. Seedlingscannot stand the strong desiccation demandfrom a soil humidity that usually, at best,remains in the 60–80% range in verticalV-shaped slots. Therefore, many subsurfaceseedlings die before emergence in a verticalV-shaped slot in a dry soil.

It is useful to contrast this situationwith a fully tilled dry soil. In a tilled drysoil, seeds are placed in a loose and friablemedium. First, this medium probably doesnot transport enough liquid-phase water tothe seed to bring about germination. But,even for those seeds that do germinate, thereis no compacted slot wall for embryonicroots to penetrate. So subsurface seedling


Fig. 6.4. The seed position in an inverted-T-shaped no-tillage slot.

deaths in tilled soils are rare, similar toU-shaped no-tillage slots.

With U-shaped slots (Class II or IIIcover), although germination is often poor,the roots of those seedlings that do germinatehave less trouble penetrating the uncom-pacted and broader base of the slots. If theslot can be covered to Class II or Class IIIstandard, i.e. at least loose soil or a mixtureof soil and residue, the likelihood of desi-ccation of subsurface seedlings is alsoreduced. Humidity is likely to remain in the70–90% range. The result in U-shaped slotsin a dry soil is that a reasonable percentageof the subsurface seedlings survive, althoughthere may not be many that germinate untilrain (or even dew) arrives, which means thatseedling emergence may be spread over along time.

Figures 6.5 and 6.6 show four wheatplants that were extracted from dry no-tillageplots in Australia. In Fig. 6.5, the plants areoriented so that the slot is running in thesame direction as the wire fence (i.e. acrossthe field of vision). The two plants on theleft were sown with a vertical double discopener (V-shaped slot) and the two on theright were sown with a wide, hoe-typeopener (U-shaped slot). Root development

along each of the rows is approximatelyequal for all four plants (i.e. for both slots).

In Fig. 6.6, all four plants have beenrotated 90° and are now oriented with thedrill rows running towards the camera.Clearly the roots of the plants on the left(vertical V-shaped slot) have hardly movedsideways out of the slot at all, but havestayed essentially within the slot walls.The roots of the plants on the right (wideU-shaped slot), on the other hand, havespread about as much sideways as they hadlengthwise (Fig. 6.5). This illustrates thedifficulty that young (and even, in this case,mature) roots have in penetrating theslot walls of some vertical V-shaped slots,compared with U-shaped slots.

With inverted-T-shaped slots (Class IVcover), humidity usually remains in the90–100% range because of the residue-covered slot. While this will result in high(if sometimes slow) counts of germination,its most important function is that it removesmost of the desiccation or transpiration stressfrom the subsurface seedlings, with theresult that their survival rate is also high.

Embryonic root exploration out of theslot zone is no more restricted with inverted-T-shaped slots than with U-shaped slots.

78 C.J. Baker

Fig. 6.5. Wheat plants from a no-tilled crop in New South Wales, Australia; slot direction is parallel tothe fence (from Baker et al., 1996).

The combined result is that, with inverted-T-shaped slots in a dry soil, most of thesubsurface seedlings survive, leading torapid and consistent seedling emergence.

Figure 6.7 illustrates the relative ratesof humidity loss from the three contrastingslot shapes (Choudhary and Baker, 1994).

Scientists in New Zealand tried cover-ing vertical V-shaped slots with strips of

plastic to artificially trap water vapour inthe otherwise open slots and create artifi-cial Class IV cover (Choudhary, 1979). Thehumidity increased, but fungal growth soonalso became evident in the slots, probablyindicating that air circulation had beenreduced. Therefore, nature had the perfectcovering medium in the form of organicmulch and residue. Mulch breathes, as well


Fig. 6.6. Wheat plants from a no-tilled crop in New South Wales, Australia; slot direction is towards thecamera (from Baker et al., 1996).

Fig. 6.7. The relativerates of loss of soilhumidity from V-, U- andinverted-T-shapedno-tillage slots (fromCarter, 1994).

as trapping humidity. Plastic does notbreathe, even if it traps humidity, and it isquite impractical to cover every slot drilledwith plastic strips.

It is little wonder, therefore, that deci-duous trees flower, set seed and drop theirseeds to the ground before they drop theirleaves. Nature’s intention seems to havebeen to cover the seeds with mulch.

Seedling Emergence

The more Xs in the total for a slot in Fig. 6.1,the less effective that slot is at promotingseedling emergence from a dry soil. Con-versely, the more ✓s in the total, the betterthe slot.

In summary, the order of ranking withregard to dry soils is:

1. Inverted-T-shaped slots – Class IVcover – excellent germination, excellentsurvival and thus excellent emergence.2. U-shaped slots – Class II or III cover –poor germination, adequate survival andthus substandard emergence.3. Vertical V-shaped slots – Class I or IIcover – excellent germination, poor survivaland thus poor emergence.

Table 6.1 (Choudhary, 1979) lists typicalpatterns of wheat (Triticum aestivum) seedand seedling responses to the three slotshapes in dry soils. These results illustratethe separate mechanisms of failure of ver-tical V- and U-shaped slots, i.e. subsurfaceseedling mortality and germination failure,respectively.

With vertical V-shaped slots, seedlingemergence was poor (27%), although germi-nation had been reasonably good. Only 9%of the seeds failed to germinate, the same asfor the inverted-T-shaped slot. On the otherhand, a high percentage (64%) of thesegerminated seedlings remained un-emergedbeneath the soil in the vertical V-shapedslots, and most of them died.

With U-shaped slots, although a higherpercentage (51%) emerged than withV-shaped slots, 23% of the seeds had notgerminated in the first place. For those thatdid germinate, subsurface seedling survivalwas reasonably good. Only 26% of the seed-lings remained un-emerged beneath the soil,similar to the inverted-T-shaped slots (27%).

The distinguishing feature of theinverted-T-shaped slots was that 64% of theseeds germinated and emerged. In addition,27% germinated and remained alive beneaththe soil, awaiting rain. Only 9% did notgerminate in the first place.

Figure 6.8 shows typical seedlingemergence patterns of wheat, no-tilled intoa dry soil under controlled dry conditions(Baker, 1976b). Clearly the seeds sown inthe inverted-T-shaped slots emerged in muchgreater numbers (78%) than from U- (28%)or vertical V-shaped slots (26%). Therewas a few days’ delay before the seeds inthe inverted-T-shaped slot started to emerge,possibly because they were taking upvapour-phase water rather than the liquid-phase water that the other two slots weresupplying; but thereafter the emergence ratewas very rapid compared with the othertwo slot shapes.

80 C.J. Baker

Double disc openerVertical V-shaped slot

Class I cover

Hoe openerU-shaped slotClass II cover

Winged openerInverted-T-shaped slot

Class IV cover

Seedling emergence 27% 51% 64%Germinated seeds that

had failed to emerge64% 26% 27%

Un-germinated seeds 9% 23% 9%Total seed pool 100% 100% 100%

Table 6.1. Wheat seed and seedling responses to no-tillage openers and slot shapes in a dry soil.

This phenomenon is also illustrated inFig. 6.9, which shows field seedling emer-gence patterns of peas in a dry soil in Oregon,USA (Wilkins et al., 1992). Vertical V-, U-and inverted-T-shaped slots were used, which

were represented by ‘double disc’, ‘strip-till’ and ‘cross-slot’ openers, respectively.

Emergence from the U-shaped slots wasspread over a 2–3-day period and reached amaximum of 65%, 5% better than V-shaped


Fig. 6.8. Wheat seedlingemergence patterns fromV- (——), U- (- - - -) andinverted-T-shaped (.....) no-tillageslots in a dry soil (Baker, 1976b).

Fig. 6.9. Pea seedlingemergence patterns fromV-, U- and inverted-T-shapedno-tillage slots in a dry soil (fromWilkins et al., 1992).

slots, which otherwise spread their emer-gence pattern over the same length of time.Seedlings in the inverted-T-shaped slotsdid not start to emerge until 1–2 days afterthe other two slots, but then almost all ofthe plants came up in a single day andattained a total of 90% emergence. Theevenness and consistency of emergenceshown by the inverted-T-shaped slot hasimportant consequences for eventual cropmaturity and yield; and, of course, 90%emergence contributes to greater yieldsthan 50–65% emergence.

A further experiment by Choudhary(1979), shown in Table 6.2, illustrates theeffectiveness of the three slot shapes in adry soil compared with the same soil whenrewetted. The most noticeable effect wasthat both the vertical V- and U-shaped slotsresponded positively when the moisturestatus of the soil was raised. Their seedlingemergence counts increased by fourfoldand twofold, respectively. The inverted-T-shaped slots increased by only 9%because their dry soil counts were reason-ably high in the first place.

As in Table 6.1, vertical V-shaped slotshad a high count (72%) of un-emerged seed-lings in the dry soil, which decreased onlyslightly (to 58%) in more moist conditions,indicating that many seedlings had alreadydied. U-shaped slots had a relatively highcount (47%) of un-germinated seeds in thedry soil, which was later eliminated altoge-ther (to 0%) when the soil moisture level wasraised, indicating that all the un-germinatedseeds had remained viable. This illustrates

again that the causes of failure in a dry soilfor vertical V- and U-shaped slots are quitedifferent from one another. In the case of ver-tical V-shaped slots, it is failure of seedlingsto survive beneath the soil, while, inU-shaped slots, it is failure of seeds to germi-nate in the first place. With inverted-T-shaped slots, most of the seeds hadgerminated even in the dry soil and aboutthe same number as for U-shaped slotsremained un-germinated beneath the soil.

The question arises as to what happensto the subsurface seedlings that have notemerged from a dry soil in field situations.The fate of such seedlings depends on twothings: (i) how soon after drilling rainoccurs; and (ii) how effectively the slotmaintains the subsurface seedlings ina viable state awaiting that rain. The highhumidity of inverted-T-shaped slots willmaintain seedlings in a viable state formuch longer than U-shaped slots, which arethemselves better in this respect thanvertical V-shaped slots. In the laboratory,germinated wheat seedlings have remainedviable beneath a dry soil with Class IV coverfor 3 weeks. In one field situation, however,on a very light soil of volcanic ash origin,ryegrass (Lolium perenne) seedlings sur-vived beneath the surface of Class IV cover(inverted-T-shaped slot) for 8 weeks beforerain finally fell, at which time they emer-ged, apparently none the worse for havingspent that amount of time beneath the soil(S.J. Barr, 1990, unpublished data).

Provided that rain or irrigation occursbefore the subsurface seedlings have died

82 C.J. Baker

Double disc openerVertical V-shaped slot

Class I cover

Hoe openerU-shaped slotClass II cover


Class IV cover

Moist Dry Moist Dry Moist Dry

Seedling emergence 42% 10% 70% 31% 68% 59%Germinated seeds that

had failed to emerge58% 72% 30% 22% 32% 23%

Un-germinated seeds 0% 18% 0% 47% 0% 18%Total seed pool 100% 100% 100% 100% 100% 100%

Table 6.2. Wheat seed and seedling responses to no-tillage openers in a dry soil and soil of adequatemoisture.

from desiccation, it might be possible to geta positive response to watering after drillingwith both vertical V- and U-shaped slots.By irrigating 22 days after a dry soil hadbeen drilled under no-tillage, Baker (1976a)obtained an increase in emergence countsfrom 21% to 75% with V-shaped slots, andfrom 38% to 92% with U-shaped slots.With inverted-T-shaped slots, the increasewas much more modest, from 78% to 86%,again because seedling emergence hadalready been high when the soil was in adry state prior to irrigation.

The Effects of Pressing

One of the most common practices in tilledseedbeds is to press on the rows after cover-ing. The practice seeks to improve seed–soilcontact and attract water to the seed bycapillary action. Undoubtedly it improvesseed–soil contact but its function in attract-ing water to the seed is dubious. Cross(1959) demonstrated that, in a dry soil, con-solidation under the seed was more import-ant than consolidation above the seed, andthere has always been doubt about the realbenefits of pressing on tilled soils anyway.

It seems that pressing after coveringin an untilled soil is of even less benefit.Choudhary (1979) and Choudhary and Baker(1981b) conducted experiments that com-pared pressing on the soil after coveringwith covering alone and pressing on theseed before covering. They found no benefitat all for pressing on the covered slots in adry soil. Most importantly, they found sub-stantial benefits from pressing on the seedsin the slot before covering, but only in verti-cal V- and U-shaped slots. With inverted-T-shaped slots, seedling emergence wasalready high in the absence of pressing,so there was little improvement from anysubsequent pressing action.

In U-shaped slots, pressing the seedinto the base of the slot ensures that the seedhas good contact with the water-bearing soil.Since there is usually insufficient watervapour in U-shaped slots to germinate theseed and seed–soil contact is otherwise poorfor liquid water uptake, pushing the seed

into the undisturbed soil ensures that atleast liquid water uptake is available inmuch the same way as for V-shaped slots, asillustrated in Fig. 6.10.

In vertical V-shaped slots, pressing theseed into the base of the slot has a differenteffect. Embedding the seed directly into theundisturbed soil ensures that the radicle(first root) emerges directly into soil, fromwhich it will derive its all-important wateruptake (Fig. 6.11), thus bypassing the stressperiod when embryonic roots otherwiseattempt to penetrate the slot wall. Thus,pressing on the seeds prior to covering of


Fig. 6.10. The position of seeds after pressing inthe base of a U-shaped no-tillage slot.

Fig. 6.11. The position of seeds after pressing inthe base of a V-shaped no-tillage slot.

both U- and vertical V-shaped slots hassignificant benefit in terms of improvingseedling emergence from a dry soil.

Field Experience

In New Zealand a field experiment sought todrill with three contrasting no-tillage openertypes each second Monday for 6 summermonths regardless of soil or weather condi-tions in order to gauge how often limitingconditions occurred in that region (Choudharyand Baker, 1982). By chance, on one occa-sion the soil moisture level was close tothe permanent wilting point. On this occa-sion, inverted-T-shaped slots obtained 50%emergence of wheat, whereas U- and V-shaped slots in the same soil produced vir-tually no seedling emergence. It is doubtfulif any seeds would have emerged from atilled soil at or near PWP either.

It is little wonder, therefore, that repeatsurveys of operators of drills with openersthat created inverted-T-shaped slots in NewZealand, covering some 40,000 hectares peryear in both spring and autumn sowing(Baker et al., 2001), revealed a 99% successrating for the drilling process and technology.

Summary of Drilling into Dry Soils

1. The descending ranking of biologicalperformance of slot shapes in dry soils is

inverted-T-, followed by U-, then verticalV-shaped slots.2. The descending ranking of effective-ness of slot cover in dry soils is Class IV toClass I.3. Inverted-T-shaped slots trap watervapour within the slot, which germinatesseeds as well as sustaining subsurfaceseedlings.4. The predominant cause of failure ofvertical V-shaped slots is subsurfacedesiccation of seedlings, not germinationfailure.5. The predominant cause of failure ofU-shaped slots is germination failure.6. Pressing on the soil after covering theseed has negligible effect with any slot shape.7. Pressing on the seeds in V- andU-shaped slots before covering improvestheir performance noticeably.8. Surface residues are an importantresource for promoting seedling emergencefrom dry soils, provided the openers utilizethem correctly in the covering mediumto trap humidity. Inverted-T- and slantedV- (but not vertical V-) shaped slots aremost effective.9. It is possible to obtain more effectiveseedling emergence from a dry soil usingno-tillage rather than tillage, provided thecorrect technique and equipment are used.10. With inverted-T-shaped slots, it is pos-sible to obtain seedling emergence fromuntilled soils that are too dry to sustaineffective crop growth.

84 C.J. Baker

7 Drilling into Wet Soils

C. John Baker

The biological ranking of no-tillage openerperformance for wet soils is almost identicalto that for dry soils, but for different reasons.

Unlike dry soils, it is usually impossible tophysically drill into soils that are alreadyvery wet because of limitations in drillperformance, limited traction or excessivecompaction. Thus, in considering wet soileffects, it is important to distinguishbetween two different situations:

1. Drilling into soils that are sufficientlywet to make them sticky and/or plastic innature and yet are still able to be drilled.2. Drilling into soils that were not exces-sively wet at the time of drilling but thatbecome very wet soon after drilling.

Drilling Wet Soils

The most pressing problem to drill analready wet soil without plugging (situation1 above) from an operational point of viewrelates to the physical ability of openers.There are few common principles that dis-tinguish one opener from another in thisregard. In general, all openers with rotatingcomponents have limitations in wet soils,especially in wet soils that are also sticky.The use of subsurface scrapers on some disc

openers will extend their tolerance of wetsoils.

Where an opener employs press orgauge wheels of the semi-pneumatic (‘zero-pressure’) type, the operational limit of thewhole opener in wet and/or sticky soilsis the limit to which these tyres can con-tinue to operate without plugging. Semi-pneumatic tyres are particularly good atshedding mud (see Chapter 10), so it isillogical to expect an opener to handle wetsoils any better than its tyres.

Putting to one side the ability of differ-ent openers to operate without plugging,there are important biological effects thatalso arise as a result of the physical actionof different openers in wet soils. The mostimportant biological factor is the amount ofcompaction, smearing and crusting createdby different openers. Smearing is very local-ized compaction within the slot (perhapsonly 1–2 mm thick) and crusting is usuallya smear that has dried hard.

Dixon (1972) illustrated the effects ofvertical double disc openers (V-shapedslot), simple hoe openers (U-shaped slot)and simple winged openers (inverted-T-shaped slot) at different soil moisture con-tents, one of which was quite wet (27%)(Fig. 4.1). Several others have also studiedthe tendencies of different openers tocompact the base and side walls of the slot


(Dixon, 1972; Baker and Mai, 1982b;Mitchell, 1983). From these studies andcountless field observations, the compac-tion, smearing and crusting tendencies ofdifferent openers can be summarized asfollows.

Vertical double (or triple) disc openers(V-shaped slots)

These have the strongest compaction ten-dencies of all no-tillage openers. Compac-tion occurs at both the base and side wallsof the slot. They also have a strong smearingtendency, which is accentuated by the openslot. Because the smears are open to the ele-ments, they often dry after passage of theopener and soon become internal crusts,which restrict root penetration.

In sticky wet soils, soil clings to theoutside of the discs, which lift soil and seedfrom within the slots and deposit themalongside, thus negating the true V shape ofthe slots. Figure 4.5 shows a slot made by avertical double disc opener in a stickyAustralian soil. The slot has been severelydisrupted by soil sticking to the disc.

Vertical double or triple disc openershave a strong tendency to tuck (or hairpin)residue into the slot, as described in moredetail later. The slot cover is typically Class I.

Slanted double (or triple) disc openers(slanted V-shaped slots)

These are somewhat less likely to compactthe seed zone but only if the seeding openeris preceded by another double or triple discfertilizer opener slanted in the oppositedirection. Because of the slant, the upperside of the slot wall created by the firstopener actually heaves the soil upwardsand loosens it somewhat. Although the sec-ond slanted opener actually compacts thesoil beneath it more than if it had been ope-rating in a vertical position, the pre-looseningof this soil by the first opener, which nor-mally operates somewhat deeper than thesecond opener, negates most of the harmfuleffects.

Where a slanted double or triple discopener is not preceded by a similar openerslanted in the opposite direction, the com-paction beneath the opener will be greaterthan if the opener had been operating verti-cally. Compaction above the opener will berelieved, but loosening will have little effecton root penetration of seedlings, although itwill improve the moisture-retention proper-ties of the slot, which in turn will reducethe risk of the internal surfaces of the slotdrying to form crusts.

Slanted double or triple disc openersotherwise have all of the same problemsassociated with their vertical counterparts,including hairpinning of residue into theslot zone and a tendency for sticky soils tocling to the outside of the disc and disruptthe integrity of the slot shape. The slotcover varies from Class II to Class IV.

Vertical angled flat (or dished) discopeners (U-shaped slots)

These have little or no compaction tenden-cies and little or no tendency to smear or liftsoil in sticky conditions. Covering of theslots may be difficult, however, in conti-nued wet weather, for the same reasons lateroutlined for hoe-type openers. Angled discopeners also tend to tuck (or hairpin) resi-due into the slot (see below). The slot coveris typically Class I or II.

Hoe-type openers (U-shaped slots)

These usually result in little compaction,unless they are of a design that has a largeflat base, in which case they may compactthe base of the slot, but not the side walls. Inwet soils they almost invariably createsmears on the base and side walls of theslot. These become important if the slotremains uncovered after drilling and thesmears are allowed to dry to form crusts.

Covering is a particular problem. Hoeopeners rely on the covering device collect-ing up the spilled soil alongside the slot andbrushing it back over the slot as coveringmaterial. In a wet soil, such covering material

86 C.J. Baker

is unlikely to become crumbly, so the slot isdifficult to cover at all, encouraging even-tual crust formation.

If covering needs to be a separate opera-tion, its effectiveness depends on allowingsufficient drying for crumb to form in thedebris alongside the slot, but not so muchdrying as to allow any smears within theslot to become crusts. Thus, although hoeopeners can be used successfully in wetsoils, they require a high level of skill toovercome their shortcomings. Hoe openerscan experience problems in sticky soils ifsoil accumulates on the sides of the openerand changes its shape and dimensions. Theslot cover is typically Class I.

Power till openers (U-shaped slots)

These mostly compact the base of the slotand may smear that zone as well. Thissmearing and compaction, however, areseldom severe and, because the soil is notoften spilled completely out of the slot, thesmears are usually not at risk of becomingcrusts unless a very severe drying periodfollows drilling.

Power till openers mechanically aeratethe soil more than any other opener type,which can be beneficial in wet soils withlow residue levels and only small popula-tions of earthworms. On the other hand,some power till openers may become totallyinoperable in sticky wet soils due to ‘plug-ging’ between the cutting blades. The slotcover is typically Class IIIb.

Winged openers(inverted-T-shaped slots)

These smear the base of the slot about asmuch as most hoe openers but result inminimal compaction. Like power till open-ers, winged openers have an advantage inthat they either close the slot themselves ormake closure by a separate device easy andnot dependent on moisture or weather.Thus, smears do not become crusts andtherefore do not restrict root growth.

Winged openers handle sticky soilsreasonably well. The disc version of theopener uses subsurface scrapers to over-come the tendency of sticky soils to cling tothe disc. Figure 7.1 shows the benefits ofscrapers used on a winged opener in thesame sticky Australian soil as depicted inFig. 4.5. The integrity of the slot and the res-idue cover have remained intact. The slotcover is typically Class IV.

Figures 7.2 and 7.3 show sections ofsoil in the side walls of two no-tillage slotsphotographed with an electron microscope(Mai, 1978). The lighter grey areas in theuncompacted soil in Fig. 7.2 are naturalvoids and macropores. In addition, muchorganic matter in the form of roots andburied residue is visible. In contrast, thecompacted soil in Fig. 7.3 has almost nomacropores and little visible organic matter.Instead, it contains only a few cracks inwhich soil oxygen can circulate. It is obvi-ous why earthworms prefer soil surround-ing inverted-T-shaped slots to that whichsurrounds V-shaped slots.

Soil type is also important in wet-soilseeding. If a small handful of soil can be‘ribboned’ by rubbing it between the thumband forefinger, it will probably becomesmeared by those openers that have smear-ing tendencies. In general, sandy soils andwell-structured loamy soils with reasonablyhigh levels of organic matter seldom take onsmears or become permanently compactedby passage of no-tillage openers. Many claysoils take on a smear readily when wet.Montmorillonitic clays may become stickyinstead. Silty soils lie in between clays andsands.

Many of the sticky montmorilloniteclays produce good crops because of theirincredible water-holding capacity. Theyalso have a strong tendency to shrink whendrying. This produces internal cracking,forming quite deep fissures in the soil.During the early stages of drying and crack-ing, the soil mass breaks itself into smallerparticles by shrinkage, almost as if it hadbeen tilled. Such soils are said to beself-mulching. They produce a dilemma fortillage practices. Because they are so stickywhen wet, they are difficult to work in that

Drilling into Wet Soils 87

state with tillage equipment. But waitinguntil they dry and are easier to work riskssacrificing valuable soil water during thedrying and tillage periods.

No-tillage offers a realistic option forsuch soils, since it allows sowing directlyinto the untilled soil with minimal distur-bance. This is best done when only a small

88 C.J. Baker

Fig. 7.1. Class IV slot cover remaining intact after passage of a winged opener, equipped withscrapers (inverted-T-shaped slot), through a damp sticky soil (compare with Fig. 4.5).

Fig. 7.2. Electron-microscopic section of soil from the wall of an inverted-T-shaped slot(from Baker and Mai, 1982b).

amount of surface drying has occurred.Avoiding inversion of the deeper, moremoist layers during drilling then becomesan important function of the no-tillageopeners, both because such inversionbrings up wet soil that sticks to everythingand because it results in unnecessary loss ofsoil moisture. This contrasts with continu-ous tillage, in which the resistance of soilsto compaction and smearing declines withtime and continuous working. Vehicle traf-fic exacerbates the situation, leading to acumulative decline in the usefulness ofsuch soils when they are worked in a wetstate. Since the practice of no-tillage gradu-ally increases SOM levels and structureover time, many soils are likely to becomeless liable to smear or compact with timeand therefore better able to be drilled whenwet.

Drilled Dry Soils that Become Wet

Drilling dry or moist soils that have yet tobecome wet will not create substantivesmearing or compaction problems with anydesign of opener. Thus, the differencesbetween openers reflect the abilities of the

various slot shapes to create micro-environments that will remain beneficial toseeds, seedlings and growing plants evenafter the soils have subsequently becomewet. The most important criterion is theireffect on the oxygen status of the soil, sinceroots breathe, and saturation by water willotherwise drown both seedlings and bene-ficial soil fauna.

Wet soils, especially when they havenot been tilled, have a complex relationshipwith seeds. For example, if the soil has notbeen tilled for some time and has a reason-able population of earthworms, the earth-worms will have an important effect onoxygen diffusion in the seed zone and waterdrainage. Their burrowing activity provideschannels for air entry and water exit.

Earthworms also need feeding. Theyrespond rapidly to the presence or absenceof food supplies. There are several speciesof earthworm and each species prefersto occupy a certain depth range of soil.Those that feed on surface residues (e.g.Lumbricus rubellus Hoff and Allolobophoracaliginosa Sav) live near the surface and arethe first to react to excess water on the soilsurface. They also react to the presence orabsence of residues, which comprise theirfood supply, even to the extent that their


Fig. 7.3. Electron-microscopic section of soil from the wall of a V-shaped slot(from Baker and Mai, 1982b).

burrowing and casting will reflect thepresence of surface residues only a fewcentimetres apart.

In experiments with no-tillage openersin soils that were to become wet, Chaudhry(1985) tested the effects of the presence orabsence of surface residues. ‘Residue’ plotshad long, rank ryegrass (Lolium perenne)growing on them, which was sprayed.‘Non-residue’ plots had this grass removedat ground level just before drilling. Within24 h of mowing, the earthworm populationsin the ‘non-residue’ plots had halved,presumably as a response to the removalof their principal food source.

It has also been observed that earth-worms appear to have a preference for thedisturbed slot zone in a soil after drilling, asopposed to the undisturbed soil alongside,but only if this slot zone is covered with aready source of food (residue) and only if itis not compacted. Presumably they findthe loosened soil easier to burrow throughand the covering of residue provides animproved environment and a convenientfood source.

Table 7.1 shows the effects on seedlingemergence of barley (Hordeum vulgare) ina wet soil by the three common slot shapeswith and without surface residues (Chaudhry,1985; Chaudhry and Baker, 1988). The tablealso shows the numbers of earthwormsrecovered from 120 mm diameter × 100 mmlong soil cores centred on the drilled rows.The index of earthworm activity, measuredas the percentage of the area of ground cov-ered by earthworm casts, showed similartrends to the numbers of earthworms countedin the soil cores. To create very wet condi-tions after drilling in this experiment, thesoil was irrigated with 20 mm of simulatedrainfall per day over a 4 h period, for 20 days(total, 400 mm in 20 days). In a field situation,such an intensity of repeat rainfall would beexpected to produce supersaturated condi-tions and surface puddling in a short timespan. In the free-draining bins used in thisexperiment, supersaturation did not occurbut the soil none the less remained above‘field capacity’ most of the time.

There were three strong trends in thedata of Table 7.1. First, the greatest seedling

emergence was promoted by the surfacebroadcast treatment (87%) and inverted-T-shaped slots created by winged openers(76%) (no statistical difference). Next wereU-shaped slots created by hoe (65%) andpower till (63%) openers. The verticalV-shaped slots created by double discopeners and the U-shaped holes createdby a simulated punch planter performedpoorly (24% and 17% seedling emergence,respectively).

Secondly, the number of earthwormsfound in cores of soil centring on the drilledrows mirrored very closely the seedlingemergence counts. Most earthworms werefound in the vicinity of the slots created bythe winged (25), hoe (22) and power till (23)openers, together with surface broadcasting(22) and perhaps the punch planter (18),but the vertical double disc opener (9)performed poorly.

Thirdly, the presence or absence of resi-dues had a very positive effect on both seed-ling emergence and earthworm numberswith the inverted-T- and some of theU-shaped slots and holes, but not withV-shaped slots or with surface broadcast-ing. Residues improved seedling emergencewith the inverted-T-shaped slots from 48%to 76% and earthworm numbers from 13 to25. The effect on U-shaped slots was notquite so marked, but residues none the lessimproved seedling emergence from 40% to65% and earthworm numbers from 13 to 22with the hoe opener.

In contrast, residues actually depressedseedling emergence with the vertical dou-ble disc openers (from 25% to 17%) andpunch planter (from 17% to 14%), but hadno effect with surface broadcasting or thepower till openers. The latter phenomenonis not surprising since the power till openerchopped up the surface residues (and pro-bably a number of earthworms) and incor-porated them into the soil. With surfacebroadcasting, the seeds were left lying ontop of the ground, making them less likelyto be affected by earthworm activity takingplace beneath the surface. Further, becausemoisture was not limiting, it is not surpri-sing that residues on the soil surface had nodirect effect on emergence with broadcasting.

90 C.J. Baker


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These results suggest that all threeobserved trends are linked in a wet soil.Indeed they are. The third line of Table 7.1illustrates emergence when earthwormswere eliminated from the soil by poisoningin an otherwise identical experiment.

Without earthworms, seedling emer-gence was weakened with all drillingtreatments. Most residue advantages withinverted-T- and U-shaped slots disappearedin the absence of earthworms, indicating astrong linkage between the three factorswhen they were present. This also demon-strates one of the longer-term benefits ofno-tillage, that of building up earthwormnumbers and organic matter, which work tothe advantage of this farming system, pro-vided that appropriate equipment is used tomaintain and capitalize on those benefits.

The data of Table 7.1 also illustratesthat mechanical aeration can to some extentsubstitute for the absence of naturalaeration caused by earthworms and othersoil fauna. The chemical treatment to killearthworms also kills some of the otherchannel-forming soil fauna. Although theuse of power till openers may only be ofshort-term benefit when drilling into soilsthat subsequently become wet, this was theonly opener to promote more than 24%seedling emergence in the ‘sterilized’ soil.

Even then, the 43% emergence obtainedwith this opener in residue and the 41%without residue cannot be regarded as satis-factory and do not compare with the 76%obtained with the winged opener in thepresence of both earthworms and residues.

Surface broadcasting promoted thehighest seedling emergence counts in theabsence of earthworms (89% both withand without residue), presumably becauseseeds on the surface were unaffected byearthworm activity beneath it. But this treat-ment can hardly be considered a recom-mended field practice unless one canguarantee 400 mm of rainfall for the first20 days after sowing. It was used in thisexperiment solely to compare the seed’sneed for oxygen and water.

Figure 7.4 illustrates similar responsesto those just presented for inverted-T-shaped slots, hoe (U-shaped slots) and verti-cal double disc (V-shaped slots) openers. Themost noticeable effects are that the seedlingemergence trends follow the trends of earth-worm numbers with all openers and thatresidues increased both emergence andearthworm numbers with the inverted-Tand hoe openers but not with verticaldouble disc openers.

To further understand the interactionsbetween opener types, the moisture status

92 C.J. Baker

Fig. 7.4. Responses of seedling emergence and earthworm numbers to three contrasting, no-tillageslot shapes and surface residues in a wet soil (from Baker et al., 1996).

of the soil and the level of residues present,Chaudhry (1985) conducted an experimentin which these factors were varied indepen-dently. The results are shown in Table 7.2.

The data show that most openers per-formed reasonably well in favourable soilmoisture conditions, regardless of the levelof residue (range, 65–90% seedling emer-gence). When the conditions became wet,however, the shortcomings of the verticaldouble disc opener (V-shaped slot) becameprogressively more apparent as the lengthof the residue increased. In the wet soil,emergence from the V-shaped slot droppedfrom 38% with no residue to 35% withshort residue and 30% with long residue.The winged and hoe openers, in contrast,performed best when long residue coveredthe wet soil, which was attributable to theincrease in earthworm activity in responseto the long residue. As the residue lengthwas reduced with these two openers, theiradvantages over the vertical double discopener were reduced or eliminated.

Although the hoe opener respondedpositively to long residue, it is difficult toactually make a hoe-type opener function inlong residue in the field. It is one thing to dothis on a plot scale for experiments but, inthe field, hoe openers soon block because oftheir raking action. In practical terms, there-fore, of the two openers that performed wellin wet soils with long residue, only thewinged opener (inverted-T-shaped slot),which is able to handle residues in its discform, can be regarded as a practical option.

Opener performance

The performance of various seeding openersin soil (that is, wetted after seeding) can besummarized as follows.

Power till openers (U-shaped slots)

These openers, in the absence of earth-worms, will provide some compensatorymechanical aeration. The presence of earth-worms, however, will not necessarily resultin any improvement to seedling emergencebecause the gains that mechanical aerationbrings to an earthworm-populated soil areoffset by physical burial of the food sourcefor any surface-feeding earthworms. Therewill also be some actual destruction ofearthworms in the slot zone, but becausethe width of tillage by such openers is nor-mally very narrow, it is likely that the slotzone will be rapidly recolonized by earth-worms from the undisturbed soil alongside.

Punch planting (V- or U-shaped holes)

This is not likely to produce good results,with or without earthworms, althoughfurther work needs to be conducted withsuch openers. The poor performance of thepunch planter in these experiments wassomewhat surprising since the method usedto make holes did not result in any compac-tion. In practice, punch planters almostinvariably produce V-shaped holes, whichcould be expected to behave in much the


Seedling emergence %

Vertical double disc openerV-shaped slot Class I cover

Hoe opener U-shaped slotClass I and IIIa cover


Class IV cover

LR SR NR LR SR NR LR SR NR

Adequatemoisture

65 84 82 86 70 76 90 76 82

Wet soil 30 35 38 68 36 42 75 43 47

LR, long residue; SR, short residue; NR, no residue.

Table 7.2. Effects of openers, residue levels and soil moisture status on barley seedling emergencefrom a soil containing earthworms.

same way as continuous V-shaped slots. Inthis case, however, a small coring devicewas used to remove cores of soil withoutcompaction.

Vertical double disc openers(V-shaped slots)

These can be expected to perform poorly inwet soils for two reasons. First, compactionand smearing, together with crust forma-tion, result in earthworms avoiding the slotarea. Thus, not only does the opener dis-advantage the seeds directly, it discouragesnatural processes (earthworms) from repair-ing the damage.

To examine the tolerance of earth-worms to smearing, Chaudhry (1985) placeda number of earthworms on the surface ofa damp, smooth soil contained in twohigh-sided pots (to prevent escape of theearthworms). Before placing the earth-worms on the soil, he lightly smeared thesurface of one of the plots with his finger.Overnight, all of the earthworms on theun-smeared soil had burrowed into the soilwhile only half had achieved the sameresult in the smeared soil, indicating thedifficulty earthworms have in burrowingthrough smears.

Chaudhry (1985) also tested the toler-ance of earthworms to compaction andfound much the same result as for smears.Because wet soils are softer than dry soils,the action of vertical double disc openersacting through surface residues on wet soilsis more one of pressing than cutting. Thisaccentuates their compaction tendency.Slots that are both smeared and compactedare largely avoided by earthworms and donot benefit from their burrowing or nutrientcycling (Baker et al., 1987, 1988).

Secondly, double disc openers tuck (orhairpin) residues into the slot. In wet soils,Lynch (1977, 1978) and Lynch et al. (1980)showed that the decomposition of this resi-due produces fatty acids, in particular aceticacid, which tend to kill seeds and germinat-ing seedlings. They looked at ways of coun-tering this problem, ranging from applyinglime with the seed to neutralize the acid toseparating the seed from the residue.

Apparently, separation of the two byonly a small distance will largely avoid theproblem since acetic acid is very quicklybroken down in the soil by bacteria. Theresidue tucking problem is reflected inthe negative response to the presence ofresidue by the vertical double disc openerand the fact that this negative responseincreased as the length of residue (and sizeof hairpins) increased.

Although slanted double disc andangled disc openers were not included in theabove experiment, it is known that both ofthese openers also tuck residue into the seedzone, in much the same manner as verticaldouble disc openers. They can therefore beexpected to experience acetic acid fermenta-tion and its detrimental effects on seeds, butshould experience fewer problems asso-ciated with smearing or compaction.

Winged openers (inverted-T-shaped slots)

These return most of the residue to a posi-tion over (not inside) the slot. This encour-ages earthworms to colonize the slot zonebecause when the residue is removed, theearthworm numbers decline noticeably.The central disc of the disc version of thewinged opener will hairpin residues, incommon with every other disc-type opener.But the winged side blades of this openerplace the seed to one side of the central slitand therefore remove the seed from contactwith the hairpinned residue. This is proba-bly the only disc-type opener that effec-tively prevents seeds from lodging withinhairpins and for this reason benefits fromthe presence of residues even in wet condi-tions. When long residue was positionedover the slot, the inverted-T slot producedmore seedling emergence than any otherdesign.

Hoe openers (U-shaped slots)

These behave in a similar manner to wingedopeners except that instead of placing theresidue over the slot, they tend to push it toeither side. As a consequence, although hoeopeners will produce a positive response tothe presence of residue (in terms of seedling

94 C.J. Baker

emergence and earthworm numbers), thatresponse is not likely to be as strong or aspositive as for winged openers.

The seedling emergence responses ofthe various openers and surface broadcast-ing have also been reflected in root andshoot weights of the seedlings, as shown inFigs 7.5 and 7.6 (with and without earth-worms, respectively).

Without earthworms, there were fewdifferences between openers. Only themechanical aeration of power till openershad any positive effect. With earthworms,however, the seedling growth closely para-lleled the trends of seedling emergence andearthworm numbers.

Figure 7.7 shows typical oxygen diffu-sion rates within the soil containing earth-worms associated with winged and doubledisc openers (Chaudhry, 1985; Baker et al.,1987, 1988). Oxygen diffusion rate is mea-sured by passing a current through plati-num electrodes placed in a grid patternaround the sown slots and measuring therate of consumption and replacement ofoxygen in the vicinity of the electrodes (seeChapter 19).

Figure 7.7 shows that the wingedopener had no negative effect on the oxygenstatus of the soil. The oxygen status sur-rounding the hoe, power till and punchplanter openers (not shown) was very simi-lar to that of the winged opener. In fact, allof these openers had similar patterns to thatof the undisturbed soil, indicating that noneof them had any detrimental effect on theoxygen diffusion rate of the soil. But, inall cases, the presence of residues movedthe high-oxygen zones closer to the seeds,probably as a result of increased earthwormactivity.

In contrast, the double disc opener hada marked negative effect on the oxygenstatus of the soil, regardless of the presence orabsence of residues. Essentially, this opener,because of its wedging action, squeezes thehigh-oxygen zones away from the immediatevicinity of the seeds altogether and replacesthem with compacted zones of low or, at best,medium oxygen diffusion.

Also of note is that the effects ofwetness on the soil, both with and withoutearthworms, seems not to be related tohow the soil becomes wet. For example,


Fig. 7.5. Root and shoot weights ofno-tilled barley seedlings in responseto opener types and residue in thepresence of earthworms (from Bakeret al., 1988).

Chaudry (1985) had earlier conducted twoexperiments with earthworms and residue,identical in all respects except that oneused simulated rainfall to wet the soil afterdrilling and the other used a rising watertable. He was particularly interested inwhether or not persistent rainfall had some

sealing effect on the internal faces or thecover, or, alternatively, washed the seedout. He found no differences in barleyseedling performance between wetting thesoil from above or below, but both experi-ments confirmed the differences betweenopeners and residue.

96 C.J. Baker

Fig. 7.6. Root and shoot weights ofno-tilled barley seedlings in responseto opener types and residue in theabsence of earthworms (from Bakeret al., 1988).

Fig. 7.7. Oxygen diffusion rate profiles around winged and double disc no-tillage openers operatingin a wet silt-loam soil, in the presence and absence of surface residues (from Baker et al.,1988).

Later, Giles (1994) quantified the rateof accumulation of earthworm biomass inthe top 100 mm of soil as a function of dif-ferent levels of barley straw on the surfaceof the ground in New Zealand. He found analmost linear relationship, in which thetotal biomass of two surface-feeding species(L. rubellus Hoff and A. caliginosa Sav)had accumulated to 9 t/ha under 11 t/ha ofstraw and 5.1 t of earthworms under 6.4 t/haof straw. During that period the recoverablebiomass of the straw had decreased from11 t/ha to 3.2 t/ha and 6.4 t/ha to 1.2 t/ha,respectively. For the first 6 months, theheavier rate of residue remained wetter thanthe lighter rate, which might help accountfor the faster decomposition of the former.At the termination of the experiment, a part

of the residues appeared to have decom-posed while another part had simply beenburied by earthworm casts.

It should be appreciated that theselevels of cereal straw were deliberately setvery high to test the ability of earthwormsto cope with ‘overload’ conditions underno-tillage. In general terms, such strawlevels equate with grain yields of about thesame magnitude.

Finally, experiments relating to wetsoils would not be complete without alsomeasuring the infiltration of water into theslot zones in the field. Figure 7.8 shows theresults of a field experiment that comparedthe infiltration rates of a range of openers ina residue-covered silt-loam soil containingearthworms (Baker et al., 1987). The results


Fig. 7.8. Infiltration rates ofno-tillage slots in a silt-loam soil(from Baker et al., 1987).

reflect earthworm and seedling emergencetrends. The winged opener (inverted-T-shaped slot) produced the most rapid infil-tration (110 mm/h after 2 h), which is notsurprising since it had promoted thegreatest earthworm activity and seedlingemergence. Next was a group of openersincluding hoe, power till (U-shaped slots)and punch planter (U-shaped holes),together with the undisturbed soil, all ofwhich averaged 70 mm/h after 2 h. Thepoorest infiltration was with the doubledisc opener (V-shaped slots), with only20 mm/h infiltration after 2 h. Waterremained puddled in the V-shaped slotsfor hours after the experiment.

Summary of Drilling into Wet Soils

1. The ranking for the three basic slotshapes from poorest to best (V, U andinverted-T) in wet soils containing earth-worms and residues is exactly the same as fordry soils, but for somewhat different reasons.2. Seeds need ready access to oxygen in awet soil, and different openers create differ-ent oxygen environments around the seedsin wet soils.3. Double disc openers have an adverseeffect on the oxygen diffusion rate of thesoil surrounding the seed slot.4. Inverted-T, hoe and power till openers,together with punch planters, have either aneutral or positive effect on oxygen diffu-sion around the slot.5. Both earthworms and surface residuesgive clear-cut advantages if managed cor-rectly. Both will increase with time underno-tillage and have an increasingly positiveeffect on aeration, drainage and infiltration.6. Winged and hoe openers encourageearthworm activity in the slot zone.7. Surface residues encourage earthwormactivity, with the amount of activity beingproportional to the amount of residue.8. The ability of the inverted-T-shapedslot (winged opener) to retain residue overthe slot is as important in wet soils as it is in

dry soils because it encourages earthwormactivity within and around the sown slot.9. Double, triple and angled disc openers,together with punch planters, tend to tuck(hairpin) residue into the seed zone, whereit has a negative effect on germination andseedling vigour. This is especially true oflong, stringy and damp residue.10. Winged, hoe, power till and furrowopeners effectively separate decaying resi-due from direct contact with seeds.11. In the absence of earthworms, mechan-ical aeration of the slot by power tillopeners may have a short-term benefit.12. Surface broadcasting can perform wellif regular daily rainfall is available for3 weeks after sowing, but obviously thiscannot be regarded as a practical option.13. V-shaped slots and punch planterholes tend to be compacted and/or smeared.Class I cover (or lack of cover) allows thesesmears to dry to form crusts.14. Smears and/or crusts discourage earth-worm activity in the slot zone.15. U-shaped slots created by hoe, powertill and furrow openers may be smeared butonly minimally compacted. If Class II coveror better is possible, the smears should notdry to become crusts.16. U-shaped slots created by angled discopeners will not be smeared or compacted.17. Inverted-T-shaped slots created bywinged openers may be smeared but notcompacted. Class IV cover will preventdrying of smears.18. Excellent water infiltration is possiblewith inverted-T-shaped slots but infiltra-tion is likely to be poor with V-shaped slotscreated by double or triple disc openers.But infiltration between the rows can beexpected to be greater with no-tillage thanwith traditional tillage anyway, particularlywith increased earthworm populations andorganic matter.19. Excellent seedling emergence can beobtained by inverted-T-shaped slots in wetsoils, and satisfactory emergence can beobtained by most of the openers that createU-shaped slots.20. Poor seedling emergence will resultfrom V-shaped slots or holes in wet soils.

98 C.J. Baker

8 Seed Depth, Placement and Metering

C. John Baker and Keith E. Saxton

Accurate seed placement is more important inno-tillage than in tillage.

When an opener on a no-tillage drill orplanter deposits seed, and perhaps ferti-lizer, into the soil, its ability to control thefinal placement and environment of eachdepends on a number of sometimes contra-dictory functions. The required combinedcapability of the drill or planter and soilopener includes:

1. Continuously following the soil surfaceof each row and maintaining precise seed-ing depth.2. Dispensing seed under the soil, on themove, in a consistent band relative to theopener itself.3. Covering the seed (and perhaps ferti-lizer) or at least making provision for effec-tive covering after the opener has passed.4. Separating the seed from the fertilizer ifthe two are being placed at the same timeand optimizing the positions of each rela-tive to one another so as to maximize bio-logical responses.5. Metering and dispensing seed at thedesired spacing and in the desired patternalong the row.6. Transferring seed from the meteringmechanisms to the openers without dis-rupting the intended spacing or pattern.

Functions 1–3 are important for properseed placement and function. Function 4 isimportant for fertilizer placement, as des-cribed in Chapter 9. Functions 5 and 6 (and,to some extent, 1) are dependent on the designof the whole drill or planter, especiallythe drag-arm configuration and downforcemechanism, as well as the openers.

Placing seed and fertilizer in the soil isa function of opener design. For optimumperformance, openers need to have theability to:

● Ignore or control soil disturbancebeneath the ground surface (or lack of itwhen soils are wet).

● Ignore soil stickiness.● Cope with stones and other obstructions

beneath the surface.● Avoid depositing seeds in hairpinned

residue.● Prevent seed bounce.● Cover the slot to a consistent depth.

Covering might be a separate operationperformed by a separate machine (e.g. har-rows), in which case the openers shouldcreate the slots in such a way that the cover-ing operation will result in a consistentdepth of cover (see Chapter 5).

Seed metering is a function of the seedmetering mechanism of the drill or planter


and is not peculiar to no-tillage. In general,a precision planter is distinguished from adrill by the fact that a planter dispenses sin-gle seeds with the intention that the seedsare placed a predetermined distance apart.A drill, on the other hand, dispenses seedsin bulk so that a given number (or weight) ofseeds is deposited in a given length of row(or area) in an approximately uniform dis-tribution with no attempt at individual seedspacing.

Transferring seed from the meteringmechanism to the opener might seem amundane function, but, with precisionmetering especially, this transfer mustmaintain the continuity of metered seedtiming for accurate spacing in the row.Agronomists argue about the effects of vari-ations in seed spacing on crop yield, espe-cially when this is traded off against thenatural variation between plants and theirabilities to compensate for imperfect spacing.But most experts agree that there is littleagronomic disadvantage from having seedsspaced at precise intervals along the row.Recent evidence for maize suggests that uni-form seeding depth and emergence are likelyto be more important than plant spacing.

Seeding Depth and SeedlingEmergence

Almost everyone agrees that seeding depthshould be as consistent as possible. But sur-prisingly there have been few studies quanti-fying the target depths for seeds sown underno-tillage (as distinct from tillage) or the

crop performance effects of variations aroundthat target depth. Obviously, the importanceof this factor will vary with the compensa-tory growth potential of any given crop orspecies.

To quantify the effects on seedlingemergence of imperfect drilling depth underno-tillage, Hadfield (1993) measured thevariations in germination and emergence ofwheat (Triticum aestivum) and lupin (Lupinusangustifolius) drilled in inverted-T-shapedno-tillage slots at various depths. The resultsare shown in Table 8.1.

Hadfield concluded that the particularvariety of wheat he used (cv. Otane) wasless sensitive to depth of sowing than lupinin the 20 mm to 50 mm depth range, butboth were seriously affected by depths greaterthan 50 mm. Overall, seedling emergencewith this variety of wheat decreased by 4%for each 10 mm increase in drilling depthbetween 20 mm and 70 mm. But other vari-eties of wheat have been observed to havequite different tolerances of depth. In com-parison, in these experiments lupin emer-gence declined by 17% for each 10 mmincrease in depth between 20 mm and70 mm. In both cases, the reduction in seed-ling emergence was not caused by failure ofseeds to germinate but by subsurface mor-tality of seedlings that had already germi-nated. This confirmed earlier observationsby Heywood (1977).

Campbell (1981, 1985) also studieddrilling depths of a small-seeded pasturelegume, red clover (Trifolium pratense),sown in inverted T-shaped no-tillage slots.He concluded that seedling emergence of


Seedling emergence* (plants per square metre in parenthesis)

Nominal drilling depth Wheat Lupin

20 mm 79% (209) a 93% (66) a30 mm 80% (210) a 87% (62) b50 mm 73% (192) a 60% (43) c70 mm 61% (160) b 24% (17) d

Unlike letters in a column denote significant differences, P < 0.05.*% seedling emergence = % of the estimated number of seeds sown from the known weightsof seeds sown.

Table 8.1. Effects of drilling depth on seedling emergence of no-tilled wheat and lupin.

pasture legumes was particularly sensitiveto drilling depths above and below his mid-treatment, 13 mm. The results are shown inTable 8.2.

Salmon (2005) examined the effects ofseeding depths (from 0 to 50 mm) on theemergence of brassica seedlings when sowninto a range of no-tillage soils in New Zealandusing the disc version of winged no-tillageopeners. He also sought interactions withseed treatments, which ranged from coated(Superstrike), insecticide-treated (Gaucho®),to bare (untreated) seed.

He concluded that, with this particularopener, which is known to create a favour-able environment for both seeds and seed-lings, depths of sowing from 10 to 25 mmhad no significant effect on the rates or finalcounts of seedling emergence, but that zerodepth and 50 mm depth reduced emergencemarkedly. There were no interactions betweenseeding depths and seed treatment.

Salmon was not able to test the effectsof low seed vigour, other brassica speciesand/or other no-tillage opener types in theseexperiments. It is doubtful, however, if anyof these factors would have improved therange of sowing depths found possible,which was considered to already be unusu-ally broad in Salmon’s experiments.

Maintaining ConsistentOpener Depth

Maintaining a consistent depth of seeding isone of the most demanding tasks that any

no-tillage machine must perform. This is forseveral reasons:

● The surfaces of untilled soils do not getsmoothed in the same way that tilledsoils do.

● Untilled soils are often harder than tilledsoils and therefore have less cushioningeffect, causing more bounce of the open-ers, especially at higher speeds.

● The harder soils require greater down-forces to push the openers into theground. Variations in ground resistancetherefore result in larger variations inseeding depth than where soils aresofter and smaller downforces are used.

● The hardness or strength of untilled soilsusually varies across a field as a result ofnatural settling of the soils. Regularpulverization by tillage virtually elimi-nates these differences in soil strength.

● No-tilled soils are often covered withsurface residues, which might interferewith the opener’s ability to manipulatethe soil beneath it and further accen-tuate the surface roughness.

We shall consider each of the above aspectsseparately.

Surface following

Control of opener depth is partly a functionof the opener and partly a function of thesupporting drill or planter frame. Withno-tillage, there is little or no opportunity tosmooth the soil surface prior to drilling.No-tillage openers must therefore havesuperior surface-following ability comparedwith their counterparts for tilled soils. Theextent of vertical mechanical movementalone should increase from approximately± 75 mm (total 150 mm) travel for tilledsoils up to ± 250 mm (total 500 mm) travelfor untilled soils.

Depth-gauging devices

One of the important contributions thatopeners make to controlling seeding depthis the presence or absence of depth-gauging

Seed Depth, Placement and Metering 101

Nominaldrilling depth

Seedlingemergence* (%)

0 mm 53% b13 mm 89% a38 mm 56% b

Unlike letters in the column denote significantdifferences, P < 0.05.*% seedling emergence = % of the estimatednumber of seeds sown from the known weightsof seeds sown.

Table 8.2. Effects of drilling depth on seedlingemergence of no-tilled red clover.

devices (wheels, skids or bands), which‘track’ the soil surface. Penetration forcesare generally higher for untilled soils thanfor tilled soils. Further, the soil strength oftilled soils is usually quite uniform acrossthe entire field as a result of the tillage pro-cess, while soil strengths of untilled soilsvary quite widely on a metre-by-metre basis.

The result is that, if an opener reliessolely on the penetration downforce reach-ing equilibrium with the soil’s resistance topenetration in order to maintain a consis-tent seeding depth, as is common in tilledsoils, seeding depths in untilled soil willvary just as widely as the soil strength. Con-sequently, any opener designed to operateat a consistent depth in an untilled soil willneed at least some form of depth-gaugingdevice. With such an attachment, a down-force can be applied in excess of thatrequired to just attain target depth for thatparticular metre of soil. The additional forceis carried by the gauging device withoutmaterially altering the depth of seeding.

Clearly, depth-gauging devices foruntilled soils need to have the capacity toabsorb quite large variations in applied forceto operate satisfactorily in the inherentvariability of such soils. Fortunately, untilled

soils also have an inherently high abilityto withstand surface loading and avoidfurrowing.

There are differences in the accuracy ofdepth-gauging devices according to howclose to the point of seed release the gaugingdevice is located. Obviously, being closer tothis position results in more effective depthcontrol. The effectiveness of the device maysuffer if it is located too far from the seeddeposition zone since, for example, it mayregister on a small hump when the seed isbeing released into a small hollow.

There are often mechanical limitationsto where the gauging device can be locatedon an opener in relation to where the seed isfinally ejected into the soil. Probably thenearest any opener designs have come togauging depth precisely at the seed exitpoints are those on which a specially shapedsemi-pneumatic tyre operates alongside(touching) the base of a disc at the pointwhere the seed is ejected. Figure 8.1 showssuch an arrangement.

Where possible, it is desirable to com-bine the depth-gauging function of wheelswith the additional function of slot cover-ing and/or closure, so long as one func-tion is not markedly compromised by the


Fig. 8.1. Depth-gauging wheels located alongside the point of deposit of seed in a no-tillage opener.

requirements of the other. The depth-gaugingwheels on the disc version of winged openersare located close to, but slightly rearwardof, the seed-ejection zone so that they canperform these dual functions without signifi-cant compromise to either (see Fig. 4.27).The wheels in Fig. 8.1 do not perform a slot-closure function.

Almost universally, the gauging devicesmost favoured by opener designers arewheels, although skids and depth bands arealso used on less expensive opener designs.The problems with skids in no-tillage arethat they gather and block with residue andthe higher down forces result in high wearrates as they slide along the ground.

Depth bands are sometimes attached tothe sides of discs to limit the depths of theirpenetration, but the depth of seeding cannotbe conveniently adjusted for different cropswithout removing the band and replacing itwith a band of different diameter. They alsotend to accumulate soil in the corner betweenthe band and the disc, effectively increasingthe diameter of the band and decreasing theseeding depth.

Gauge wheels are not without theirproblems either. Because wheels can onlybe attached by their axles, designers have totrade off the disadvantages of attaching thembehind the opener against the disadvantagesof attaching them beside the opener, wherethey might interfere with residue clearanceand are unlikely to be able to function in aslot-closure capacity as well.

Since most no-tillage openers for residueconditions involve a disc of some nature asthe central component, the disadvantage oflocating gauge wheels behind the openercan also take on a new and additional dimen-sion because the distance from the seedzone then increases by at least the radius ofthe disc. Consequently, despite their advant-ages for controlling depth of seeding, manyno-tillage opener designs do not use gaugewheels at all. With those that do, most arelocated either beside the opener or partlybeside and partly behind it.

A further complication arises whengauge wheels are required to perform theadditional function of covering the slot.Wheels that only function for covering are

called ‘press wheels’, those that only gaugedepth are ‘gauge wheels’ and those that per-form both functions are ‘gauge/press wheels’.

Few openers have gauge/press wheels.One reason is that, for accurate depth con-trol, the wheel should operate alongside theseed deposit zone, while for effective press-ing the wheel should follow behind theopener. Furthermore, the wheel must roll onundisturbed soil to maintain depth control,while for useful slot pressing the wheelshould be on either the loose soil over theslot or in the slot itself (see Chapter 5). Thesesomewhat contradictory requirements oftenlead either to two separate wheels or to oneof the functions being compromised in theinterests of cost and residue clearance. Ingeneral, if the wheels on openers are sup-ported by springs, they will probably bethere solely for the press wheel functionrather than also as gauge wheels.

The wheel on the opener shown inFig. 8.1 is solely a gauge wheel. A smallerseparate press wheel can be seen operatingat an angle behind the disc.

An example of combined press/gaugewheels is shown in Fig. 4.27, where twowheels are used on either side of a centraldisc and slightly rearwards of the seed zone.The wheels are sufficiently wide to registeron the undisturbed soil alongside the opener(the gauge wheel function) but are alsoangled so that they fold the flaps of residueand soil back over the inverted-T-shaped slotand gently press on it (the press wheel func-tion). Inverted-T-shaped slots do not requirepressing on the seed in the slot, so there isno disadvantage from only pressing on thetop of the covered slot (see Chapter 6). Thedepth-control function of this opener isslightly compromised because the wheelsare not located exactly at the seed releasepoint, but there are other systems employedwith this opener (see below) that more thancompensate for this shortcoming.

The value of semi-pneumatic tyres

It is appropriate here to pay tribute tosemi-pneumatic tyres, which are used onmost modern press wheels and gauge wheels.


This often undervalued invention is one ofthe most successful adjuncts to agriculturalmachinery. Until semi-pneumatic tyres wereinvented, all gauge/press wheels were eitherrigid wheels or, at best, solid rubber, plasticor fully inflated tyres.

Because press wheels on seed drillsalmost invariably operate at least partiallyin a disturbed soil zone, even in no-tillage,they are very inclined to accumulate mudin damp conditions. Flexure is the mosteffective means for a wheel to shed accu-mulated mud. Fully inflated tyres under nor-mal pressures and rigid wheels do not flexsufficiently to shed mud. Some no-tillagesituations may require enough downforcefor a limited flexing by fully inflated tyres.

A method had to be found to combineflexure with maintaining the accuracy ofthe gauging radius of the wheel, i.e. it had tobe able to flex but still retain a predictableloaded radius, regardless of the loading onit. This is where semi-pneumatic tyres excel.Although they are hollow (in a multitude ofcross-sectional shapes), there is no air pres-sure within them. Indeed, most have a smallbleed hole so that air cannot be permanentlytrapped inside. The distance between theouter wall and the inner wall (against therim) is relatively small. In operation, wherethe footprint zone contacts the ground, theouter wall collapses temporarily and pressesagainst the inner wall and thence the rim.As it leaves the ground, the resilience of therubber causes the outer wall to return to itsoriginal position. In so doing, the outer wallcontinually flexes in and out, which dis-lodges mud. The operating radius remainspredictable so long as there is sufficientforce applied to collapse the outer wallagainst the inner wall and rim in the foot-print zone.

Walking beams

Another adjunct to no-tillage openers is theuse of ‘walking beams’ for mounting thegauge wheels, such that a pair of wheelscan independently move vertically whilecontinuing to share the down pressure.These are simple mechanical leverage

systems, which are applicable where thereare at least two gauge wheels. A single link-age, pivoted at its centre, joins the mount-ing brackets for the two wheels in a pivotalmanner. The two wheels find their ownpositions by equalizing the footprint forcesabout the pivoting walking beam. The equal-ized positions of the two gauge wheelsconstantly change as each wheel in turnencounters changes in the soil surface. Asone wheel moves upwards, the other wheelmoves downwards.

The point of this arrangement is that aseach wheel encounters a small rise or hollowthe whole opener is forced to rise or fall byonly half the height of the rise or depthof the hollow. Thus surface roughness issmoothed by a factor of a half, which isimportant for no-tillage in the absence ofgeneral smoothing by tillage.

Figure 8.2 shows a walking beamarrangement for a pair of gauge wheels.


Fig. 8.2. A walking beam arrangement forequalizing the loads carried by two independentgauge wheels.

Disc seed flick

The tendency of double disc openers toflick seeds out of the ground arises whenseeds become clamped between the twodiscs at or near the pinch point where theytouch. At speed, as the discs move apartagain behind this point, the clampingaction, followed by sudden release of theseeds, may propel them upwards and rear-wards, expelling them from the slot.

The problem is overcome by droppingthe seeds behind the pinch-point zone and/or by inserting covering plates in the zonebetween the two discs at their rearmostedges.

With all disc openers in sticky soils, atleast one surface of the disc can becomesticky. Seeds may either adhere to the discand be lifted from the slot or soil may stickto the disc and carry seeds out with it.

With double disc openers, the seed isreleased against the inside surfaces of thediscs that are not in contact with the soil.Thus, seeds seldom stick to the discs butsoil sticking to the outside of the discs canseriously disrupt the integrity of slot forma-tion and carry seeds, which have alreadybeen deposited, out of the slot (see Fig. 8.3).

With angled discs, the seed side of thedisc is largely sheltered from soil contact,which helps to avoid seeds sticking directlyto the disc.

The disc version of the winged openerhas special subsurface scrapers designed towipe sticking seeds off the disc below theground (Thompson, 1993; Fig. 4.27).

Soil disturbance

With most disc openers, even when operat-ing in non-sticky soils, a certain amount ofsoil disturbance occurs as the disc leavesthe bottom of its rotation. This also occurswith hoe openers as the rigid shank movesforward in the soil. While seeds might notbe flicked out of the soil by this soil move-ment, it may redistribute the seeds so thatthey occupy more random vertical positionswithin the soil than would otherwise beexpected.

With some power till openers, the soilis deliberately disturbed and the seed isdeposited into the rotor area while slot tilthis being formed, with the intention of tho-roughly mixing the seed and soil. While thisundoubtedly achieves its aim, the resultingvariation in the depths of individual seedsdoes little for consistency of germination,emergence and maturity.

Residue hairpinning or tucking

The tendency of discs in any configurationto hairpin, or tuck, residue into the slotwithout actually cutting the residue oftenleaves the seeds embedded in or on thisresidue rather than in contact with cleansoil. Many poor no-tillage plant stands haveresulted from the hostile seed environmentcreated by residue tucked directly into theseed slot. This occurs with both dry and wetresidues, although the cause of the problemis different in the two cases.

With tough resilient residue, such as wetmaize stover, the residue may quicklystraighten out again after passage of the disc,in which case it may flick a portion of theseeds out of the slot. Figure 8.3 shows a soy-bean (Glycine max) seed that has been flickedcompletely out of a slot by a maize stalk afterpassage of a vertical double disc opener.

But, even if seeds are not flicked out,when they become embedded in dry hair-pinned residue, they will not have effectiveseed–soil contact, this affects imbibitionand germination. In wet soils, the fattyacids that are the products of decay of theresidues cause seed and seedling mortality(see Chapters 6 and 7).

Opener bounce

Hoe-type and simple winged openers,which are under considerable downforcefor penetration, often bounce in response tovariations in soil strength, particularly athigh speeds, disrupting the accuracy of seedejection into the soil.

But disc-type openers are not immuneeither. Any opener is capable of leaving


seeds on the surface after encounteringstones in the soil. Hoe-type openers tend topush stones aside or flick them out of theground, whereas disc-type openers tend torise up and over stones and deposit seedson top of the ground.

Seed bounce

As a result of high operating speeds andseeding into dry cloddy soils, large seedsoften bounce upon contacting the soil. Insevere cases, some seeds bounce right out ofthe slot.

The problem is accentuated with someair delivery systems when excessive deli-very velocity of the air and seeds is used,which, combined with a high forward speedof the opener, may cause severe seed-bouncing problems.

Slot closure

Problems such as seed bounce can belargely overcome if the opener self-closesthe slot immediately after it has been

opened to receive the seed. Some wingedopeners, slanted double disc openers andpower till openers are examples of openerswith good self-closing abilities.

Drill and Planter Functions

Downforce mechanisms

The most common downforce mechanismsfor conventional drills and planters aresprings. But springs change their loadingforces in a linear fashion with changinglength (i.e. they change their forces by thesame proportion as their lengths change).This might be acceptable for tilled seedbedsbecause: (i) the loads applied are relativelysmall and the springs are not significantlycompressed; (ii) the variations in groundsurface and therefore spring lengths are rela-tively small; and (iii) springs are relativelycheap and trouble-free.

For no-tillage seedbeds, however, theopposite is true: (i) spring loads are high;(ii) surface changes can be quite large; and(iii) no-tillage drills are generally more robustand expensive. Because spring loads are high,


Fig. 8.3. A soybean seed (lower centre) that has been flicked completely out of a no-tillage slot madeby a double disc opener (from Baker, 1981a, b).

no-tillage drills tend to use either very heavyand unresponsive springs or smaller-section,longer springs compressed to short lengths.Because the changes in spring force arerelated to a spring’s compressed length at thetime, having a spring compressed to a shortlength to achieve opener penetration magni-fies the force changes relative to lengthchanges. Accordingly, some no-tillage drillsand planters are designed with inordinatelylong springs (Fig. 8.4), or, alternatively, thesprings are positioned near to the pivotpoints of the drag arms so that dimensionalchanges are minimized.

The force relationship with the lengthof springs applies equally well if the springsare arranged to be working in tension or incompression. Compression is more common,as it is difficult to overload a spring in com-pression compared with a spring in tension.For reasons of compactness, a few no-tillagedrills and planters use springs acting intension.

Either way, it is virtually impossible tomaintain constant downforces with springs.A number of innovative designs have beenused with the objective of reducing theshortcomings of springs. Some of these areillustrated in Figs 8.5 and 8.6. In Fig. 8.5,

the mechanical springs have been replacedwith rubber buffers acting very close to thepivot (fulcrum) of the drag arms to reducethe required travel of the springs for anyone change in position. Rubber acts in analmost identical manner to spring steelwith regard to the force it exerts in rela-tion to changes to its compressed length.But problems from prolonged exposureof rubber to ultraviolet light and retentionof ‘memory’ after long periods of com-pression have made this an unpopularchoice.

In Fig. 8.6, the designers have attemptedto better equalize the spring forces acrossthe drill, to accommodate, for example, pass-ing over a hump on one side of the drill, bydividing the bar that compresses the springsinto shorter articulating lengths. The effectis similar to walking beams described abovefor press wheels.

Another way to overcome the dis-advantages of springs for downforce appli-cation is to provide the gauge wheels withvery large footprints and then apply exces-sive downforces to ensure that the springforce is sufficiently large to allow for leng-thening of the springs for the deepest hollowlikely to be encountered by the openers.


Fig. 8.4. Long compression springs on a no-tillage drill.

Figure 4.24 illustrates a design thathas gone to the other extreme. In this case,the total vertical opener travel has beenrestricted by the use of spring tines thatmove largely horizontally (backwards) inresponse to increases in loading. The ground

surface-following ability of such drills ispoor, restricting their use to relativelysmooth fields and/or seeds that are verydepth-tolerant.

Regardless of the measures outlinedabove, springs are generally an unsatisfactory,


Fig. 8.5. No-tillage openers pressed into the soil with rubber buffers acting close to the fulcrum of thedrag arms.

Fig. 8.6. A no-tillage drill with an ‘equalizing’ spring arrangement.

though still the most common, way ofapplying downforces to no-tillage openers.Characteristically, their shortcomings canregularly be seen in the field as too shallowdrilling through hollows and too deep drill-ing over humps, leading to poor seedlingemergence in both situations. Figure 8.7shows the travel of a no-tillage openerwith superior surface-following ability.Unfortunately, not all no-tillage drills arecapable of achieving this degree of surfacefollowing.

Compressed air

Fortunately, there are alternatives to springs.The two most useful to date have been theuse of air and oil (hydraulic) pressure, act-ing through rams or cylinders (Morrison,1988a, b). The air pressure option uses largevolumes of air acting on large-diametercylinders attached to the drag arms.Because it is difficult to compress air tosufficiently high pressures to allow small-diameter cylinders to be used, there are

limits to the amount of downforce obtain-able with compressed air.

On the other hand, air is free and largevolumes can be compressed, with the resultthat changes in volume resulting frommovement of openers up and down can bedesigned to have a minimal effect on themagnitude of the downforces. It should beappreciated that any gas under pressurehas the same characteristics as mechanicalsprings. At any given temperature, a changein volume of the compressed gas will belinearly proportional to its pressure. Withair, however, the volume can be made solarge that pressure changes with movementof the openers can be minimized.

The biggest disadvantages of using airdirectly are the limited amount of pressurethat can be practically obtained and the factthat the oxygen in air under high pressurecan be explosive and that high-pressure aircylinders need to be independently lubri-cated, which is a problem in a semi-staticsystem such as this. Lubrication is easiestwhere a continuous flow of compressed air


Fig. 8.7. An example of excellent surface following through a hollow by no-tillage openers (gas-over-oildownforce).

is used, such as with air tools. But in thiscase the compressed air is contained withina closed system, so lubrication is difficult.

Gas-over-oil systems

A more workable option has been to use oilin a hydraulic system in equilibrium with acompressed inert (non-explosive) gas (usu-ally nitrogen) contained in one or moreaccumulators. This is referred to as a ‘gas-over-oil’, ‘oil-over-gas’ or ‘nitrogen-cushionedhydraulic’ system. The volume of gas in theaccumulator(s), when the system is at itslikely operating pressure(s), needs to besufficiently large to reduce changes in pres-sure, arising from changes in opener posi-tion, to a minimum.

In reality, if the hydraulic cylinders onall openers are connected in common (para-llel) to the hydraulic system, when oneopener rises in response to a rise on the soilsurface, another opener is likely to be fall-ing in response to a hollow somewhere elseacross the drill or planter. Thus these twoopeners simply exchange oil between themwithout affecting the overall volume ofoil or pressure of the system to any greatextent.

Because of this, the need for large volu-metric changes by the hydraulic system as awhole is much reduced. In contrast, mechan-ical springs can only work with individualopeners unless a very complicated linkageis used to obtain some measure of combinedaction, as illustrated in Fig. 8.6.

Another advantage of the gas-over-oilsystem is that, if the individual hydrauliccylinders are of the double-acting type (i.e.they can be powered in both directions),these downforce cylinders can also be usedto lift the openers for transport. This elimi-nates the need for a separate lifting assem-bly on the drill or planter.

The biggest advantage of either gas-over-oil or air cylinders is that they can bearranged so that the downforce on the open-ers remains virtually unchanged throughoutthe entire length of opener travel upwardsand downwards because the force exertedby the cylinders remains constant through-out their entire stroke length. This in turnallows much greater vertical travel to bedesigned into the openers for surface fol-lowing and depth control.

Figure 8.8 shows a no-tillage drill witha gas-over-oil downforce system sowing atthe same depth on the top of an irrigation


Fig. 8.8. An illustration of the extraordinary surface-following ability of a gas-over-oil openerdownforce system on a no-tillage drill.

border dyke as on the flat surface alongside,and even part-way up the slope. Tillage drillsare never required to provide this muchopener travel and many simple no-tillagedrills do not achieve it either.

Automatic down force control (ADF)

A further refinement to the gas-over-oil sys-tem is to equip the drill or planter with asensing device that measures the hardness ofthe soil as the opener travels through it. Thissignal is relayed to the hydraulic valving sothat, as the soil hardness changes (whichwould otherwise alter the penetration depthof the opener), the oil pressure is automati-cally adjusted on the move to ensure that theopeners get the correct amount of downforceto correctly maintain seeding depth ineach metre of the field. This sophisticationprovides a fully automatic seeding depth-control capability, unparalleled with currenttechnology.

Weights

One school of thought suggests that attach-ing weights to individual openers would bean effective way to ensure that each openerexperiences the same downforce throughoutits entire range of movement. But addingand removing individual weights for a mul-titude of openers on any one drill is imprac-tical and would require the operator to carrysurplus weights around in order to changethe downforces for new conditions. It wouldalso make changing the downforce on themove within a field impractical, but, thenagain, only the most sophisticated gas-over-oil systems with ADF allow this to be done.

Another downside to the use of weightsis that, when an opener rises or falls, theinertia of the weight alters the effectivedownforce and that this inertia is highlydependent on the forward speed of themachine, which determines the speed ofthe rise and fall. For the technically minded,inertia is proportional to the square of speedin the direction of movement.

Where weights have their greatest useis for single-row drills, since many of thedisadvantages above apply less to a single

opener than to multiple openers on a largerdrill and weights are often the cheapestand most effective option available wherelimited budgets apply (see Chapter 14).

Drag-arm design

The design and configuration of the dragarms that attach the seed opener to the drillframe are an important feature of drills orplanters that have an impact on seed place-ment. A drill that has drag arms pivotallyattached to the drill or planter frame willbe designed to move the openers upwardsand downwards to accommodate changesin the ground surface. This motion is pro-vided either by a hinged attachment to thedrill frame or by flexure of the drag armsthemselves.

In the case of flexed drag arms, the wholedrag arm must be constructed of spring steel.There are advantages in that this eliminateswearing joints, which, under the high forcesinvolved in no-tillage, can become a main-tenance problem. Such a desirable arrange-ment, however, must be balanced against thedisadvantages of using mechanical springsas the downforce system in the first placeand the difficulty in preventing the openersfrom also flexing sideways, which interfereswith accurate row spacing.

With fully articulated (hinged) dragarms, the most common arrangement withconventional drills is to use a single armpivoting on a simple unlubricated joint, asshown in Fig. 8.9. Because large forces arerequired to push openers into and drag themthrough the soil, there are quite large forcesacting on the pivot, especially if the sourceof downforce is located close to the pivotitself. As a result, the wear rate within thepivoting mechanisms can be substantial.

This is an important issue with manyseemingly advanced no-tillage machines.As new machines, they might appear to beof sound design. But as the pivoting jointswear, such machines soon provide poorseeding accuracy and become unserviceable,which creates an unforeseen cost penaltyagainst no-tillage.

More sophisticated no-tillage drilldesigns provide pivots with lubricated and


sealed bearings or heavy-duty bushings.While this adds to the initial cost, it canextend their service life to near that of thetractors that pull them.

Parallel linkages

To ensure correct functioning, some no-tillageopeners must be maintained at a set angleto the horizontal in the direction of travel.Winged openers are a case in point. Suchopeners often employ two drag arms (upperand lower) arranged as a parallelogram insuch a way that the horizontal angle of theopener remains unchanged throughout theentire range of its vertical travel.

The disadvantages of such an arrange-ment are the cost of the arms and pivots andthe fact that four pivots have greater potentialto create diagonal instability of the openersthan one or two pivots if they become worn.To compensate, parallelogram drag arms areusually wider and more robust than singledrag arms and utilize better-quality bush-ings or bearings in the pivots. Undoubtedly,they go another step towards perfectingprecision seed placement in no-tillage, butto date they have only been included onadvanced planter and drill designs.

Figure 8.10 shows a no-tillage openermounted on parallelogram drag arms andthe extraordinary range of travel providedby its gas-over-oil downforce system. Thehydraulic cylinder is difficult to see but canbe located from the position of the supplyhoses (top right).

A variation on parallelogram drag armsis one where the parallelogram is designedto be deliberately imperfect (i.e. a trape-zium). It is designed for operation withwinged openers that are pushed into theground with mechanical springs (Fig. 8.11).

The objective has been to reverse the geo-metrical changes that occur with single-pivot drag arms, in which the angle of thewings normally becomes less in hollowsand increases over humps. The effect is usu-ally to accentuate the change in mechanicalspring forces by drawing the wings into theground more on humps than in hollows.But, in this design, the wing angle increaseswhen the openers are in hollows anddecreases when they go over humps. Sincethe steeper wing angle assists the opener topull itself into the ground, the arrangement


Fig. 8.9. A simple single-pivotdrag-arm arrangement (slightlymodified from Baumer et al.,1994).

Fig. 8.10. A winged no-tillage opener mountedon parallelogram drag arms and pushed down witha gas-over-oil system, showing its extraordinarilylarge range of vertical travel, which is important inno-tillage.

goes some way towards countering thedisadvantages of variable downforces withmechanical springs.

Comparisons

The authors compared the capabilities oftwo different no-tillage drills (both of whichfeatured gas-over-oil downforce systems)in terms of their abilities to ignore surfaceirregularities (Baker and Saxton, 1988).Three types of tillage tool were used to causesurface roughness in an otherwise smoothuntilled soil that had been chemicallyfallowed. The roughness treatments were:(i) chiselled with a shank chisel at 380 mmcentres operating 200 mm deep, which leftthe roughest finish; (ii) cultivated with250 mm wide sweeps operating 100 mmdeep (the next roughest finish); (iii) discedonce with a heavy double disc (the nextroughest finish); and (iv) no tillage at all,which left a smooth surface finish. Thedrills used are labelled in the diagrams as‘Cross Slot’ (disc version of winged openersthat created inverted-T-shaped slots) and‘Double Disc’ (vertical double disc openersthat created V-shaped slots).

The plant stands from the two drillsand four surface roughnesses are shown inFig. 8.12, and the resulting yields of winterwheat are shown in Fig. 8.13. The ‘CrossSlot’ drill had higher plant counts andyields than the ‘Double Disc’ drill for allsurfaces, but significantly more so for therougher surfaces. The much heavier ‘Dou-ble Disc’ drill had difficulty maintainingdepth control in the more loosely tilled,rougher surfaces. The no-tillage surface waseasily penetrated by both drills, but thedouble disc openers ‘tucked’ considerableresidue into the seed slot, which probablycontributed to the lower stands with thatdrill in the very dry seeding conditions thatwere experienced (see Chapters 6 and 10).

Seed metering and delivery

With small seeds sown on a mass basis, suchas grasses, legumes, brassicas and small-grained cereals, the seed metering deviceson drills are designed to distribute a conti-nuous trickle of seeds with no attempt tosingle, or handle individual seeds separately.


Fig. 8.11. A no-tillage opener in which a deliberately imperfect ‘parallel’ (trapezium) linkage is utilized.

As a result, such a trickle of seeds is largelyunaffected by the length or shape of the deliv-ery tubes that transport them from the seederto the opener, so long as there is sufficientslope on the tubes for gravity to keep thetrickle moving consistently or a stream of airto blow them along. Gravity delivery can be aproblem when drilling up and down hill-sides, where the drop tubes become too flatto maintain the seed flow. With air seeders,which substitute air flow for gravity, the airflow transports the seeds in a consistentmanner to the openers and gravity playsonly a minor role.

Seed metering and delivery are gen-erally similar for no-tillage drills and drillsused in tilled soils, with only minor differ-ences. The seed metering mechanisms and

delivery tubes can be expected to be com-mon to both; however, the openers ofno-tillage drills are often spaced furtherapart to clear residues and their verticaltravel may be greater than for tilled soils.As a result, the seed delivery tubes may belonger and have further to span from themetering boxes to the openers, which maycause them to lie at flatter angles. Compen-sation for this loss of fall may involve rais-ing the seed boxes higher on the drill or theuse of multiple sets of seed boxes. Airdelivery becomes an attractive option,since gravitational fall is then assisted bythe air flow (see Chapter 13). An exampleof an advanced no-tillage drill with air-assisted seed and fertilizer delivery isshown in Fig. 8.14.


Fig. 8.12. The effects of surfaceroughness on wheat seedlingemergence using two contrastingdrills (from Baker and Saxton,1988).

Fig. 8.13. The effects of surfaceroughness on yields of wheatusing two contrasting drills (fromBaker and Saxton, 1988).

Precision seeders that select single seedsat regular intervals, such as maize, cotton,beet and vegetable planters, provide a differ-ent situation. Ritchie (1982) and Carter(1986) showed that, once a single seed isreleased from the metering mechanism intoa tube, its pathway through that tube may besomewhat random. It will have a tendency tobounce from wall to wall and at each bounceit will lose an unpredictable portion of itsdrop velocity. Consequently, any two seedsseldom arrive at their destinations at exactlythe same time intervals from when they werereleased from the metering mechanism.

Thus, even if a precision meteringmechanism selects individual seeds at pre-cise intervals, the precision of the intervalsat which consecutive seeds reach the groundwill depend on the pathways each followsafter leaving the metering mechanism. It iseven possible for a seed that took a moredirect route down a delivery tube to catchup with and pass an earlier seed that bouncedon its way down the same tube.

For this reason, precision seed meter-ing mechanisms in tilled soils are located asclose to the soil as possible so that the seeds

have only a short drop, often without touch-ing the sides of any tubes at all. Commonly,the distance of drop is about 50 mm andoften less. This free-drop approach is possi-ble only because tilled soils are prepared soas to have no surface residues and are assmooth and fine as possible, allowing thebulky seeding mechanism to pass close tothe ground surface without the risk ofblockage or damage.

In no-tillage, however, surface residuesoften protrude 300–500 mm above the ground,are variable in their nature and extent andare often quite woody. Vertical clearance istherefore necessary to avoid blockage. Fur-ther, there is little or no opportunity tosmooth the surface of the soil. Consequently,no-tillage openers are larger and more robustthan their tillage counterparts and the meter-ing mechanisms have to operate higherabove the ground. This necessitates seedshaving to be delivered up to 600 mm fromthe metering mechanisms.

Free drop of seed is not an optionover such a distance in no-tillage because ofthe effects of wind, slope and machinebounce.


Fig. 8.14. An advanced design of no-tillage air drill.

The result is that, although the sameprecision metering mechanisms are usedfor tillage and no-tillage planters and thesame numbers of seeds need to reach theground in a given length of row in both cases,precise spacing between individual seedsunder no-tillage is more difficult to achievethan in tillage.

Opener bounce is likely to be greaterunder no-tillage. Attempts to qualify theeffect of openers’ bounce were reported in2004 (Anon., 2004). The tests found that fourconventional vacuum-type precision seedmetering devices of European origin wereall adversely affected by shifting from atilled soil surface to an untilled surface andthat the adverse effects increased withincreasing forward speed.

The key question of whether or notthese sources of inaccuracy have a measur-able effect on the final yield of large,compensatory-growth plants, such as maize,will continue to be debated (for example,there is mounting evidence that precisionseeding depth may be more important thanprecision spacing, due to inter-plant compe-tition) but the fact remains that precisionspacing has become an important marketingobjective for machines designed for tilledseedbeds. Since there is no known agronomicdownside to precision spacing, it makessense for designers of no-tillage planters toattempt to duplicate these levels of preci-sion spacing as closely as possible if theywant to persuade farmers to make the switchfrom tillage to no-tillage.

Summary of Seed Depth, Placementand Metering

1. Wheat seedling emergence in no-tillagemay decline by approximately 4% for every10 mm increase in drilling depth below20 mm and even more beyond 50 mm.2. Lupin seedling emergence in no-tillagemay decline by approximately 17% for every10 mm increase in drilling depth below20 mm.3. Red clover seedling emergence inno-tillage will decline markedly at drillingdepths above and below 10–15 mm.

4. The ability of no-tillage openers tomaintain a constant seeding depth is veryimportant but very demanding.5. Harder ground, rougher surfaces andthe presence of residues on the surfaceaccentuate the depth-control challengeunder no-tillage.6. Because of the large opener downforcesrequired in no-tillage, seeding depth controloften uses one or more gauge wheels oneach opener.7. Press wheels are often also used oneach opener to cover the slot.8. Few no-tillage openers have both gaugewheels and press wheels, and even fewerhave combined gauge/press wheels.9. Zero-pressure tyres are a useful adjunctto gauge wheels.10. Walking beams are also a useful adjunctto gauge wheels.11. Mechanical springs are a poor meansof providing downforce for no-tillageopeners because their forces change withlength.12. Compressed-air cylinders are some-times used to provide downforce but areseldom a practical option.13. Removable weights are useful on single-row no-tillage drills but are not practical formulti-row machines.14. Gas-over-oil systems offer advantagesby using hydraulic cylinders to bothapply the downforce and lift the openers fortransport.15. Automatic downforce control systemsoffer further refinement to gas-over-oilsystems by changing the downforces onthe move in response to changes in soilhardness.16. No-tillage openers should provide upto 500 mm vertical travel compared with amaximum of 150 mm for tilled soils.17. Single-pivot drag arms on drills andplanters are less useful in no-tillage than intillage.18. Parallelogram drag arms maintain theopener angle but are mechanically moredemanding.19. Lubricated bearings or bushes used forthe pivots on no-tillage openers contributeto a realistic service life of machines thatoperate under difficult conditions.


20. The function of no-tillage openers indepositing seed consistently in an uninter-rupted horizontal band in the soil isimportant.21. The function of no-tillage openersdepositing fertilizer in a separate band isalso important, as discussed in Chapter 9.22. The delivery of bulk-metered seeds tono-tillage openers is made more demand-ing by their large horizontal and verticalspacing.

23. Air delivery of bulk seeds to no-tillageopeners offers advantages.24. Single-seed spacing along the row fromprecision planters may be compromised inno-tillage because of seed bounce downlong delivery tubes.25. No-tillage openers may have specialproblems, such as seed flick, seed stickingto the disc, soil turbulence, residue ‘hair-pinning’, opener bounce, seed bounce andslot closure.


9 Fertilizer Placement

C. John Baker

Simultaneous banding of seed and fertilizerby the openers is more important in no-tillage

than for tilled soil and follows somewhatdifferent principles.

It is especially important in no-tillage tosow fertilizers at the same time as the seed,but only if the fertilizer can be placed in aseparate band from the seed. Much recentexperience has documented the growth andyield advantages from fertilizers bandednear the seed at the time of seeding. Forautumn seeding this is often only a ‘starter’amount of fertilizer, while for springseeding it is usually the total seasonalrequirements.

Crop responses to banded fertilizer atthe time of seeding are nearly always largerin no-tillage than in tillage. There areseveral reasons for this.

● Tillage mineralizes organic matter torelease nitrogen and this becomesreadily available to the newly establish-ing plants. The downside is that,because no fertilizer is actually added tothe system, the nitrogen is from ‘mined’,mineralized, SOM, which depletes thisprecious resource cumulatively.Because mineralization and nitrogenrelease are minimal under no-tillage,young no-tilled plants can appearnitrogen-deficient, particularly during

early growth. Banding nitrogen fertilizeralongside the seed during no-tillageseeding cures the problem.

● Surface residues are often decompos-ing about the same time as seeding inno-tillage. The microorganisms respon-sible for residue decomposition tempo-rarily utilize (‘lock up’) nitrogen duringthis process. Even though the nitrogenthey demand may become availableagain later in the growth cycle as themicroorganisms themselves die, it istemporarily made unavailable to youngno-tilled plants.

● Soluble nutrients, nitrogen in particular,broadcast on to a no-tilled soil surface (asis common practice in tilled fields) areoften preferentially carried by water flowdown earthworm channels and otherbio-channels (e.g. old root channels),which largely bypass young plant roots.In tilled soils, these bio-channels aredestroyed and replaced by a smaller,more evenly dispersed pore system,which provides a more uniform infiltra-tion of water and broadcast fertilizers.

● Under repeated no-tillage, surface-applied nutrients that readily attach tosoil particles, such as phosphorus, accu-mulate in a narrow layer near the groundsurface and may not be readily availableto young plants.


Many of these factors often combine underno-tillage regimes to make nutrients lessreadily available to both seedlings andgrowing crops. Thus banding of fertilizerssimultaneously at seeding becomes all themore important.

Numerous experiments and field obser-vations have confirmed that the broadcast-ing of fertilizers during no-tillage oftenresults in poor crop responses. Figure 9.1illustrates a typical field response. A con-tractor (custom driller) had been sowingpasture species in New Zealand with wingedopeners into an otherwise fertile field whilesimultaneously banding 300 kg/ha of anN : P : K fertilizer mix alongside (but nottouching) the seed. Near the end of the fieldthe contractor ran out of fertilizer. Thefarmer asked him to carry on sowing seedalone while he (the farmer) broadcast thesame rate of fertilizer on the remaining area,which he did. Inadvertently the farmerhad set up a comparison of banded versusbroadcast fertilizer. Figure 9.1 clearly showsthe difference in plant response 8 weeksafter drilling.

Nor are such responses restricted tograsses. In fact, responses to placed ferti-lizer under no-tillage were first identifiedwith wheat in the USA in the 1980s (Hyde

et al., 1979). Almost every crop and soilhave the potential to show a similar res-ponse to that illustrated in Fig. 9.1. Bothnarrow-leaved (monocotyledonous) andbroadleaved (dicotyledonous) plants haveregularly shown similar responses.

Figure 9.2 shows a marked response tobanded fertilizer in France with maize. Thefour rows in the centre and left of centre inthe photograph had broadcast fertilizerapplied at the same rate as the placed ferti-lizer in all other rows. The differences areremarkable.

There are two important consider-ations when applying fertilizer by bandedplacement:

1. Possible toxicity of the fertilizer to theseeds and seedlings, often referred to as‘seed burn’.2. Yield responses of the growing plantsto the placed fertilizer.

We shall discuss these two aspectsseparately.

Toxicity

There are three options for applying ferti-lizer under no-tillage: (i) broadcasting on

Fertilizer Placement 119

Fig. 9.1. Pasture established by no-tillage in New Zealand with broadcast fertilizer in the foregroundand banded fertilizer in the background at 8 weeks’ growth.

the surface; (ii) mixing with the seed; or(iii) banding separately from the seed at thesame time as the seed is sown.

Since broadcasting of fertilizer is aseparate operation either before or afterseeding and not a function of the no-tillagedrill or planter, we shall not consider itfurther here.

Mixing of fertilizer with seed is a riskyundertaking at any time because of poten-tial toxic chemical damage to the seed andseedlings. In tilled soils, a measure of dilu-tion of the fertilizer with loose soil willoften reduce the risk of ‘seed burn’. But inan untilled soil, particularly one that isdamp, soil dilution by mixing becomesminimal.

In general, fertilizer–seed toxicity willbe affected by the following:

● The formulation of the fertilizer. Mostforms of nitrogenous and potassic ferti-lizers are likely to ‘burn’ seeds, as wellas some forms of phosphatic fertilizers.

Secondary nutrients such as boron andsulphur can be particularly toxic.

● The form of the fertilizer. Dry granularfertilizers are more often placeddirectly with the seed than liquid ferti-lizers. While it is easier to direct theliquid placement away from the seedthan the granular, either form willcause toxicity.

● The age of the fertilizer. ‘Fresh’ super-phosphate may contain free sulphuricacid, although this dissipates over timein storage.

● The moisture content of the soil. Drysoils concentrate the fertilizer salts inthe limited soil solution, which maydamage or kill the seeds by the effectsof reverse osmosis.

Mixing seed and fertilizer and sowing themtogether or alternatively allowing them tomix in the opener or the soil is therefore avery unsatisfactory way to provide nutri-ents for young no-tilled plants. At best,small amounts of starter fertilizer might beapplied in this manner. Usual upper limitsare considered to be at about 15–20 kg/ha ofnitrogen. But a higher level of risk must beaccepted compared with separate bandingof seed and fertilizer.

Banded fertilizer

For separate banding of seed and fertilizer,the seed and fertilizer must be placed in dif-ferent positions in the soil and remain inthese positions after the opener has passedand the slot has been closed.

There are three realistic geometricoptions. The fertilizer can be placeddirectly below, to one side of or diagonallybelow and to one side of the seed. Placingfertilizer above the seed is not a logicaloption because this is very similar tobroadcasting.

The ability of no-tillage drills andplanters to simultaneously band seed andfertilizer without the two coming into con-tact with one another is widely recognizedas one of their most essential functions.Indeed, an informal survey of no-tillage

120 C.J. Baker

Fig. 9.2. The difference between broadcastfertilizer (left-of-centre four rows) and bandedfertilizer (all other rows) in no-tilled maize(France).

experts in the USA in the 1980s revealedthat separate banding of seed and fertilizerwas unanimously regarded to be the singlemost important design improvement thatshould be made to no-tillage openers.Unfortunately, providing this function hasproved to be an elusive capability for manymachinery manufactures.

Some no-tillage drills and plantersemploy two separate openers, one for seedand another for fertilizer. Others combinethe two openers together into one (oftencomplicated) ‘hybrid’ opener, while stillothers use one dedicated fertilizer openerbetween each pair of seed openers. Butthere are also modern openers designedspecifically for no-tillage that band seedand fertilizer in the same slot without com-promising seeding accuracy, row spacing orresidue handling for a wide range of for-ward speeds, soils and residue conditions.

Vertical banding versushorizontal banding

The absence of friable soil makes verticalseparation of seed and fertilizer moredifficult in no-tillage than in tilled soils,even by successive openers or duplicatedcomponents.

Some drills and most planters in looseor tilled soils use a leading opener to placefertilizer at a given depth and then followthat with a scraper that fills the slot withloose soil. This in turn is followed by theseeding opener which opens a new slot thatis either shallower and/or to one side of thefertilizer slot. Such repeated manipulationof loose soil is generally not possible ordesirable under no-tillage, so the choice isto either broadcast or inject the fertilizer asa separate operation before seeding orsimultaneously seed and place (band) thefertilizer to one side of the seed by aseparate opener.

Experience with tilled soils suggeststhat vertical separation of seed and fertilizershould be at least 50 mm (known as ‘deepbanding’). Experience with no-tillage, how-ever, shows that extrapolation of resultsfrom tilled soils requires adjustment for the

nature of the soils and the machineperformance.

The disc version of winged openersprovides a physical barrier between the twosides of a horizontal slot in the soil, thusallowing seed to be deposited on one sideand fertilizer on the other to provideadequate horizontal separation or banding.As the disc withdraws from the soil it tendsto draw the soil up a little, resulting ina final horizontal separation distance of10–20 mm. Figure 9.3 shows the horizontalseparation of seed and fertilizer in aninverted-T-shaped slot created by a wingedopener.

It is also possible to separate the seedand fertilizer vertically with this opener byarranging a long and short blade on thesame side of the disc. Figure 9.4 shows aprototype winged opener with long andshort blades to provide vertical separationof seed and fertilizer.

Yet another option exists with thisopener using a long and short blade onopposite sides of the disc, thus creatingdiagonal separation (i.e. both vertical andhorizontal). Figure 9.5 shows an excavatedslot created by a winged opener in whichthere is a distinct step down from the seedshelf to the fertilizer shelf (i.e. diagonalbanding). Figure 9.6 is a diagrammatic rep-resentation of diagonal banding using twoseparate disc openers. Similar placementpatterns have recently been achieved withmodified hoe-style openers using configu-rations to introduce the seed and fertilizerat different depths of penetration.

Baker and Afzal (1986) compared theeffects of vertical and horizontal separa-tion distances of ammonium sulphate(21 : 0 : 0 : 24) fertilizer from canola (rape,Brassica napus) seed in an untilled silt-loam soil using a winged opener. Canolaseed is known to be particularly sensitiveto the presence of ammonium sulphatefertilizer. Figure 9.7 shows seed damagedetermined by counts of seedling emer-gence, and Table 9.1 shows the seedlinggrowth.

Figure 9.7 shows that horizontal sepa-ration by as little as 10 mm was equivalentto vertical separation by twice that distance


122 C.J. Baker

Fig. 9.3. A cross-section of an inverted-T-shaped slot showing the horizontal banding of seed (left)and fertilizer (right) (from Baker and Afzal, 1986).

Fig. 9.4. A prototype winged opener with long and short blades for vertical separation of seed andfertilizer (from Baker and Afzal, 1986).

(20 mm) for reduced germination andemergence.

Table 9.1 shows that not only was thereless seed damage from 20 mm horizontalseparation, there was also a significantgrowth advantage for the 20 mm horizontalseparation option compared with mixing ofthe seed and fertilizer together or separatingthe two by 10 mm either horizontally orvertically. Neither the horizontal nor thevertical separation by 20 mm was signifi-cantly different from where no fertilizer hadbeen applied, which confirmed that no seeddamage had occurred.

Afzal (1981) also compared the effec-tiveness of horizontal separation by awinged opener in tilled and untilled soils,to gauge the extent to which results fromtilled soils could be safely extrapolated tountilled soils. Table 9.2 shows the results.At all three sampling dates (10, 15 and 20days after sowing), the no-tilled soil con-tained more plants than the tilled soil, indi-cating that some seeds in the tilled plotshad either been killed by the fertilizer, orhad failed to germinate for other reasons.

An explanation for the effects inTable 9.2 seems to lie in the fact that, with


Fig. 9.5. Diagonal separation of seed and fertilizer in the soil (fertilizer below the seed towardsbottom of photo) using a winged no-tillage opener with an elongated blade on one side.

Fig. 9.6. A diagrammaticrepresentation of diagonal fertilizerbanding with two angled disc openers.

124 C.J. Baker

Fig. 9.7. Effects of the position of fertilizer placement, relative to the seed, on seedling emergenceof no-tilled canola (from Baker and Afzal, 1986).

Number of true leaves Plant height (mm) Plant weight (g)

No fertilizer 4.1 ab 63 ab 46 abSeed and fert. mixed 3.3 b 36 b 22 bHorizontal separation by

10 mm 3.3 b 34 b 19 b20 mm 4.3 a 71 a 80 a

Vertical separation by10 mm 3.3 b 38 b 25 b20 mm 4.2 ab 60 ab 54 ab

Unlike letters in a column denote significant differences (P < 0.05).

Table 9.1. Effects of method of fertilizer placement on seedling performance of no-tilled canola.

Days after sowing

Establishment method 10 15 20

No-tillage (plants/square metre) 25.1 a 50.7 a 55.2 aConventional tillage (plants/

square metre)19.4 b 41.6 b 44.8 b

Increase of no-tillage overconventional tillage

29% 22% 23%

Unlike letters in a column denote significant differences (P < 0.05).

Table 9.2. Effects of tillage and no-tillage on horizontal separation of canola seed andfertilizer in the slot.

this particular opener design, the centraldisc cuts a thin vertical slot in the soil50–75 mm deeper than the horizontalshelves on which the seed and fertilizer areplaced. In an untilled soil, the integrity ofthis disc cut remains more distinct than in atilled soil, where the friable nature of thesoil allows soil to collapse into the disc-cutzone as the disc withdraws from the soil.

It is thought that this disc cut, in anuntilled soil, effectively interrupts solutemovement from the fertilizer, which mightotherwise reach and damage the seed orseedling roots. It is also possible that thehigh humidity in the inverted-T slot in anuntilled soil helps prevent reverse osmosis,which is one of the mechanisms by whichseeds are damaged by high salt concentra-tions in dry tilled soils (see Chapters 5 and6). Because the general humidity of a tilledsoil is lower than that of an untilled soil,due to the artificially high porosity and theabsence of surface residues, even theinverted-T-shaped slot is unable to main-tain a high humidity zone around the seedwhen operating in a tilled soil.

Another important point in the tilled/no-tilled soil comparison is that the effectsof separating the seed from the fertilizer aremost apparent as the soil became drier.Collis-George and Lloyd (1979) had earliernoted that, in tilled soils, dryness tended toresult in more fertilizer damage to seedsthan where the soil was moist. Baker andAfzal (1986) examined whether or not thistrend extended to untilled soils, using awinged opener.

Their results, shown in Table 9.3, indi-cate that plants suffered with both verticalseparation and mixing together when thesoil became dry, but these were equivalentto the other treatments in the moist soil.

The only treatment that almost ignored themoisture status of the soil was the horizon-tal separation within an inverted-T-shapedslot. This may have been partly the result ofthe high humidity this slot maintains andpartly the result of the disc cut. The result isthat the optimum horizontal separation dis-tance within an inverted-T-shaped slot wasless than the distance commonly recom-mended for vertical separation by otheropeners and for tilled soils.

Field experience has shown that theparticular disc version of the wingedopener used in these experiments is equallywell suited to separating seed from liquid orgaseous fertilizers as it is to separating itfrom dry powdered and granulated forms offertilizer.

In two separate experiments (C.J. Baker,unpublished data), the author found thatthe upper limit of dry urea (46 : 0 : 0 : 0)application with this opener, sowing maizein 750 mm spaced rows, was about200 kg/ha of urea (92 kg/ha/N), equivalentto 15 g urea per metre of sown row, beforeseed damage was detectable. Field applica-tions of 780 kg/ha of 30% potassic super-phosphate (0 : 6 : 15 : 8) with peas in150 mm rows (117 kg/ha/K) have also beenachieved with this no-tillage opener withno measurable toxicity damage to seedgermination when compared with nofertilizer.

K.E. Saxton (unpublished data) alsotested the ability of the same winged openerto effectively separate wheat seed from toxi-city damage arising from the use of a rangeof rates and two forms of nitrogenous ferti-lizers sown in 250 mm rows in the USA. Hefound no detrimental effect on the seedfrom applying either dry urea (46 : 0 : 0 : 0)or liquid ‘aqua’ (ammonium hydroxide


Horizontal separation by 20 mm Vertical separation by 20 mm Mixed together

Dry soil Damp soil Dry soil Damp soil Dry soil Damp soil

89 81 64 90 58 85

Table 9.3. Effects of position of fertilizer placement and soil moisture status on germination ofno-tilled canola (germination %).

solution in water: 40 : 0 : 0 : 0) at concentra-tions of up to 140 kg/ha of nitrogen.

Operators in New Zealand commonlyapply up to 400 kg/ha of high-analysisfertilizer mixes (which sometimes includeboron and/or elemental sulphur) in the fieldwith this opener with no measurable effectfrom ‘seed burn’ but with substantial posi-tive growth and yield responses (Bakeret al., 2001).

Although horizontal separation appearsto be somewhat more beneficial than verti-cal separation in most instances, a rangeof vertical separation systems have beendesigned. Hyde et al. (1979, 1987) reportedattempts to separate seed and fertilizer ver-tically with a single opener by modifyinga hoe opener so that it deflected soil backover the fertilizer before the seed exited theopener. The deflecting action, however,was dependent on forward speed and soilmoisture conditions, especially plasticity.In favourable conditions, its crop yieldperformance was comparable to horizontalseparation by winged openers.

One solution that allows vertical sepa-ration of seed and fertilizer in no-tillage tobe largely independent of soil moistureconditions is the use of slanted double discopeners. The leading (fertilizer) opener cutsa slanted slot and places the fertilizer atits target depth. The seed opener, whichfollows, is positioned either vertically or atthe opposite slant and shallower, therebyplacing the seed in the undisturbed soilabove the fertilizer. This option appears tobe effective but the downforces required tomake two double disc openers penetrate thesoil for each row limits it to reasonably softsoils. Figure 4.8 shows two slanted doubledisc openers so configured.

Another, more laborious but effective,method is to pre-drill the fertilizer as a sepa-rate operation to drilling of the seed at ashallower depth, and this can be achievedwith virtually any design of opener.

Retention of gaseous fertilizers

Inverted-T-shaped slots are known to retainwater vapour in the slot (see Chapters 5

and 6). It is possible that this slot alsoretains volatile gases from nitrogenous fer-tilizers (especially ammonia) within theslot in a similar manner to water vapour.It is well known that soil injection ofboth organic (animal waste) and inorganicforms of nitrogen as gas or liquid leads toproblems with ammonia gas volatilizing andescaping into the atmosphere. With disposalof animal waste using knife-type openers(U-shaped slots), this is often overcome bydeep (0.5 m) injection. Inverted-T-shapedslots also offer the option of shallow injec-tion of this material (Choudhary et al.,1988b).

During the no-tillage drilling of seeds,simultaneous deep injection of inorganicnitrogen is impractical because of the limi-tations on depth of placement and availabletractor power. The result of simultaneousshallow placement has usually been anoticeable smell of ammonia at drilling as itescapes from the sown slots.

With the winged opener, less ammoniasmell is evident, indicating entrapment ofthe valuable fertilizer within the slots. Thiswas first noticed in the field in the USA byfarmers using a winged opener. They wereintrigued by the fact that the farm dogs ranalong behind the drill. This apparently didnot occur with other drills because theescape of ammonia from the soil immedi-ately behind the drill made an unpleasantenvironment for the dogs.

Crop Yield

As previously discussed, broadcast fertiliz-ers on no-tilled fields are often infiltratedby water moving into preferential flowpaths and bypassing the early plant roots, orthose constituents that bind to the soilremain on the soil surface. In contrast, tilledsoils have more diverse flow paths throughtheir microporosity and blend those bind-ing constituents within the tilled zone. As aresult, while broadcasting of fertilizers hasbeen practised successfully for years withcrops grown in tilled seedbeds, under no-tillage the same crop responses to broadcast

126 C.J. Baker

fertilizer cannot be relied upon. Hyde et al.(1979) highlighted the problem in thePacific Northwest of the USA, and a long-term experiment conducted by the authorsover a 6-year period in New Zealand alsoillustrated the problem (Baker and Afzal,1981).

In the New Zealand experiment, thescientists compared the continuous grow-ing of summer maize, sown with a wingedopener, on the one hand, into untilled soiland, on the other hand, into a convention-ally tilled seedbed. It also coincided withsome important technological develop-ments of winged openers, which had animpact on the experiment.

Figure 9.8 illustrates the first 5 years ofthe maize yield results. To eliminate sea-sonal variations in yield, conventional till-age was given the arbitrary value of 100%each year and no-tillage was compared withit on a percentage basis. The seed was sowninto inverted-T-shaped slots on all occa-sions with Class IV cover.

In year 1 no fertilizer was applied,either at planting or after the crop becameestablished. The crop relied solely on thealready high fertility of the soil, which hadbeen under intensive pasture for 20 years.The maize yield under no-tillage was notsignificantly different from that undertillage.

In year 2 again no fertilizer was used.By this time, however, the advantages ofmineralization, which is enhanced by thetillage process, had become evident. Onlyslow mineralization rates occur under no-tillage because of the absence of soil distur-bance. As a result, the no-tillage maize yieldwas only 35% of that under tillage.

In year 3 a comprehensive NPK starterfertilizer (10 : 18 : 8 : 0) was surface-appliedat 300 kg/ha by broadcasting on to all plots.At that time, simultaneous banding of seedand fertilizer by winged openers was notpossible without risk of seed damage. Theseed was sown with the simple originalwinged opener and mixing of seed and fer-tilizer together was not considered a viableoption.

The disc version of the winged opener,which allows simultaneous banding, hadnot by then been invented. None the less,the surface-applied fertilizer lifted the yieldunder no-tillage to 60% of that undertillage.

In year 4 it was decided to apply agreater amount of broadcast NPK fertilizerthan in year 3 (400 kg/ha) to both treat-ments to try to raise the no-tillage yield stillfurther. Doing so had the opposite effect,however, and the no-tillage yield of maizefell to an all-time low of only 30% of theyield under tillage.


Fig. 9.8. Relative dry matter (DM) yield of no-tillage compared with tillage as affected by fertilizerapplication on no-tillage maize yields over a 5-year period (from Baker and Afzal, 1981).

Year 5 coincided with the developmentof the disc version of the winged opener con-cept, which, amongst other things, allowedseed and fertilizer to be banded simulta-neously with 20 mm horizontal separationin inverted-T-shaped slots.

The effect on the yield of no-tilledmaize was immediate and spectacular. Itraised the yield to again be not significantlydifferent from the tilled yield.

In year 6 the experiment was altered todirectly compare banded and broadcastfertilizer application under tillage and no-tillage and to check if the year 5 resultswere repeatable. Indeed, they were.

Table 9.4 presents the results for year 6.Clearly, the no-tilled soil benefited morefrom banding of fertilizer than the tilledsoil. The final yields of the two methodswith banded fertilizer were not signifi-cantly different.

Perhaps just as important were theyields of maize obtained from plots that hadnot received any fertilizer in the entire6-year period. Although the unfertilizedyields from both the tilled and untilled soilswere poor in comparison with the fertilizedplots, the enhanced mineralization that hadoccurred in the tilled soil each year pro-duced plants almost three times as big asthose under no-tillage. This mineralization,however, represents a ‘burning out’ of theSOM, with associated loss of soil quality,and is the reason why tillage is no sub-stitute for no-tillage where fertilizers areapplied correctly, in terms of both sustain-ability and crop yield.

An on-farm comparison was made in2004 by a New Zealand farmer. He chose 11fields and sowed a forage brassica crop intoa randomly chosen selection of the fields

over a 17-day period with two differentno-tillage drills (M. Hamilton-Manns, 2004,unpublished data).

One drill was equipped with verticaltriple disc openers. The triple disc openershad wavy-edged leading discs, which reducethe compacting effects normally associatedwith such openers. But they were not capa-ble of banding fertilizer, so diammoniumphosphate (DAP) fertilizer was broadcast at300 kg/ha. The other drill was equippedwith the disc version of winged openers,which banded the same amount of fertilizer20 mm to one side of the seed at the time ofseeding. Soil moisture conditions were notlimiting and seedling germination was ade-quate with both drills.

The fields drilled with triple disc open-ers and broadcast fertilizer yielded, on aver-age, 7069 kg dry matter (DM)/ha. The fieldsdrilled with winged openers and banded fer-tilizer yielded, on average, 10,672 kg DM/ha.

While it cannot be said with certaintythat the entire 51% average difference wasthe result of banded fertilizer alone (theremay also have been opener differences),there is little doubt that most of the differ-ence was due to fertilizer banding, and theheavier crops were worth, on average,US$468/ha more than the smaller crops.

Banding options

We have already seen that the need to bandfertilizer beneath the soil without ‘burning’the seed is greater under no-tillage thanwith tilled soils. Mixing of seed and ferti-lizer risks ‘seed burn’.

Recourse to ‘skip-row’ seeding, inwhich every third opener sows only ferti-lizer in order to fertilize the two seeded rowseither side of it (Little, 1987), has not been afeasible alternative either, although cer-tainly better than broadcasting. Choudharyet al. (1988a) showed only mixed successwith the ‘skip-row’ option, even when sownin narrow (150 mm) rows. Table 9.5 showstheir results.

The ‘skip-row’ treatment produced thelowest fertilized barley yield (2072 kg DM/ha)but was equal to all other treatments when

128 C.J. Baker

Fertilizerplaced

Fertilizerbroadcast

No fertilizerapplied

No-tillage 10,914 4,523 1,199Tillage 10,163 5,877 2,999

Table 9.4. Effects of fertilizer placement on yieldof maize (DM yield kg/ha) in the sixth year of a6-year experiment.

fodder radish was sown. In the latter casemixing of the seed with the fertilizer gavethe poorest yield (2809 kg DM/ha). All othertreatments were not significantly different.

Two other important points are evidentin Table 9.5. The results are the mean of twosoils, one of which was a fine sand, in whichfew, if any, preferential flow channels werepresent because of the exceedingly friablenature of the soil. Thus, even in its untilledstate, surface-applied nitrogen fertilizer wouldhave flowed more or less evenly throughsuch a profile as if it had been tilled andshowed less difference in favour of bandingthan where the soil was more structured.

The other point is that one of thefertilizer/seed combinations used in thisexperiment (DAP and barley) was not par-ticularly damaging to barley seed. Conse-quently, mixing of barley seed and fertilizertogether showed no disadvantage. On theother hand, mixing of the DAP fertilizerwith the more susceptible brassica cropshowed results similar to those of Afzal(1981) and Baker and Afzal (1986), who hadused an even less compatible mix (canolaand ammonium sulphate).

There is no evidence from any experi-ments conducted by the authors that greateramounts of fertilizer are needed underno-tillage. That which is applied just needsto be used more effectively by banding italongside the seed. In fact, data from sevendifferent experiments involving wheat(Triticum aestivum), drilled with doubledisc openers in a skip-row configuration(where every third row was sown with

fertilizer only, at 100 mm depth), comparedwith horizontal separation by 20 mm witha drill equipped with winged openers,showed that fertilizer rates could actuallybe reduced with the latter openers (Saxtonand Baker, 1990). Figure 9.9 shows theresults.

On average, the winged openers showeda 13% increase in wheat yield comparedwith the skip-row drilling with double discopeners. Until then, that particular skip-row configuration had out-yielded all othermethods with which it had been comparedin the USA.

Not only did the plants sown with hori-zontal banding out-yield those sown withthe skip-row method, but further measure-ments showed that the plants had been morevigorous from the outset. The improved vig-our is likely to have been partly because ofthe positioning of the fertilizer and partlybecause of the high-humidity environmentin which the seedlings developed beneaththe ground in the horizontal (inverted-T-shaped) slots.

Table 9.6 shows analyses of the carbonand nitrogen contents of seedlings grownby these two fertilizer banding methods.Figure 3.1 had earlier shown the contrastingdevelopment of the seedlings in which theheavier and more fibrous nature of the rootsystems (more root hairs) from the horizon-tal banding and inverted-T-shaped slot wasclear. Apparently, both the carbon andnitrogen levels were higher in the plantssown by the winged openers with horizon-tal banding of fertilizer compared with


Barley grain DMyield (kg/ha)

Fodder radisha (whole plant)DM yield (kg/ha)

No fertilizer 1889 b 3240 abHorizontal separation by

20 mm2580 a 3763 a

Fertilizer and seed mixed 2538 a 2809 bBroadcast fertilizer 2432 a 3543 aSkip-row separation 2072 b 3526 a

Unlike letters in a column denote significant differences (P < 0.05).aBrassica napus L.

Table 9.5. Effects of fertilizer application method on yield of two no-tilled crops.

those sown with the double disc opener and‘skip-row’ fertilizer application.

Even where vertical banding of seedand fertilizer has been accomplished usinga single opener, no clear advantage has yetbeen shown for this option.

Further, the technical difficulty ofachieving satisfactory vertical banding in awide range of conditions with a singleopener makes implementation on a fieldscale unreliable. The problem is that, toachieve vertical separation, the fertilizer isusually drilled first at a greater depth thanthe target depth for the seed. In tilled soils itis relatively easy to induce soil to fall on tothe fertilizer before the seed is sown. But inuntilled soils this is much more difficult toachieve, particularly when the soil is damp

and ‘plastic’. For this reason, horizontalseparation has become a more ‘fail-safe’alternative since effective separation is notaffected by soil looseness, surface cover oroperating speed.

A comparison of horizontal banding(winged opener) and vertical banding (proto-type hoe opener with a deflector to scoopsoil on to the fertilizer prior to deposit of theseed) was made over several years by theauthors. The results are shown in Fig. 9.10.

The figure shows that the wingedopener with horizontal banding produceda greater yield in the first year of springwheat (SW 87) and perhaps in the final yearof winter wheat (WW 89), but there wereno differences in yield in the other threeseasons.

130 C.J. Baker

Fig. 9.9. Wheat yield comparisons from no-tillage using two different fertilizer banding options(from Saxton and Baker, 1990).

Opener type Field no. Carbon (% DM) Nitrogen (% DM)

Winged opener (inverted-T,horizontal banding)

12

38.0038.60

4.164.70

Mean 38.30 4.43Double disc opener (V-shaped

slot, skip-row application)12

36.5034.69

4.003.83

Mean 35.60 3.92

Table 9.6. Carbon and nitrogen contents of no-tilled wheat seedlings sown with twodifferent openers.

A long-term double cropping experi-ment in Australia compared yields of soy-bean crops sown under no-tillage and tillagefor 14 years using winged openers (Grabskiet al., 1995). For the first 2 years (1981/82and 1982/83) the conventional tillage yieldswere superior, presumably because of theprevious history of tillage. But for the follow-ing 12 years the no-tillage treatment wasnever bettered and averaged 30% higheryield of soybean than conventional tillage.

How close should banded fertilizerbe to the seed?

Ferrie attempted to answer this question inIllinois, USA, in 2000. His results werereported by Fick (2000). Ferrie comparedseveral diagonal distances of separation ofstarter fertilizer from maize seed sown withdouble disc openers, ranging from 90 mmdeeper than and 50 mm to one side of theseed to 15 mm deeper than and 20 mm toone side of the seed. He concluded that, in

terms of crop responses, ‘the closer thestarter was to the seed the better’, providedthat the fertilizer was not actually mixedwith the seed and the action of banding thefertilizer did not disturb the accurate place-ment of the seed. The treatment with thegreatest separation distance actually pro-duced no measurable yield response to thestarter fertilizer at all.

Ferrie also pointed out that slot wallcompaction could have an effect on theability of juvenile roots to access the fertil-izer, especially in clay soils. He felt that, insuch soils, even a narrow knife openercould cause problems.

Dianxion Cai (1992, unpublished data)tested two options for placing dry and liq-uid nitrogenous fertilizers at increasingrates of applied N, using winged openersand drilling wheat seeds 25 mm deep. Thetwo options were: (i) standard horizontalbanding 20 mm to one side of the seed (i.e.the fertilizer was also drilled 25 mm deep);and (ii) diagonal banding in which thefertilizer was banded 20 mm to one side ofand 13 mm deeper than the seed (i.e. thefertilizer was drilled 38 mm deep). Figure9.11 shows the effect on plant stand andFig. 9.12 shows the resultant crop yields.

From Figs 9.11 and 9.12, it is apparentthat the effects on seedling emergence(stand) were similar to the effects on yield,demonstrating the importance of initialplant population for final yield. In bothexperiments the horizontal banding (25 mm)produced more plants and heavier cropsthan the diagonal banding (38 mm) withboth urea and aqua. These differencesbecame most pronounced at an applicationrate of about 120 kg N/ha. At higher appli-cation rates, while the differences remainedlargely unaltered, both the plant stands andcrop yields began to decline, possiblybecause of fertilizer toxicity. The decline ofboth plant stand and crop yield at the highapplication rates (160 kg N/ha) used inthese experiments was considered to be ofno consequence because these applicationrates were well in excess of normal applica-tion rates of nitrogen in any form (160 kgN/ha is equivalent to 350 kg urea or 400 kgaqua/ha).


Fig. 9.10. No-tillage wheat yields from verticalbanding of fertilizer with a hoe opener andhorizontal banding with a winged opener.

Conclusion

One of the more noteworthy advances inno-tillage technology has been to develop a

machine with the capability to separate fer-tilizer from the seed in horizontal bandsand effectively entrap volatile forms ofnitrogen in the slot. At the same time, these

132 C.J. Baker

Fig. 9.11. Wheat stand responses to horizontal and diagonal banding of two forms of nitrogenousfertilizer separated from inverted-T-shaped slots.

Fig. 9.12. Wheat yield responses to horizontal and diagonal banding of two forms of nitrogenousfertilizer separated from inverted-T-shaped slots.

openers maintain the effectiveness of theseparation function without being materi-ally altered by forward speed, soil type, soilmoisture content or the presence or absenceof surface residues. From a field perspec-tive, farmers find it easier to identify withthis single factor, among all others, whenassessing the performance of no-tillage ver-sus tillage, and even when assessing themerits of competing no-tillage systems andmachines.

It is interesting to speculate how manyexperiments and field observations show-ing poor yields for no-tillage crops havebeen the result of opener inability toadequately band the fertilizers.

Summary of Fertilizer Placement

1. Less nitrogen is available by organicmatter mineralization under no-tillage thanunder tillage, making nitrogen applicationparticularly important at drilling underno-tillage.2. Some temporary nitrogen ‘lock-up’ mayalso occur under no-tillage as soil bacteriadecompose organic residues.3. Broadcast fertilizers are less effective inno-tillage than in tillage because solublenutrients often bypass roots by infiltrationoccurring in preferential channels createdby earthworms and decayed roots.4. ‘Deep-banding’ of fertilizers at drillingis less effective or necessary in untilledsoils than in tilled soils.5. Fertilizer close to the seed is better than ata distance, so long as the two are not mixed.6. Horizontal separation between seedsand fertilizer at distances as small as 20 mmhave been more effective in no-tillage thanvertical separation by any distance.

7. Relatively few no-tillage openers pro-vide effective seed and fertilizer bandingwith a proper distance or direction.8. Of those no-tillage openers that do pro-vide effective separation, horizontal separa-tion is preferable to vertical separation.9. Where no-tillage openers are incapableof separating seed from fertilizer, otheroptions include:

● Drilling every third row with only fer-tilizer (‘skip-row’ planting).

● Mixing seed and fertilizer together inthe slot.

● Doubling the number of openers on adrill so as to provide separate fertilizer-only openers in addition to seed-onlyopeners.

● Surface broadcasting of the fertilizer.● Drilling seeds and fertilizer as two

separate field operations at differentdepths.

10. Most double disc openers are incapableof banding fertilizer separately from theseed with a single opener.11. Some angled disc openers have pro-vided a fertilizer-banding capability.12. One version of winged openers with asingle disc effectively separates seed andfertilizer horizontally or diagonally.13. Crop yields with winged openers havebeen good when using horizontal separa-tion of seed and fertilizer, due to impro-ved seed/seedling micro-environment andfertilizer response.14. Only recently designed hoe openersseparate seed and fertilizer in any direction.15. Two disc openers (double or angled)slanted in opposite directions may be capa-ble of providing vertical separation of seedand fertilizer.


10 Residue Handling

C. John Baker, Fatima Ribeiro and Keith E. Saxton

Successful no-tillage openers not onlyhandle surface residues without blockage

but also micro-manage these residues so thatthey benefit the germination and seedling

emergence processes.

The second most valuable resource inno-tillage is the residue left on the groundsurface after harvest of the previous crop.The only resource more valuable than resi-due is the soil itself – in its untilled state.

Unfortunately, the history of tillage islittered with descriptions of methods fordisposing of residues so that they do notinterfere with the operation of machinery.In tillage, surface residues have beenregarded as a major nuisance and thereforehave often been referred to as ‘trash’. Thosewho take no-tillage seriously have dispen-sed with the term ‘trash’ in favour of theterm residue. Trash is something unwanted.Residue is something left over, but in thiscase wanted and useful.

Before considering how well variousopeners and machines handle or manipulatesurface residues, it is necessary to identifythe various forms that residue can take(Baker et al., 1979a). Then it will be appro-priate to look at how the residues shouldbe macro-managed on a field scale(Saxton, 1988; Saxton et al., 1988a, b; Vesethet al., 1993) and finally at the options for

micro-managing residues in, around andover the slot zone (Baker and Choudhary,1988; Baker, 1995).

The Forms that Residues can Take

Short root-anchored standing vegetation

Pasture (either growing or recentlykilled by herbicide)

Short root-anchored pasture is commonlyencountered by no-tillage drills designedfor pasture renovation or renewal in inten-sive animal grazing agricultural systemsand for crop establishment in integratedcrop/animal systems. In such systems, ani-mal management can usually be sufficientlycontrolled to allow deliberate intensivegrazing of selected fields prior to drilling,thus reducing the length of grass and there-fore the residue-handling demands on suchmachines. This allows relatively inexpen-sive drills to be used for such conditions.

Short standing pasture usually presentsfew residue-handling problems as the vigo-rous root anchorage and firm soil beneaththe plants allows even a ‘rigid’ tine or shank,without a pre-disc, to burst reasonablycleanly through it. If the pasture has beenrecently killed, the time-interval between


spraying and drilling can have a profoundeffect on the handling properties of thisresidue. As decomposition starts soon afterdeath of the plant, the material becomesprogressively weaker and more likely tobreak away from its anchorage. At anadvanced stage of decay, it may break awayfrom the soil anchorage altogether and startto behave more like loose-lying residuethan short anchored residue and thereforebe more prone to causing blockage. Some-times it pulls free in large pieces.

Pasture plants that have stoloniferousor rhizomatous growth habits (i.e. with hori-zontal and/or underground connectingstems), even though they might be grazedshort by animals, present a different pro-blem, since their creeping habit makes themlikely to become entangled in non-disc-typeopeners. At least a pre-disc is essential forsatisfactory handling of such residues withtine or chisel openers.

Short clean crop stubble after direct-headingwith a combine harvester and

baling of the straw

Clean crop stubble that has negligible loosestraw lying on or amongst it offers only mod-erate residue-handling problems becausethe standing plants can usually be pushedaside by relatively unsophisticated no-tillageopeners. In common with pasture plants, thekey element is the anchorage offered by theroot systems. The time interval betweenharvesting and drilling and the interveningweather will also influence the level ofdecay that has set in by the time drillingtakes place. In the case of crop stubble,however, because harvesting normallytakes place at a dry time of the year, theonset of decomposition may be slower thanwith pasture plants.

Standing stubble has important addi-tional functions in no-tillage systems thatexperience snow and freezing winters orin which the crop is swathed prior toharvesting.

Where swathing takes place, long stub-ble, especially in narrow drill rows, willhold the cut swathe off the ground, whichaids drying and makes harvesting easier as

it aids the pickup mechanisms on combineharvesters compared with when the swathelies close to the ground.

Where snow is expected, stubble holdsthe snow from blowing away. Snow, inturn, provides effective thermal insulationof the soil beneath and may be responsiblefor maintaining soil temperatures some 10°to 15°C higher than in soils that have nosnow cover and are allowed instead tofreeze (Flerchinger and Saxton, 1989a, b). Inthis respect, long stubble is better than shortstubble (see below).

In either case, at the end of a cold win-ter, when such soils are drilled, stubble thathas endured the cold months is usuallybrittle, though often it has not actuallydecayed much. It may break off at groundlevel, but due to its shortness will seldompresent major residue-handling problemsfor no-tillage drills. On the other hand,no-tillage systems increasingly require thatthe full amount of residue disgorged fromcombine harvesters (including the threshedstraw as well as the standing stubble) remainson the ground over the winter in suchclimates. This combination presents quiteanother problem as far as residue handling isconcerned, which will be discussed later.

Standing stubble also has an importantfunction in dry climates, by reducing windvelocity at the soil surface, which signifi-cantly reduces drying and soil movement.In windy conditions, standing stubble mayprotect young seedlings sown betweenthe stubble rows from being blasted bywind-blown sand and other soil particles.In Australia, for example, planting betweenthe rows of tall stubble offers wind protec-tion to the new plants, while, in England,long stubble has another value, that ofcamouflaging wildlife, such as pheasants.Since many farmers in that country rate thecommercial shooting of pheasants as animportant source of farm income, no-tillageoffers an opportunity through stubble reten-tion for an extended game-shooting periodthat was not possible with tillage.

In tropical climates, tall standing stub-ble can result in etiolation of the new crop.But short standing residues lead to morevegetative material entering the combine

Residue Handling 135

harvester, resulting in a higher powerrequirement, more fuel consumption ordecreased field capacity.

For all of these reasons, there has beenrecent interest in the use of stripper headersin association with no-tillage because suchharvesting devices maximize the length ofthe standing stubble.

Tall root-anchored standing vegetation

Tall grass, sprayed-off cover crops and tallclean stubble (300 mm and longer),together with bushy weeds, present some-what greater problems than short vegeta-tion, even with root anchorage, but lessthan lying straw. There is a critical heightabove which each of these plants will col-lapse in the pathway of no-tillage openers(or simply over a period of time), at whichpoint the residue behaves more like lyingstraw than standing stubble. Taller mate-rial may also trap a more humid micro-environment within, with the result thatdecay of the bases of the straw may be initi-ated more quickly than with short stubbleand breakage is more likely.

Figure 10.1 shows the effect of drillingwith the disc version of a winged openerthrough a partially standing matted legumecrop 0.75 m high that had been sprayed.It is not common to drill into such verytall residue; not only because of thespatial constraints, but because it is diffi-cult for seedlings to obtain sufficientlight during early development to emergesatisfactorily.

Lying straw or stover

Detached stalk material, of any length, pre-sents the most difficult residue-handlingproblems for no-tillage drills but is also avery valuable biological resource unique tono-tillage. Where such residues lie on firmground (e.g. after a no-tilled crop has beenharvested, or even when hay has been feddirectly on to an established pasture andnot fully consumed by animals), therewill be less tendency to block no-tillageopeners than where the residues lie onsofter ground. Similarly, if the residuesremain dry and brittle, they will be easierto handle and cut than where they have


Fig. 10.1. The effects of drilling with the disc version of winged openers into heavy partiallystanding residue.

become damp. Often dampness is a func-tion of both the amount of straw (yieldof the crop) and the weather. Heavy resi-dues may generate their own dampnessand increase in temperature from bacterialaction.

The immediate history of the field mayalso be important. If the previous annualcrop was established into tilled soil, forexample, the soil background against whichdisc components of no-tillage openers willneed to push to shear the straw, will besofter than if the previous seedbed had beenuntilled. This ‘anvil effect’, of course, will beinfluenced by soil type, which has an impor-tant influence on the effectiveness of someresidue-handling mechanisms and presentsfarmers with some difficult choices whenconverting from tillage to no-tillage.

For example, a no-tillage machine thatis good at drilling into residues previouslyestablished in a tilled seedbed (during thechangeover period) may not be the bestmachine for drilling into residues previouslygrown in an untilled seedbed. Further, somefarmers believe (usually erroneously) thatthey will still need to occasionally till theirsoil even under a predominantly no-tillageregime. There may be little logical basis forthis belief, but it will none the less influencethe farmer’s choice of machine, perhapsto the detriment of the true no-tillage phase.The problem seldom exists when drilling intopasture because it is unusual for pasture tohave been established for less than 12 months,during which time even a previously tilledsoil will have consolidated again.

Fortunately, some no-tillage openersare equally well suited to soft and firm (oreven hard) soils. The function of mosttine- or shank-type, power till and wingedopeners is relatively unaffected by soilsoftness or firmness (except for downforceor power requirements), but those that tendto hairpin residue into the slot (doubledisc, angled flat disc and angled disheddiscs) have their hairpinning tendenciesaccentuated by softer soils. On firmer soils,they are more likely to shear the straw(which is desirable) than to push it bentover into the slot (which is undesirable). Infirm soils, however, some openers are also

more likely to compact the soil in the slotzone.

Lying residues have no anchorage tothe ground and are therefore very easilygathered up to become entangled in ‘rigid’machine components. Firmer ground pro-vides greater friction (traction) for discs thatmay operate in conjunction with rigid com-ponents, ensuring that they keep revolvingwhen they encounter lying residues. Somediscs are especially shaped to further assisttraction. Wavy-edged discs and notched orscalloped discs are cases in point. Even so,if the height of the lying straw is above theaxle height of an approaching disc, it islikely to stall the disc, causing sledging andblockage. This is accentuated by dampnessunder the straw, especially if such damp-ness results in partial decay close to theground. The decaying straw can becomequite slippery on the ground and will oftenslide ahead of a disc, rather than allow thedisc to grip and ride over or cut through it.Straw lying amongst standing stubble is lesslikely to slip than where it is lying on bareground.

This sliding tendency is dependent tosome extent on plant species. It is also soil-dependent and obviously weather-dependent.For example, pea straw becomes particu-larly slippery when partially decayed, espe-cially on firm untilled soil, while mostcereal straws do not. Sparse straw, such assoybean, canola, cotton or lupin, is lesslikely to remain damp long enough to pro-mote decay close to the ground than cropsthat produce heavier vegetative growth.Further, the rigidity of the cut stubble ofthese somewhat woody crops helps preventsliding of the lying residue.

Numerous methods have been devisedto handle lying straw. Some of these aresummarized below. The successful meth-ods almost invariably involve openerswhere discs are used, either simply as theopener itself or where the discs assistthe operation of other rigid components,such as winged blades, chisels or tines.In both cases, discs have become a com-mon, though not exclusive, component ofno-tillage openers designed for the handlingof residues.


Management of Residues on aField Scale

Macro-management refers to the way inwhich the residues are managed on a fieldscale. Their management is discussed sepa-rately for: (i) large field-scale no-tillage; and(ii) small-scale no-tillage. But in either case,surface biomass, whether from killed covercrops or harvested residues, plays a key rolein no-tillage systems. For any no-tillagesystem (large or small), the handling ofresidues should:

1. Assist (or at least not hinder) the pas-sage of no-tillage openers.2. If possible, contribute to the biologicalfunctions of the openers.3. Ensure that the residues decomposeand add to soil carbon but at the same timeremain on the soil surface long enough toprotect the soil from erosion, keep the soilcool in tropical climates, retain soil mois-ture and suppress weeds;4. Ensure that the residues do not com-pete with the sown crop.

These are demanding and sometimes com-petitive requirements, and compromises areoften necessary. For example, tine (shank)-or knife-type openers do not handle resi-dues well, so some farmers resort to burningor otherwise removing the residues to avoidblockages when drilling a field. But thiscompromises some of the other listed func-tions. For this and other reasons, the burn-ing of residues is banned in severalcountries, although up to 45% of the bio-mass will be in the roots that remain evenafter burning.

In this respect, it is interesting to notethat it makes little difference whether har-vested residues are baled, burned or buriedin terms of the amount of carbon they pro-vide for the soil (see Chapter 2). Unless theyare left to decompose on the soil surface,much of the carbon content of the above-ground plant residues will be lost from thesystem (oxidized and lost as carbon dioxideto the atmosphere). Therefore, to get the bestout of a no-tillage system, the challenge formachinery designers is to provide no-tillage

openers that can cope with any amount andtype of surface residue without blockage.But, more than that, as is explained inChapter 5, an opportunity exists for openersto harness the surface residues as an import-ant resource to aid germination and emer-gence of the new crop.

Large field-scale no-tillage

Weed control and management ofcover-crop residues

In larger field-scale no-tillage, weeds andcover crops are normally killed by herbi-cides. Indeed, the very feasibility of themodern concept of no-tillage owes its exist-ence to the development of ‘non-residual’herbicides in the 1960s and 1970s. Thiscontrasts with small-scale agriculture (seebelow), which is more dependent on mech-anical means of plant competition control.

No attempt is made here to analyse thepros and cons of specialist sprayingmachinery or different herbicides. Sufficeto say that the control of existing compe-tition is the first step in any no-tillageprogramme and that, unless this is achievedeffectively, all other steps will be compro-mised. Effective chemical weed control is afunction of understanding the biology of theplants to be killed and the efficacy of theherbicide(s) to be used and the mechanicalperformance of sprayers. Some herbicides(e.g. glyphosate) work best on actively grow-ing unstressed plants, while others (e.g.paraquat) are more effective when plantsare stressed. And, of course, there arespecies differences (and sometimes varietaldifferences) in the resistance of plants todifferent herbicides.

Management of harvested residues

CHOPPED OR LONG? The first and mostimportant opportunity to correctly manageresidues on a field scale occurs at harvest-ing. Once crops have been threshed and theresidues ejected from a combine harvesterin discrete windrows, they are very difficultto spread out again.


Modern combine harvesters gathertogether the material from cut widths of5–10 m and process it in such a way that,unless spreading devices are added to thecombine harvester discharge, the residuesare ejected out of the back in the form of awindrow of light fluffy straw 2–3 m wide.Underlying this windrow will be the chafffrom the separation processes, which con-sists of very short pieces of straw, awns, leafmaterial, empty glumes, chaff, dust andweed seeds. The chaff row forms a densesurface covering, somewhat narrower thanthe straw windrow covering it.

In contrast to these somewhat concen-trated zones of residue, good no-tillagerequires that the residue be spread evenlyover the entire field. There are no-tillageopeners that can physically cope with theconcentrated windrows and tailings, butthis capability is somewhat academic sincethe effect of surface residues on germina-tion, emergence and crop growth is so vitalthat an uneven crop will almost certainlyresult from grossly uneven chaff and strawdistribution. Uneven spreading can alsoaffect the efficacy of herbicide applications.

Most combine harvesters have optionalstraw spreaders. These are different fromstraw choppers in that spreaders do notchop the straw into shorter lengths. Theyspread the straw with beaters rather thanwith wind assistance (see Fig. 10.3). Moststraw choppers spread as well as chop. Strawspreaders are not high power-demandingadditions and are easily fitted and operated.They are essential standard equipment onall combine harvesters for no-tillage sys-tems, as indeed they already are on somemakes and models.

Whether or not a chopper is also nee-ded will depend on the residue-handlingcapabilities of the no-tillage drill or planterto follow. Straw choppers are unpopular insome respects because they consume up to20% of the total power requirement of thecombine harvester (Green and Eliason,1999). Chopping damp straw requires morepower than chopping dry straw, althoughthe distribution of damp straw on the soilsurface may be more even than that of drystraw.

Generally, if the straw needs choppingto avoid the no-tillage openers blocking,this reflects inadequate performance on thepart of the openers.

CHAFF. Another area of concern is the tail-ings or chaff. With some openers, this thickmat of fine material is more troublesomethan thick straw. Fortunately, in recogni-tion of this, many combine harvesters nowoffer chaff spreaders (or tailings spreaders)as well as straw choppers or spreaders (seeFig. 10.2).

Most straw choppers/spreaders can beadjusted to produce longer or shorter cutsand to spread the residues different dis-tances through adjustments of the deflec-tor, the vertical positions of the knives andthe speed of the chopper (Siqueira andCasão, 2004).

Some modern straw choppers useimproved cutting principles and blowersupport for spreading. For example, augertypes can be applied to both straw andchaff with spreading widths up to 10 m ineither direction without visible separationof different fractions (Lücke and vonHörsten, 2004).

SPREADING AFTER HARVEST. There are limi-ted residue management options avail-able where it is not possible to spreadthe residue with the combine harvester.Re-spreading of the residues evenly afterharvest has been only partially successfulbecause most straw is light and fluffy, mak-ing it difficult to throw or blow any dis-tance. One way of handling the situationafter harvesting is to pass the materialthrough a large fan or forage harvester andblow it as high into the air as possible on amildly windy day. In this manner the windwill spread it reasonably evenly, but itrequires a tractor with cab and good air fil-tration system or an operator who can tol-erate dusty conditions. Variations on thishave been attached to combine harvestersto create ‘straw storms’.

Another way is to use straw harrows,which consist of feely rotating angledspikes that are pulled at an angle and flickthe residues more evenly across the field.


They also double as a convenient way todisturb weeds seeds and induce them togerminate so they can be killed with a her-bicide before drilling the next crop (referredto as ‘chitting’ in Europe).

Small-scale no-tillage

The killing of cover crops on a smallscale is not as dominated by herbicidesas is the case for large-scale no-tillage.


Fig. 10.2. A straw and chaff (tailings) spreader on a combine harvester. Note the dust associatedwith spreading chaff.

Fig. 10.3. A pair of simple beater-type straw spreaders on the rear of a combine harvester.No attempt is made to spread chaff (tailings) with such a device.

Mechanical destruction is frequently used,or a combination of mechanical and chemi-cal methods. Mechanical destruction isfavoured because it results in lower repeti-tive cash outlays and less exposure by smallfarmers and their families to chemicals,although chemicals such as glyphosatehave a high level of safety associated withtheir use. But other herbicides (e.g. paraquat)are less safe and more difficult for farmersoperating on small fields to take properprotective measures against than in largeroperations, where fully enclosed vehiclecabs with filtered air supplies are common.Mechanical methods for cover-crop handlingin small-scale agriculture are therefore beingwidely promoted.

Mechanical destruction of growingplants is achieved by slashing, chopping,

crushing, spreading or bending the plants.Each method is suited to different condi-tions and results in different amounts ofplant material being left on the soil surface.

Manual slashing

Manual slashing is a very labour-intensiveoperation. Schimitz et al. (1991) reportedthat labour requirements of 70 man-days/hafor manual slashing have been measuredwhen managing a 3-year-old grass-residuefield yielding 10 t/ha dry matter.

Knife roller

Knife rollers are amongst the more usefulresidue-management tools to achieve evenlydistributed plant material on the soil surface.Figures 10.4, 10.5 and 10.6 show examples of


Fig. 10.4. Side view of a knife roller: (1) frame; (2) bearings; (3) transport wheel; (4) protectionstructure; (5) shaft (from Araújo, 1993).

Fig. 10.5. Animal-drawn knife rollers: (left) with full-width knives and (right) with short knives.

typical knife rollers. They have the advan-tage of allowing non-chemical organicproduction methods to be combined withno-tillage. For example, such implementsare in common use for no-tilled organicsoybeans in southern Brazil (Bernardi andLazaretti, 2004) and are available for bothanimal and tractor power.

Knife rollers have flat metal knivesmounted on a roller with a frame for sup-port, wheels for transport and a protectivestructure. The knives are mounted onthe roller in various patterns, most com-monly perpendicular to the direction oftravel. The effect of the knives is to bend,crush and chop off plant material. Theireffectiveness depends upon the width,diameter and weight of the roller, thenumber, height, mounting angle and sharp-ness of the knives, speed of operationand the fibre and moisture content of theplants (Schimitz et al., 1991; Araújo et al.,1993).

Rollers are constructed from eithersteel or wood. Steel rollers are often filledwith sand, so that their weight can beadjusted according to the condition of the

plant material and the desired result ofchopping, crushing or bending. But onslopes the sand can move to one side ofthe roller and affect the evenness of perfor-mance and stability. Monegat (1991) recom-mended roller widths between 1 and 1.2 mas a compromise between stability on hill-sides and an ability to stay in contact withirregular surfaces.

Knives may be the same width as theroller (Fig. 10.5 – left) or in short sections(Fig. 10.5 – right). Shorter sections increasethe pressure exerted as each knife impactsthe ground and spreads the impact forcesmore evenly, which is important for draughtanimals in particular. For a given diameterof roller, the effectiveness decreases as thenumber of the knives increases because thepressure on each knife is reduced (Schimitzet al., 1991). For the best cutting action, theknives should be perpendicular (i.e. notangled) to the surface of the roller (Siqueiraand Araújo, 1999).

Tables 10.1 and 10.2 show recommen-dations for the construction of knife rollersfor draught animals and tractors, respec-tively (Araújo, 1993).


Fig. 10.6. A tractor-pulled knife roller operating in oats.

The design, construction and opera-tion of knife rollers must also take safetyconsiderations into account. When workingon slopes, it is advisable to use a fixedshaft instead of chains, so that the shaft willwork as a brake for the roller. Other consi-derations are manoeuvrability, includingreversing (Schimitz et al., 1991), and theuse of protective shields. Figure 10.7 showsa protective shield, which is important toboth the draught animal and the operator.

The force required to pull a knife rollerin black oats at the milky seed stage (sownat a density of 100 kg/ha) was measured atapproximately 3430 N (350 kgf) per metreof width (Araújo, 1993).

Time requirements for handling blackoats with a knife roller are about 3 h/ha foranimal-drawn and 0.9 h/ha for tractor-pulled (Fundação ABC, 1993; Ribeiro et al.,1993), although Schimitz et al. (1991)reported requirements as high as 6 days/hawith animal-drawn units.

The crushing action of knife rollersinterrupts the flow of sap through the plant,which will kill many annual plants ifthe timing is correct (see Fig. 10.8). In thisregard, it is best if the cover crop is uniformand rolling is undertaken at the beginningof the reproductive stage, when seeds arenot yet viable. This is at full flowering forleguminous species and at the milky stagefor cereals (Calegari, 1990). In some envi-ronments, such as sub-Saharan Africa, it isdesirable that the cover crop remains greenas long as possible to avoid burning duringthe dry season. In this situation, a kniferoller should be used at the beginning of therainy season, prior to planting.

Different methods of cover-crop resi-due handling will result in different ratesof biomass decomposition. Araújo andRodrigues (2000) compared the decomposi-tion rates of black oats (Avena strigosa) as afunction of mechanical treatment. Theyfound that after 68 days the residues


RollerDiameter

(cm)Height of

knives (cm)Number of

knivesMaterial Density (kgf/m3)

Eucalyptus wood 1040 60 5 510 615 6

Steel + sand 2000 40 10 460 5 10

10 10

Table 10.1. Recommendations for the construction of animal-drawn knife rollers(1 m wide) operating at 1 m/s (3.6 km/h) (from Araújo, 1993).

RollerSpeed,

m/s (km/h)Diameter

(cm)Height of

knives (cm)Number of

knivesMaterial Density (kgf/m3)

Eucalyptus wood 1040 2 (7.2) 40 5 410 415 6

Steel + sand 1500 2 (7.2) 30 15 123 (10.8) 25 8 4

Table 10.2. Recommendations for the construction of tractor-mounted knife rollers (1 m wide)(from Araújo, 1993).

remaining in relation to the initial amountwere 59% for a knife roller, 48% for a flailmower and 39% for herbicide application.A similar study carried out by Gamero et al.

(1997) indicated that after 75 days theamount of black oat dry matter was 68% fora knife roller and 48% for a flail mower.The authors also found a lower weed


Fig. 10.7. A protective structure for the draught animal and operator alike.

Fig. 10.8. Black oats killed with a knife roller.

population when the knife roller was usedcompared with a flail mower.

Yano and Mello (2000) evaluated thedistribution of various cut lengths of pigeonpeas (Cajanus cajan) as a result of differentmechanical treatments of cover-crop resi-dues. A flail mower resulted in 70% of thecut lengths being 100 mm or less comparedwith 45% for a rotary mower and 22% for aknife roller.

Another advantage of mechanical treat-ment of heavy cover-crop residues is that,if the crop is sprayed with herbicidebefore mechanical treatment, the maincanopy may prevent the herbicide getting tolower-growing weeds beneath the canopy.Alternatively, the cover crop can be treatedwith a knife roller and then sprayed, pro-vided that sufficient time is allowed for theweeds to appear through the bent-overcanopy so that they can be targeted by thespray. This option is best suited to heavycover crops. Spraying options are mosteffective where the cover crop is not heavy.

Can a knife roller substitute for herbicides?

Knife rollers are not designed for weed con-trol, even though the mulch they producemay contribute to weed suppression. Butone purpose of growing a cover crop is topre-suppress the weeds with a dominantmonoculture, which can itself be killed by aknife roller at the appropriate time prior toplanting the main cash crop. If the covercrop is vigorous and the weed incidence islow, a knife roller alone may be sufficient toprepare the field. In Tanzania, for example,Schimitz et al. (1991) reported that a kniferoller had been effective for weed control ingrass up to 3 m high after a fallow. The fac-tors that make such a totally mechanicaloption viable are:

1. Perform the planting operation as closeas possible to the destruction of the covercrop.2. Use planters with minimal slot distur-bance.3. For planters that create substantial slotdisturbance, plant before the cover crop istreated so that the residue will cover theslot opened by the planter.

Management of Residues byOpeners, Drills and Planters:

Micro-management of Crop Residues

Micro-management refers to how the resi-dues are handled by the openers themselvesand the role the residues play in the openerfunctions. It is a sad fact that the designersof many no-tillage openers still treatresidues as an unwanted nuisance. Whilerecognizing the macro-value of residues tono-tillage, these designers often show littlesign of recognizing the micro-value of resi-dues for opener function and seeding res-ults. As explained in Chapter 5, the highlydesirable Class IV slot cover is only possibleif the ground is residue-covered in the firstplace and then only if the openers are desig-ned in such a way as to retain that residueover the slot itself.

Opener handling of residues

Chopping (strip tillage)

All power till openers chop the surface resi-dues with the soil. There is no practical wayto avoid their doing this. Where the surfaceresidues consist of undecomposed accumu-lated organic matter in colder climates,such incorporation may be of benefit, but,in all other circumstances, some of the valueof no-tillage is lost when the residues areincorporated, even on a strip scale. Besides,strip tillage itself defeats some of the objec-tives of true no-tillage in the planting zone.

Sweeping aside

Hoe, knife, shank, angled flat disc andangled dished disc openers all push soiland some of the surface residues aside asthey proceed through the soil. Disc openersmay also push some of the residue into thesoil to form hairpins in the seeding slot.With hoe- and shank-type openers, if theresidue is reasonably thick and of somelength, it will accumulate on the shank ofthe opener rather than be pushed aside,causing opener blockages. Angled disc-typeopeners do not have this problem, but, in


either case, residue that is pushed asidewill have negligible influence on the micro-environment within the slot that is beingcreated.

On the other hand, because the residueis usually heaped to one or both sides of theslot (Fig. 10.9), careful choice and operationof a subsequent covering device may suc-ceed in collecting some of this residue andguiding it back into the slot zones (Class IIIcover), although it is then likely to be mixedwith soil. This process will occur if the soilremains dry and friable. If the soil becomesdamp, the covering device is likely to createa smearing effect and the value of the resi-due will be lost by becoming smeared intothe soil alongside but not over the slot.

Pushing down or through

All discs, to a greater or lesser extent, pushdown through surface residues. Double ortriple disc openers mostly push down,whereas angled discs sweep aside as well aspush through. The problem with pushingdown is that, because it is impossible to cutall of the residue all of the time, a propor-tion of residue is doubled over and pushed(tucked) down into the slot in the form of a‘hairpin’.

The tendencies of different discs tohairpin depend on several factors:

1. Sharpness of the disc. Sharper discs aremore likely to cut than to hairpin, but it isimpossible to keep discs sharp all of thetime.2. Brittleness of the straw. Brittle strawis more likely to break than fibrous straw.Brittleness itself is a function of cropspecies, dampness and stage of decay.3. Softness of the soil. Firm soil will assistshearing by a disc (the anvil effect) morethan soft soil. More hairpinning will occurin soft soils.4. Speed. Faster operating speeds gener-ally reduce the incidence of hairpinning.The straw has less time to bend because ofits inertia and is therefore more likely to becut or broken.5. The presence of chaff and tailings.Where straw is lying over a mat of finetailings, as is often the case, the tailingsprovide a soft mat beneath the straw, whichacts like a soft soil and encourages hair-pinning. Worse, a portion of the tailingsthemselves may be pushed down into theslot, where they make the hairpinning pro-blem worse by coming into contact with theseed.


Fig. 10.9. Residue swept to one side of a no-tillage slot.

6. Diameter of the disc. Smaller-diameterdiscs, because of their reduced footprintarea, will put more pressure on the residuethan larger discs and are therefore morelikely to cut the residue than to hairpin it.But small discs are also more likely tosledge, since larger discs have a flatter cut-ting angle at the soil surface.7. Disc design. Wavy-edged discs, becauseof their self-sharpening tendencies, will cutbetter than plain discs. Notched discs donot remain any sharper than plain discs butcut more residue because of the slicingaction of the sides of the ‘points’ and theincreased footprint pressure of the ‘points’.

Folding up from beneath

The disc version of winged openers mani-pulates the surface residues by first pushinga notched disc down through the residuesand then using the lateral wings of the sideblades to fold the residue and soil upwardsand outwards while the seed and fertilizerare deposited in the slot. A pair of followingpress/gauge wheels then fold the materialback over the seeded slot. The end result isa horizontal slot covered with soil andresidue (Class IV cover) in much the samelayering as the soil and residues had beenbefore seeding.

The limited amount of vertical hair-pinning caused by the notched disc is oflittle consequence because, unlike with allother no-tillage openers, the seed is placedto one side of the central disc slot away fromany hairpins. In this way the seed is effec-tively separated from any hairpinned mate-rial and instead benefits from the presence ofresidues over the slot (see Chapter 5).

Row cleaners

One method of assisting no-tillage openersto operate in residues is to clean the row ofresidues immediately ahead of the openers.The devices designed to achieve thisare known as ‘row cleaners’ or ‘residuemanagers’.

With small-scale no-tillage, it is oftennot feasible to use disc openers because of

the weight required to push them into theground compared with tine- or shank-typeopeners. ‘Row cleaners’ require little addi-tional weight since most of them only workon the surface of the ground. But in suchsituations they may make the differencebetween being able to undertake no-tillageor not.

With large-scale no-tillage, whereweight is less of a problem, ‘row cleaners’are often used in springtime to remove resi-dues from over the immediate row area soas to allow sunlight to warm the soil morequickly after a cold (and often freezing)winter.

Most ‘row cleaners’ consist of spikedrotating wheels, notched discs or rakes setat an angle to the direction of travel andoperating ahead of the openers. The spikesjust touch the ground, which causes them torotate much like a finger-wheel rake forturning hay. In the process, they sweepthe residues to one side or both sides whileat the same time moving as little soil aspossible.

With tougher residues, such as maizestover, two wheels may be set at oppositeangles to one another and the spikes aresynchronized at their fronts to reduce theside force on the whole device by sweepingresidues to both sides of the row rather thanto one side. Figure 10.10 shows a ‘rowcleaner’ consisting of a pair of synchronizedspiked wheels. Figure 10.11 shows unsyn-chronized notched discs designed to pushresidues aside.

Chopping of straw into short lengths

There is a critical length for most straws,above which they will bend and thus wraparound approaching rigid tools (e.g. tines).Chopping all straw into relatively shortlengths allows short lengths to fall awayfrom rigid tools rather than wrap aroundthem. Other objectives for chopping strawtrace their origins to tillage by making thestraw easier to incorporate into the soil andenhancing the decomposition process.

To drill into maize stover with shank-type openers, Green and Eliason (1999)


recommended that the cut lengths shouldbe no longer than the shank spacing of theopeners.

Chopped straw may also settle downon to the ground more easily and closelythan long straw and may therefore provide amore effective mulch. On the other hand, aneffective no-tillage opener will ensure that

even long straw is replaced on the groundafter its passage (see Fig. 10.1).

One of the most effective ways to obtainchopped straw is to fit a straw-chopper tothe rear of a combine harvester. Such devi-ces are not readily favoured by operators,however, because they consume consider-able power and are yet another component


Fig. 10.10. A pair of synchronized star wheels (row cleaners) for pushing residues aside.

Fig. 10.11. A pair of angled, notched, disc row cleaners designed to push residues to either sideof the row ahead of the opener.

that must be adjusted correctly on analready complicated machine. In any case,they seldom chop every single straw, withthe result that the long straws that persistmay eventually accumulate on openers notequipped to handle them.

Other methods produce chopped strawwith a separate chopper. Some of thesemachines incorporate the straw into the soilas they chop it, which departs from trueno-tillage because of the general soil distur-bance. Others simply chop it and redistri-bute it back on the ground again.

Yet a third approach is ‘vertical mulch-ing’, where the straw is chopped and thenblown into a vertical slit created simulta-neously in the soil by a large soil opener onthe machine (Hyde et al., 1989; Saxton,1990). The result is a series of vertical slitsfilled with straw, thus solving a disposalproblem as well as providing an entry zonefor water infiltration.

Because no general tillage takes place,vertical mulching complements no-tillage,but the absence of a horizontal surfacemulch reduces the options for maximizingthe benefits of true no-tillage. Figure 10.12

shows a prototype vertical mulchingmachine in the USA.

Random cutting of straw in place

The most obvious way of handling long sur-face residues in place is to cut a pathwaythrough them with some form of sharp tool.Generally, discs are the most commonlyused device but other forms of tool haveincluded rigid knives and powered rotatingblades.

Rigid knives

These have been known to work for shortperiods only if their cutting edges remainsmooth and very sharp, but extended useis impossible because of random damageand dulling by stones and soil abrasion.Figure 10.13 shows a knife-edge opener wherethe sweeping action of a tapered front wascombined with a sharp edge in an attemptto slide past and/or cut residues. The slid-ing action was unsuccessful because smallimperfections soon developed in the other-wise smooth edge from contact with stones,


Fig. 10.12. A prototype vertical mulching machine.

resulting in straw catching as it slid downthe face. This led to deterioration of thecutting effect and blockage.

Rotating blades

These, such as on power till openers, arenot always successful either. To be mosteffective as a soil pulverizer, power tillblades are usually L-shaped. The horizontalportion of the L is important because it ele-vates and accelerates the soil upwards andthrows it against the surrounding cowling,breaking it into smaller particles. Unfortu-nately, the horizontal L is also a perfectcatch for wrapping of residue. As a conse-quence, backward-facing C-shaped bladesare often used in residue situations becausethey allow the residue to be brushed off asthey rotate. C-shaped blades, however, donot have a truly horizontal portion to theblade and the trade-off is that they are lesseffective as a soil pulverizer.

Discs

These can be most effective for breakingthrough or slicing straw, but, as explainedpreviously, their action is highly dependenton the firmness of the background soilagainst which they must shear the straw andthe brittleness of the straw itself. No matter

what design of disc is used, no disc will cutall of the residue all of the time.

Cutting damp fibrous straw is particu-larly difficult. Cutting it against a soft soilbackground is even more so. One variationthat has been tried is to power the disc sothat it rotates faster than its peripheral for-ward speed. The aim is to create a slicingaction as the disc presses the residue aga-inst the ground. Figure 10.14 shows a proto-type powered disc. A further variation is tocause the disc to vibrate as it rotates byusing a power drive on the disc hub. Both ofthe powered disc options, however, are dis-advantaged by the cost and complexity ofproviding individual drives to a multipli-city of openers together with the interrup-tion to residue flow between adjacentopeners brought about by the bulkiness ofsuch drives in the vicinity of the disc hubs.Besides, some unpowered designs havemanaged to achieve comparable results at afraction of the cost.

The most appropriate diameter of discsfor handling agricultural residues is alwaysa matter for debate. Small-diameter discshave a smaller footprint and are thereforeeasier to push into the soil than larger discs.For this reason they also cut residues betterthan larger discs. However, the closer thedisc axle is to the ground, the easier it is tostop the disc rotation (stall) when the


Fig. 10.13. A prototype knife-edge opener designed to sweep and cut residue (from Baker et al., 1979a).

thickness of residue exceeds the height ofthe disc axle. Also, a large-diameter dischas a flatter angle of approach between theleading edge of the disc and the ground,making it less likely to push (‘bulldoze’)the residue ahead of it and more likely totrap it in the ‘pinch zone’ and then roll overor cut through it. The most appropriate discsize is a compromise between getting suffi-cient penetration and avoiding disc stall.The most appropriate disc diameters usedin agriculture seem to be between 450 mm(18 inches) and 560 mm (22 inches) and areused extensively on no-tillage openers.

DISC DESIGNS. Another debatable aspect isthe design of the disc. Essentially discs canbe of five designs.

PLAIN FLAT DISCS (FIG. 10.15). These are used onmore no-tillage openers than any other form.They are the least expensive option to manu-facture and have a sharpened edge, althoughexperiments have shown that sharpening ofthe edge is not altogether necessary in allsituations. They have the least traction of allalternate designs to ensure turning, whichis not a disadvantage when used in short

standing residue, but can be a disadvantagein long lying residue. When sharpened, theiraction is intended to be one of cutting theresidue, but as the edge becomes dull theytend to trample rather than cut some of theresidue. As such, they have a strong ten-dency to hairpin when configured as doublediscs, angled flat discs or a single verticalpre-disc.

One redeeming feature of flat discs isthat they are able to handle large woodysticks better than most other discs. Thesmooth edge tends to push such sticksaway, whereas other disc types may sliceinto and catch on the sticks without actu-ally cutting them, which then prevents thedisc from rotating.

WAVY-EDGED ‘FLAT’ DISCS (FIG. 10.16). T h e s eare designed to gain maximum traction byinterrupting the smooth sides of plain discswith a series of ripples. These ripples aredesigned to ‘gear’ the disc to the soil, ensur-ing the disc will rotate in even the heaviestlying residue. For reasons that are not wellunderstood, the ripples also result in thediscs being self-sharpening. As such, theiraction is more one of cutting than with


Fig. 10.14. A powered disc opener designed to rotate faster than the speed of travel through the soil.

plain discs, making them somewhat lesslikely to hairpin. Penetration forces aresimilar to those of plain flat discs. Althoughwavy-edged discs are sharper than plaindiscs, making penetration easier, theirwaviness actually increases their footprintarea and increases rather than decreasesrequired penetration forces.

Their self-sharpening tendency alsoresults in relatively high wear rates. The rip-ples also become collection zones for stickysoils, interrupting their effective function-ing. Their most common use is as a singlepre-disc ahead of rigid components suchas hoe openers. They may also have thefunction of loosening the soil ahead ofthe double disc openers so as to counter thecompacting tendencies of such discs. Theyare sometimes known as ‘turbo-discs’ for thisreason.

NOTCHED, OR SCALLOPED, FLAT DISCS (FIGS 4.27

AND 8.10). These have semicircular notchescut from their peripheries, leaving about50% of the periphery as ‘points’ (actuallythey are not points, as such, but simply aportion of the edge of the original plain discleft unaltered) and 50% as gullets. Theobjective is to reduce the footprint area onthe ground, which aids penetration whencompared with plain discs, and to ‘gear’ thedisc to the soil to assist traction. The‘points’ of the disc penetrate the soil firstand present approximately half the foot-print area of a plain disc of the same diame-ter, although the gullet zones of the notchesalso eventually penetrate the soil to a


Fig. 10.15. A plain flat disc.

Fig. 10.16. A wavy-edged ‘flat’ disc.

shallower depth. The net effect, therefore, iseasier penetration than with plain or wavy-edged discs.

Furthermore, as the ‘points’ penetratethe soil, they change their angle of attackslightly as they progress further around therolling circle. One important effect of this isthat the near-vertical edges from the ‘points’to the gullets slide into the soil at a range ofangles and thus produce a slicing actionagainst a portion of the residue. This cutsthat portion of the residue more effectivelythan when it is simply pressed on fromabove, as with all other disc types.

DISHED, OR CONCAVE, DISCS (SEE FIGS 4.10 AND

4.11). These are nearly always angled to thedirection of travel. As such, the frictionagainst them is increased compared withplain discs travelling straight ahead. Theytherefore have good traction and are lesslikely to stall in heavy, flat residue thanplain discs, but have all of the other attri-butes of plain discs, including power require-ments and a tendency to hairpin residue.

One of the difficulties with all angleddiscs is delivery of the seed to the U-shapedslot created behind the lee (back) side of thedisc. Usually, a boot is positioned close tothe disc beneath the ground, but the gapbetween this boot and the disc is a collec-tion point for random residue when used inno-tillage. Unless this gap is continuallyadjusted, blockage soon results.

One way of solving the problem is tospring-load the boot so that it rubs on thedisc at this point. An advantage of disheddiscs is that their curvature provides con-siderable strength, allowing the discs to bemade from thinner steel than is common forflat discs of any nature. This in turn hasclear advantages as far as penetration andsharpness are concerned. For example, a3 mm thick disc will require only 60% ofthe penetration force required for a 5 mmdisc, although with dished discs this advan-tage is offset by the resistance to penetrationof the convex (back) side of the disc.

NOTCHED DISHED DISCS. These combine theattributes of dished discs with those ofnotched discs. Although such designs have

been used extensively in heavy residues forcultivating new land from native scrub andfelled bush, there are no known no-tillageopeners that use the principle in a morerefined role. Similarly, there are no knownno-tillage openers that use a wavy-edgeddished disc.

Realigning residue on the ground

A novel approach to avoiding hairpinningwith plain discs has been to use realigningfingers ahead of the discs. One drill of USorigin had vertical spring tines designed toagitate and jostle the lying straw so as tocause each straw to lie end-to-end with theapproaching disc. This was intended toavoid the tendency of discs to pass acrossstraws, the starting point of all hairpinning.The tangled nature of many straw residues,however, ensured that this approach wasnever wholly successful.

Flicking

Another novel approach to the operation ofsingle plain or wavy-edged discs ahead ofrigid tines has been to attempt to flick offany residue that collects on the leadingfaces of the tines, since a single disc operat-ing ahead of a rigid tine will not allow thattine to pass cleanly through lying residueall of the time. Clean-cutting ahead of a tinecan sometimes be achieved with short cutstraw and often with anchored residue, butlong and lying residues are another pro-blem. Regardless of how well the disc cutsthe residue, there will always be some strawremaining uncut and passing the disc tocollect on (or wrap around) the tine. Evenwhen the disc is positioned close to, or eventouching, the front edge of the tine, residuewill collect on this front edge. Besides, it ismost difficult to ensure that a disc remainspermanently touching a tine when both aresubject to normal wear.

Scottish designers created a self-flickingdevice (Fig. 10.17). Two spring-loaded fin-gers were attached to the hub of the disc insuch a way that, as the disc rotated, the fin-gers became tensioned against the ground.At a certain point in the rotation, each of the


fingers was suddenly released from theground, whereupon it flicked upwards athigh speed past the front edge of the tineand dislodged residue that had collectedthere. Similar devices have been used bythe authors, but these were attached toseparate wheels that ran alongside the tine.

While the flicking devices worked inlight and dry residues, heavy residues,especially when wet, tended to interferewith the flicking action. Failure to dislodgeall of the straw from the tine with any oneflick became a cumulative problem, leadingeventually to total blockage of the tine.

Treading on residues

To overcome the ‘hit-and-miss’ nature offlicking, recourse to more predictable tread-ing has been tried with mixed success. Toachieve this, wheels are located alongsidethe tines so that they continuously roll on toone side of the residues wrapped around theleading edges of the tines. The intention is tocause the residue to be pulled off to one side.Even though they may achieve this objec-tive, the presence of the wheels themselvesgenerally interferes with free passage ofother lying residue between the openers.

Self-clearance by free fall of residuesoff tines

Provided that sufficient space can be pro-vided around each tine, most accumulatedresidue on the front of tines will eventuallyfall off, simply as a function of its own accu-mulated weight. Unfortunately, this doesnot always occur, especially with wet resi-due, necessitating irregular stops to clearwhat can become a sizeable mound of accu-mulated debris. Not only do these moundsof debris on the ground interfere with sub-sequent operations, their clearing is invari-ably a source of annoyance for operators atseeding time.

The most serious disadvantage of thisprinciple, however, is the spatial demandson the drill required for clearance betweenindividual tines. Drills of this type are lim-ited to relatively wide row spacing (250 mmor greater) and the extended area occupiedby the tines interferes with accurate surfacefollowing by individual tines and seeddelivery.

Unfortunately, there are some design-ers and operators who are willing to widenthe row spacing of their drills beyond whatis agronomically desirable, expressly to


Fig. 10.17. A flicking device designed to self-clean stationary tines.

provide more clearance for residue. But, ifanything, no-tillage, by conserving soilmoisture, should allow closer row spacingto be used than for tilled soils, with resul-tant higher potential crop yields. An exam-ple of a drill with wide row spacing isshown in Fig. 4.15.

Combining rotating and non-rotatingcomponents

An important new residue-handling prin-ciple was designed in 1979 (Baker et al.,1979b). This involved rubbing the entireleading edge of a rigid component (such as atine, shank or blade) against the verticalface of a revolving flat disc. For the rubbingaction to be self-adjusting (so as to accom-modate wear of components), the stationarycomponent needs to be wedge-shaped sothat it presents a sharp leading edge againstthe disc but tapers outwards away from thedisc towards the rear. In this way it is heldagainst the disc by lateral soil forces as thesoil flows past. If two such rubbing compo-nents are positioned one on either side ofthe disc, all of the soil forces become sym-metrical, thus avoiding undesirable side-loading on the discs and their bearings.

The design is illustrated in Figs 4.27and 8.2. In the design of the disc version ofa winged opener, an opportunity was takento deliver the seed to the base of the slot bydirecting it to fall between one such station-ary blade and the corresponding face of thedisc. By directing fertilizer in an identicalmanner down the other side of the disc, aneffective method of horizontal separation ofseed and fertilizer in the slot was achieved(see Chapter 9).

There are four important principlesinvolved in the rubbing action:

1. The intimate contact between the sta-tionary blades and the revolving disc allowsany residue passing the disc to also pass thewhole assembly, thus making openersinvolving a rigid tine or blade at least asable to handle residues as a pure discopener. This combination of disc and rigidcomponent has achieved a remarkableresidue-handling ability. This is important

because all pure disc openers compromiseat least some of the slot-shape functions toachieve residue handling. The best micro-environments for seeds in no-tillage aregenerally created by horizontal slots formedby a rigid tine (see Chapter 4).2. The contact between the rigid compo-nent and the revolving disc is lubricated bya thin film of soil (Brown, 1982). Thismeans that the rigid component can bemanufactured from material that is muchharder (and therefore more wear-resistant)than the disc, without cutting into the faceof the disc to any appreciable extent.3. There needs to be a small amount ofpre-load between the rigid component andthe disc, even though, in operation, the soilcontinually presses the two together. As thedevice enters the soil, and before the soilforces have pressed the two componentstogether, a single piece of straw may occa-sionally become wedged between the twocomponents if there is no pre-load betweenthem. This residue will hold them fraction-ally apart for a short period. Other pieces ofstraw are then likely to enter the gap, withthe result that blockage eventually occurs.4. There is a disc-braking effect on thedisc from the rubbing of the rigid compo-nents. For this reason, traction of the discmust be maximized. Notched flat discs aremost commonly used for this type ofopener, although plain flat discs have alsobeen used. Wavy-edged discs are unsuitablebecause a flat surface is necessary for theblade and disc contact to be effective.

Wet versus dry straw

The action of most openers is affected bythe brittleness of the straw, which is itself afunction of dampness or dryness as well asother physical attributes, such as fibre con-tent. After spraying or physical killing ofgrowing material, the residue will losewater and become increasingly ‘stringy’.Sometimes best results will come fromwaiting 10–15 days so that the residues willdry completely and be more easily cut bydiscs. This also allows root material tobegin decaying, which makes the soil more


crumbly and usually leads to better slot for-mation. In other situations, drilling mightbe undertaken before or immediately afterthe residues are killed, provided that com-petition for soil water does not take placebetween the crop and the cover crop beforethe latter is killed.

On the other hand, harvested straw willnormally be at its most brittle shortly afterharvest. Discs are most effective when operat-ing on brittle straw in warm dry weather andwhen the background soil is firm. Standingresidue often becomes increasingly brittle asit ‘ages’ over winter, making spring no-tillageseeding more easily accomplished.

The case for and against scrapers

A natural reaction to problems of accumula-tion of sticky soil and/or residues on rotatingcomponents of openers is to strategicallyplace scrapers and deflectors to remove theunwanted material. Such scrapers anddeflectors can range from those designedto deflect residue from ever coming nearthe opener (e.g. Fig. 10.18) to those designedto protect a specific part of the opener. Fig-ure 10.19 shows a circular scraper designed

in Canada to remove soil from the inside ofdouble disc openers.

However, most scrapers create moreproblems than they solve. Often, they sim-ply present yet another point on whichunwanted material can accumulate. Whilethey may remove the original problem frominterfering with a critical part of the opener,they seldom result in a total cure from accu-mulated debris. With the disc version ofwinged openers, both the side blades andthe disc-cleaning scrapers (Fig. 10.20) oper-ate beneath the ground and are thereforeself-cleaning.

Clearance between openers

Even if individual openers are designed tofreely handle surface residues withoutblockage, arranging multiples of such open-ers to handle residues in narrow rows isoften a difficult problem in its own right.The main principles generally involve lat-eral spacing. To provide sufficient lateralspace between adjacent openers for resi-dues to pass through, the openers need tohave a minimum of 250 mm clearance.Even then, the actions of different openers


Fig. 10.18. Residue deflectors on a maize planter.

may interfere with their neighbours andtherefore require greater clearance.

For example, while 250 mm might besufficient for openers that create minimal

disturbance of the soil (e.g. double disc),greater distances may be required for thosethat either throw the soil (e.g. angled flatdiscs and angled dished discs), push itaside (hoe) or fold it back (winged). In suchcircumstances, each alternate opener needsat least to be offset forwards or rearwards ofits neighbours so as to give diagonal as wellas lateral clearance (referred to as stagger-ing). An alternative to staggering is tocreate greater lateral distances betweenopeners, but this usually means increasingrow spacing, which may be agronomicallyundesirable.

The problem is further complicated bythe greater downforces required for openerpenetration under no-tillage, which is usu-ally applied to the drag arm connecting theopener to the drill frame. The strengthrequired of drag arms to transmit these largedownforces discourages the use of alter-nately long and short drag arms to createstaggering, especially if such drag arms arealso of the parallelogram type with multiplepivots. In contrast, long and short dragarms are common on drills designed fortilled soils because the forces are small incomparison.

One way of overcoming this problemhas been to operate the openers from twoseparate tool bars, one in front of the other.


Fig. 10.19. Circular scrapers for double discopeners.

Fig. 10.20. Underground scrapers on the disc version of a winged no-tillage opener.

This allows the openers on each tool bar tobe spaced twice the distance apart as therow spacing. If used, it also allows thelonger drag arms for a stagger arrangementto be of robust construction without inter-fering unduly with the between-openerspacing.

The problem of lateral spacing largelyapplies to drills and not to planters, becausedrills may have row spacing as close as75 mm, while planters seldom require rowspacing closer than 375 mm.

Summary of Residue Handling

1. The most serious physical problemrelating to the handling of surface residuesis mechanical blockage.2. The most serious biological problemrelating to the handling of surface residuesis hairpinning (or tucking) of residues intothe seed slot.3. Macro (whole field)-management ofsurface residues starts with the combine har-vester and is important for soil and resourcemanagement of no-tillage in general.4. Macro-management should aim at evenspreading of both straw and tailings over theentire field. Chopping of straw is optional.5. Micro-management of surface resi-dues is a function of no-tillage openers andis important for controlling the micro-environment of the seed slots.6. Micro-management should strive toreturn the residue over, but not into, theseed slot (Class IV cover).7. Large-scale no-tillage almost invariablyinvolves the use of herbicides to kill exist-ing vegetation.8. Small-scale no-tillage relies predomi-nantly on mechanical or manual residuemanagement.9. Knife rollers are a useful tool for man-agement of residues in small-scale no-tillage.10. Residue can be classified as ‘shortroot-anchored’; ‘tall root-anchored’; ‘shortflat’; or ‘long flat’.11. ‘Long flat’ residue is the most difficultto handle.

12. Relying solely on the cutting of resi-dues is seldom effective. No device will cutall of the residue all of the time.13. Most pure disc-type openers handleresidues well, but also tend to hairpin(or tuck) straw into the slot, which is unde-sirable.14. Most rigid component openers (hoe- orshank-type) handle residues poorly withregard to blockage but do not hairpin.15. Most power till openers handle resi-dues poorly except when the blades areC-shaped.16. Wavy-edged and notched discs handleresidues better than plain discs.17. Small-diameter discs penetrate soil andresidues more easily than larger discs, butare more likely to form blockages in heavyresidues.18. Firm soils provide a better medium forresidue handling and cutting by openersthan soft soils, thus reducing hairpinning.19. Small no-tillage machines often havepoor performance by having tined openers(due to cost) but benefit from the manualattention that can be given to residue man-agement by operators.20. Wet soil and/or wet residue are moredifficult to handle than dry soil and/or dryresidue.21. Unless operating beneath the ground,most scrapers are of limited value becausethey accumulate residue on themselveswhile they are removing it from else-where.22. Vertical mulching consists of disposingof straw into deep vertical slits in the soil.23. Any rigid opener component, such as atine or shank, will accumulate residueregardless of the design or positioning of adisc ahead of it.24. Only when the leading edge of a rigidtine is forced to rub in intimate contact withthe side face of a revolving flat disc will atine/disc combination handle residues aswell as a disc alone.25. The minimum distance between adja-cent openers for self-clearance of residues isapproximately 250 mm, either laterally ordiagonally, or both.


11 Comparing Surface Disturbance andLow-disturbance Disc Openers

C. John Baker

The surface disturbance of soil and residuesoften represents the most visible difference

between no-tillage openers; yet the real effectsmay lie underground.

The passage of a seeding drill over ano-tilled field causes a wide variety of soiland residue disturbances, largely dependingon the opener design, soil condition andoperation speed. These disturbances arequite visible and yet the impacts on cropestablishment and subsequent yields mayonly become obvious in stress conditions.

In the first part of this chapter, werevisit the seeding principles of the previouschapters to relate the disturbance effects tothe effectiveness of common no-tillage slotshapes. In the second part, we compare thedesign features of common disc-type open-ers, since it is mainly disc openers that createminimum-disturbance slots.

Minimum versus Maximum SlotDisturbance – How Much Disturbance

Is Too Much?

The largest concern centres on openers thatcreate significantly different amounts of dis-turbance, such as a single, straight-runningdisc versus a broad hoe or chisel opener.These results are recognized as minimum

versus maximum opener disturbance drills.Minimum disturbance creates just enoughsoil movement for the seed insertion with asingle cut through the overlying residuewhile maximum disturbance moves a sig-nificant volume of soil to create a seed slotand allows the soil to fall or be moved backover the slot with the residue moved wellaway from the seed row.

Crop residues are the lifeblood ofno-tillage. Indeed, they are the lifeblood ofsustainable agriculture itself. In the past,debates about surface residues have mostlycentred on their macro-management: thepercentage of ground that is covered by resi-dues in relation to erosion control, surfacesealing, shading and the ability of machinesto physically handle them. Recent empha-sis has been to reduce the amount of residuedisturbance during drilling for the erosionprotection that greater amounts of groundcover offer.

Micro-management of residues centreson the influence that residues have on seed,seedling and plant performance in indivi-dual rows, all of which ultimately affectcrop yield.

One aspect relates to soil erosion. Theother to crop yield. Is one more importantthan the other?

Unless crop yield is maintained, fewwill undertake no-tillage and the soil erosion


benefits become irrelevant. Therefore it couldbe said that micro-management of surfaceresidues should be the first objective in anyno-tillage system. But, sadly, history showsthat that has seldom been the case.

Then again, minimum slot disturbancemeans different things to different people.For example, an allowable limit of 30% slotdisturbance means that the disturbed zonein 150 mm spaced wheat rows can only be45 mm wide – a difficult but achievableexpectation for many no-tillage openers.But 30% disturbance in rows of maize orcotton sown in 750 mm–1 m rows repre-sents 225–300 mm of disturbance – a muchmore generous objective.

So the development of no-tillage open-ers for wheat and other narrow-row cropsmay take a very different course from thatfor wide-row crops. But, since there is twiceas much wheat sown in the world as thenext most common crop, the constraints onopeners for narrow-row crops provides thegreatest challenge for machinery designers.

Minimum-disturbance no-tillage is cre-ated by openers that disturb the surface of theground as little as possible, retaining at least70% of the surface residues intact after theirpassage, with residues evenly distributedover the surface of the ground. Minimum-disturbance openers include double and tri-ple disc (so long as the soil is not sticky); thedisc version of winged openers; some nar-row knife openers operating in low-residueconditions; and some angled disc openersoperating at slow speeds on flat ground andin non-friable soils.

Maximum-disturbance no-tillage iscreated by openers that either burst the soilaside or deliberately till a strip at least 50 mmwide. Maximum-disturbance openers includemost hoe, shank and sweep types; angleddiscs operated at high speed and/or on hills;double or triple disc openers in sticky soils;dished disc type openers; and poweredtill-type openers.

Disturbance effects

No-tillage opener design has the biggestinfluence on the amount of slot disturbance

that occurs, and this in turn can have adirect influence on multiple factors directlyrelated to the effectiveness of no-tillageseeding. Each will be discussed using manyof the principles previously introduced, butmore specifically related to the amount ofvisual soil and residue disturbance as theseeding is accomplished.

Slot cover

In tilled seedbeds, it is relatively easy tocover the seeds with loose soil. Therefore,aiming to create localized tilled strips dur-ing no-tillage has been an obvious objectiveof some no-tillage machinery designers. Butno one has ever advanced a good biologicalreason for regularly tilling or disturbing thesoil in the slot zone other than to compen-sate for the inadequacies of the openers thatplace the seed.

Many low-disturbance no-tillage openerscut a vertical slot in the soil. Even thoughthis creates minimal surface disturbance(which is desirable), unless the soil is dryand crumbly at the time, closure of suchslots is difficult and is worst in damp and‘plastic’ soils. No-tillage slots that remainopen dry out and attract birds, insects andslugs, which may cause crop failures evenbefore the plants emerge from the ground.This problem has probably been responsi-ble for more crop failures in no-tillage thanany other single factor.

Covering problems can largely besolved while still retaining minimal resi-due disturbance by creating horizontal orinverted-T-shaped slots (winged openers).The seed is located on a horizontal soilshelf on one side of these slots and withadvanced designs fertilizer is banded on anidentical shelf on the other side. Horizontalflaps of soil with residue covering the soilare folded back to cover both. Even if thecentral slit dries and cracks open, as isinevitable in some untilled soils, neither theseed nor the fertilizer becomes exposed.

Viewed from the surface, inverted-T-shaped slots may appear similar to verticalV-shaped slots. Both are usually classifiedas minimal disturbance. The difference isbeneath the ground. Vertical V-shaped slots

160 C.J. Baker

may have compacted near-vertical sidewalls and get narrower towards their bases.It is often difficult to push a finger intothem. They usually provide class I or, at best,II cover. On the other hand, inverted-T-shaped slots are loosened beneath the sur-face, get wider with depth and are usuallyvery easy to push a finger into, providingClass IV cover.

In-slot micro-environment

Minimum slot disturbance does notalways equate with a beneficial slot micro-environment. But nor does maximum slotdisturbance. In fact, the best in-slot micro-environment that maximum-disturbanceslots can provide is seldom better than atilled soil, but may be better than poorlymade and covered V-shaped slots (Class Icover).

Within the various minimally disturbedslots, horizontal slots (inverted-T-shapedwith Class IV cover) create about as favour-able a micro-environment as possible bytrapping vapour-phase soil water in the slot(see Chapter 5). Seeds will germinate on theequilibrium relative humidity (RH) con-tained within the soil air, so long as this RHremains above 90%. Tilled soils seldom con-tain an equilibrium RH greater than 90%due to air exchange with the atmosphere,whereas untilled soils nearly always havean equilibrium RH between 99% and 100%.The problem is that unless the seed slot cre-ated in an untilled soil has sufficient cover-age to trap the air (which usually meansresidues overlying soil), the potentiallysuperior micro-environment in an untilledsoil will be lost and seeds must then rely ona slot micro-environment that is no betterthan a tilled soil.

Vertical V-shaped slots (Class I or IIcover) do not trap in-slot RH and are there-fore about the least tolerant of all no-tillageslots of dry conditions.

All slots that involve strip tillage ofsome nature (Class III cover) fall into themaximum-disturbance category. They arelikely to be more tolerant of adverse con-ditions than vertical V-shaped slots, simplyas a function of the friable soil within the

slot, but will still be inferior to horizontalinverted-T-shaped slots, which contain RHas well as liquid-phase water.

Slots created by angled discs fallbetween the extremes. As a general rule ofthumb, if a slot made by an angled discresults in minimal surface disturbance, itwill contain a better slot micro-environmentthan where such slots are more disturbed.

Carbon dioxide loss

Slot shape and residue retention may affectthe ability of no-tillage slots to retain carbondioxide. There is no doubt that all no-tillageoffers major advantages over tillage in thisregard (Reicosky, 1996; Reicosky et al., 1996),but differences in no-tillage slot distur-bance may also affect the amount of carbondioxide that is lost from the slot zone.

In-slot moisture and temperature

Some studies have shown that slot shapeand residue retention have only minimalshort-term effects on liquid-phase soil watercontent and temperature within the sownslots, even though they are both affected ona macro-scale by residue retention (Baker,1976a, b, c). On the other hand, the practiceof removing residues from over the slot toraise the soil temperature in the slot zone inspring has a measurable effect.

The objective of this process is toexpose the slot zone to direct sunlight whensoil is warming up (such as in springtime),which in turn causes drying, thereby raisingthe soil temperature in the row. This begsthe question whether seeds sown shallowbeneath a residue canopy (Class IV cover)experience any lower soil temperature regi-mes than seeds sown deeper in uncoveredslots, because the former option provideswater for germination at shallow sowingdepths and involves minimal-disturbanceof the residues.

Seed germination

Chapters 5 and 6 showed that, while mostminimum-disturbance slots promote highgermination counts in dry soils, not all suchslots perform well in wet soils, even though

Comparing Disc Openers 161

some do, such as the inverted-T shape. Nordoes good germination always translate intogood seedling emergence in dry soils (seebelow).

Maximum-disturbance slots are neitherthe best nor the worst for promoting germi-nation. They attempt to emulate tilled soilsand as a result usually perform similarly totilled soils.

Seedling survival and emergence

The most critical time for no-tillage seed-lings is the time between germination andemergence, as discussed in Chapter 5.Retaining surface residues over the slot(inverted-T-shaped slots, Class IV cover)sustains seedlings beneath the surface ofthe soil awaiting emergence better thanloose soil (Class II–III cover), which is betterthan no cover (Class I). In addition, theretained residues are desirable from a soilerosion point of view. Not all minimum-disturbance slots create Class IV cover,depending on the residue amount and con-dition. Some may even be as poor as Class Icover. Most maximum-disturbance slotscreate Class II–III cover.

Soil-to-seed contact, smearing andcompaction

The amount of slot disturbance visible fromthe ground surface is not always a goodindicator of what is taking place beneaththe soil in terms of soil-to-seed contact.For example, V-shaped slots in heavy soils(minimal-disturbance) may create neatlycut, smeared (if wet) and even compactedslot walls but still have adequate soil-to-seed contact, even in dry soils, because theseeds become wedged between the near-vertical slot walls. But such seeds may ger-minate and die (see Chapter 6), even withadequate soil-to-seed contact. In other cases,seeds sown into highly disturbed dry slotsmay have good soil-to-seed contact but failto germinate because loose soil conductsliquid-phase soil water poorly.

In inverted-T-shaped slots (minimal-disturbance) without vertical slot walls,soil-to-seed contact may be little different

from highly disturbed U-shaped slots, but,because inverted-T-shaped slots are cov-ered with residue (Class IV cover), the pres-ence of water vapour will ensure germinationand emergence take place.

Root development

Vertical V-shaped slots create minimal sur-face disturbance but may restrict root devel-opment more than other openers, especiallyin heavy damp soils. The use of wavy-edgedpre-discs with such openers reduces rootrestrictions but increases surface disturbance.

Most maximum-disturbance openers,together with most winged openers, presentlittle, if any, restrictions to root growth.

Infiltration into the slot zone

Slot disturbance has a direct effect on infil-tration. Earthworms and other soil fauna thatfeed on surface residues create channels thathave a positive effect on infiltration. Earth-worms, in turn, respond to the positioningof the residues. Minimum-disturbance slotsthat leave or replace the residues over theslot encourage earthworms to colonize theslot zone, which increases infiltration.

Maximum-disturbance slots may killearthworms in the immediate vicinity. Thewider and more severe the disturbance(especially if a power till mechanism isinvolved), the greater the earthworm morta-lity. But nearby earthworms will recolonizethe disturbed zone shortly afterwards.

Other factors may also contribute.Minimum-disturbance slots created by ver-tical double or triple disc openers compactthe side walls of the slot. This has a directnegative effect on infiltration from sealingas well as an indirect negative effect becauseearthworms avoid the compacted zone.

Hairpinning of residues

The most quoted negative effect fromresidues positioned close to the slot zonehas been tucking of residues into theslot, termed ‘hairpinning’ (see Chapter 6).Decomposing residues in wet (and espe-cially anaerobic) soils produce acetic acid,which can kill seeds or seedlings that are

162 C.J. Baker

touching the residue. In dry soils, seedssuspended in hairpins have difficultyaccessing liquid-phase water.

All disc-type no-tillage openers hairpinresidues at least some of the time. But no onehas yet designed an opener that can physi-cally handle surface residues in closelyspaced rows without the assistance of discs.The disc version of the winged openerphysically separates seeds from direct con-tact with hairpinned residues and thusavoids the problem. Acetic acid is rapidlybroken down in the soil by bacteria, sosmall separation distances are effective. Butall double disc and angled disc openers(whether slanted or upright) experiencehairpinning problems because the seedsremain embedded in the residues.

Fertilizer banding

Banding of fertilizer close to, but not touch-ing, the seeds at seeding is vital to maxi-mize crop yields (Baker et al., 1996; Fick,2000). Some designers achieve this by com-bining two openers together, which increasesinter-row spacing and surface disturbance,or by using ‘skip-row’ planting (one row offertilizer between every two rows of seed).Others use altogether separate fertilizeropeners, which increase slot disturbanceeven more. But there are other ‘double-shoot’openers (e.g. disc version of winged open-ers) that have been purpose-designed withno sacrifice of row spacing or surface dis-turbance (Baker et al., 1979b).

Soil erosion

Since retention of surface residues is themost effective mechanism for controllingsoil erosion, the more of the surface thatremains covered with residues after seeding,the better.

Pests, diseases and allelopathy

Early predictions of uncontrollable residue-related pest and disease problems attribut-able to no-tillage and residue retention haveproved to be exaggerated and, in most cases,groundless. In early trials with no-tillage,poor crop results were often attributed to

toxic exudates from dying residues (allelo-pathy). But, as scientists have come tounderstand what really affects seed germi-nation and seedling emergence duringno-tillage (particularly the role of residuesin improving the slot micro-environment),examples of true allelopathy have becomedifficult to find.

In any case, the advantages of residueretention are so great that they far outweighany minor residue-related disease or pestproblems that might occur from time to time.

Disc opener feature comparisons

No comparison would be complete withoutexamining the designs of a selection ofmainstream openers and/or machines. Inthis case, we have compared three differentdesigns of disc openers: the disc version ofa winged opener; angled vertical discs; anddouble discs.

Comparisons in Table 3.2 showed thatthe risk of impaired crop performance withthe disc version of the winged opener wasrated at 11%, while the angled vertical discopener was 30% and the double discopener 53%. Table 11.1 lists the causes ofthese differences. Shank-, hoe- and tine-typeopeners were not compared because thedesigns and performance of such openersvary widely and are affected by soil condi-tions and operating speed; thus the resultsare difficult to generalize.

Summary of Comparing SurfaceDisturbance and Low-disturbance

Disc Openers

1. The dual objective of minimizing theamount of disturbance to surface residueswhile at the same time maximizing seed,seedling and plant performance is possibleto achieve with modern no-tillage tech-niques and equipment.2. Not all minimum-disturbance openerswill create optimum crop yields, but allmaximum-disturbance openers will reduce


164 C.J. Baker

Ope

ner

feat

ures

Dis

cve

rsio

nof

win

ged

open

erA

ngle

dve

rtic

aldi

scop

ener

Dou

ble

disc

open

er

Ris

kof

impa

ired

perf

orm

ance

11%

30%

53%

Ope

ner

desc

riptio

nO

pene

rco

mpr

ises

ave

rtic

alno

tche

ddi

scw

ithtw

obl

ades

with

horiz

onta

lwin

gsan

dsc

rape

rsin

intim

ate

cont

actw

ithei

ther

side

ofth

edi

sc

Sin

gle-

shoo

tfor

mof

open

erha

sa

sing

leve

rtic

aldi

scar

rang

edat

anan

gle

toth

edi

rect

ion

oftr

avel

.Dou

ble-

shoo

topt

ion

has

dupl

icat

efe

rtili

zer-

only

open

ers

Sin

gle-

shoo

tfor

mha

stw

odi

scs

arra

nged

atab

out1

0°ve

rtic

alan

gle

toon

ean

othe

r.D

oubl

e-sh

ooto

ptio

nha

sdu

plic

ate

fert

ilize

r-on

lyop

ener

sE

ffect

sof

forw

ard

spee

dF

unct

ions

are

notg

reat

lyaf

fect

edby

forw

ard

spee

dF

unct

ions

are

affe

cted

byfo

rwar

dsp

eed

beca

use

ofth

ean

gle

(7°)

ofth

edi

sc(s

)to

the

dire

ctio

nof

trav

el

Som

efu

nctio

ns(e

.g.s

eed

flick

)ca

nbe

affe

cted

byhi

ghfo

rwar

dsp

eeds

Max

imum

spee

dC

apab

leof

oper

atin

gat

spee

dsup

to10

mph

(16

kph)

For

war

dsp

eed

islim

ited

byco

nditi

ons,

butm

axim

umis

less

than

10m

ph(1

6kp

h)W

ithad

equa

tede

flect

ors

agai

nsts

eed

flick

,ca

pabl

eof

spee

dsup

to10

mph

(16

kph)

See

dco

verin

gS

eed

cove

ring

(Cla

ssIV

)is

resi

due

laye

red

over

soil,

whi

chsc

ient

ific

expe

rimen

tsha

vesh

own

tobe

supe

rior

toal

loth

erfo

rms

ofco

ver

See

dco

verin

gis

mos

tlylo

ose

soil

butt

heco

verin

gfu

nctio

nis

very

spee

d-de

pend

ent

(Cla

sses

I–III

)

Ofte

nco

verin

gis

very

diffi

cult

toac

hiev

eat

all

beca

use

ofth

ew

edge

dV

-sha

ped

slot

.Rip

pled

pre-

disc

help

sin

this

resp

ect(

Cla

sses

I–III

)

Slo

t com

pact

ion

No

in-s

lotc

ompa

ctio

noc

curs

In-s

lotc

ompa

ctio

noc

curs

onon

esi

deon

lyS

ever

ein

-slo

tcom

pact

ion

occu

rson

both

side

sS

lot sm

earin

gA

nyin

-slo

tsm

earin

gth

atoc

curs

rem

ains

moi

stan

dth

eref

ore

ofno

cons

eque

nce

Mos

tin-

slot

smea

ring

that

occu

rsre

mai

nsm

oist

and

ther

efor

eof

noco

nseq

uenc

eIn

-slo

tsm

earin

gis

com

mon

and

diffi

cult

topr

even

tfro

mdr

ying

,whe

nit

form

sin

-slo

tcr

ustin

g,w

hich

isev

enw

orse

Sur

face

resi

dues

over

slot

Ret

ains

70–9

0%su

rfac

ere

sidu

eco

ver

Ten

dsto

push

resi

dues

asid

era

ther

than

repl

acin

gth

em.H

ighe

rsp

eeds

push

resi

dues

furt

her

asid

e

May

reta

in70

%re

sidu

egr

ound

cove

rex

cept

inst

icky

soils

,whe

nre

sidu

ere

tent

ion

decl

ines

Vap

our

moi

stur

eR

etai

nsm

axim

umva

pour

moi

stur

eat

seed

zone

Med

ium

vapo

urm

oist

ure

rete

ntio

nif

loos

eso

ilco

vers

slot

(Cla

ssIII

)P

oor

vapo

urm

oist

ure

rete

ntio

n

Res

idue

hairp

inni

ngW

illcr

eate

hairp

ins

butt

hese

eds

are

effe

ctiv

ely

sepa

rate

dfr

omth

eha

irpin

sso

they

are

ofno

cons

eque

nce

Cre

ates

hairp

ins

and,

beca

use

seed

sre

mai

nem

bedd

edin

the

hairp

ins,

this

affe

cts

germ

inat

ion

inbo

thdr

yan

dw

etso

ils

Cre

ates

hairp

ins

and

beca

use

seed

sre

mai

nem

bedd

edin

the

hairp

ins

this

affe

cts

germ

inat

ion

inbo

thdr

yan

dw

etso

ilsS

eedl

ing

emer

genc

eH

igh

seed

ling

emer

genc

e,al

mos

tre

gard

less

ofso

ilor

clim

atic

cond

ition

sS

eedl

ing

emer

genc

eis

depe

nden

ton

favo

urab

leso

ilan

dcl

imat

icco

nditi

ons

See

dlin

gem

erge

nce

ishi

ghly

depe

nden

ton

favo

urab

leso

ilan

dcl

imat

icco

nditi

ons

Cro

pfa

ilure

Low

crop

failu

rera

teM

ediu

mcr

opfa

ilure

rate

Hig

hcr

opfa

ilure

rate

Tab

le11

.1.

Com

paris

onof

sele

cted

feat

ures

ofth

ree

disc

-typ

eno

-till

age

open

ers.

Comparing Disc Openers 165C

rop

yiel

dsR

egul

arly

prod

uces

supe

rior

crop

yiel

dsto

both

tilla

gean

dot

her

no-t

illag

eop

ener

sR

equi

res

doub

le-s

hoot

vers

ion

topr

oduc

ebe

stcr

opyi

elds

,but

farm

erco

nfid

ence

isno

thig

h

Pro

duce

sac

cept

able

crop

sin

favo

urab

leco

nditi

ons,

buty

ield

sar

ere

stric

ted

byin

abili

tyto

band

fert

ilize

rE

mer

genc

ere

tard

ing

See

dlin

gem

erge

nce

isno

tret

arde

dby

soil

flaps

inw

etpl

astic

soils

beca

use

seed

lings

follo

wpa

thw

ayto

the

surf

ace

prov

ided

byth

eve

rtic

aldi

scsl

it

See

dlin

gem

erge

nce

isno

taffe

cted

byso

ilfla

ps,b

utex

posu

reof

seed

sca

nbe

apr

oble

m

See

dlin

gem

erge

nce

isno

tres

tric

ted,

but

desi

ccat

ion

and

bird

dam

age

ofex

pose

dse

edlin

gsca

nbe

apr

oble

m

Ban

ding

fert

ilize

rS

imul

tane

ous

and

sepa

rate

seed

and

fert

ilize

rba

ndin

goc

curs

onei

ther

side

ofa

sing

ledi

scon

the

sam

eop

ener

No

sepa

rate

band

ing

ofse

edan

dfe

rtili

zer

byea

chop

ener

.Req

uire

sdu

plic

ate

open

ers

for

doub

le-s

hoot

ing

No

sepa

rate

band

ing

ofse

edan

dfe

rtili

zer

byea

chop

ener

.Req

uire

sdu

plic

ate

open

ers

for

doub

le-s

hoot

ing

Fer

tiliz

erpl

acem

ent

The

refo

reon

eco

mpa

ctop

ener

isus

edto

sow

both

seed

and

fert

ilize

rD

oubl

e-sh

ootin

gof

seed

and

fert

ilize

rre

quire

sei

ther

aco

mpl

exdo

uble

d-up

open

eror

dupl

icat

ion

oftw

oop

ener

s.T

his

incr

ease

sth

eco

mpl

exity

and

spac

eoc

cupi

edby

each

com

posi

teop

ener

and

enco

urag

esfa

rmer

sto

only

doha

lfth

ejo

bby

purc

hasi

ngth

ech

eape

rsi

ngle

-sho

otop

tion

No

know

ndo

uble

-sho

otin

gop

ener

sex

ist.

The

refo

redu

plic

ate

open

ers

are

the

only

optio

n,w

ithth

esa

me

prob

lem

sth

atan

gled

disc

open

ers

have

Row

spac

ing

Can

bear

rang

edin

clos

ero

wsp

acin

gsdo

wn

to5.

5in

ches

(140

mm

)M

inim

umro

wsp

acin

gof

doub

le-s

hoot

vers

ion

is7.

5in

ches

(190

mm

)N

odo

uble

-sho

otop

tion.

Min

imum

row

spac

ing

ofsi

ngle

shoo

tis

4.72

inch

es(1

20m

m)

Hill

side

oper

atio

nE

ffect

ive

onhi

llsid

esN

otef

fect

ive

onhi

llsid

esbe

caus

eof

the

angl

eof

the

disc

Effe

ctiv

eon

hills

ides

Prio

rtil

lage

Effe

ctiv

ein

tille

dan

dm

inim

um-t

illed

soils

Not

very

effe

ctiv

ein

tille

dan

dm

inim

um-t

illed

soils

Effe

ctiv

ein

tille

dan

dm

inim

um-t

illed

soils

Ser

vice

wea

rA

llm

ovin

gpi

vots

use

seal

edbe

arin

gs,

lead

ing

tolo

ngtr

oubl

e-fr

eese

rvic

eM

ostv

ersi

ons

use

man

ysi

mpl

epi

vot

arra

ngem

ents

with

limite

dse

rvic

elif

eM

ostv

ersi

ons

use

man

ysi

mpl

epi

vot

arra

ngem

ents

with

limite

dse

rvic

elif

e

Pen

etra

tion

forc

eIn

divi

dual

hydr

aulic

ram

son

each

open

eren

sure

cons

iste

ntdo

wnf

orce

that

can

beva

ried

infin

itely

onth

em

ove

from

the

driv

er’s

seat

and

auto

mat

edto

adju

stto

soil

hard

ness

onth

em

ove

Mos

thav

edo

wnf

orce

sprin

gsw

ithst

epw

ise

setti

ngs

and

each

setti

ngch

ange

sits

dow

nfor

cew

ithel

onga

tion

and

cont

ract

ion

Mos

thav

edo

wnf

orce

sprin

gsw

ithst

epw

ise

setti

ngs,

and

each

setti

ngch

ange

sits

dow

nfor

cew

ithel

onga

tion

and

cont

ract

ion

Con

tinue

d

166 C.J. Baker

Ope

ner

feat

ures

Dis

cve

rsio

nof

win

ged

open

erA

ngle

dve

rtic

aldi

scop

ener

Dou

ble

disc

open

er

Dep

thga

uge

Pre

ss/g

auge

whe

els

loca

ted

clos

eto

seed

zone

On

som

em

odel

sga

uge

whe

els

loca

ted

right

alon

gsid

ese

edzo

neG

auge

whe

els

som

etim

esbe

hind

seed

zone

,but

othe

rve

rsio

nsar

erig

htal

ongs

ide

seed

zone

Dep

thco

ntro

lT

his

resu

ltsin

supe

rbop

ener

dept

hco

ntro

land

mak

esdr

illin

gov

erco

ntou

rba

nks

and

varia

ble

soils

effe

ctiv

e

Spr

ings

limit

open

erde

pth

cont

rol,

espe

cial

lyw

hen

drill

ing

over

cont

our

bank

san

dsu

rfac

ech

ange

s,bu

tgoo

dlo

catio

nof

gaug

ew

heel

she

lps

Lim

ited

open

erde

pth

cont

rol,

espe

cial

lyw

hen

drill

ing

over

cont

our

bank

san

dsu

rfac

ech

ange

s

Dow

nfor

ceco

ntro

lE

lect

roni

cm

onito

ring

ofpr

ess

whe

elfo

otpr

inta

llow

sth

edo

wnf

orce

tobe

alte

red

onth

em

ove

inre

spon

seto

chan

ging

soil

hard

ness

Dow

nfor

ceca

nnot

bech

ange

don

the

mov

eD

ownf

orce

cann

otbe

chan

ged

onth

em

ove

Dow

nfor

cera

nge

Nor

mal

dow

nfor

cera

nge

is0–

500

kgM

ostd

esig

nsha

vea

dow

nfor

cera

nge

0–25

0kg

Mos

tdes

igns

have

ado

wnf

orce

rang

e0–

250

kgM

axim

umdo

wnf

orce

Hig

h-do

wnf

orce

ram

s(1

100

kg)

are

avai

labl

efo

rop

ener

sop

erat

ing

inth

ew

heel

trac

ksof

com

pact

able

soils

No

high

-dow

nfor

ceop

ener

sav

aila

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the effectiveness of erosion control and soilimprovements offered by no-tillage.3. Minimum slot disturbance is an opti-mum no-tillage objective, with full consi-deration given to the several other seedingrequirements for stand establishment.4. Horizontal (inverted-T-shaped) slotsprovide good slot coverage with minimalresidue disturbance (Class IV). V-shapedslots provide poor slot coverage and residuecover (Class I).5. Minimum-disturbance slots do notnecessarily create favourable slot micro-environments unless adequately coveredwith soil and residue. Horizontal minimum-disturbance slots most readily createfavourable slot micro-environments whilevertical minimum-disturbance slots do not.Maximum-disturbance slots create slot micro-environments similar to tilled soil.6. Minimum-disturbance slots are likelyto lose somewhat less carbon dioxide thanmaximum-disturbance slots.7. The amount of residue cover over theslot has minimal long-term effect on liquidmoisture content. Minimum-disturbanceslots trap water vapour, while residue-freeslots warm more quickly in spring.8. It is possible to have both minimumresidue disturbance and maximum seedgermination.9. It is not always desirable or necessaryto sacrifice residue disturbance to encour-age seedling emergence. Depending on thedesign of opener and the climatic condition,it may, in fact, have the opposite effect.10. Slot disturbance by itself is not neces-sarily a good indicator of soil-to-seed contact.

The amount of residue disturbance mayhave little effect on soil-to-seed contact.11. Some, but not all, maximum-disturbanceopeners may enhance early root growth.Restrictions by some minimum-disturbanceopeners may occur with unfavourable soilconditions.12. Provided that compaction is not a factor,most minimum-disturbance slots encourageearthworm activity, and thus increaseinfiltration compared with maximum-disturbance slots. In the absence of earth-worms, maximum-disturbance slots mayhave greater infiltration than the best ofminimum-disturbance slots.13. All non-disc openers, especially thoseassociated with maximum residue distur-bance, avoid hairpinning problems butexperience residue-handling problems. Mostdisc openers, except those that create hori-zontal slots, have hairpinning problems.14. Some no-tillage drills that band ferti-lizer are less capable of minimizing residuedisturbance or close row spacing, or both.But there are notable exceptions, such asthe disc version of winged openers.15. No-tillers should ensure that surfaceresidues are well distributed and minimallydisturbed.16. Disturbing surface residues as little aspossible in the slot zone will have morepositive effects on seed, seedling and cropperformance than harmful effects by patho-gens or allelopathy.17. Disc-type openers vary widely intheir specific designs, which in turn affecttheir biological functions, including slotdisturbance.


12 No-tillage for Forage Production

C. John Baker and W. (Bill) R. Ritchie

The establishment and/or renovation of foragespecies is a special no-tillage case requiring

additional techniques and management.

Pastures and other forage crops providefood for foraging animals in countries,regions or seasons in which animal pro-duction is profitable. In some situationsanimals are grazed outdoors, often all yearround. In other situations, forage crops areharvested for storage or transport to theanimals housed indoors for at least part ofthe year. Many of the world’s pasture plantsare self-sown native species on rangeland,which have survived in the ecosystemsto which they are adapted. Most of thesespecies, however, produce relatively poorfeed for domestic animals in terms of qua-lity and quantity.

In the improved pastures of temperatecountries, genetically superior species havebeen sown into the rangelands and, togetherwith the judicious use of fertilizers androtational grazing management, have led tovastly improved animal productive capa-city. Over time, however, some of theseimproved pastures have slowly reverted tothe original, less productive species, requir-ing intermittent renewal or renovation withimproved species. In other situations, thecontinual genetic improvement of pasturespecies dictates their introduction into

otherwise ‘permanent’ grazing systems toimprove animal performance, regulate sea-sonal production or repair damage frompests, flood, drought or natural mortality.

We shall discuss the drilling of foragespecies and pastures separately, although inreality they are as often integrated into asingle system as they are dealt with inisolation.

Forage Species

Forage crops are similar to arable cropsfor their establishment requirements by no-tillage except that small-seeded species areoften involved, which require very accuratedepth control from the openers. Many bra-ssica species are used for forage cropping,along with grasses, legumes and herbs, allof which require shallow seeding. But awide range of cereal species are also used,often for whole-crop silage, which have agreater tolerance of the depth of seeding.

One problem is that farmers often valuetheir forage crops lower than arable crops,presumably because the cash returns fromforage crops are derived by indirect animalharvesting rather than directly throughmachine harvesting of seed, fibre or grain.When a forage crop fails, there will often bean alternative forage crop nearby that can be


used to compensate, or, at worst, animalscan be sold to reduce demand. In contrast,when an arable crop fails, that source ofincome is lost for ever and cannot bereplaced. For this reason, there seems to bemore acceptance by animal farmers of sub-standard no-tilled forage crops than is thecase with arable farmers. Even those peoplewho farm integrated animal and arable sys-tems put less value on the forage crops thanon the arable crops, possibly because thelatter usually comprise the major part of thefarm income.

Further, because pastures are regularlygrazed or mowed, differences in individualplant performances are more difficult todetect by eye. As a consequence, rather thanattracting greater precision at drilling, muchpasture establishment actually attracts lessprecision.

But this situation is changing. Animalfarmers in New Zealand, for example, arefinding that a new level of animal intensifi-cation is possible using ‘fail-safe’ no-tillagethat rivals arable cropping, in terms of bothreturns per hectare and risks.

Animals are often grown on ‘permanent’forage species (usually pastures), which arecharacterized by uneven growth cycles dur-ing the year. Maximum forage productionand quality of feed occur in warm moistmonths, while minimum production andquality occur in cold and/or dry months.Management of animal systems that rely onsuch feed supplies is constantly restrictedby the lowest-productivity months. Oftenthis involves the use of feed supplements,either purchased in or saved as silage or hayduring the more productive months.

But a new level of productivity can beachieved by replacing ‘permanent’ foragespecies with highly productive, short-rotation, speciality forage species, which arere-established at least once (and often twice)per year and are chosen according to theirsuitability for specific growth periods or ani-mal requirements during the year. Some arecold-tolerant; others are dry-tolerant; stillothers produce a quality of feed suited toparticular stages of growth of the animals.The possible combinations are virtually end-less and can be regularly changed.

But they all depend on the availabilityof ‘fail-safe’ no-tillage techniques and sys-tems. Such systems of forage productioncannot be accomplished using tillage becausefew productive soils can stand being tilledcontinuously once or twice per year. Thesoils would quickly deteriorate to unman-ageable conditions, and utilization byanimals would become almost impossible.

Although the quality and quantity (andtherefore productivity) of short-rotationforage species grown under continuous no-tillage regimes are superior to those obtain-able from ‘permanent’ pastures, the newsystem puts much pressure on the ability ofthe no-tillage system and equipment todeliver maximum crop yields for eachsuccessive crop.

Because the forage crops are establishedat least once and often twice per year, it is a‘high-input’ and ‘high-output’ system, butsome of those practising it have reportedtripling the numbers of stock grown toslaughter weight per year on the same area.Outdoor weight gains from lambs and beefcattle in the order of 400 and 1000 g perday, respectively, have been common whenthe animals are fed in situ on a continuingsupply of short-rotation no-tilled forage crops.

A variation on this system is to growcontinuous short-rotation silage and haycrops for cash sale rather than grazing byanimals. In some systems, animals neverenter the fields. This restricts the choiceof forage species to those that can be con-verted into hay or silage, but again thesystem is totally dependent on no-tillage.

Integrated Systems

The optimum diversification is to integrateanimal and arable crop production systems.This is a common practice in countrieswhere climate allows animals to graze out-doors all year. Typically one or more arablecrops are grown during the most productivetime(s) of the year and forage crops aregrown between the arable crops and eitherfed directly to animals or mechanically har-vested and fed indirectly to them. Up to

No-tillage for Forage Production 169

three integrated crops can be grown peryear in some climates.

Where no-tillage is not available, suchintensive cropping will not sustain soilstructure and tillage delays planting. Forthis reason, typical tillage-based rotationshave included a period in permanent pas-ture with the objective of repairing the dam-age to the soil structure by previous tillageand readying the soil for further destructivecropping processes to follow.

No-tillage changes all of that by allow-ing continuous cropping (forage and/orarable) to take place almost indefinitelywithout significant damage to soil structure.Crop rotations are then not constrained bythe need for a remedial pasture phase andcan be selected for the relative values ofcrops at any one time.

Figure 12.1 is an example of where twocrops of summer turnips (Brassica spp.),one established by tillage and the other byno-tillage on a light organic soil, have been

grazed by dairy cattle in situ. The differencein soil damage is clear.

Of course, severely wet weather andheavy concentrations of stock will damageeven untilled ground eventually. The ques-tion then becomes: ‘How serious must thedamage be before some form of tillage is jus-tified?’ Figure 12.2 shows severely damagedsoil from repetitive hoof treading in a gate-way when the soil was wet. The soil dam-age in Fig. 12.2 is about the upper limit thatwinged, hoe or angled disc no-tillage open-ers can be expected to repair without assist-ance from tillage tools. Indeed, the resultfrom a single pass with a disc-versionwinged opener drill can be seen on the left.Double or triple disc openers would not copewell with such surface damage becausethey have only a minor smoothing effect asthey travel through the soil.

Damage beyond that shown in Fig. 12.2is best repaired with a shallow tined imple-ment or rotating spiked harrow, the actions

170 C.J. Baker and W.R. Ritchie

Fig. 12.1. Two turnip crops sown with angled disc openers and fed in situ to dairy cattle inNew Zealand. The upper photograph shows a wide view of the treading damage to the tilled soil on theright compared with the untilled soil on the left. The lower photograph shows close-up views of therespective soil surfaces. Note that the soil surface under no-tillage (left) has not been broken open at all,whereas the tilled soil (right) is heavily scuffed.

of which are to drag or flick surface soil intothe hollows rather than invert the soil. Moresevere treading damage may also compactthe surface layers (to about 300 mm) of thesoil profile. This is best relieved with ashallow subsoiler with narrow vertical tinesor sweeps that leave the soil surface reason-ably smooth so that no-tillage may takeplace again without further smoothing beingrequired.

Where the integration of animal andarable enterprises is practised, it is commonfor last-minute decisions to be made betweenthe growing of one or more arable crops orforage crops based on expected relativereturns. Such flexibility is only possible iflast-minute crop-establishment decisionsare based on no-tillage. No-tillage providesthe flexibility that allows truly integratedanimal and arable systems to develop tonew heights.

Arable crops are sometimes rotatedwith pastures where land is retired or ‘setaside’ to allow it to revert to native grassesand/or scrub for periods of 10 years or moreto protect the soil from erosion or reduceagricultural production. With the world’sdemand for food continuing to expand,however, such land is likely to be returnedto arable farming in due course. When itis, it will be more important than ever toretain the sustainability of the soil health,which will, in most cases, have reached

new heights from the retirement process, byadopting no-tillage from the outset. Thismeans learning how to drill or plant intoheavy ‘unmanaged’ sod.

No-tillage of Pasture Species

In some circumstances when drilling pas-ture species, it is not appropriate to kill allof the competing species. If the competingspecies are other desirable grasses and notdestroyed, this is known as ‘pasture renova-tion’. In other circumstances, it is necessaryto kill all of the existing species. If the newspecies to be sown are also pasture plants,this is known as ‘pasture renewal’.

Pasture renewal

One-quarter of the world’s surface, some3000 million hectares, is grassland (Kim,1971; Brougham and Hodgson, 1992).Renewal and establishment of this valuableresource are a major effort, which can beenhanced with no-tillage practices.

Pastures are traditionally renewedeither to improve the productivity of exist-ing vegetation (e.g. bush, scrub, nativegrasses or introduced swards) or to replace aharvested annual crop with grazable pasture.


Fig. 12.2. Severely hoof-damaged soil that is about the upper limit that can be repaired by a singlepass with the disc version of winged openers (seen on left).

The objective can be to establish a long-term‘permanent’ sward of monoculture (singlespecies) pasture, including lucerne, or amixed sward of several grass species and/orcompatible legumes, such as clovers orlotus species. A further objective can beto establish a short-term (usually singlespecies) temporary pasture to utilize landbetween successive arable crops.

Not all pastures will be grazed directlyby animals. Many are harvested by machineor hand and fed to animals either directly asgrain or as silage or hay, or are regularlymowed to keep them short (e.g. sports turf).This has some importance for the establish-ment method used. For example, if a pas-ture is to be directly grazed by cattle, theyoung plants may be damaged by treadingor pulling. No-tillage offers clear advant-ages over tillage in this respect because thestability of the untilled soil resists treadingdamage and provides better root anchoragethan tilled soils. No differences betweenno-tillage openers have so far been found inthe pulling resistance during grazing (Thomet al., 1986).

Where pasture plants are mechanicallycut, pulling damage is minimized. Surfacedamage to the soil may result from heavyvehicle traffic under wet conditions. Inthis respect, the improved soil structure byno-tillage offers significant advantages overtillage.

The largest problem with pasturerenewal by no-tillage is meeting the require-ments of many pasture seeds for depth ofsowing and germination micro-environment.The more rapidly establishing grass species,such as ryegrasses, are usually tolerant ofsowing depths from 5 to 30 mm, but sufferreduced germination outside this range. Themore weakly establishing species, such aslucerne, clovers and some grasses, are muchless tolerant of improper depth, preferring thenarrower range of 5–15 mm.

In a tilled soil, a narrow depth-tolerancerange is relatively easy to achieve becausethe soil has been previously prepared toa uniform physical consistency and iseasily penetrated by drill openers. Accuratesowing depth in a tilled soil favours largeflotation-type openers (such as on V-ring

roller drills), which are unable to operatein no-tillage because of the more denseuntilled soil.

No-tillage openers for pasture renewaltherefore need mechanisms for depthcontrol and surface following and to becapable of creating a desirable slot micro-environment within the top 10–15 mm ofsoil. These are demanding requirements.

The choice of drilling pasture plants inrows compared with random scattering ofseeds followed by harrowing has been dis-cussed because the objective is to utilize allthe available ground space. With no-tillage,random scattering (oversowing or broad-casting) almost invariably results in poorestablishment because untilled soils offerlittle loose soil or debris to cover undrilledseeds by harrowing. Trampling of the seedinto the ground by stock is no substitute forpositive placement by a drill opener. Nonethe less, where the operation of drills hasbeen impossible (such as on steep hillsidesand on some sports turfs), the practiceof oversowing by aircraft, hand or lightmachine has been undertaken, with accept-able establishment by pelleting the seedand/or increasing the seeding rate tocompensate for mortality.

Row spacing

Where no-tillage drilling can be success-fully undertaken (i.e. tractors can access theland), the debate shifts to the most desirablerow spacing and drilling times. Commondesign and space limitations of drills pro-vide a narrowest practical row spacing ofabout 75 mm, with wider spacing up to300 mm used in dry climates for pasturespecies with surface creeping habits or forforage seed production.

Research in New Zealand using a rapidlyestablishing ryegrass species (Inwood, 1990;Thom and Ritchie, 1993; Praat, 1995)showed little or no production differencesbetween: (i) single-pass drilling with wingedopeners in 150 mm rows; (ii) single-passdrilling with the same openers in 75 mmrows; and (iii) cross-drilling in 150 mm rowswith the same openers. In the last case, twopasses were made at approximately 30° to


one another, sowing half the intendedapplication rate with each of the two passes(Thom and Ritchie, 1993).

Results in Table 12.1 (Praat, 1995)show that a slowly establishing species (tallfescue, Festuca arundinacea) initially bene-fited from narrow (75 mm) row spacing as aresult of reduced weed population. Cross-drilling had no long-term benefits over150 mm spacing, possibly because the gainsof closer plant spacing were offset by greaterstimulation of weed seed germination bythe second pass of the drill.

Single-pass drilling of tall fescue in75 mm rows produced greater 5-monthgrowth than single-pass drilling in 150 mmrows, but was not significantly differentfrom the cross-drilling in 150 mm rows. Thelatter two treatments were themselves notsignificantly different from one another.The advantage of the 75 mm rows at 5 monthswas not repeated with ryegrass. By 23 monthsthere were no significant differences amongany of the drilling or species treatments.

Since the only differences were duringthe early stages of pasture growth, and thenonly with a slowly establishing species, thesingle-pass 150 mm row option is preferredbecause it is less expensive, both in terms ofdrill design and operational costs. An addedadvantage is that most no-tillage drills canalso be used for drilling small-grainedcereals, pulse crops, oil seed crops andforage crops.

In mild, wet winter climates, pasturesand sports turfs are often renewed by till-age, in autumn because weeds are moreeasily controlled than in the spring andpost-drilling soil moisture levels are likelyto be more reliable than in the hotter

summer periods. With no-tillage, however,the availability of herbicides and reductionin physical stimulation of dormant weedseeds largely eliminates the disadvantage ofspring weed germination.

Further, the moisture conserved withno-tillage reduces the risk to new pasture andturf seedlings in dry summer soils. These fac-tors have led to more spring drilling of newpastures and sports turfs using no-tillage thanwith tillage, but the majority of such swardsare still established in the autumn.

Even in the autumn, the debate aboutrow spacing has centred on the ability ofpasture plants to quickly tiller and spreadto occupy otherwise bare ground so as tocompete with expected natural weed germi-nation between the rows. Data in Table 12.2(Praat, 1995) show the results of autumnno-tillage drilling of ryegrass and tall fescueinto a recent alluvial soil containing a highweed seed population.

Only the two-pass cross-drilling treat-ment using winged openers increased weedseed germination and growth comparedwith single-pass drilling in 75 mm and150 mm rows. Even then, these differences(approximately 20%) occurred only withinthe first 5 months after sowing. Thereafterthere were no significant differences betweendrilling methods.

On the other hand, data in Table 12.3(Hamilton-Manns, 1994) show a clear trendof declining weed growth with date of sow-ing in autumn and early winter, using thesame pasture species sown in a single passwith winged no-tillage openers in 150 mmrows in a similar soil.

At the earliest sowing there were twiceas many weeds in the tall fescue pasture


5 months after sowing 23 months after sowing

Treatment Ryegrass Tall fescue Ryegrass Tall fescue

75 mm rows, single pass 1893 a 2066 a 1399 a 1827 a150 mm rows, single pass 1911 a 1525 b 1449 a 1734 a150 mm rows, cross-drilled 2196 a 1826 ab 1453 a 1711 a

Unlike letters following data in a column denote significant differences (P = 0.05).

Table 12.1. Pasture production from differently spaced no-tillage drill rows, kg/ha dry matter yield atthe time of sampling after sowing.

(10.7%) at 70 days after sowing comparedwith the ryegrass pasture (4.5%), becausethe more slowly establishing tall fescue pas-ture took longer to colonize the inter-rowspaces. Thereafter there were no differencesbetween these two pasture species in termsof weeds. As the season became colder(from early autumn to early winter), the per-centage of weeds in both pastures steadilydeclined from an average of 7.6% to1.3–1.4%, reflecting increasingly less favour-able conditions for weed seed germination.

For total pasture production in NewZealand, Hamilton-Manns (1994) also foundgreater yield potential from early autumnsowing (March) than later winter sowing(June) if sufficient soil moisture was avail-able to sustain early seedling development.This held true for both rapidly establishingspecies (e.g. ryegrasses) and slowly estab-lishing species (e.g. tall fescue). The earlier

sowings and warmer temperatures favouredtiller development of the sown species,although there was also an increased (thoughmanageable) weed problem.

The retention of crop residues from aharvested summer crop or the fallowing ofground in the spring by spraying the previ-ous pasture will help offset potential prob-lems of weeds and low soil moisture levelsduring early autumn no-tillage sowing ofnew pastures. During winter in temperateclimates, the retention of residues mayresult in increased earthworm populations(Giles, 1994).

In drier climates, improved establish-ment of new pasture species in the autumnhas been achieved by chemical fallowingof fields over the dry summer. Residentspecies are sprayed out during late springwhen they are still actively growing andreceptive to herbicides, after which the


5 months after sowing 23 months after sowing

Sown grassesand clover Weeds

Sown grassesand clover Weeds

75 mm rows, single pass 902 a 531 a 2086 a 119 a150 mm rows, single pass 835 a 545 a 2146 a 125 a150 mm rows, cross-drilled 796 a 675 b 2123 a 178 a


Table 12.2. Effects of no-tillage drilling method on herbage composition of pasture species, kg/ha drymatter at time of sampling.

Time of sowingPasturespecies sown

% weeds present at70 days after sowing

Mean % weeds forboth species

Early autumn Ryegrass 4.5 b 7.6 aTall fescue 10.7 a

Early–mid-autumn Ryegrass 4.8 b 4.8 bTall fescue 4.9 b

Mid-autumn Ryegrass 3.4 b 3.7 bTall fescue 3.6 b

Late autumn Ryegrass 0.6 c 1.3 cTall fescue 2.0 c

Early winter Ryegrass 1.1 c 1.4 cTall fescue 1.8 c


Table 12.3. The effects of time of sowing on the proportion of weeds in a no-tillage pasture.

fields are left fallow for several dry months.If sufficient residue remains on the surfaceas a mulch, considerably less soil moistureis lost compared with unsprayed pasturesbecause the spraying reduces moisture lossby transpiration and evaporation. Moisturegains as high as 12-fold have been reported(Anon., 1995).

The potential loss of pasture produc-tion over summer in dry climates is smalland a more moist soil environment is main-tained for early autumn establishment. Con-trol of resident species is enhanced by usinga more appropriate time of year for spray-ing, and there is also the opportunity for anautumn herbicide application prior todrilling, if required.

In climates with adequate summerrainfall, autumn establishment of new pas-ture species may be enhanced by drilling aforage crop the previous spring. This notonly provides the opportunity for a doubleapplication of herbicide, but it also providestime and stock trampling to break down theintense root mats that exist with some nativepasture species in low-fertility situations.

The emphasis with most of these tech-niques is to ensure effective long-term con-trol of resident species to provide thegreatest opportunity for a competition-freeenvironment into which the new speciescan vigorously establish.

Pasture renovation

Pasture renovation, where at least partialrecovery of the existing vegetation canbe expected, adds another requirement tono-tillage seeding. The existing vegetationmust be suppressed or managed such thatit will not unduly compete with the intro-duced species. This renovation method isoften referred to as overdrilling or sod seed-ing (see Chapter 1).

The renovation of existing pasturesmay be undertaken for several reasons:

1. To introduce a more productive long-term pasture species into an existing pasture.2. To introduce a short-term pasture spe-cies that is more suited to a particular time

of the year or animal performance than theexisting species.3. To repair damage from natural mortal-ity, drought, flood, erosion, pests, physicaldamage or poor drainage.4. To compensate for management or fer-tility limitations for particular fields, soilsor climates.5. To capitalize on nitrogen fixationbrought about by previously introducedlegume species.

No-tillage pasture renovation wasaccomplished before the modern conceptof general no-tillage. Early reports showrenovation of animal pastures began in themid-1950s (Blackmore, 1955; Cross, 1957;Robinson, 1957; Cullen, 1966; Dangol, 1968;Kim, 1971). Sports turf renovation came later(Ritchie, 1988).

In the 1950s the dominant reason foroverdrilling was to capitalize on nitrogenfixation (Robinson and Cross, 1957). Low-fertility hilly pastures and pastures sowninto bush burns on recent volcanic ash soilstended to become clover-dominant becauseof their low natural fertility. With time,however, this legume base improved thefertility and organic matter levels of suchsoils to a stage where they could sustainproductive grass growth from pastureplants, mainly ryegrasses. The problem washow best to introduce the new grasses with-out destroying the clover base, or tilling andburying the organic matter layer of suchfragile soils.

Since herbicide use was new at thattime and, in any case, all available herbi-cides had a residual action of several weeksin the soil, early overdrilling machines con-centrated on mechanical destruction ofexisting plants in a limited-width track (upto 50 mm wide) centred on the seed row.The objective was to provide a competition-free habitat for the new seedlings thatwould remain so until regrowth eventuallyrevegetated the strips. By that time thenewly introduced species were expected tobe competitive with the resident species.

Even today, several designs of no-tillageopeners for pasture renovation, e.g. powertill and furrow openers, rely on physical,


rather than chemical destruction or sup-pression of the resident species to tempo-rarily check the existing competition.

Band spraying

More recent research has shown that physi-cal removal of vegetative matter from theslot cover zone has a negative effect onthe micro-environment within the seed slot,thus seeding into less than optimal soilconditions. Fortunately, the advent of non-residual herbicides now permits selectivespraying of a strip of existing vegetation(band spraying) at the same time as the seedis sown with openers. This creates a vegeta-tive mulch, while at the same time suppress-ing the competing vegetation. Figure 12.3shows an example of a band-sprayed anddrilled pasture.

Figure 12.4 shows the trade-off effectsof the various options for overdrilling ofvegetation in comparison with the variousslot shape options for promoting germina-tion and seedling emergence. The top leftillustration is of a slot left by a hoe- orshank-type opener without any attempt tocover the seed. The bursting effect of theopener has a positive effect on competition

removal by physically pushing it aside.This is represented by a tick alongside theillustration. But the open (uncovered) slothas a negative effect on seedling survival(represented by a cross alongside the illus-tration). Therefore there is some risk offailure from this technique.

The centre left illustration shows thatcovering the slot with loose soil willimprove seedling survival (tick and cross)while still having a positive effect on com-petition removal. The risk of failure isdecreased.

The lower left illustration shows thatan uncovered V-shaped slot created by adouble disc opener has a negative effect onboth seedling survival and competitionremoval. The risk of failure is high. In thiscase, however, the absence of physicalbursting allows band spraying to be used tokill a strip of vegetation over the slot. Thetop right illustration shows that this has apositive effect on competition removal butdoes nothing to improve seedling survival.But the risk of failure decreases accordingly.

The centre right illustration shows aslot left by a winged opener. While suchan opener might have a positive effect onseedling survival, the absence of physical


Fig. 12.3. The effects of band spraying and simultaneous drilling of pasture.

bursting has a negative effect on competi-tion removal (the risk of failure is medium).

Only when band spraying is used inconjunction with winged openers does thecombination have a positive effect on bothseedling survival and competition removal,as shown in the lower right illustration. Therisk of failure is low.

There can be debate about how muchsuppression of existing vegetation is neces-sary or desirable to bring about the mostproductive pasture possible as a conse-quence of overdrilling an improved speciesinto an existing sward. At one end of thescale is complete eradication of all existingspecies (blanket spraying by herbicide),producing a competition-free environmentover the entire field, in which the newspecies can be expected to express itsmaximum yield potential. But, during theeradication and establishment period, pro-duction from the original sward is lost andmust be deducted from the total pastureproduction for that year or season.

At the other end of the scale is no sup-pression at all, in which the new species isforced to compete with the existing speciesfrom the outset. Lost production from thisoption is only minor from damage to theexisting sward, but the early and continuingcompetition adversely affects the yield andgrowth potential of the introduced species.

Between these two extremes is band orstrip spraying, where a strip of existing vege-tation is sprayed simultaneously as the newseeds are sown, or strip tillage. These arecompromises and the loss of yield of the oldspecies and realization of yield potential ofthe new species both reflect this by fallingmidway between the other two extremes.

Figures 12.5, 12.6 and 12.7 show theeffects of the three spraying options withoverdrilled ryegrass. With blanket spraying,the distinct rows of the new species areclear and vigorous. Where no spraying wasundertaken, the new rows are less obvious,while band spraying lies in between. On theassumption that the new species has agreater yield potential than the existingspecies, any pasture that promotes vigorousgrowth of the new species is likely to have agreater long-term yield potential than theoriginal sward.

To quantify the three options discussedabove, scientists in New Zealand measuredmilk production from the yields of pasturesrenovated by the three methods (Lane et al.,1993). They also took account of the relativecosts of undertaking each practice andexpressed their findings in terms of the timetaken to recover those costs from the rela-tive milk production figures for each of theoptions under the prevailing conditions.Their findings are shown in Table 12.4.


Fig. 12.4. The risk factors of vegetative control and slot micro-environmental control whenoverdrilling pastures.

The blanket spraying option was themost expensive compared with band spray-ing and no spraying, but this option alsocreated the best pasture, resulting in greaterreturns from milk fat per hectare. When thecosts were offset against the returns, how-ever, there was little difference between thethree options and all repaid themselveswithin 8 months or a year. After the pay-back period, however, the extra pasture pro-duction becomes clear profit to the farmer,since the establishment costs would not berepeated annually. This clearly favoursblanket spraying since returns from thattechnique are higher than from either of theother two options.

The technique of band spraying wasfirst tried by L.W. Blackmore (1968, per-sonal communication) and later developedby Collins (1970), Baker et al. (1979c)and Barr (1980, 1981). The most desirableband width was not obvious because thecost benefits described above suggest thatband spraying is somewhat inferior to

blanket spraying. Altering the band width is asimple matter of raising or lowering the spraynozzles. Collins (1970) and Barr (1980) there-fore studied different band widths in termsof their effects on yield of both the intro-duced species and resident species duringpasture renovation. Table 12.5 records theresults of band spraying during overdrillingwith winged openers in 150 mm spaced rows.

Clearly, the wider band (75 mm) reducedthe competition from the resident speciesmore than the narrower (50 and 25 mm)bands. This was reflected in lower yield ofthe resident species with the wider band.

The effects on yield of the introducedspecies (even at the early stage of 12 weeks)reflected the levels of competition withinthe bands. The wider band produced thegreatest yield of juvenile plants. Since thedrilling row spacing was 150 mm, an opti-mum sprayed band width of 75 mm bandsrepresents 50% removal of the competingvegetation. The results shown in Table 12.4did not involve bands as wide as 75 mm, sothe band spraying treatment may have been


Fig. 12.5. Ryegrass establishment by overdrillingwith blanket spraying.

Fig. 12.6. Ryegrass establishment by overdrillingwith band spraying.

disadvantaged somewhat in the analysis ofLane et al. (1993).

In Barr’s (1980) experiments, there wasalso an effect from fertilizer placement,which at first seemed to be at odds withtrends described earlier (see Chapter 9). Oncloser examination, however, the effectswith overdrilling are predictable and logi-cal. It appears that by placing fertilizer withthe seed in these circumstances, those resi-dent plants left alive are able to utilize thenutrients before the introduced speciesbecause of the mature root systems of theresident species. This disadvantages theyoung introduced plants through increasedcompetition, as seen in Table 12.6.

The addition of fertilizer at drillingincreased the yield of resident species by25%, which in turn competed with thedrilled species and reduced its yield at12 weeks by 18%. Ryan et al. (1979) hadearlier illustrated the relative superiority ofblanket spraying by comparing blanketspraying, 50 mm band spraying and nospraying. They obtained 1413 kg/ha drymatter yield with blanket spraying, 930 kg/ha


Fig. 12.7. Ryegrass establishment by overdrillingwith no spraying.

Blanket spray Band spray No spray

Contract cost of renovation (US$/ha) 113 100 70Extra pasture production (kg dry matter/ha,

first year)2049 1187 1146

Extra cows/ha able to utilize this pasture 0.43 0.26 0.24Returns from extra cows (US$/ha)a 170 102 96First-year return on investment (%) 150 98 137Time to recover renovation costs (years) 0.7 1.0 0.7

aAssumes that 25 kg of extra pasture production in New Zealand results in 1 kg of extra milk fat, whichsells for US$3.24/kg.

Table 12.4. The cost–benefits of renovating dairy pasture by three different methods.

Sprayed band width DM yield of drilled species (kg/ha) DM yield of resident species (kg/ha)

25 mm 130 129850 mm 143 118475 mm 196 776

Table 12.5. Effects of spray band width on dry matter (DM) yield of overdrilled ryegrass 12 weeks afterdrilling (Barr, 1980).

with band spraying and 906 kg/ha using nospray at all.

It is recommended, therefore, that, withoverdrilling where the resident species havenot been totally killed, fertilizer applicationshould be delayed until after emergence (oreven after the first grazing) of the drilledspecies. This is the only no-tillage situationfor which such a recommendation is made.If, for example, pasture is being establishedinto an untilled seedbed in which all ofthe existing competition is dead, the recom-mendation would be to band fertilizer withthe seed at drilling if the openers used arecapable of separating the two in the drilledslot.

Although the parameters for optimumresults with band spraying are now welldefined as above, the practice representsanother function from the drill, increasingthe opportunity for error. Further, the totalyield of the new pasture is seldom as highafter 12 months as from blanket spraying(total kill), so the technique is not used asmuch as drilling into the weed-free envi-ronment offered by blanket spraying.

Band spraying represents a realisticoption when total kill is not desirable; thus,the techniques and designs of equipmentneeded to undertake the technique areincluded. Situations where band sprayingis appropriate include:

1. The rejuvenation of lucerne standswhere the stand has become thin with age(as is typical) but the surviving plants arehealthy and strong, favouring their reten-tion along with newly introduced plants.2. The temporary balance change of a pas-ture, e.g. where a legume pasture becomessemi-dormant over the winter months, thetemporary injection of an annual ryegrassor winter forage cereal in autumn mayincrease winter production.

3. The repair of pest-, trampling- ordrought-affected pastures where the surviv-ing species are assumed to be resistant tothe factors that killed many of the otherplants in the pasture and are therefore con-sidered to be a valuable resource worthretaining.4. The introduction of a new speciessuited to the habitat created by a residentspecies, such as in the fertility build-updescribed earlier in this chapter.

Band spraying equipment

Early designs of band spraying devices cen-tred on placing a spray nozzle ahead ofthe opener. The option of spraying behindthe opener was quickly discarded for tworeasons (Collins, 1970):

1. The herbage is often covered by soilafter passage of the opener, which tends todeactivate paraquat or glyphosate herbicides.2. Paraquat is phytotoxic to many seeds,which might be exposed in the slot beforecovering has had a chance to be completed.

For the nozzle to remain a constant dis-tance above the ground, it has to either bemounted independently on its own height-gauging device (Fig. 12.8), or, if mounteddirectly on the opener, the latter has to havea positive height control of its own, whichis necessary for adequate control of seedingdepth anyway.

Even with adequate height control,there are other problems with spray noz-zles. The application rates of water that themanufacturers of herbicides recommend beapplied per sprayed area are difficult toachieve because the narrow bands meanwater application becomes concentrated onto a very small area for each nozzle. Thisrequires very fine nozzles, which require


DM yield of drilled species (kg/ha) DM yield of resident species (kg/ha)

With fertilizer 141 1207Without fertilizer 172 966

Table 12.6. Effects of fertilizer application at drilling on overdrilled ryegrass plants 12 weeks afterdrilling (DM, dry matter).

micro-filtration to avoid blockage by waterimpurities that would otherwise be accept-able to farm boom sprayers. Further, becausethese nozzles operate close to the soil(50–75 mm), they are subject to blockagefrom random soil splash and debris anddamage through contact with stones, etc.

Hollow cone nozzles are most suited tosingle-nozzle band application, althoughfan-type nozzles have been used success-fully, largely because the inherent variationsacross the band are acceptable when theobjective is only to suppress rather than killall of the target plants. Hollow cone nozzlesgenerally have a more uniform pattern froma single nozzle than fan-type nozzles.

An innovative method of applyingbanded herbicides has been used with thedisc version of winged openers. Becausethis opener is equipped with two semi-pneumatic rubber gauge/press wheel tyres,the herbicide can be dripped on to the topof the tyres at low pressure and rolled on tothe ground in much the same way as a lawnmarker (Ritchie, 1986a, b). This avoidsproblems of blockage, micro-filtration, winddrift, the presence of tall plants and physicaldamage, common with small nozzles, andintroduces the feasibility of ground-metering

of the herbicide. Figure 12.9 shows a driproller arrangement.

Ground metering involves using a posi-tive displacement pump driven by theground wheel of the drill in such a way thatits output per metre of travel remainslargely constant, regardless of travel speedor pressure. Such a system is impracticalwith pressurized nozzles because inevitablevariations in ground speed cause variationsin nozzle pressure, which in turn causevariations in band width because the widthof the spray pattern from a nozzle is partlydependent on its operating pressure. Withthe drip roller system, the output pressureis very low and unimportant, since there isno pattern of spray to maintain and, even ifthere is, this is aimed at the top of the tyre,which then delivers the herbicide to theground as a wet film on the bottom of thetyres, rather than directly as a jet.

In one respect, the rolling on of herbi-cide is a disadvantage because the tyresoperate behind the opener and inevitablypick up soil, which quickly turns to mudon the wet tyres. Their use for this task isonly possible with winged or double discopeners because of the minimal surface soildisturbance each of these openers creates.


Fig. 12.8. A band spraying nozzle mounted on separate skids to control spraying height.

Any soil contamination that does occur iscountered by the improved efficacy ofuptake of most herbicides from being rolledrather than sprayed on to the leaves. Theresult from many thousands of hectares offield-testing is that the 75 mm wide bandscreated by rolling on of herbicides works aswell as spraying the same width of bandand has a greater tolerance of the conditionsunder which it can be used.

Depth control and slot formation

Control over the drilling depth of pasture,sports turf and many forage crop speciesis particularly demanding. Most drillsdesigned expressly for pasture renovationhave been promoted on a low-cost basis.Because of this, the control mechanisms fordepth of seeding are generally primitiveand sometimes non-existent.

For example, the simple low-cost drillsthat dominate the pasture drill markets inAustralia and New Zealand are almost allequipped with ‘Baker Boot’ versions of sim-ple winged openers (inverted-T-shaped slot).While the choice of slot shape is appropri-ate, the ability of these openers to followthe surface is limited by the simplistic

drill designs to which they are attached,particularly the mechanisms for articulatingeach opener up and down. This causes theangles of the opener wings to changethroughout their arcs of travel (see Chapter4). To avoid complete loss of wing angle inhollows, the preset angle for level ground isabout 10°. This relatively steep wing anglemeans that the shallowest this opener candrill and still maintain a true inverted-T-shaped slot without breaking through thecovering surface mulch is about 25 mm.

In contrast, the more sophisticated discversion of winged openers is mounted onparallelogram drag arms, ensuring that thewing angle never changes. The preset wingangle is reduced to 5° to allow the wings tooperate with integrity at depths as shallowas 15 mm. There is a major advantage,therefore, in being able to drill pasture witha machine equipped with similar techno-logy demanded for the more highly valuedarable crops.

While many drill designers considerpasture and sports turf to be the most diffi-cult of media to drill, with winged openersthe matted roots of pasture and turf plantsprovide a mulch medium of considerableelasticity and tensile strength, which can


Fig. 12.9. Herbicide being dripped on to the press/gauge wheels of a no-tillage opener.

be readily folded back and replaced whileretaining the integrity of the inverted-T-shaped slots (Ritchie, 1988).

Seed metering

Most pasture and forage crop seeds are small,light and/or fluffy. Many pasture seeds alsohave awns attached. This presents severalhandling and metering problems.

First, they are difficult to meter accu-rately. Small-grain metering devices thatcommonly dispense several hundred kilo-grams of seed per hectare are often not welladapted to dispensing less than 1 kilogramof small seeds per hectare. Further, if theseeds have large awns or are fluffy, theywill have a tendency to bridge above themetering device, interrupting the feed. Thisrequires an agitator to be fitted to the drill tocontinuously avoid bridging. Often, drillsfor sowing small and/or difficult seeds usean auxiliary hopper designed especially forsuch seeds.

Many pasture species are sown as blendsof two or more species. Common blends areclovers and grasses. Clover seeds are gen-erally round and dense. Grass seeds are gen-erally elongated and often fluffy and light. Apreviously mixed blend of such differentseeds may partially separate into its indivi-dual components within the seed hopper of adrill in response to the continual vibration ofthe machine. To reduce separation and aidmetering, the small seeds are often mixedwith inert filling material such as sawdust orrice hulls to bulk up the material and reducesettling. Separation can be a problem withthese mixes as well, especially if they aremetered and dispensed by an air-deliverysystem. In these circumstances the high-speed airstream may blow some lighter,fluffier seeds out of the seed slot altogetherbefore it has been covered.

Summary of No-tillage for ForageProduction

1. Farming systems that depend on anintensive forage supply demand maximum

and consistent feed supplies, which favourthe use of successive forage crops in prefer-ence to more traditional ‘permanent’ pastures.2. Establishment of successive foragecrops is only sustainable on a long-termbasis using no-tillage.3. The integration of forage and arablecropping systems is desirable in climatesthat permit economic utilization of foragecrops by animals.4. Farmers generally place lower valueson forage crops than on arable crops andwill more readily accept inferior results.5. Drills for pasture and many foragecrops need to have more accurate depthcontrol and sow at shallower depths thanequivalent machines for arable crops.6. Drills for pasture and forage crop spe-cies need to be able to meter small seeds.7. Forage crops should generally betreated with the same care and attention asarable crops, but they seldom are.8. Drills for pasture need to handle tightlyroot-bound soil and also utilize this cover-ing medium to advantage.9. With pasture renovation by over-drilling, there may be a trade-off betweenproviding a suitable environment for germi-nation and emergence and reducing compe-tition from the existing sward.10. Because the drilling time of foragecrops and pastures is usually not as criticalas with arable crops, there is more opportu-nity to wait for suitable weather to offsetsubstandard openers.11. On a cost-recovery basis, blanket spray-ing of the existing competition will give agreater long-term return than band spray-ing, which gives a greater return than nospraying.12. Cross-drilling slowly establishingpasture species may produce greater short-term weed infestation than single-passdrilling.13. Drilling early in the autumn is likely toproduce more pasture production than laterdrillings, provided adequate soil moistureexists at the time.14. Early autumn drilling and spring drill-ing are likely to produce more weed pro-blems than later autumn drilling, especiallywith slowly establishing pasture species.


15. Single-pass drilling in 75 mm rowsmay produce a short-term yield advantagewith slowly establishing pasture speciescompared with single-pass drilling in150 mm rows.16. Neither single-pass drilling in 75 mmrows nor cross-drilling in 150 mm rows hasany long-term agronomic advantage com-pared with single-pass drilling in 150 mmrows, or any short-term advantage withrapidly establishing pasture species.

17. With band spraying for overdrilling,75 mm wide bands are preferred with150 mm spaced rows.18. With overdrilling for pasture renova-tion, fertilizer should not be applied at thetime of drilling but should instead beapplied about 3 weeks post-emergence.19. With complete pasture renewal, thenew pasture should be drilled and fertilizerapplied during drilling, similar to an arableor forage crop.


13 No-tillage Drill and PlanterDesign – Large-scale Machines

C. John Baker

A no-tillage seed drill is no more nor less thana device designed to service the functions of

its openers.

While most of the desirable functions ofno-tillage drills and planters can indeed berelated back to the desirable functions oftheir openers, other components and func-tions are also important. These will beexamined in a general sense with no attemptto approve or disapprove design criteria forindividual commercial drills or planters.

Manufacturers and designers who seri-ously consider the desirable functions ofdrills and planters and variations requiredto achieve these most often will present arange of design options. Consumers mustthen ascertain for themselves what repre-sents the best value after having weighedthe risk, performance and cost factors.

For example, drills for pasture renova-tion might not need to be as sophisticated asthose to establish cash crops, becauseresidue handling is seldom a high require-ment with pasture establishment and theremay be more time flexibility allowable inchoosing an appropriate sowing date. Thisin turn permits a delay in drilling untilfavourable weather patterns arrive. The tar-get sowing dates for cash crops, on the otherhand, are often dictated by a narrow win-dow of climatic opportunity or harvesting

and seldom allow the luxury of being ableto wait very long for favourable conditions.Cash-cropping drills and planters, there-fore, must function to their maximumpotential with less dependence on weatherand therefore need to be more sophisticatedthan pasture renovation drills.

This chapter considers large field-scaleand tractor-drawn machines. The followingchapter considers small field-scale andanimal-drawn machines. In both cases weconsider drill and planter design underseveral headings:

● Operating width.● Surface smoothness.● Power requirements.● Downforce application.● Transport considerations.● Matching to available power.● Storage and metering of product.

Operating Width

The most important factors that shouldinfluence the design width of no-tillagedrills and planters are the total time avail-able to establish a given crop and the tractorpower available to pull the machines.Unfortunately, many converts from tillageto no-tillage expect no-tillage to achieve the


same rates of ground coverage as each oftheir previous tillage machines. Such expec-tations fail to account for the fact thatno-tillage machines are only going to coverthe field once and can therefore afford tooperate at a slower rate of ground coverage.Because most no-tillage drills and plantersare capable of operating at equivalent for-ward speeds to tillage machines, this meansthey can be narrower.

A sensible and practical comparisonwas made by an English farmer, whoconcluded that, so long as he could drillwith his no-tillage machine at the same rateas he could previously plough, he would begaining by adopting no-tillage. Despite suchpragmatism, it is common to hear otherfarmers demanding that no-tillage mach-ines must be the same width as conven-tional tillage machines. Some machinerydesigners accede to this request but in sodoing are forced to select openers with lowpower demand. Almost invariably, thelower the power demand from no-tillageopeners, the less work they do on theuntilled soil and the greater will be the riskof biological failure.

For example, a farmer practising mini-mum tillage will cover the field at leasttwice and probably three times to establisha crop. If each of the machines used forminimum tillage (including the drill) was4.5 metres wide, the effective workingwidth would be 1.5 metres (4.5 ÷ 3). Andyet many such farmers complain that a3 metre wide no-tillage drill would be toonarrow for them, even although once-overwith a 3 metre wide drill would completethe whole job in half the time that threetimes over with 4.5 metre minimum-tillagemachines could achieve. While seeminglysimple, it is surprising how often thisargument is voiced.

For ‘diehard’ tillage exponents, suchan argument seems to be an excuse foravoiding the issue. For others already prac-tising no-tillage with wide low-power-demanding drills, it reflects ignorance ofthe benefits that the more sophisticatedno-tillage technologies offer (which arealmost invariably accompanied by greaterpower demand).

While increases in both the power anddownforce demand from openers translateinto increases in tractor power and machineweight, these are relatively cheap andreadily available inputs. Increases in bio-logical reliability and crop yield fromimprovements in opener design are muchmore expensive and sophisticated inputs.Some operators choose to minimize poweror weight requirements rather than maxi-mize biological reliability. It is a matter ofhow individual operators approach thewhole concept of no-tillage: whether theyare yield-driven or cost-driven.

Those that see no-tillage as short-cutting tillage, but still regard tillage as thebenchmark, will probably rate cheapness,maximizing working width and minimiz-ing power and weight requirements as highpriorities. Those that see no-tillage as theultimate goal and regard tillage or mini-mum tillage as having been only interimlearning steps (albeit practised for centu-ries) will take a different view. They willseek to maximize biological performance,almost regardless of cost, weight and width,and readily add the changes needed totheir management practices. The world isfull of people with both of these outlooksand is not likely to change in this respect.

The design and desirability of anoperating width include a number of func-tions beyond that of the associated opener:power available, field topography, amountof product to be carried and field-to-fieldtransport, to list a few. Each added functionintegrates into the overall design and mach-ine width. Example machines shown inFigs 13.1 to 13.4 have a range of widthsfrom 4 to 18 m, all outfitted with the sameinverted-T opener but with widely variedconfigurations.

Surface Smoothing

The opportunity to smooth the ground priorto drilling is lost under a no-tillage regime.Thus, the drill or planter openers need tobe able to faithfully follow significantchanges in the surface of the soil without

186 C.J. Baker

detriment to drilling depths or functions.This is a demanding requirement (seeChapter 8), but for general drill or planterdesign it places limitations on overallmachine width and design considerations.

Six metres (20 feet) seems to be aboutthe upper limit a machine can be expected

to span in a single frame and allow theopeners to rise and fall sufficiently to fol-low each hump and hollow. Even then,unless the openers are pushed in with adownforce device capable of exerting con-sistent force as the openers move verticallyapproximately 0.4 metre (16 inches), some

Large-scale Machine Design 187

Fig. 13.1. A 4.5 metre wide rigid-frame end-wheel no-tillage drill.

Fig. 13.2. A 12 metre trailed toolbar with folding wings for transport.

inconsistent seeding depth will result froma 6 metre wide drill or planter. Wherewidths greater than this are required, multi-ple units or folding wings from a centralunit should be considered. Even a 6 metrewidth with good opener surface-followingability is feasible only on reasonably flat

ground. A more universal size would be4.5 metres.

Nor does it make any differencewhether the openers are spaced 150 mmapart or up to 1 metre apart. Each indivi-dual opener must rise and fall in responseto surface irregularities independently of

188 C.J. Baker

Fig. 13.3. A 4 metre rigid toolbar that is lifted clear of the ground for transport.

Fig. 13.4. An 18 metre toolbar that is end-towed for transport.

its neighbours. Its inability to do so willresult in a missed row, regardless of howmany other rows there are.

Because the micro-contour of theground surface remains undisturbed, thegauge/press wheels of no-tillage openersmust operate on a rougher surface thanwith tillage. Cushioning of this roughnesscan be achieved by springing the gauge/press wheels, but this virtually eliminatestheir gauging (or depth-control) function,since the relationship between the positionof the wheels and the base of the slot (posi-tion of the seed) constantly changes whengauge wheels are sprung. Alternatively,mounting the wheels on walking beamseffectively halves the magnitude of eachsurface irregularity, which will smooth thepassage of an opener equipped with rigidor semi-pneumatic gauge wheels, withoutcompromising their gauging function.

Then there is the question of speed.Obviously the faster the drill or planter ispulled, the rougher will be the ride. This isespecially important with planters, becausethe accuracy of seed selection and finalspacing is affected by the smoothness ofride. A speed that is acceptable for operat-ing a given precision seeder on tilled soilmay well be too fast when the same seederis operated on untilled soil. This is a nega-tive factor as far as no-tillage is con-cerned but must be balanced against the factthat several passes with tillage tools wouldhave been necessary before planting waseven attempted into a tilled soil. Therefore,if a slower planting speed is necessary forno-tillage planting, it will only reduce, notreverse, the advantages associated withno-tillage. And, with drilling of small seedscompared with precision planting of largerseeds, there are almost no speed restrictions.Indeed, some no-tillage drills operate atfaster speeds than their tillage counterparts.

Power Requirements

No-tillage drills and planters require morepower to pull them through untilled soilsthan do their tillage counterparts. This is

partly due to the fact that the openers aredesigned to break untilled ground andpartly because the machines are heavier.Typical power requirements are 3 to 9 trac-tor engine kilowatts (kW) (4 to 12 horse-power (hp)) per opener (see later in thischapter). This amount of power alsorequires an associated traction increase;thus four-wheel-drive and tracked tractorsare used more with no-tillage drills thanwith drills used in tilled seedbeds.

This power requirement places con-straints on the number of openers that canbe pulled with any given tractor. For exam-ple, a 25-opener drill operating on flat, lightsoil might require a tractor engine ofapproximately 150 kW (200 hp), while thesame drill operating on silty and/or hillysoils or in dense sod might require a tractorwith 50% more power.

Power requirements are also related todrilling speed. Some openers can operatesatisfactorily at relatively high speeds (upto 16 km/h). Others should not be usedabove 7 km/h. The tractor power require-ment will increase at higher speeds, but thiswill be put to good use by covering the fieldmore rapidly.

Planters gain an advantage over drillswith respect to tractor power requirement.The smaller number of openers on planters,due to their wider row spacing of up to1 metre, means that tractor size will seldombe the limiting factor to machine size. Gen-erally, it will be the surface-followingability of the openers that will dictate theupper limit of planter size, whereas withdrills available tractor power is often thelimiting factor. As a rough guide, for anygiven width of operation, a planter willrequire half the tractor engine power of asimilar-sized drill.

Finally, drill width will be determinedby a combination of opener number androw spacing. In general, crops benefit fromcloser row spacing under no-tillage thanunder tillage because of the improved mois-ture availability of untilled soils. On theother hand, the physical limitations imp-osed by residue handling dictate that no-tillage rows are seldom spaced less than150 mm apart on drills.


Weight and Opener Forces

Each design of no-tillage opener requires adifferent downforce to obtain its target seed-ing depth. Required downforce is deter-mined by a number of variables:

1. Soil strength, which determines thesoil’s resistance to penetration.2. Soil moisture and density, which affectsoil strength.3. The presence or absence of stones andtheir sizes.4. The presence or absence of plant rootsthat directly resist penetration.5. The decay stage of plant roots, which isaffected by the interval between spraying orharvest and drilling.6. Operating speed, because openers pen-etrate better at slower speeds than at higherspeeds.7. The draught of the openers (their resis-tance to moving through the soil).8. The attachment geometry of the open-ers to the drill frame, because, as an openermoves downwards into a hollow, the verti-cal component of pull increases, actingupwards, opposing and reducing the down-force pushing the openers into the soil.

Mai (1978) measured both the down-forces and the draught forces, at 38 mmseeding depth at very slow speeds, of verti-cal triple disc and simple winged no-tillageopeners operating in sprayed turf in a siltloam soil at two moisture contents. Theresults are shown in Table 13.1.

Data of Table 13.1 show that, while thevertical triple disc opener required aboutfour times as much force to penetrate to38 mm depth as the simple winged opener,it required 50% less force to pull it throughthe soil. The penetration action of the tripledisc opener is one of wedging the soil side-ways and downwards, accounting for itshigh downforce requirement. The wingedopener, on the other hand, tends to heavethe soil upwards, reducing its penetrationforce. In fact, soil acting on the upper sur-faces of the inclined wings tends to drawthat portion of the winged opener intothe ground, although this is more thancountered by the resistance to penetrationof the pre-disc, the vertical shank portion ofthe opener and the lower frontal edges ofthe wings.

The vertical triple disc opener is com-prised entirely of rolling discs. Once it hasattained operating depth, the forcesrequired to pull it through the soil aresmaller than with the winged opener,which cuts roots and shatters a wider zoneof soil than the triple disc opener as itmoves forward. This is reflected in thedownforce : draught ratios for the two open-ers, which averaged 0.65 for the verticaltriple disc opener and 0.11 for the simplewinged opener.

Not surprisingly, the wetter soil req-uired less downforce and draught force fromboth openers than the drier soil, but thedownforce : draught ratios remained reason-ably consistent, regardless of soil moisturecontent.

190 C.J. Baker

Vertical triple disc openera Simple winged openerb

Moisture content (g/g) 23% 28% 23% 28%Downforce (N) 882 842 221 203Draught (N) 1684 1210 2096 1852Downforce : draught ratio 0.53 0.70 0.11 0.11

Conversion: N (newton) = 0.2 lb force.aThe vertical triple disc opener had a flat 3 mm thick pre-disc of 200 mm diameter; the double discs were3 mm thick and 250 mm in diameter.bThe simple winged opener had a flat 3 mm thick pre-disc of 200 mm diameter; the wings of the tinemeasured 40 mm across.

Table 13.1. Downforce and draught requirements of two no-tillage openers.

Baker (1976a), in three separate experi-ments, measured the downforces requiredfor 38 mm penetration by a range of openersinto a dry, fine, sandy, loam soil coveredwith sprayed pasture residue and at mois-ture contents ranging from 14.1% to 18.2%(g/g). The results are shown in Table 13.2.

Data of Table 13.2 show that the differ-ence in downforce between the verticaltriple disc and simple winged openers isslightly less than in Table 13.1, probablybecause of the softer (sandier) soil. The hoeopener was similar to the winged opener,suggesting that the draw-in effect of thewings on the winged opener played only asmall role, since hoe openers do not havewings.

The angled flat disc opener requiredthe least downforce of all openers tested, butthe angled dished disc opener required moredownforce than all other openers exceptthe vertical triple disc, possibly because ofthe resistance to penetration of the convex(back) side of the angled disc.

For a drill or planter to operate, itsweight or downward drag component mustbe sufficient to provide the required com-bined downforces of all its openers whenoperating in the worst (usually driest) condi-tions in which its openers can obtain seed-ling emergence. This concept is particularlyimportant and often confuses would-be pur-chasers of drills when faced with the claimsand counterclaims of manufacturers. Forexample, vertical double or triple disc open-ers are known to perform poorly in termsof seedling emergence in dry soils (see

Chapter 6). With few exceptions, drills andplanters featuring such openers generally donot provide sufficient downforce (weight)for them to obtain drilling depth in dry soils.The drills therefore often appear to be rela-tively light in construction, giving the erro-neous impression that they can penetrate theground more easily than other drills, whenin fact the reverse is true.

Winged openers, on the other hand, cantolerate very dry soils, in biological terms, sotheir drills and planters are often built to beheavy enough to force the openers into soilsthat might otherwise be biologically hostile.Thus, the overall weight of a drill or planterdoes not necessarily reflect the penetrationrequirements of its openers in any givensoil. It may, in fact, reflect more the biologi-cal tolerance (or intolerance) of its openersto dry soils than anything else.

But there is more to forcing openers intothe ground than just dead weight. Figure 13.5shows four geometrically different arrange-ments for attaching openers to drill frames.

The first (and simplest) arrangement is tofix the openers rigidly to the drill frame, pre-venting articulation between the two. Thisgives the drill a very poor ability to followground surface changes, but the downforceprovided for each opener will remain reason-ably constant and largely predictable.

The second arrangement uses a lengthof heavy spring steel to: (i) introduce a sepa-rate drag arm between the drill chassis andthe opener; and (ii) provide limited move-ment between it and the drill frame. Toaccomplish the second function, the upper


Verticaltriple disca

Simplewingedb Hoec

Angled flatdiscd

Angled disheddisce

Downforce (N) 770 281 263 133 445

Conversion: 1 N (newton) = 0.2 lbs force.aVertical triple disc design was as for Table 13.1. The value is the mean of three experiments.bThe simple winged design was as for Table 13.1. The value is the mean of three experiments.cThe hoe opener had a flat 3 mm thick pre-disc of 200 mm diameter, and the tine was 25 mm wide.The value is the mean of three experiments.dThe angled flat disc was 3 mm thick and 250 mm in diameter. The value is for a single experiment.eThe angled dished disc was 2 mm thick and 250 mm in diameter. The value is for a single experiment.

Table 13.2. Downforce requirements of a range of no-tillage openers.

portion is extended and often coiled severaltimes to increase its flexibility. In operationthe soil drag on the opener tends to causethe drag arm to pull backwards as well asdeflect upwards, but the actual displace-ment in either direction is relatively small.This means that the point of action of theapplied downforce in the soil remains rela-tively constant in relation to the drill frame,and there is therefore little change indownforce as the openers traverse undula-tions in the ground surface.

This design limits their ability to faith-fully follow variations in the ground surface.In addition, many similar designs allow theopeners to wander sideways, with the resultthat inter-row spacing varies somewhat,although this also gives them an ability tohandle large surface stones with less block-age than either rigid openers or drag armsthat move only in the vertical plane.

The third arrangement is commonlyused for conventional drills for tilled seed-beds and has been simply transferred tomany no-tillage drills with adjustmentsonly for robustness and the magnitude ofthe applied downforces. It consists of apivot-mounted single drag arm, which ispushed down from above or sometimespulled down from beneath. The opener can-not deflect rearwards, only upwards anddownwards in a limited arc about the pivotpoint between the drag arm and the drillframe. Because the force applied by the

tractor to create forward movement (dragforce) acts through this pivot point and isopposed by the resistance of the opener atthe point of soil contact, these forces can beresolved into their vertical and horizontalcomponents by triangulation.

Figure 13.6 shows the resulting forcediagram. The drag, or draught force appliedby the tractor is opposed by the soil resis-tance to forward movement (P) through thesoil. This is shown as the horizontal compo-nent of pull (H) in the diagram. The verticalcomponent of pull (V) is derived from theresultant line of pull (R) which passes thro-ugh the point of attachment of the opener tothe drill and the centre of resistance (X) ofall soil forces, which is the point of equili-brium of all soil resistance forces on theopener and is located somewhere beneaththe soil. The vertical component of pull (V)acts upwards and, together with the verticalforce arising from the soil’s resistance topenetration, has to be overcome by the netvertical downforce (D), which is appliedseparately by springs or other means on thedrill (not the tractor) for the opener to remainin the ground.

All of these forces find an equilibrium,but a problem arises when the position ofthe opener changes relative to the drillframe. For example, as the opener passesinto a slight hollow and moves downwards(relative to the pivot point or drill frame),the horizontal component of pull (H) may

192 C.J. Baker

Fig. 13.5. The geometrical options for attachment of drag arms to a no-tillage seed drill. *Opener alsomoves forward, but since the whole machine is moving forward anyway this is ignored as it does notaffect the function of the opener in any way.

not change, but the vertical component ofpull (V) will increase because the resultantline of pull acting through the pivot point(R) will have become steeper.

This means there will then be a greaterupward force opposing the net verticaldownforce (D) on the opener, which at bestremains constant, resulting in shallowerdrilling. It would be a big enough problem ifthe applied downforce did in fact remainconstant, but, where the mechanism ofdownforce application on the drill is com-monly a spring, the downforce will actuallydecrease somewhat as the opener movesdownwards because the spring lengthens.The net effect is a significant reduction inthe net vertical downforce (D) applied tothe opener, resulting in shallower drillingfor that portion of the field.

The opposite effect occurs when anopener passes over a hump. Characteristi-cally, openers with this common geometricalarrangement drill ‘hollows’ too shallowly and‘humps’ too deeply.

However, the problem does not stopthere. If the soil resistance to forward move-ment (P) increases because the drill encoun-ters an area of harder soil, the magnitude ofthe resultant line of pull (R) will increase,even though its slope may remain thesame. This in turn will increase the verticalcomponent of pull (V), which, unless it is

compensated for by an increase in netvertical downforce (D), will also result inshallower drilling.

In reality, both the soil surface and resis-tance to forward movement of individualopeners continually change under no-tillage.Therefore, so too does the vertical compo-nent of pull, causing penetration variation.

The fourth arrangement (Fig. 13.5) iscommon on precision planters and moresophisticated no-tillage drill designs. Herethe single pivoting drag arm used in thethird arrangement is replaced by two paral-lel drag arms of equal length arranged as aparallelogram, illustrated on the right ofFig. 13.5. The objectives of this configura-tion are fourfold:

1. To maintain a predictable relationshipbetween several components on an openerassembly. Some planter openers, for exam-ple, have up to six separate components fol-lowing one another in a fixed relationship.If the assembly were mounted on a singlepivot drag arm (Figs 13.5 and 13.6) andmoved in an arc as it rose and fell, the ver-tical relationship between the forward andrear components would alter appreciably asit travelled vertically.2. To maintain a given approach angle ofcritical components to the soil, regardless ofthe vertical position of the opener assembly.


Fig. 13.6. The distribution of forces acting on a no-tillage opener as it is pulled through the soil.

Winged openers, for example, have soilwings that slope downwards towards thefront at an angle of 5–7° to the horizontal sothat they can operate at shallow depthswith the wings still beneath the ground. Ifthe opener were mounted on a single-pivotdrag arm, the preset wing angle would needto be increased to about 10° to ensure that apositive wing angle remained at the bottomof the arc of movement. But in the mid-position an angle of 10° would limit theshallowness of drilling because the wingswould break through the surface of the soil.3. To reduce the magnitude of the forcesopposing the downforce. Although a paral-lelogram arrangement will have little or nobeneficial effect on the vertical componentof pull opposing the downforce, there is yetanother force that also opposes the down-force on single-pivot drag arms. This is therotational force arising from the horizontalsoil drag acting rearwards on the base of theopener (which is always positioned lowerthan the pivot itself). With a single-pivotdrag arm arrangement, this rotational forcecauses the opener to attempt to rotateupwards, regardless of the opener positionor angle of the drag arm, and opposes thedownforce. The actual magnitude of thisopposing force is somewhat self-cancellingbecause, if the opener rotated upwards, thesoil drag would then be reduced becausethe opener would be drilling more shal-lowly. On the other hand, when the armsare horizontal in a parallelogram arrange-ment, this rotational force is eliminatedaltogether and has no effect on the down-force. Most drills and planters are designedso that the drag arms are nearly horizontalin the normal drilling position.4. To facilitate the design of long andshort drag arms without changing the posi-tion or geometry of the downforce applica-tion. The force mechanics of parallelogramsis such that, if a downforce is appliedpart-way along one of the horizontal arms,there will be a resulting vertical downforceat the rear pivots. Further, if a rigid hori-zontal frame is attached to these rear pivots,the same downforce will be applied at anypoint along this rigid frame. Since anopener attached to the rear pivots of a

parallelogram acts as a rigid horizontalframe, this principle applies to openersmounted on parallelogram arms.

In drill designs, this allows openers ofdifference lengths to be attached to parallel-ogram linkages in order to create stagger forresidue-clearance purposes, and each openerwill experience the same downforce as itsneighbour.

Although the best of the innovationsand geometric arrangements discussed abovego a long way towards ensuring that no-tillage openers receive constant downforcesthroughout their extended ranges of travel, itshould be emphasized that the magnitudeand direction of the main opposing forces(i.e. the upward vertical components of pulland soil resistance) vary with soil condi-tions and the position of the opener at anyone point in time and are therefore seldomconstant. Thus, no geometrical arrangementso far devised has the ability to maintain atruly consistent net penetration downforceon an opener.

Re-establishing Downforce

An adjunct to the general downforce requi-rements of no-tillage drills and planters isthe range of methods used to ensure that adrill or planter re-establishes the downforceto its preselected level after the openershave been raised from the ground for trans-portation and/or cornering. Repetitive rais-ing and lowering of the openers are morecommon in no-tillage than in tillage becauseturning sharp corners with the openersengaged is difficult in untilled ground. Someof the systems used are:

1. Manual return to a guide mark. Where adrill or planter is designed to raise theopeners using one or more hydraulic ramson the machine frame, the resetting of thoserams to their original positions is achievedby the operator watching a guide mark toindicate where the ram(s) had extended orcontracted to previously and stopping thecycle at that point. The potential exists foroperators to forget to watch the guide mark

194 C.J. Baker

and, in any case, such a repetitive manualtask adds to operator fatigue. On the otherhand, this system allows the downforce onall openers to be altered by the operatorwithout leaving the tractor seat.

If a drill or planter is three-point linkage-mounted to the tractor or has a separatelycontrolled set of transport wheels, thedepth adjustment is usually achieved bychanging a mechanical linkage, a screw ofsome description, or the pressure in a sec-ond independent hydraulic system. Thisadjustment remains unaltered during drill-ing and transportation cycling. Return ofthe machine to the ground after transporta-tion automatically re-establishes the magni-tude of the original downforce, since nothingwill have been altered in that respect duringtransportation. While this reduces operatorfatigue, alterations to the downforce oftenrequire the operator to leave the tractor.2. Return to an automated stop or pres-sure. Where a drill or planter is designed toraise and lower its openers hydraulically,an adjustable hydraulic or mechanical con-trol valve can be positioned on the machineso that a predetermined mechanical move-ment or oil pressure build-up will trip thevalve and halt the hydraulic system at anydesired position commensurate with agiven downforce. While this increases con-venience for the operator, a time delay stillresults while the tractor hydraulic systemmoves the ram to its predetermined posi-tion, and alterations to the magnitude of thedownforce still require the operator to dis-mount from the tractor.

One tractor manufacturer for manyyears provided a pressure-modulating sys-tem on the internal hydraulic source withintheir tractors. This system allowed the oper-ator to vary the hydraulic pressure from thetractor seat, useful for pressurizing rams ondrills or planters. Repeatability of the sys-tem simply relied on the setting of a stop onthe tractor’s hydraulic controls. The opera-tor returned the lever to this position afteractuating the lifting and transport cycles ofthe hydraulic system.3. Automated return. A hydraulic ‘mem-ory valve’ is supplied on some no-tillagedrills and planters that utilize the same

hydraulic rams for both downforce andlifting. The memory valve increases therepeatability of settings during frequenttransportation and drilling cycling byautomatically storing the downforce oilpressure in the oil-over-gas nitrogen accu-mulator(s) when the lifting (transport) cycleis actuated. Upon return of the openers tothe ground, the memory valve automati-cally and instantly returns the original oilpressure to the downforce system withoutfurther attention from the operator. Thisgreatly increases the speed of cycling fromdrilling to transport modes, and vice versa,which is important for field efficiency,operator fatigue and operator accuracy.The operating down-pressure can be changedat any time from the tractor seat.

One of the major problems with allno-tillage drills is that the magnitude of theforces involved for downforce and draughtplaces unusually high stress loadings ondrag arms, openers and their supports. Thisproblem is exacerbated when drills or plan-ters are required to operate around corners.The more durable designs have used ball orroller bearings in the drag-arm pivots,where simple bushings would usually havesufficed for the same function with conven-tional drills in tilled soils.

Unfortunately, some of the previouslyused simple designs of conventional drillshave also been extended to less expensiveno-tillage drills. These units often experi-ence early failure of components and loss ofaccuracy. For example, as pivots of dragarms become prematurely worn, openersare difficult to maintain in vertical or track-ing alignment, resulting in inaccurate depthof seeding and uneven row spacing. The fre-quency of breakages increases and residuehandling often suffers. These machine fail-ures cause frustration for the operators andresult in a decline of enthusiasm for no-tillage farming.

Wheel and Towing Configurations

A major distinguishing feature of no-tillagesoils compared with tilled soils is their


long-term ability to sustain wheel trafficwithout compaction damage and their resist-ance to surface damage from the scuffingcaused by machinery wheels and tracks.Even when compaction does occur, as thepopulations of soil fauna and bacteria returnto sustainable levels in response to decreasedtillage disruption and increased organic mat-ter, the natural restorative processes of livingsoils soon ameliorate most problems.

No-tillage drills and, to a lesser extent,planters are inherently heavier than theirtillage counterparts, but it is seldom neces-sary to increase the footprint area of theirwheels, tyres or skids on a proportionalbasis to their weight because of the increasedload-bearing strength of the soils on whichthey operate. None the less, there is littlepoint in subjecting even untilled soils tofootprint pressures from drills that are sig-nificantly in excess of the tyres on the trac-tors that pull them. Tractor tyres usuallyexert footprint pressures in the range of50–85 kPa (7–12 psi) and tracks in the30–50 kPa (4–7 psi) range.

As with conventional drills and plant-ers, there are several optional wheel configu-rations. Some of these, with their attributesand limitations, are outlined below.

End wheels

End-wheel designs, as the name suggests,have wheels positioned at either end of thedrill or planter chassis. Some planters,because of their wide row spacing, have thewheels positioned between the rows somedistance from the ends of the machines.This reduces side forces during corneringand allows two or more such machines to beconveniently joined together end to end.

End-wheel designs are suitable formachines up to 6 metres in width. Theend wheels provide excellent manoeuvra-bility and stability on hillsides and are usu-ally less expensive than other options. Mostdesigns use single wheels on each end ofthe machine, making them unsuitablefor end-towing for road transportation with-out the addition of special transportwheels. Some designs use paired wheels on

walking beams, which double the footprintarea, reduce bounce and provide an opportu-nity for convenient conversion to end-towing.

End-wheel drills and planters are notwell suited to the joining of several unitstogether side by side. Where joining mach-ines is contemplated, it is necessary to arr-ange the multiple units in an offset patternfrom a common and separate towing frame(as illustrated in Fig. 13.7). On the otherhand, no-tillage farming saves so muchtime that had been previously devoted totillage before drilling that the need for wide,multiple drills and planters is reducedconsiderably.

Fore-and-aft wheels

Fore-and-aft wheel configurations involveone or more self-steering wheels on eitherthe front or rear of the machine and at leasttwo fixed wheels on the opposite end. Theconfiguration reduces the lateral distancebetween the wheel positions, permittingwider machines to be designed than withend wheels. Because there are no wheelstructures on the ends of the machines,multiple units can be conveniently joined,as illustrated in Fig. 13.8. Such multiplearrangements need a much less compli-cated common towing facility than do mul-tiple end-wheel arrangements.

Another arrangement permits two drillunits to be used either as a narrow-row drillor as a wide-row planter. The row spacingof each unit is fixed to the desired spacingfor the wide-row planter configuration andtwo such units are arranged end to end toproduce a double-width planter (seeFig. 13.9). When narrow-row drilling isrequired, the two units are arranged in tan-dem fashion, with the rows of the rear unitsplitting the rows of the front unit, thushalving the row spacing.

Of course, for this convenient arrange-ment to be functional, the seed meteringmechanisms must be capable of sufficientaccuracy to satisfy the needs of both theplanter and the drill. Very few seeders arecapable of this degree of flexibility. Eitherduplicate seeders are used (which is

196 C.J. Baker


Fig. 13.7. End-wheel drillsarranged in an offset multiplearrangement.

Fig. 13.8. Fore-and-aft wheeldrills arranged for multiple unitoperation.

expensive and mechanically complicated)or one or the other of the two seed meteringfunctions is compromised.

The options for transportation conver-sions with fore-and-aft wheel configura-tions are many and varied. An example of aconvenient arrangement for a three-unitganged drill is shown in Fig. 13.10. The twoouter drill units fold forwards after thewhole machine is raised clear of the groundfor transportation. Other options includefolding the outer units upwards, but thisoption is limited to air seeders and planterswith lockable lids on their product hoppersto avoid spillage. The product hopperson air seeders are located on the centraldrill unit and not involved in the foldingprocess.

Yet another arrangement for transport-ing two fore-and-aft wheel drills is shownin Fig. 13.11.

Matching Tractors to Drills andPlanters

In conventional tillage, tractors are usuallyselected to match the heaviest power-

demanding implement(s) used, from primarytillage (usually ploughing) to drilling. Sincedrills and planters in conventional tillageare among the least power-demandingimplements, tractors are seldom selected tomatch drills and planters, or vice versa.Indeed, often a smaller available tractorthan the main tillage tractor(s) is used fordrilling and/or planting.

In no-tillage farming, the sprayer is theonly light power-demanding implementin the system. Drills and planters are theheaviest power-demanding implements,and this power requirement may exceed thepower required by any one of the tillageimplements it replaces. This is not to saythat no-tillage is energy-inefficient. On thecontrary, this single input of energy isseveral times more energy-efficient in termsof total litres of tractor fuel used per sownhectare than the sum of all of the multiplesmaller inputs of energy during tillage.

With planters, the maximum number ofwidely spaced rows to be sown by any onemachine seldom exceeds 12. The powerrequirement for such machines is thereforeless likely to be a limiting factor, evenunder no-tillage, than with no-tillage drills,which may have up to 50 such openers.

198 C.J. Baker

Fig. 13.9. Two-wide row units arranged in tandem to produce a drill with half-row spacing.

First-time no-tillage farmers must oftenchange their evaluations to correctly matchtractors with drills and planters. Difficultiesarise in several ways:

1. Farmers are not used to thinking ofdrills in terms of their power requirements.2. There is little information available toinform farmers about the specific power


Fig. 13.10. A folding arrangement for multiple drills.

Fig. 13.11. A towingarrangement for twofore-and-aft wheel drills.

and/or draught requirements of differentdrills and/or openers.3. Because no-tillage drills are often con-siderably heavier than their tillage counter-parts, some of the power requirements willbe needed to move the machine weight,especially on hilly land.4. Since no-tillage drills and plantersbreak untilled and often hard ground, theyare more sensitive to speed than tillagedrills as far as power demand is concerned.5. On the other hand, because no-tillage isso much more time-efficient than tillage,high drilling/planting speeds may not beimportant.6. Often, in no-tillage, the traction of atractor will be more important than its avail-able engine power. Thus, four-wheel-driveand tracked tractors are likely to becomemore useful.7. Because turning corners while drillingwith no-tillage drills is more difficult thanwith tillage drills, more fields are drilled instrips (‘lands’). This demands sharp turningon headlands or looped turns on corners,requiring a tight turning-circle capabilityfrom the tractor and drill.8. The annual tractor use for drilling/planting is likely to be reduced substan-tially under no-tillage compared with till-age. This means that total annual tractorcosts are lower, tractors last longer in termsof time and replacement scheduling, butthe actual hourly cost may be increased.9. The necessity to continuously moni-tor drill/planter functions from the tractorseat is increased, because under no-tillage afarmer has but one chance to get everythingcorrect. Tractors therefore need to be elec-tronically as well as mechanically compati-ble with their drills and planters.10. The soil in wheel tracks under no-tillage is often loosened because of the highdemand for traction, whereas under tillagethe result is almost invariably compactionin the wheel tracks. Tractors working nearthe traction limit in no-tillage will causemore soil loosening and therefore greaterdifferences of opener performances bet-ween those within and outside the wheeltrack areas.

It is difficult to generalize power require-ments of no-tillage drills because they havea large range of weight and draught.Ignoring the weight of the drill, some general-izations can be made about the power req-uirements of individual no-tillage openersfrom Table 13.1. While draught requirementsfor only two openers (triple disc and winged)are shown, these two designs are near eitherend of the range of draught requirements forno-tillage openers. Thus, their requirementsmay reflect a range of power requirements forno-tillage openers in general.

The power required to pull an openerthrough the soil is given by the expression:

power (kW) =pull (newtons) speed (km/h)

3600×

or

power (hp) =pull (pounds) speed (miles/ h)

375×

It can be seen in Table 13.1 that at aspeed of 5 km/h (3 mph) a single triple discopener would require up to 2.3 kW (3 hp) anda single simple winged opener up to 2.9 kW(3.8 hp). At 10 km/h (6 mph) the respectivepower requirements would be 4.6 kW (6 hp)and 5.8 kW (7.6 hp).

In general, the power requirements ofno-tillage drills and planters might rangebetween 2 and 6 kW (2.5 and 8 hp) peropener, depending on the drilling speed, theground conditions, the soil type, the densityand state of decay of root material in the soil,the contour of the field, the method of work-ing the field, the design of the opener andthe weight of the machine. Allowing for atractive efficiency of 65% by the tractor, thiswould require a tractor engine size rangefrom 3 to 9 kW (4 to 12 hp) per opener, whichclosely matches field experience.

Product Storage and Metering

For handling products such as seed, ferti-lizer and insecticides, the most distinguish-ing feature of no-tillage drills in comparisonwith their tillage counterparts arises from

200 C.J. Baker

the need for openers to be spaced widelyapart to clear surface residues. With plant-ers, the openers are spaced widely apart,usually in a single line, anyway. So no majordistinction is made in this regard betweenplanters for tillage and for no-tillage.

With drills, the wider-than-normalopener spacing is usually achieved byincreasing the longitudinal staggering ofalternate openers, since the row spacingbetween openers cannot be altered withoutaffecting the agronomy of the crop. Thisincrease in longitudinal spacing results inlong seed delivery tubes and shallow dropangles between the hoppers and openers forthese tubes if supplied by a single hopper.Such shallow angles interrupt normal grav-ity flow, especially on hilly land. The prob-lem is overcome in one of three ways:

1. Raising the product hoppers to greaterheights above the openers so as to increasethe angles on the delivery tubes (Fig. 13.12).2. Doubling the number of hoppers sothat each hopper is positioned over theopeners at normal height and delivery tubeangles.3. Utilizing air delivery of product to theopeners from a central hopper (Fig. 8.14).

There are arguments for and againsteach option. Doubling the number of hop-pers, for example, adds to the capital cost ofthe drill but increases the amount ofproduct that can be carried and thereforereduces the number of times the machineneeds to be out of service for filling, as wellas temporarily adding to the weight of themachine, which may help with downforce.Air seeders are inexpensive but largerdesigns carry the weight of the product on aseparate axle where neither it nor theweight of the hoppers themselves contri-butes to the overall weight of the machineto assist downforce.

High hoppers are inexpensive but aredifficult to fill and contribute to drill insta-bility on hillsides. On very steep hills, atleast one drill that carried liquid fertilizertanks provided a facility to slide the tank tothe uphill side of the drill to assist stability(Fig. 13.13). There are no known designsthat shift dry hoppers on the move.

Because the surface residues commonin no-tillage provide a habitat for pests (andtheir predators), it is often necessary toapply insecticide(s) with the seed at drill-ing. Thus, dry granule hoppers and/orliquid insecticide facilities are common on


Fig. 13.12. A no-tillage drill with elevated product hoppers.

some no-tillage drills and planters. Someplanter manufacturers have cooperatedwith chemical manufacturers to provideclosed transfer systems for insecticides.This provides for safer handling of chemi-cals, although operators need to be cautiousof pesticide residues on drill and plantercomponents during maintenance.

The concept of drilling and sprayingsimultaneously by mounting a spray boomon the drill or planter was investigated inNew Zealand. While such an achievementwould have made no-tillage a truly one-pass operation, the idea was judged notpractical for several reasons:

1. It was possible to drill on days on whichit was not wise, or possible, to spray becauseof wind or rain that might otherwise compro-mise the efficacy of weed and pest controlformulations. By restricting drilling oppor-tunities to those times when spraying waspossible, some of the time advantage ofno-tillage would have been lost.2. It introduced yet another function to beobserved by the operator and/or monitored,increasing the potential for error.3. Some openers displace, or indeedthrow, soil, causing dust, which inactivates

the most commonly used herbicides inno-tillage (glyphosate and paraquat). Spray-ing is better performed with a separateoperation by a specialist prior to drilling.

Although blanket application of herbi-cides at the time of drilling appears to beimpractical, banded application on each rowhas been used successfully (see Chapter 12).

Summary of No-tillage Drill andPlanter Design – Large-scale

Machines

1. Designs of no-tillage drills need to bemore sophisticated than those of tillagedrills.2. No-tillage drills are invariably heavierthan tillage drills and are more stressedduring operation.3. Wear and general maintenance aremore important and expensive on no-tillagedrills and planters than on tillage drills andplanters.4. The tractor engine power required tooperate no-tillage drills and planters rangesfrom 3 to 9 kilowatts (4 to 12 horsepower)per opener.

202 C.J. Baker

Fig. 13.13. A no-tillage drill with sliding liquid fertilizer tank.

5. The power requirements for no-tillagedrills and planters are more sensitive tooperating speed than those for tillage drillsand planters.6. Larger tractors are generally requiredfor no-tillage drilling.7. Because tractors are operated fewerhours per year than tillage tractors, theirhourly operating costs are higher than thelatter but their total annual costs arereduced.8. The total energy expended per sownhectare and the annual operating cost of allequipment are much lower in no-tillagethan for full tillage.9. No-tillage drills are generally narrowerthan tillage drills because of the increasedpower requirement. No-tillage plantersmay be the same width as tillage plantersbecause of fewer openers.10. Although it is not as necessary to travelas fast during no-tillage drilling or plantingas in tillage because of the time efficiency ofthe system as a whole, some no-tillage drillsand planters are actually capable of higherspeeds than their tillage counterparts. Onthe other hand, other no-tillage designsrequire low speeds.11. Time analyses to cover a field with arelatively narrow no-tillage drill comparedwith a wider tillage drill often fail toaccount for the multiple tillage passes madebefore the tillage drill begins work.12. Downforce systems on no-tillage drillsand planters need to be more sophisticated,exert greater force and have a greater rangeof travel than for tillage machines.13. The geometry of no-till opener drag-arm attachments must compensate for theincreased drag forces.

14. Parallelogram drag arms with either gasor oil-over-gas hydraulic pressurized down-force systems provide the most consistentdownforces and seeding depths.15. Drill and planter frames should be sus-pended on wheel arrangements that mini-mize bounce from uneven ground.16. Turning corners while drilling or plant-ing is more difficult in no-tillage than intillage because of the firmer soils.17. The firmer ground in no-tillage is betterable to withstand scuffing from the wheelswhen turning corners than with tilled soils.18. Automated systems that return theopener downforces quickly to preselectedvalues after raising the openers for transportare desirable in no-tillage because of theneed to raise the openers more frequentlyduring operation.19. End-wheel drill and planter configura-tions are generally the cheapest option buthave a maximum width of approximately6 metres (20 feet).20. Fore-and-aft wheel configurationsallow greater drilling widths and simplerside-by-side joining of two or more drills orplanters.21. Delivery of product from hoppers tono-tillage openers is somewhat moredemanding than for tillage drills because ofthe need for wide spacing between adjacentno-tillage openers to clear surface residues.22. Because both tillage and no-tillageopeners on planters are widely spaced,there are fewer special requirements forproduct delivery on no-tillage planterscompared with drills.


14 No-tillage Drill and PlanterDesign – Small-scale Machines

Fatima Ribeiro, Scott E. Justice, Peter R. Hobbs and C. John Baker

Small-scale no-tillage farming is not onlypractical but may be the most important

improvement to crop production andresource protection for developing nations

to be advanced this century.

Characteristics

Small-scale no-tillage is usually character-ized by small field sizes and limited avail-ability of energy, often also accompaniedby limited financial resources. Operationof large-scale tractor-drawn implements isneither practical nor possible for manyfarmers on small properties. For these rea-sons, most small-scale farmers use eitherhand-operating jabbing devices or drillsand planters with one or two rows. Sometriple-row planters are also available but arereasonably rare.

The limited number of rows influencesseveral functions, including opener design.Some of these influences are beneficial. Oth-ers are not. For example, many of the moreadvanced opener designs discussed else-where in this book require up to 12 horse-power per opener, which is often beyondthe resources of small farmers. Also, non-symmetrical openers, such as angled discs,are seldom regarded as an option on single-row machines because the side forces are

too difficult to counteract while keeping themachine heading in a straight line.

But small-scale no-tillage is benefitedby the operator attention to each squaremetre being planted, and weeds and resi-dues are often manipulated by hand or col-lected for heating fuel or animal bedding.

Another benefit is that most small-scaleplanters sow fertilizer and seed simulta-neously in separate slots. In this way theymay be considerably more sophisticated thanmany of their larger counterparts, some ofwhich do not sow fertilizer at all underno-tillage because of the mechanical com-plexity of achieving such a desirable functionwith multiple rows spaced closely together.

Thus, while small-scale no-tillage mightbe disadvantaged in some respects by thenecessary simplicity of drills, planters andavailable power, it may also benefit in otherrespects for the same reasons.

Range of Equipment

There is a wide range of small-scale no-tillageseeding equipment available, each suited todifferent sources of power and field condi-tions. The range includes hand jabbing,animal-drawn planters, power tillers andplanters for limited-powered tractors. Despitethe differences in power requirements, the


designers of most small machines recognizethe need to be able to handle residues, openan appropriate slot, meter seed and perhapsfertilizer, distribute this to the opener(s),place it in the soil in an acceptable pattern,and cover and pack the seed and thefertilizer.

Hand-jab planters (dibblers)

Hand-jab planters are popular amongstsmall-scale farmers. Some form the primarymeans of sowing seeds under no-tillage.Others are kept in reserve for filling inspaces in crops otherwise sown with open-ers in rows. Since the residue-handlingability of small drills and planters is oftenlimited, spaces occur if and when residuehandling suffers along the row.

Hand jabbers may have either separatehoppers for seed and fertilizer or one hop-per for seed only. Figure 14.1 illustrates atypical double-hopper jab planter.

A common seed metering device usedon hand jabbers is a rectangular plateplaced inside the hopper. When the hand-les are pulled apart, the seeds drop into theholes, which are delivered to the outlet andthe discharge tube. Plates with differenthole sizes are available according to theseed size. Seeding rates can be adjustedaccording to the number of holes in the seedplate that are exposed in the outlet.

Part of the attraction of hand-jab plant-ers is that they do not require access to ani-mal or tractor power and they are low-cost,light and easy to operate, although someskill is required (Ribeiro, 2004). For thesereasons they are often used by women,which increases the available labour poolfor small farmers, although no-tillage itselfreduces labour demands significantly anyway.

By planting seeds in pockets, there isminimal soil disturbance so weed seed ger-mination is minimized, resulting in easyhand hoeing between plants. The small sizeof the devices makes them suitable for oper-ation on hilly, stony and stumpy areas andfor intercropping (e.g. sowing mucunabetween maize rows) and for planting infallow areas.

Their use is most suited to light soilssince penetration is sometimes too difficultin harder soils in the absence of some formof tillage. Some clay soils may also stick tothe blades when working in wet conditionsand seed coverage may be affected by theV-shaped pockets and minimal disturbance(Ribeiro, 2004). This limitation is commonto that experienced with V-shaped continu-ous slots and is not restricted to discretepockets. But during the transitional phasefrom conventional tillage to no-tillage itmay be difficult to use a hand-jab planter, inwhich case a ripper may be used to loosen anarrow strip where the hand-jab planterwill place the seeds.

Small-scale Machine Design 205

Fig. 14.1. A hand-jab planter with seed andfertilizer hoppers.

Many hand-jab planters for no-tillageare adaptations of similar devices designedfor use in tilled soils. The main modifica-tion has been to provide longer and nar-rower points to improve penetration. Suchimprovements require less downward forcefrom the operator and help to cut residuesand penetrate the soil, resulting in less-open slots. They have resulted in 28% and23.6% increases in emergence of maize andcowpeas seedlings, respectively, comparedwith shorter points operating in heavyresidues (Almeida, 1993).

Row-type planters (animal-drawn andtractor-mounted)

The principles of operation of animal-drawnand tractor-mounted small no-tillage plant-ers are the same as for larger machines.Some of these features are discussed belowand comparisons drawn between small andlarge machines in terms of the conditionsunder which they each operate.

Downforce

With small machines, an opportunity existsto use weights as the method of downforce.

Springs are also used but hydraulic down-force systems are very rare. But weightshave the same advantages as hydraulic sys-tems at a much lower cost. In its simplestand cheapest form, weight can be appliedby an operator standing on a platform on themachine. Figure 14.2 shows such a single-row machine directly mounted on a smalltractor. The advantage is that the weight iseasily applied and removed by simply step-ping on and off the operator’s platform.

Since weights apply a consistent down-force regardless of the vertical position ofthe opener, they act in a similar manner tooil-over-gas hydraulic systems applied toindividual rams on each opener, which area feature of some of the most advancedlarger no-tillage drills.

Therefore, some small-scale no-tillagedrills and planters may provide a moresophisticated downforce system than someof the less-advanced larger machines. Theelectronic modulation of downforce inresponse to ground hardness is not possibleon the smaller machines. But, then again,nor is the direct application of weights apractical option for larger machines. Opera-tors would need to be adding and removingmultiple weights every time the downforce

206 F. Ribeiro et al.

Fig. 14.2. A tractor-mounted single-row drill that relies on the weight of an operator for penetration.

was changed. Doing so might be acceptableon a single-row machine but would soonfall out of favour on a multi-row machine.

Figure 14.3 shows the main compo-nents of typical small-scale no-tillageplanters. The disc (1) cuts straw (althoughthe effectiveness of cutting straw in thismanner often leaves much to be desired –see Chapter 10). Metering devices are posi-tioned at the bases of the seed (2) andfertilizer (3) hoppers. The openers (4 and 5)open slots for placement of fertilizer andseed, respectively. Usually the fertilizeropener (4) operates deeper or off-line com-pared with the seed opener (5), in the samemanner as bigger machines. The packingwheel (6) controls the depth of seeding andfirms the soil over the slot. The effective-ness of packer wheels operating on the soilover the slot, compared with operating inthe base of the slot before covering, is dis-cussed in Chapter 6. In general, the value ofpacker wheels operating in the mannershown in Fig. 14.3 is more one of covering(which is important enough) than ofimproving seed-to-soil contact.

Discs

All of the principles of discs and residuehandling, discussed in Chapter 10, applyequally to small-scale machines as they doto large-scale machines, except that with

single-row small-scale machines there isgreater clearance around the opener for ran-dom residues to fall away without blockingthe machine.

Most small-scale no-tillage planters havediscs, the effectiveness of which are depend-ent upon the disc diameter and design (plain,notched, wavy, flat or dished), soil condi-tions, residue conditions and adjustmentsprovided on the planter. Ineffective residuecutting results in clogging of straw on theseed components, which in turn results inproblems for seed and fertilizer placementand coverage, and even seed and/or fertili-zer metering.

Uneven straw results in hairpinning bydiscs and wrapping of residues on tinedopeners, although Casão and Yamaoka (1990)claimed that the severity of blockages couldbe reduced (though seldom eliminated) withincreasing distance between the disc and anystationary tines that follow (they recom-mended a minimum distance of 25 mm).

On the other hand, some of the moresuccessful combinations of tines and discshave the discs in close association with thetine. One example is shown in Fig. 14.4(centre tine), in which a groove is created inthe leading edge of the tine especially forthe disc to operate within. Figure 4.27shows the disc version of a winged openerin which two tines actually rub against theflat face of a disc.


Fig. 14.3. The main components of typical small-scale animal-drawn and tractor-mountedno-tillage planters.

Openers

The functions of openers for small-scaleno-tillage are no different than their func-tions for larger-scale machines and are dis-cussed in detail in Chapters 4, 5, 6 and 7.On small-scale planters with tined openers,there should be independent adjustment ofthe fertilizer opener so that fertilizer can beplaced deeper than the seed (Van Raij et al.,1985). Although placing fertilizer beneaththe seed in no-tillage does not always resultin the best crop yield (see Chapter 9), withsmall-scale drills and planters it is a morerealistic option than placing fertilizeralongside the seed because the latter optionrequires the fertilizer opener to be operatingin new ground, which requires more energythan when both openers (seed and ferti-lizer) operate at different depths in a com-mon slot. In any case, placed fertilizerwithin the seed zone is far superior to sur-face broadcasting causing slow crop accessand increased weed growth.

As with larger machines, there areadvantages for slots with minimal distur-bance (see Chapters 5, 10 and 13). While thechoice of opener type might depend on soilresistance to penetration and the amount andresistance to cutting of residues, it is no morefeasible for small-scale no-tillage farmers topossess more than one no-tillage machine inorder to cope with varying conditions than isthe case for large-scale farmers.

Therefore, to be universally useful forpractising farmers (large or small), it is inevi-table that the choice of preferred openertypes will, over time, gravitate towardsthose that function best in the widest possi-ble range of conditions. Tillage has as oneobjective to reduce the physical variabilitybetween different soils so that drills do nothave to cope with widely varying condi-tions. But, when the tillage process is elimi-nated altogether, emphasis then shifts to thecapability of no-tillage openers to copeunaided with this variability. By definition,this demands increasing sophisticationfrom the designers of no-tillage openers,regardless of their scale of operation.

Double disc openers (V-shaped slotswith Class I cover) are commonly used on

small-scale drills and planters. The slots arenarrow at the surface and may be com-pacted at their bases and sides, but are lesspower-demanding than tine-disc openersthat have less compacting tendencies. Withunequal-diameter double disc openers,because the smaller disc rotates faster thanthe larger disc a degree of cutting, or ‘guillo-tine’, effect is created (Fig. 4.3 – Chapter 4).

A range of tined openers is shown inFig. 14.4. Generally, tines require less down-force than double disc openers, which con-tributes to maintaining a uniform seedingdepth if a suitable depth-control mechanismis included. Tines are preferred in hardsoils, although their drag force may becomeexcessive for the power available. And tinesare more susceptible to blockage with resi-dues and are unsuitable in stony areas.

None the less, most of the planters usedin small-scale agriculture have tines becauseof their better penetration of hard groundand ease of manufacture. In situations where


Fig. 14.4. A range of tined openers used withanimal-drawn no-tillage planters. The centreopener has a groove cut into its leading edge, inwhich the leading disc rotates.

soil crusting is a problem (such as wherecattle have trampled the soil when wet),only tractor-mounted planters with tinedopeners will break the compaction in thesoil surface, although this is often only100 mm deep.

Seed metering devices

There continues to be debate amongstresearchers about the importance of seedspacing along the row with row cropssuch as maize (Sangoi, 1990; Rizzardi et al.,1994). More recent evidence has shown thatuniform plant emergence along the rowmay be more important than plant spacingto reduce plant competition of smaller plantsby larger plants. But the fact remains that, if‘perfect spacing’ has become the acceptednorm in conventionally tilled seedbeds, no-tillage exponents need to match this norm inuntilled seedbeds in order to avoid intro-ducing an unnecessary negative factor againstno-tillage.

Seed metering devices are responsiblefor governing seed rate (number of seeds/m)and seed spacing (consistency of spacingbetween seeds in the row); thus their accu-racy must be assured.

Most crops sown by small farmers arein wide rows. Singulation of seeds is there-fore important. So emphasis is placed onseeding mechanisms and power require-ments as priority design criteria. This con-trasts with larger no-tillage planters whereslot micro-environment, residue management

and fertilizer banding assume at least equalimportance to seed spacing and energyrequirements.

No-tillage farming in Brazil provides aninteresting comparison and contrast of small-scale machines and tractor-drawn machines.Both systems are practised widely in acountry that spans many climatic and socio-economic zones, often in relatively closeproximity to one another.

Seed metering devices used on animal-drawn no-tillage planters in Brazil all fea-ture the same gravity seed plates that areused on local tractor-mounted planters,namely plastic or cast-iron horizontal plates.Figure 14.5 illustrates a horizontal plate-type metering device along with severalalternative plates. Some manufacturers pro-vide seed plates suited to small seeds (e.g.canola, hairy vetch, forage radish) as well asmaize and other larger seeds.

The use of such devices has beendriven by their relatively low cost, sincemost singulating seeders used in countriesthat do not have small-scale agriculture arenow of the vacuum, air pressure or ‘finger-picker’ type, which involves seeds beingsucked, blown or clamped against verticalplates rather than falling under gravity intoholes or notches in horizontal plates. Verti-cal plate seeding mechanisms are faster andless sensitive to seed shape and size thanhorizontal plate-type seeders, but are alsomore expensive. Of course, vacuum and airsingulators also require a powered air fan asthe basis of operation and this would be


Fig. 14.5. A horizontal plate metering device (left) used in precision planters, with an array of optionalseed plates (right).

difficult to facilitate on an animal-drawnmachine without resorting to a stationaryengine.

Horizontal plate singulators are a veryold, well-proven and refined system thatpre-dated the vertical plate systems now incommon use on larger planters. It is no sur-prise, therefore, that, when Ribeiro (2004)evaluated the uniformity of distribution ofmaize seed along the row with four modelsof plate planters in Brazil, she found no sig-nificant differences between models in theproportion of normal spacings, skips anddoubles. The results are summarized inFig. 14.6.

To be most effective, horizontal platesingulators require the seed to be gradedinto uniform sizes and the holes or cups inthe plates to be matched to the chosen seedsize. This requires having several platesizes and some experimentation when seedlines or batches are changed. But, with limi-ted numbers of rows and small quantities ofseed, this is not a difficult undertaking com-pared with multi-row machines. But it doeshighlight the importance of being able tochange plates without emptying the entireseed hopper. Figure 14.7 illustrates a closedhopper system that allows the plate to bechanged without spillage of seed.

Fertilizer metering devices

The types of fertilizer metering devicesfound on small-scale no-tillage machines


Fig. 14.6. Percentage of normal spacings, skips and multiple seeds provided by four models ofanimal-drawn no-tillage (NT) planters (Ribeiro et al., 1998). The criteria for classification of spacing isbased on Kurachi et al. (1993). Each crop has an ideal spacing (Xref), which depends upon therecommended number of plants/m. For example, if for maize the recommendation is 7 seeds/m,then Xref is 1.00/6 = 0.17 m. In this manner the following classes are established: normal(Xref < Xi < 1.5 Xref); doubles (Xi > 1.5 Xref) and skips (Xi < 0.5 Xref).

Fig. 14.7. A closed hopper system for easy seedplate change.

include rotating bottom, auger type, edgecell and star wheels (Figure 14.8). Thedischarge rate for star-wheel and rotating-bottom types is controlled by adjustableoutlets, while auger and edge-cell types arecontrolled by changing their speed of rota-tion relative to the ground speed (Ribeiroet al., 1998).

Packing wheels

While seed row packing wheels vary indesign, most are of either steel or plastic con-struction. V-shaped wheels are used wheresoil disturbed by tined openers needs to becollected and thrown into the open slots.Good coverage/compaction depends on thedepth of seed placement, the type of seedcompaction wheel and soil moisture. Open-centred wheels are better for soils with atendency towards crusting as they press thesoil laterally towards the seed.

Power requirements and ease of operation

Small-planter operation requires more inti-mate operator involvement than for largermachines. Therefore ease of operation isimportant. For example, most small plant-ers require the operator to hold a pair ofhandles and steer the machine, as well ascontrolling the animals that may be pullingthem. With small tractor-drawn machines, asecond operator usually controls the trac-tor. In either case, energy requirements areimportant. But, since the openers used onmost small planters are similar to those

used on larger machines, all of the forcesand principles of soil reaction apply equallyto both classes of machine.

Of the seven machines reviewed byRibeiro et al. (1998), four featured tinedseed openers and three featured double discopeners. Ralisch et al. (1998) evaluated thedraught and energy requirements of a smallplanter with tined seed and fertilizeropeners in an untilled soil of quite low bulkdensity, 1.07 g/cm3, operating at 100 mmdepth. They recorded a draught force of834 N, which is less than half the valuesrecorded by Baker (1976a) for a single sim-ple winged opener (see Chapter 13).

Draught forces vary widely with soilstrength, which is itself influenced by soilmoisture content, soil type, SOM and thetime under no-tillage. So it is difficult tocompare opener (or, indeed, drill) types indifferent conditions. But, at 2.4 km/h, themachine tested by Ralisch et al. (1998)would require 1.4 kW of draught power orapproximately 3.6 kW (5 hp) of tractorengine power (at a tractive efficiency of0.65). This compares with larger drills,which commonly require 4–9 kW (5–12 hp)of engine power per opener to operate at upto 16 km/h. Such high forward speeds areunobtainable by small machines, even ifsufficient power is available, because of thedifficulty in controlling them at high speed,especially if the operator walks behindthe machine. Therefore the lower powerrequirement for small machines probablyreflects the lower operating speeds morethan other variables.


Fig. 14.8. Two examples of fertilizer metering devices used on small-scale no-tillage planters.Left: edge cell (or fluted roller); right: star wheel.

According to Siqueira and Casão(2004), differences in power requirementsare primarily due to the design of theopeners, the weight of the planter and thenumber, and the contact surface area ofthe residue-cutting and groove-openingcomponents. The main characteristic thatmakes such machines suitable for smalltractors or animals is the small number ofrows: two and three rows for maize and soy-bean planters and six to seven rows forwheat and rice drills.

Some of the factors that contribute tothe physical effort by the operator in con-trolling the machine are the weight ofthe planter, the height of the handle(s),manoeuvrability, stability and ability tooperate on sloping ground. The height of thehandle(s) becomes particularly importantduring headland manoeuvres and in mostcases is adjustable. Multiple-row modelsgenerally require less manual effort from theoperator than single-row models, becauseseats or standing platforms are provided.

Models with two rear support wheelsprovide good stability when working on flatland but may be constrained on hillsides.Models with only one wheel are moreadapted to stony and stumpy areas becauseit is easier to steer such machines aroundobstacles. For those models that evolvedfrom ‘fuçador’ ploughs, improved stabilityoccurs when fixed-shaft systems are usedrather than chains. The ‘fuçador’ ploughconsists of a wooden drawbar, which isfastened to the yoke of the draught ani-mal(s), on which is mounted a leg and ashovel-like plough body (Schimitz et al.,1991). For no-tillage, the mouldboard ploughbody is replaced with no-tillage openers.The device is used in the stony and hillyareas of south Brazil.

Adjustment and maintenance

All models offer adjustments of both seedand fertilizer sowing rates. But some modelsdo not offer many adjustments either forseed and fertilizer sowing depth or for resi-due handling. On the other hand, the mostsophisticated openers do not require adjust-ments to handle a wide range of residue

types, but these are seldom used on smalldrills or planters. In general, tined openershave the poorest residue handling charac-teristics (see Chapter 10) and disc openersthe best. But certain disc openers (e.g.double disc) have a tendency to hairpinpliable straw into the slot, where it inter-feres with seed germination in both wet anddry soils. These disadvantages apply equallyto small planters as to larger equipment.

For this reason, several small planterswith tined openers provide adjustmentsthat affect their residue-cutting ability. Thetwo main adjustments are the hitchingpoint and the front ground wheel. Adjust-ments made to the disc will also affect thedepth of the fertilizer slot. For the samedepth of the fertilizer, different depths forseeds are possible through adjustments ofthe rear ground wheel.

In the simplest models, seed rates areadjusted by changing to different seed plates,while multiple-row models often providesets of gears to change the plate speed. Othermodels that do not sow widely spaced rowsprovide geared adjustment of the speed ofbulk seeders.

Animal-drawn planters

Figure 14.9 shows a range of no-tillagedrills developed in Brazil. The modelsshown in the two top photographs are moresophisticated, have a greater range ofadjustments and are likely to produce betterresults than the models shown in the twomiddle photographs, which have evolvedfrom ‘fuçador’ ploughs. They are lighter,less expensive and more adaptable to hillyand stony areas. The model shown in thebottom photograph features disc openersand platforms for an operator.

Planters adapted from power tillers

Power tillers that are normally used forconventional tillage are sometimes used forstrip tillage by eliminating some of thepowered blades to till narrow strips (20 to200 mm wide), leaving the ground between


the rows (up to 500 mm wide) untilled.Chapter 4 addresses the issues of how largerversions of such machines have beenadapted to follow the ground surface andFig. 4.22 shows an example of one suchmachine producing narrow strips.

Tractor-drawn planters

Small farmers also use animal-drawn orsmall tractor planters requiring up to 50 hp.The machines have the same straw-cutting(smooth disc) and slot-forming (tine or doubledisc) openers as the single-row machines

and most are capable of applying fertilizerat seeding time.

Some models provide bulk seed and/orfertilizer hoppers in a similar manner tolarger machines (e.g. Figs 14.10 and 14.11)while other models are set up as multi-rowprecision seeders (e.g. Fig. 14.12).

No-tillage farming in Asia

Zero-tillage (or no-tillage) has been adoptedon about 10–15% (2 million out of 13.5 mil-lions hectares) of the wheat planted afterrice in the rice–wheat cropping system inIndia and Pakistan. Spring wheat planted in


Fig. 14.9. A range of small-scale no-tillage planters developed in Brazil.

the winter season and, increasingly, otherwinter crops, such as lentils, are beingzero-tilled. Yet the gains in soil health fromthe winter season are countered by pud-dling of summer rice. In addition, the vastmajority of the zero-tillage occurs in fieldswhere the rice residue either is removed asfodder or fuel or is burned, because thecurrent low-cost zero-tillage drills have noresidue-handling capacity. In many cases,only anchored straw remains. This leads toa hybrid system where yields cannot and willnot be maintained due to soil degradation.

Long-term experiments in Mexico haveshown that zero-tillage without residue

retention in intensive maize–wheat systemsresults in more rapid decline of yields thanwhere a full tillage system is retained inwhich residues are buried. But the besttreatment has been no-tillage with residueretention (Govaerts et al., 2004). This pointsout the need for ‘rational residue retention’in the humid tropics and subtropics withheavy monsoons and sometimes triple-cropannual intensity (K. Sayre, 2004, personalcommunication).

There is currently research being ini-tiated and undertaken in some parts ofSouth Asia on direct-seeded or zero-tilledrice (RWC website). There is little or no


Fig. 14.10. A small tractor-drawn no-tillage drill.

Fig. 14.11. Two small planters with bulk fertilizer hoppers and precision seeders.

prior research on how to plant zero-tilledrice under monsoon conditions. The majorproblems facing scientists and farmers are:(i) planting time decisions influenced byerratic onset of pre-monsoon and regularmonsoon rain and little or no assured irriga-tion schedule that can otherwise keepmachinery from entering fields when theyare too wet; (ii) the enormous weed manage-ment problems brought about by the loss ofpuddle conditions in sandy soils that allowfast infiltration and therefore reduce theability to control weeds by impoundedwater; and (iii) the lack of drainage, espe-cially in the lowlands, which can submergeand kill recently emerged seedlings. Cur-rent experiments include zero-tillage oftransplanted rice, newly available herbi-cides, rice varieties that can withstand sub-mergence and varieties that do well inalternating flooded and dry conditions.

Table 14.1 summarizes the specialproblems for zero-tilled rice.

Research into residue retention is pro-gressing, but the normal Western technolo-gies, such as double disc openers, areprobably too expensive, heavy and needexcessive power. Indigenous or locally madesystems, such as openers, with inverted-T,

double disc and star-wheel injector plantersare moving forward. But research suggeststhat much cheaper strip-tillage systemsmight provide the answer to low-costhandling of residues, especially for wealth-ier farmers. For poorer farmers, residues arehighly valued for fuel and fodder and willprobably remain so for several decades.

Two-wheeled or four-wheeled tractors?

It is a problem to learn how to apply con-servation agriculture methodologies inthe intensely poverty-stricken areas ofSouth Asia. Although zero-tillage drills arebecoming more available, there is a dearthof four-wheel tractors. As a result of pov-erty, many holdings are small and sca-ttered. Intense monsoon rains providelarge challenges to researchers, conserva-tion agriculture proponents and machinerydesigners. Whichever system(s) becomedominant, it is likely that the majority ofsmall and poor farmers will not own theirown equipment but will rent from serviceproviders.

There have been efforts in recent yearsto bring conservation agriculture to two-wheeled tractor farmers. Although the area


Fig. 14.12. A small planter adapted from animal operation for tractor mounting.

of adoption is still small, engineers andresearchers feel they are finding attachmentsto fit into this complicated socio-ecologicalsystem.

Four-wheeled tractors

India is the largest tractor manufacturer inthe world in terms of numbers. Still today,only 50% of tillage is mechanized in India(perhaps 90% in the rice–wheat areas) andless than 20% in Nepal, but greater than70% in Bangladesh. The surprising gapbetween Bangladesh and the rest of SouthAsia is discussed later. Further, the Indiangovernment laws prohibit tractor manufac-turers from manufacturing implementssuch as seed drills in order to promote localsmall manufacturing.

TOOLBARS AND TOOLS. Many machine tool-bars in India and Pakistan are based on

early ‘rabi’ (winter wheat, lentil) seed drillsthat were developed in the 1970s and1980s. The manufactures of conservationagriculture machinery have for the mostpart simply strengthened the frames, barsand shanks (Hobbs and Gupta, 2004). Thetoolbars are flat (i.e. not diamond) and gen-erally made from two pieces of 50 mm anglesteel welded together to form a squaretoolbar. Two or three bars are positioned atfixed distances. There are various systemsfor attaching the shanks to the toolbars.Farmers are learning that an adjustableshank length provides more adaptabilitybut has a tendency to swing to one side oranother if not properly tightened or if ofinferior quality.

ZERO-TILLAGE DRILLS. The current level ofenthusiasm for conservation agricultureresearch and development in South Asiawas sparked by a CIMMYT (International


Problems Possible solutions

1. Majority of rice is rain-fed. Major problemsare erratic monsoon and therefore problems ofentering fields for seeding operations.

1. Planting needs to be done as quickly aspossible when the proper soil moisture isreached. Once the field is too wet seriouscompaction will occur.

2. Smaller, lighter machinery (two- and four-wheeltractors) may help.

3. Farmers may want to have the option oftransplanting by hand or machine into zero-tillfields if direct seeding is impossible.

4. Move to early dry-season irrigated rice.

2. Lack of drainage and flooding kills offemerging seedlings after a heavy downpour ofmonsoon rain.

1. Permanent beds and introduction of somedrainage capability.

2. Flood-tolerant rice varieties are also possible.3. Transplanted zero-tilled rice.

3. Problems of weed control when soils arenot kept flooded (more serious on researchstations than in farmer fields).

1. Integrated weed management will be the key,using competitive varieties, mulching, preventingseed set of weeds, rotation and various herbicidestrategies. Untilled seedbeds where the first flushof weeds are allowed to germinate and thencontrolled with herbicide is another strategy.In this system, avoiding ploughing will avoid anew flush of weeds germinating.

2. Planting of a cover crop after wheat and killing thecover crop and weeds with herbicide beforezero-tilling rice.

Table 14.1. Problems and possible solutions for zero-tilled rice.

Centre for the Improvement of Maize andWheat, Mexico) programme that importedsimple inverted-T drills from New Zealand(Baker, 1976a, b, Fig. 14.13) into Pakistan inthe early 1980s for wheat. Over a period oftime, various national and internationalprogrammes in Pakistan and India reducedthe size and cost of the initial machinesand ‘indigenized’ them. Specifically, thepopular locally made ‘rabi’ or winter wheatdrills were strengthened and locally madeinverted-T openers attached (Hobbs andGupta, 2004).

Toolbar platforms and tools for zero-tillage have become as uncomplicated andlight as possible (Fig. 14.14). Nearly anymedium-sized workshop is able to producethem. The first system to fail on locallymade tractors is the draught control systemand the second is the hydraulic lift. Manyfarmers who purchase zero-tillage machinestherefore find that their three-point-hitchhydraulic lifts soon need overhauling. Somost zero-tillage drills come with varioustypes of depth-control wheels. In Pakistan,pneumatic tyres are often used, but the

cheaper Indian and Pakistani models havemetal wheels.

STRIP TILLAGE DRILLS. Much less popular thaneither zero-tillage or bed planting arestrip tillage drills for four-wheeled tractors(Fig. 14.15). These drills were developed byIndian scientists and engineers at PunjabAgricultural University, Ludhiana, in thelate 1980s. Typically they comprise a simple2.2 metre PTO driven ‘rotavator’ with fourblades or six blades per strip and they comein nine to 11 row models. Such machinescost 50% more than zero-tillage drills. Fuelconsumption is greater than zero-tillage butmuch less than conventional tillage. Farmersremark that strip tillage helps in fields whereresidue levels are too high for the simpleinverted-T zero-tillage shanks. Yields arecomparable to those of zero-tillage (Hobbsand Gupta, 2003). Pakistan research on rotat-ing discs, smooth and serrated, reported thatthe disc wear was high.

STAR-WHEEL (PUNCH) PLANTERS. In an attemptto solve the problem of planting into


Fig. 14.13. Inverted-T openers mounted on rigid shanks attached to a square hollow toolbar.(Note that details of typical inverted-T openers can be seen in Figs 4.22, 4.23 and 4.24 – Chapter 4.)

heavy residue, star-wheel or rollingpunch planters (originally developed inZimbabwe) have been added to existingzero-tillage frames (Fig. 14.16). Modifications

have been made to assist with synchroniza-tion of seed delivery and to prevent seedfrom falling outside the punch (RWC web-site). Perhaps the biggest problem facing


Fig. 14.14. A typical zero-tillage drill on a typical Indian tractor.

Fig. 14.15. Strip tillage drill from India.

this system in South Asia is its relativelyhigh cost.

BED PLANTERS (RIDGE AND FURROW PLANTING).

Bed systems for wheat were originallydeveloped by Mexico’s Yaqui Valley farm-ers to compensate for dwindling water sup-plies. Irrigation water is saved by applyingit through the furrows between the beds,which greatly enhances water conservationand drainage. Bed-planted wheat alsoallows access to the field after planting forchemical applications and mechanicalweeding. More than 90% of Yaqui Valleyfarmers have now adopted the practice(Aquino, 1998), but they still completelyknock down the beds and reshape them forthe next crop.

Work began on bed-planted wheat inSouth Asia in the mid-1990s and currentadoption is increasing (Hobbs and Gupta,2004). The goal is to eventually have perma-nent beds, especially on the dry sandy soils,where groundwater supplies are fast receding,or on clayey soils, where wheat is prone towaterlogging. Some variations exist foradapting to the erratic monsoon problemsand low-yielding direct-seeded rice bytransplanting rice by hand on to beds usinginverted-T openers to open the slots fortransplanting. There might be good pros-pects for bed-planting of rice–vegetablerotations in India or cotton–wheat rotationsin Pakistan.

Work is still needed to successfullygrow dry-seeded rice on beds, includingselecting sowing dates, weed management,soil types and climatic and socio-economicsituations under which permanent bedswill be of benefit. There are still questionsto be answered about the shift from anaero-bic to aerobic fluctuating conditions forrice. And there are questions about the mostappropriate machinery to be used, since themore complex monsoon systems of Asiamight require more adaptation of designsfirst created in the Yaqui Valley (Mexico)ecosystem (Sayre and Hobbs, 2004).

The majority of current commercialbed-planter designs are derivatives ofzero-tillage drills, using the same framesand fluted roller seed meters, but withsimple adjustable-width furrower shovelsadded. Much work has been undertaken onthe agronomy of wheat and rice and tworows sown on 72.5 cm beds has become thestandard in rice–wheat rotations, althoughmost planters can be adjusted to three rowsand varying bed spacings. Some designsoffer zero-tillage bed-planter combinationmachines that have extra inverted-T open-ers, shovels and shapers. But these designsseem to be inadequate for permanent bedsand increased residue levels, and work hasstarted on adding double disc openers andstar-wheel punch planters.

‘HAPPY SEEDER’. The ‘happy seeder’ (Fig.14.17) was designed to handle high rates ofresidue and seed either on beds or on the flat.The drill is a combination of two machines,a forage harvester and a zero-tillage drillusing inverted-T winged openers (RWCwebsite). The forage harvester cuts, chopsand lifts the straw, providing the drill witha clean surface for zero-tillage drilling. Thechopped material is blown directly behindthe drill and floats down as mulch. Fieldtrials in India have confirmed the useful-ness of the approach. But problems withgermination and skips have persisted andresulted in the need for adjustment for thecutting height as well as strip tilling in frontof each inverted-T opener. Adaptations inPakistan have resulted in optional separa-tion of the two halves of the machine.


Fig. 14.16. A multi-row rolling punch planter.

Two-wheeled tractors

Relative poverty results in landholdingsbecoming smaller and more fragmented. Asuccessful small farmer might own 5 hec-tares while a financially poor small farmerwill own less than a hectare with an averageof five fragmented parcels. The number offour-wheeled tractors declines to virtuallyzero for poor farmers, as does other modernmachinery. The eastern India and Bangladeshareas (Fig. 14.18) have arguably the mostfertile land in all of South Asia; yet povertyand very high population density offer con-servation agriculture researchers a particu-lar difficult and restrictive socio-economicsituation.


Fig. 14.17. An example of a ‘happy seeder’.

Fig. 14.18. The South Asian ‘poverty square’, where 500 million farm-supported families each live onless than 1 hectare of land per farm.

If conservation agriculture is to beintroduced and adopted by farmers of thisregion, the equipment must be adapted toeither bullock or two-wheel tractor powersources. These power sources must also bemade widely available, as there are cur-rently large areas where even the simplestpower sources are not available. Two-wheeledtractors have been seen as appropriateand socially equitable (Justice and Biggs,2004a), since the cost of keeping a pair ofbullocks for land preparation and sometransport are becoming prohibitively expen-sive. Many farmers seek alternatives toanimal-drawn options, but developers hereand perhaps in other underdeveloped regionsface many extra hurdles:

1. The inherent conservative nature of allfarmers, but particularly those who areresource-poor and can ill afford to takecropping risks.2. A substandard infrastructure, includ-ing local manufacturers and extension sys-tems, together with low literacy, slowsinterest in or adoption of any technology.3. All farmers focus on low-cost machin-ery investment and forgo quality for price.4. The limited research and developmenton conservation agriculture attachments fortwo-wheeled tractors compared with four-wheeled models.5. Emphasis on four-wheeled tractors andindigenous production has limited theavailability and competitiveness of two-wheeled models.

THE ROLE OF TRANSITIONAL TECHNOLOGIES.Despite these hurdles, sales of two-wheeledtractors and the common ‘rotovator’ haveincreased in the last decade, especially inBangladesh, where it is estimated that morethan 400,000 Chinese-made two-wheeledtractors undertake more than 70% of landpreparation by Bangladeshi farmers. Thisdramatic increase was brought about bychanges in government policy and devel-opment of a vibrant market for tractors fol-lowing a severe cyclone disaster and floodsin 1987 that decimated the animal popula-tion. A similar picture is emerging inNepal and to some extent in India. Special

projects in Nepal have made farmers moreaware of the benefits of owning such powersources to generate income or to providecontractor services for non-owners of trac-tors (Justice and Biggs, 2004b). The avail-ability of such power sources now allowsconservation agriculture methods andtechniques to be made available to farmersin these regions.

Besides providing power for conserva-tion agriculture, these tractors undertake amultitude of other activities, such as reap-ing, pumping, seeding and tillage. The trac-tor, or its engine, is also used as a powersource for threshers, winnowing fans, mill-ing and transport for people and goods,both on land (pulling 2 t trailers) and onwater (thousands of country boats in Ban-gladesh). They also reduce the drudgery ofpuddling rice paddies when cage wheelsare fitted. All these functions speed upfarm operations (timely land preparation,sowing and harvesting), improve yields andincrease cropping intensity and efficiencyof crop production. These results are allvital for an area where population densi-ties exceed 1000 people per square arablekilometre.

Land preparation costs for both wintercrops and summer puddling of rice are one-third less per unit of land with two-wheeledtractors than with four-wheeled tractors (Sahet al., 2004). The time spent by four-wheeledtractors in turning and backing is also elimi-nated with two-wheeled tractors, especiallyin small fields. The challenge has been toextend these advantages to conservationagriculture. First, a toolbar concept has beenused in zero-till and bed planters; and, sec-ondly, a reduced-till/shallow-till seed drillhas been modified to strip-till and form bedsin one operation.

TOOLBARS. As with four-wheeled tractors,toolbar designs for two-wheeled tractors arelargely based on modifications of the fami-liar ‘rabi’ flat-bar seed drills. The mountingplate for the toolbar is bolted to the rear ofthe transmission of two-wheeled tractors.Such a rigid mounting system in unevenfields is a problem compared with moreflexible three-point-hitch systems. None the


less, it has proved to be a robust platformfor conservation agriculture implements.Generally, two bars are used to attach toolsand implements.

TOOLBAR ZERO-TILLAGE DRILLS. Most two-wheeled tractors are capable of pulling up tofour-row zero-tillage seeders. Designers havesimply adapted the designs of the four-wheeled tractor zero-tillage drills to thereduced row numbers, using full-sizedinverted-T openers and the same shanks buthaving downsized the seed and fertilizer hop-pers (Fig. 14.19). The effective field capacityof such machines is typically 0.20 ha/h forsimultaneous seeding and fertilizer applica-tion. Planting cost for wheat and maize hasbeen reduced by some 50% compared withconventional tillage methods.

TOOLBAR BED PLANTERS. Bed planters thatsimultaneously till the soil and form thebed are not considered, regardless ofwhether or not they also sow seed and fer-tilizer, although such a practice may even-tually lead to a full no-tillage programmeinvolving permanent beds.

Bed width is limited mainly by limita-tions on wheel spacing of two-wheeled trac-tors. The standard rice–wheat bed is 65–70 cmwide. Problems occur when first formingbeds if the land is not previously prepared.The shovels grab at clods, pulling themachine off course, which may cause han-dling problems if one wheel travels into a

furrow and tilts the bed former. Clods areless of a problem under permanent bed con-ditions where light reshaping of the bed isperformed and the wheels track nicely inthe furrows and greatly reduce fatigue of theoperator.

REDUCED-TILLAGE SEED DRILL. A Chinese-designed reduced-tillage/single-pass seeddrill was introduced into Nepal in 1989 andBangladesh in 1996 by CIMMYT. It hasbeen the only conservation technologyavailable from China for two-wheeled trac-tors in those regions and has undergonemuch research by Pradhan et al. (1997),Meisner et al. (2003) and Sah et al. (2004),who demonstrated consistently high yieldsfor the following reasons:

1. It was able to drill wheat, lentils andother winter crops into very wet soils (up to30% moisture content) immediately follow-ing the rice harvest, avoiding late planting.2. It provided a very fine soil tilth, whichensures germination.3. It placed seeds at a uniform depth.4. It reduced weed problems associatedwith the previous rice crop.

Although the machine cannot be consid-ered a true no-tillage drill when in itsfull-tillage mode (Fig. 14.20), it representsan excellent transitional (and flexible) tech-nology from multiple ploughing to zero- orstrip-tillage (Fig. 14.21). The drill’s threemain components are:

1. A 48-blade, 120 cm wide high-speedshallow tillage (maximum 10 cm deep)‘rotovator’.2. A six-row fluted roller seed meter (11and 17 flutes available) and seed bin.3. A 120 cm roller for planking, compac-tion and depth control.

STRIP TILLAGE. Research on strip tillage ismore recent (Justice et al., 2004), but resultshave been promising using the Chinese-designed machine. Field efficiency improvesby 15–20% with less fuel and time con-sumption. The soil area disturbed can beadjusted from 15 cm to as little as 2–3 cm(with straightened blades). For narrow


Fig. 14.19. A zero-tillage flat-type toolbar showingthe mounting plate for a two-wheeled tractor.

stripping, additional blade holders arewelded to the axle to compensate for theabsence of a normal spiral pattern andto reduce vibrations. Work in Mexico,

Bangladesh and Nepal has shown that thissystem’s high-speed ‘rotovator’ blades (whichrotate at greater than 400 rpm) are able tocut and seed into loose straw and may


Fig. 14.20. A two-wheeled reduced-tillage machine in full-width tillage mode.

Fig. 14.21. A two-wheeled reduced-tillage machine in strip-tillage mode.

present an inexpensive machinery solutionfor the residue retention problems through-out this region for two- and four-wheeledtractors. Figure 14.21 shows a self-propelledtwo-wheeled strip tillage machine creating50% disturbance and sowing wheat in100 mm spaced rows.

PERMANENT CONSERVATION AGRICULTURE BEDS.

The flexibility of the Chinese-designed drillhas recently been extended to making newbeds and seeding in permanent beds withvery few modifications. When it is neces-sary to reshape permanent beds, the toolbarsystem with shovels can be used, or only afew rotary blades in the furrow might movesoil back on to the undisturbed bed.

STRIP TILLAGE ON PERMANENT BEDS. If the bedsdo not require reshaping, the same machinesimply strip-tills on the existing beds. InMexico and Bangladesh, modifications toconventional strip tillage machines havebeen carried out by CIMMYT as follows:

1. Two depth-control wheels are posi-tioned in the furrows in place of the roller.2. The furrow openers are extended downabout 7 cm.3. The standard ‘C’-type blades arestraightened to cut through residue andreduce the amount of soil movement.4. Extra blades are added to reduce vibra-tion (circled in Fig. 14.22).

Figure 14.22 shows a modified strip tillagemachine/seed drill, in this case used fordrilling mung bean after wheat on permanent

beds. The straightened ‘C’-type blades(inset) are able to cut the residue, leaving iton the surface of the bed with minimal soildisturbance or raking, which is otherwisefound with fixed inverted-T openers.

There has been much debate about themost desirable height for beds of this type.Most bed planters can only make beds up to10–12 cm high. Early attempts to createhigher beds are now recognized as wastingenergy and are often agronomically unde-sirable as they dry out more quickly. It isnow generally accepted that beds need onlyto be as high as is necessary to allow waterto move from one end of the field to theother for irrigation or to drain the field.Because many fields are small (average lessthan 0.2 ha), lower beds are sufficient.

Strip tillage systems based on two-wheeled tractors also involve compara-tively lightweight machines that allowseeding into wetter soils compared withfour-wheeled tractors and their associatedbed planters. This is important in conserva-tion agriculture systems in South Asia withboth flat and low-bedded applications.

On the negative side, two-wheeledstrip tillage on permanent beds does notallow access back into the field after thecrops are established. It would be desirableto facilitate banded top dressing, inter-rowcultivation and spraying as with four-wheeled tractor models.

Results of recent tests with wheatestablishment in Bangladesh (Rawson,2004) found full tillage and strip tillage tobe initially superior to bed planting and


Fig. 14.22. A strip tillage drill operating in heavy residues on a permanent bed, sowing mungbean.

zero-tillage, but also noted that resultsimproved after operators had learned toplant at the correct soil moisture content,especially with no-tillage. As a result, itis now believed that bed-planting andno-tillage with two-wheeled tractors may bethe future of conservation agriculture inthat region.

Summary of No-tillage Drill andPlanter Design – Small-scale

Machines

1. Most small-scale farmers use eitherhand-operated jabbing devices or drills andplanters with one or two rows pulled byanimal or small tractor power.2. Small-scale no-tillage farming benefitsfrom increased operator attention to seed-ing and weeding details.3. Many designs of hand or animal plantershave evolved from simple ancient designs.4. Small-scale opener designs have manyof the same requirements and designs usedon larger-scale farming presented in previ-ous chapters.5. Some small-scale opener designs arerestricted by power, downforce and symme-try requirements.

6. Providing separate fertilizer and seedplacement at seeding time is important toenhance early crop availability and reducedweed growth.7. Seed and fertilizer metering devicesmost commonly resemble adaptations ofthose used in larger machines.8. Hoe openers are more common in small-scale farming due to increased penetrationcapability compared with disc openers.9. Residue handling is often easier withsmall-scale machines as a result of fewerrows and openers.10. No-tillage in Asia presents specialproblems associated with rice–wheat rota-tions and monsoonal rains.11. Extreme poverty is a further problem inareas of Asia, which limits the sophistica-tion of no-tillage equipment and consultingservices to service farmers.12. Widespread use of simple winged(inverted-T) openers has opened opportuni-ties for no-tillage in Asia.13. Bed planting and/or strip tillage is seenas an interim step towards full no-tillage inAsia.14. ‘Happy seeders’, which combine forageharvesters and seeders, allow residues tobe placed over the seed during no-tillage,simulating some of the advantages oflarger-scale no-tillage machines.


15 Managing a No-tillage SeedingSystem

W. (Bill) R. Ritchie and C. John Baker

The overall success of a no-tillage seedingsystem will be no greater than the leastsuccessful component of that system.

Most of this book relates to the physical,biological, chemical and economic risksassociated with equipment. But even thebest equipment available will not provideoptimum results if other input factors arenot of equal or similar standard. Conse-quently, we must seriously consider theother factors required to put together a suc-cessful no-tillage seeding system that willfully minimize the risks. We obviously can-not provide a ‘recipe’ for fail-safe no-tillageseeding in every condition. Each successfulpackage must be tailored to suit an indivi-dual farm, field or field component.

This chapter briefly highlights the rangeof factors that can influence the outcomefrom no-tillage crop or pasture seeding whenundertaking a no-tillage system. A moredetailed outline of the way such factors inter-act and how they determine the success orotherwise of a no-tillage system as a whole isgiven in Successful No-tillage in Crop andPasture Establishment (Ritchie et al., 2000).

Site Selection and Preparation

There is often little choice as to which fieldor fields will be no-tilled. In other cases,

however, farmers may be in a position to bemore selective about fields, especially ifthey are just beginning to convert fromtillage to no-tillage. If this is the case, it isimportant to review the criteria that shouldbe considered.

Many who convert to no-tillage farmingdo so on areas with a history of intensivetillage that has resulted in poor soil struc-ture, low SOM, low soil microbial activity,low earthworm numbers and possibly highsoil compaction. Such conditions are notconducive to high yields from crops underany crop-establishment system. Althoughno-tillage would be expected to repair thedamage over time, the technique may bedisadvantaged in the short term. No-tillagemay not be an overnight cure for such con-ditions, even though it is certainly along-term cure.

If correctly managed, no-tillage canprovide a sustainable method of crop pro-duction while at the same time allowing thenatural processes of soil formation to con-tinue. These processes take time, perhapsyears and decades. Until a certain degree ofrepair has occurred, yields may even bereduced, especially if the farmer does notapply the best-known inputs into the sys-tem. But in other cases, where farmers haveused high levels of inputs, includingbanded fertilizer, there are numerous fieldexamples where crop yields have not


suffered, even in the first year; and mosthave steadily improved thereafter, often tonew levels never before experienced in thatfield.

Best results for converting to no-tillagewill come where a farmer has the option toselect fields that have high potential returnsfrom the outset. On an integrated pasture(sod) and crop farm, it may be most appro-priate to begin a no-tillage crop rotation in afield that has been in pasture or lucerne forsome time and contains soil in better condi-tion than fields that have been cropped formany years.

On farms that have been entirely tilledin the past, fields that have been leastaffected by the destructive aspects of tillageshould be chosen. It is unrealistic to expectto objectively assess the potential of a sys-tem such as no-tillage unless it has beengiven a realistic opportunity to show itstrue potential.

Effective soil drainage will have amajor influence on soil condition. Whileno-tillage will improve the natural drainagecapabilities of a soil over time, some artifi-cial drainage may also be required. Well-drained soils or fields will provide the bestresults.

The importance of no-tillage openersbeing able to faithfully follow groundsurface undulations has been outlined inChapter 8. But, whatever the merits of anygiven technology in this respect, it willperform more effectively and will allowhigher operating speeds to be used if thefield is smooth. When tilling a field priorto converting to no-tillage, extra effortshould be put into smoothing the final sur-face, a good investment for later no-tillagefarming.

It is worth noting, however, that, overtime, earthworm casting is capable of com-pletely levelling ruts as deep as 75–150 mm(3–6 inches). But, of course, increases inearthworm numbers are a medium-termresult of no-tillage rather than a short-termeffect.

Seeding with no-tillage drills or planterswill also be enhanced if fields are shaped soas to provide relatively straight lands. Thefirmer nature of untilled soils limits the

ability of many no-tillage machines to turnsharp corners. Pre-planning during sub-division can assist in this respect.

Weed Competition

Considerable discussion has centred onweed competition in relation to openers. Itis important to remember that most of theoperations during conventional tillage aredesigned to control competition with thecrop arising from weeds (unwanted plantspecies). Consequently, the importance ofthe spraying operation(s) in no-tillage can-not be overstressed. Good management willinclude careful identification of the weedspecies, followed by careful selection of themost appropriate herbicides or other weedcontrol strategy, such as mulching. Ade-quate planning is important to ensure thatany residual herbicides used will be com-patible with the immediate and other futurecrops, as well as desirable soil fauna such asearthworms. Some herbicides and pesti-cides, for example, are toxic to earthworms.

Having chosen the herbicide(s), addi-tional management input is required toensure that the specific chemical is appliedat the correct rate of the active ingredient,with the correct rate of the carrier (usuallywater) and any other allied chemical (e.g.surfactant). Appropriate weather condi-tions during and for a specified period afterspraying may be necessary. The particularstage and vigour of growth of the plants orsize of leaf material may influence theactivity of the herbicide. With some herbi-cides, there may be a minimum time periodbetween spraying and drilling. In mostcases, it is more critical to ensure that thetiming of herbicide application is opti-mized with regard to that particular formu-lation and the stage of growth of the weedsunless there is residual activity from theherbicide in the soil or danger of the ‘greenbridge’ effect (Chapter 3).

One principle that has repeatedlyoccurred has been the shift in troublesomeweed species with continued years of no-tillage. Each weed species has an optimumpattern of tillage, crop competition and

Managing No-tillage Systems 227

moisture to establish. Almost all long-termno-tillage studies with weed observationshave noted this distinct shift of both spe-cies and intensity. But the same and otherlonger-term studies show a significantlyreduced total weed incidence with contin-ued no-tillage systems that have used appro-priate control and crop rotation strategies.

Pest and Disease Control

Most of the same management principlesthat apply to the control of weeds alsoapply to the control of pests and diseases.Accurate identification is essential toensure appropriate and cost-effective con-trol. Most importantly, it is necessary torecognize that some pests and diseasesbehave differently under no-tillage com-pared with tillage. It can often be quitemisleading to assume that the control mea-sures appropriate to tilled soils can beapplied without modification to untilledsoils. These principles apply to both pre-and post-drilling/planting management.

Chemical control measures may also becomplemented by other management tech-niques, such as crop rotation, which is anessential tool in the development of sus-tainability. Not only is rotation effective tocontrol pests and diseases, but it can alsoenhance weed control by allowing a widerrange of herbicides to be used and/orenhancing the activity of particular herbi-cide treatments, modifying soil fertility andhelping to raise SOM levels. Care must beexercised, because the chemical eradicationof one unwanted pest species may be detri-mental to other wanted species, especiallyearthworms.

Managing Soil Fertility

The development of no-tillage drillingand planting technologies that provide sep-arate banding of fertilizer at the time ofdrilling/planting has opened the door to newopportunities for fertility management under

no-tillage. However, all of the old princi-ples apply.

The key to cost-effective fertilizer use isaccurate assessment of fertilizer levels andcrop requirements. Soil and plant tissueanalyses are useful tools in this process, asis accurate interpretation of the results.These results should then provide the basisfor the selection of the most cost-effectivefertilizer options, some of which might berestricted by machine limitations whileothers will not.

Considerably more site-specific researchmay be needed under no-tillage to deter-mine the most appropriate fertilizer regimefor any given combination of crop, soil typeand climate under no-tillage. Fertilizerresponses under no-tillage can differ fromthose under tillage in the same soil type. Sothe extension of experiences and researchresults under tillage may not necessarily beappropriate when applied to no-tillagesystems. But plant requirements are gener-ally not changed. No-tillage seeding withbanded fertilizers offers an opportunity forincreased application efficiency, but thetotal quantities of nutrients required, withthe exception of nitrogen, may not bealtered greatly.

Seeding Rates and Seed Quality

There is often considerable discussionabout optimum seeding rates for no-tillage.Some have argued that seeding rates shouldbe increased, presumably to counter someexpected reduction in seed germinationand/or seedling emergence. This practice hasbecome known as using ‘insurance’ seedingrates. But doing so, even with no-tillageopeners that have low emergence, can becounterproductive if ideal conditions areexperienced that result in plant populationsexceeding the optimum. And high seedingrates involve unnecessary extra seed cost.

There are few, if any, reasons for seed-ling establishment from no-tillage to be anylower than from conventional tillage if appro-priate equipment is used. In fact, withadvanced equipment and an appropriate

228 W.R. Ritchie and C.J. Baker

system, no-tillage has the potential forhigher establishment percentages than tillage.

In any case, it is not how much seedthat is sown that is important. Establishedseedlings are the final measure. Therefore,seeding rates should be based on an assess-ment of the degree of risk associated withany given situation, leading to a predictionof the likely effective seedling emergence(Ritchie et al., 1994, 2000). The first factorto incorporate is the germination potentialof the seed, which is specified on theseed certification data. Seeding rate canthen be calculated using the followingformula:

SRTSW TPP

EFE= ×

where: SR = seeding rate (kilograms perhectare); TSW = thousand seed weight(grams); TPP = target plant population(plants per square metre); EFE = effectivefield emergence (per cent).

The important principle is cost-effectiveness to produce the proper plantdensity. To be confident of achieving atarget plant population, a farmer must useseed of good quality in conjunction withseeding equipment that provides reliableseedling establishment under a wide rangeof conditions.

Another important factor is accuratecalibration of both seed and fertilizer out-put from the drill or planter. Because differ-ent lines of the same seed species can varyquite markedly in their seed weights andsizes according to the vigour of the crop andweather conditions and even the geogra-phical location at the time of harvest of theparticular line of seed, it is important tocalibrate the metering mechanism whenchanging seed lines or varieties. A check oncalibration should be kept during drilling/planting by matching seed and fertilizerused to the area covered if monitors are notavailable. Some seeders actually changetheir metering rates with changing ambienttemperatures. The warming of the day frommorning to afternoon may bring about anappreciable change in seeding rate withsuch seeders.

Farmer experience in Western Australiawith the disc version of winged no-tillageopeners showed that seeding rates for anequivalent canola stand could successfullybe reduced from 9 kg/ha under tillage to4–5 kg/ha with no-tillage using an adva-nced machine design (J. Stone, 1993, per-sonal communication). The resulting savingin seed cost alone was equivalent to theadditional machine cost. Prior to reducingthe seeding rate, the experience of this ope-rator from sowing at the higher rate withthis no-tillage drill had been an overpopu-lated crop, which remained largely vegeta-tive with poor crop yield.

Operator Skills

No-tillage is a relatively new technique totillage farmers. When undertaking conven-tional tillage, farmers can draw on a longhistory of tillage experience from most soiltypes of the world, even if that experiencewas not personal. However, only a limitedexperience-base exists with no-tillage.Further, that limited experience-base hasalready shown that the two techniques arequite distinct and that new skills must belearned.

The ‘one-pass’ nature of no-tillageleaves little latitude for error. On the otherhand, the range of implements and func-tions involved is much smaller. Therefore, adetailed knowledge of the key machines(sprayers and seeders) can be more easilygained.

Since soil physical conditions are morelikely to vary under no-tillage from field tofield, or even within a field, there is a muchgreater need for the operator to understandthe principles involved under the condi-tions and to be able to adjust the machineaccordingly. Of course, no-tillage drills andplanters vary widely in their respectiveabilities to ignore soil variations by auto-matically adjusting to them, but all willrequire a reasonable level of operator skillto achieve optimum performance.

It is likely that in the future we shallsee an increase in the use of electronic


monitoring and control of no-tillage drilland planter functions to enhance perfor-mance and reduce dependence on operatorskills. It is also likely that the operation ofno-tillage drills and planters will become amore specialized task, with an increasedemphasis on operator training.

Post-seeding Management

A key catchphrase that has been coined forthe modern age of intensive agriculture is‘knee-action farming’. The principle con-veyed by this term is the importance ofmonitoring crop performance carefully andregularly at close quarters throughout thegrowth cycle. In many situations, this moni-toring involves kneeling down to inspectthe crop, rather than inspecting it from adistance in a standing position, and oftenwith a magnifying glass in hand.

The ‘knee-action farming’ principle isnot exclusive to no-tillage systems but iscrucial to achieving consistently good crop-ping results, and is especially important tono-tillage because so many of the rules ofcrop husbandry differ from those commonunder tillage. No-tillage as a technique hassuffered in the past from a lack of analysisof the reasons for poor results. Too often,farmers and researchers have been preparedto condemn no-tillage as a system on thebasis of a poor result without determiningthe specific reason for the failure. This oftencontrasts with an acceptance of failure in aconventional tillage system on the basis ofpoor weather, an ‘act of God’ or just plainbad luck.

At times, there seems to have been a lackof realization that tillage crop failures due tosevere wind or water erosion are not causedby unfortunate timing but an inherent failureof the tillage system to protect the crop fromsuch a risk in the first place. No-tillagereduces some of those risks, but may intro-duce other risks of a different nature. Forexample, pest control becomes more impor-tant in some no-tillage situations becausethere is no physical destruction of their envi-ronment by the tillage process. All of this

means that a farmer must maintain vigilanceover the crop to promptly react to crop man-agement problems that might arise. It is a nec-essary advantage to have the skills to identifyspecific problems and how to solve them orknow where to go for assistance. Regular,close observation is an important tool for‘knee-action’ farming.

Planning – the UltimateManagement Tool

No-tillage is potentially a very flexible sys-tem. It provides farmers with the opportu-nity to respond at short notice to changesin soil or climatic conditions or marketindicators. It is also a system, however,that benefits from effective long-term plan-ning and regular reviews of the plan. Thesuccess of a crop may well depend on theimplementation of a plan from several pre-vious months. For example, crop rotationwill influence weed management, pest anddisease management, fertility levels andresidue levels. Forward planning may wellprovide key opportunities to take advan-tage of these changing circumstances andmarkets.

Residue management for no-tillage sys-tems is a case in point (see Chapter 10).Obviously, decisions at harvest of the pre-vious crop will significantly influence thenext phase of the farming rotation, whichmight occur several months hence. Theseconnecting events apply to chemical use,equipment selection, fertilizer programmes,crop rotation and harvesting patterns, all ofwhich emphasizes the role of forward plan-ning as a management tool.

Another example is the application oflime to raise soil pH, which with no-tillageshould take place at least 6 months inadvance of drilling because without tillagethere is limited opportunity to mix thislow-solubility fertilizer with the soil.

Most other general aspects of managinga crop production programme apply, suchas rigorous and regular maintenance ofdrilling, planting and allied equipment and


maintaining regular contact with suppliersand contractors to ensure that all compo-nents of the programme come togetherwhen required. Accurate record keepingis an integral part of any effective manage-ment programme.

Table 15.1 outlines the timing of manyof the key in-field management decisionsthat need to be made in New Zealand if ano-tillage programme is to succeed. It is notintended as a recipe, but only to highlightthe important issues. Since many of the


When What to do Implications

Any time beforedrilling

Ensure that drainageis OK

No-tillage will not rectify poorly drained soils


Determine how muchrisk you are preparedto take

Risk will be influenced by your choice of:herbicide (effectiveness is a function ofconditions – poor conditions need betterformulations); slug bait (heavy infestations andwet conditions need better formulations);pesticide (ensure you have identified the targetpest and have chosen the correct treatment);drill (difficult conditions and small seeds needbetter technology); seed (difficult conditions willplace more pressure on seed quality)


Check for pests thatare not specific tono-tillage

Some pests may need treating before or at thetime of drilling. Consider using insecticide-treated seed

Sometime beforedrilling

Subsoil to alleviatecompaction if it exists.Best done when soilis dry

Use a subsoiler that does not disrupt the surfacesufficiently to require tillage to smooth it outagain. Slant-legged or shallow subsoilers arebest in this regard

When heavy stock isremoved from field

Smooth out hoof marksgreater than 75 mmdeep

Most drills will smooth out 75 mm deep hoofmarks as they drill (some do it better thanothers). With deeper hoof marks use a ‘GroundHog’, shallow subsoiler or leveller to knock onlythe surface humps off when the soil issomewhat crumbly on top

6 months beforedrilling

Apply lime if soilpH is low

Lime takes longer to act when there is nocultivation to incorporate it. Do not apply limeclose to spraying time. Lime on plant leavesmay affect the glyphosate and is slow todissolve and wash into the soil

3 months beforedrilling

Take fertilitysamples

It takes time to get the results, analyse fertilizeroptions and take action. In long-term no-tillage75 mm sampling may be more appropriate than150 mm sampling

3 weeks beforedrilling

Aim to spray withglyphosate pluschlorpyrifos if springtails,aphid or Argentine stemweevil are a risk

Where farmers do not want to use the higherrates of chlorpyrifos, control of Argentine stemweevil may be obtained by waiting 3 weeksbetween spraying and drilling. However, youneed to be aware that a low rate of chlorpyrifosmay still be necessary to control springtails oraphids

Continued

Table 15.1. An example of management steps for a no-tillage programme in New Zealand.



At least 2 weeksbefore drilling

Remove stock from thefield (if it is in pasturethat has not alreadybeen sprayed)

To be most effective, glyphosate should besprayed on to as much clean, freshly growingleaf as possible. This also produces a heavymulch, which will help control weeds and retainmoisture, so long as the drill can handle theheavy mulch. If necessary, pastures can begrazed after spraying, provided that chlorpyrifoshas not been used.

Do not graze just before spraying, as leaf areawill be reduced. Besides, fresh animal manurewill reduce weed control and adversely affectsome drill openers. The time needed to ‘freshenup’ a pasture will vary with growing conditions atthe time

10 days beforedrilling

Check for the presenceof slugs

Scatter short lengths of smooth timber about eachfield and leave for 2 or 3 days. One or two slugs onthe underside of a 300 mm length of 150 × 20 timberindicates sufficient numbers to treat for

1 week beforedrilling

Pre-bait for slugs This is only necessary for severe infestations.Moderate or low infestations can be effectivelytreated by applying baits at the time of drilling.With heavy infestations, apply half the bait1 week before drilling and the other half at (orimmediately after) drilling. Some drills can applyslug bait as they drill, either surface broadcast or‘down the spout’

1–10 days beforedrilling

Spray glyphosate (tocontrol competition),together withchlorpyrifos (to controlpests)

Tank-mix chlorpyrifos with the glyphosate wherenecessary to control pests. The longer the gapbetween spraying and drilling, the more crumblythe soil will become as roots decompose. Butalso be aware that soil dries more slowly afterspraying because the plants are dead. In theevent of rain after spraying, the soil may stay wetfor longer.

When cutting pasture for silage, wait 3–4 daysafter spraying before harvesting

1–3 days beforedrilling

Look at the moisturecontent of the soil

With most drills no-tillage works best when thesoil is a little on the dry side. Being patient andwaiting a few extra days often gives a better result

At the time ofdrilling

Preferably apply all ofthe crop’s fertilizerrequirements ‘downthe spout’. Crops likewinter wheat and maizemay also need furtherfertilizer afteremergence

Only apply fertilizer ‘down the spout’ if the drill issophisticated enough to band it separately fromthe seed (not mixed with the seed). Crop yieldresponses to placed fertilizer under no-tillagecan be spectacular and there are generous limitsto what and how much can be applied. But onlya few advanced no-tillage drills do this. Wheresuch drills are not available, avoid putting anyfertilizer ‘down the spout’ at all, or be very carefulto select non-burn-type fertilizers. Broadcastingis then the main option, although some people go

Table 15.1. Continued


to the trouble of drilling fertilizer alone first andthen drilling seed at a shallower depth as asecond operation


Ensure all seed is sownat the target depthand covered

This is sometimes easier said than done unlessyou have sophisticated no-tillage openers.Where openers are not so sophisticated, a levelof risk must be accepted since germination andemergence will then be highly dependent ongood weather, smooth fields and low residuelevels


Apply slug bait This is most important with spring drilling but mayalso be important in autumn. Moderate to lightinfestations of slugs can usually be controlled byapplying slug bait either with the drill or as soonas drilling has finished. Get specific informationfrom the experts on the effectiveness of differentbaits

In the first 3 weeksafter drilling

Open slots and checkfor slug damage

There is often a small window of opportunity toapply slug baits after drilling if you have notalready done so and you find slugs feeding in theslots


Open slots and checkfor twisted seedlings

Contrary to popular belief, twisted seedlings do notindicate fertilizer burn. They indicate low-vigourseeds. Do not be reluctant to have a sample ofseed tested for vigour (not to be confused withgermination) at a seed-testing laboratory. Almostevery case of twisted seedlings we have seenhas been caused by low-vigour seeds, which youwould need to talk to your seed merchant about


Check for damage byArgentine stem weevil,springtails or aphids

All should have been controlled by tank-mixing theappropriate amount of chlorpyrifos with theglyphosate. But, if that did not occur, be extravigilant because these are the main pests ofno-tillage and can decimate an entire crop orpasture


Check for other pestsnot controlled withchlorpyrifos

Most normal pests of crop and pasture could alsobe troublesome under no-tillage. Be at least asvigilant as you would be with a tilled crop

4–6 weeks afterdrilling pasture

Check new grass plantsfor resistance to pulling(by hand)

When new grass plants are not easily pulled from theground, they should be ready to be grazed lightly.Use light stock in large mobs for a short period, ratherthan set-stocking smaller mobs for long periods

After 6 weeks Treat crops or pasturesnormally

That does not mean relax. It means that anyproblems that do arise will be no worse thanunder tillage. In fact, new no-tilled pastures,because of the firmness of the soil, can often betreated similarly to already established pastures.Utilization of turnips and swedes will improvebecause a greater proportion of the bulbs will beabove the ground

At harvest Spread crop residuesevenly

Do not burn crop residues except where the drill tobe used next will not handle them. Baling is

Continued

Table 15.1.

issues listed occur before the seed is sown,forward planning becomes one of the mostimportant issues.

Cost Comparisons

No management analysis of a no-tillage sys-tem would be complete without an exami-nation of the cost–benefits of choosing adrill or planter with different complexity,capability and cost. Economic studies(Baker, 1993a, b, c, 1994, 1995) show that,

as the annual use of a seed drill increases, apoint is reached where there is little differ-ence in the ownership and operating costsbetween simple low-cost machines andlarge sophisticated (high technology) exp-ensive machines. Table 15.2 shows a com-parison of costs. While the absolute costsand taxation rates shown in Table 15.2 willnot be generally applicable and will soon beout of date, the relative values between thevarious options are likely to be more nearlyuniversal.

At annual use levels of 50–100 hectares,the large sophisticated drills are prohibitively



acceptable but will slow down the build-up of SOM.With some drills, chopping of residues will benecessary. Others can handleany residue in any form. Still others cannothandle any residues at all. Operators need toknow what drill will be used for the next no-tilledcrop before making decisions about what to dowith the residues from the present crop

After 1–5 years ofno-tillage

Examine your soil andbank balance

Both will probably be improved. Soil structure,health, porosity, organic matter and earthwormactivity will be noticeably improved. Providedyou have managed the system correctly andused the appropriate levels of inputs for yourchosen level of risk acceptance, gross marginsshould increase progressively

Table 15.1. Continued

Area drilled(ha/year)

Simplelow-cost drills

Conventionalno-tillage drills

Sophisticatedheavy-duty drills

50 69 107 182100 45 62 95200 32 39 53400 26 29 30600 24 26 23800 23 23 20

1000 23 21 18

Simple low-cost no-tillage drills = US$15,000.Conventional no-tillage drills = US$30,000.Sophisticated advanced no-tillage drills = US$65,000.Other important assumptions: 24% marginal tax rate; inflation = 4%; interest rate = 11%; depreciationallowance = 12.5%; analysis period = 5 years; tractor costs are additional.

Table 15.2. Comparative ownership and operating costs (US$/ha) of no-tillage drills.

expensive (US$95–182/ha) compared withsimple low-cost machines (US$45–69/ha).However, from about 600 hectares per yearupwards, the differences are negligible, atUS$18–26/ha and may even favour thelarger machines. The data in Table 15.2 canbe considered conservative as they do notaccount for increased seedling establish-ment or yields likely to result from usingthe more sophisticated machines. The costsdo, however, account for higher operatingspeeds and lower maintenance for the moreadvanced machines. Saxton and Baker(1990), for example, found an advanced no-tillage drill with winged openers increasedwheat yields an average of 13%. Calcula-tions using a higher marginal tax rate than24% and/or lower interest rates than 11%will result in the larger machines becomingeconomic at a lower annual usage than 600hectares per year.

Summary of Managing a No-tillageSeeding System

1. The failure risk of a no-tillage seedingsystem can be reduced by ensuring a highlevel of input for all factors, not just theseeding equipment.2. Choose sites that will offer a highpotential return from the no-tillage system.

3. Chemicals generally replace tillage as ameans of weed control and must be selectedand applied with care.4. Crop rotation can be an effective man-agement tool when used in conjunctionwith chemicals to control weeds, pests anddiseases.5. Some no-tillage seeding equipmentpermits a wide range of options for fertilizerapplication. Accurate analysis of soil ferti-lity levels and crop requirements will makefull use of this benefit.6. Using excessive quantities of poor-quality seed to compensate for poor drill orplanter design or technique can be costlyand ineffective.7. No-tillage requires that new operatorskills be learned but also offers the opportu-nity for greater operator specialization.8. An otherwise well managed and exe-cuted no-tillage seeding programme can failfrom poor post-seeding crop observation andfollow-up.9. Good planning of all aspects of theno-tillage programme is a key part of riskmanagement.10. Advanced no-tillage drills becomeeconomic at about 600 hectares use peryear.11. No-tillage is a short cut compared withconventional tillage. Do not short cut theshort cut!


16 Controlled-traffic Farming as aComplementary Practice to No-tillage

W.C. Tim Chamen

Removing vehicle-induced compaction fromthe cropped area liberates crops and soils fromunnecessary stress, enhances their performance

and sustains production with the minimumof inputs.

What is Controlled-traffic Farming?

Controlled-traffic farming (CTF) divides thecrop area and traffic lanes into distinctly andpermanently separated zones. All imple-ments have a particular span (or multiple ofit) and all wheel tracks are confined to spe-cific traffic lanes. It should not be confusedwith tramline systems, which just provideguidance for chemical applicators but do notoffer permanent separation of wheels andcrops. Figure 16.1 shows the system based onexisting technology. In the longer term, it islikely that more specialized equipment willbe developed that will improve flexibilityand further enhance efficiency of the system.

Why Adopt a CTF Regime within aNo-tillage Farming System?

The benefits of CTF

Soils not only physically support crops;they are also the medium through which

their roots grow and extract water, nutrientsand air to sustain their development. Con-finement or restriction of roots will almostinvariably lead to a negative outcome. Remov-ing vehicle-induced compaction improvesand sustains the health of soils. More rain-fall is absorbed and available to crop roots,which in turn are better able to explore andextract nutrients. Improved porosity alsoensures effective gaseous exchange anddrainage, both of which further improve thepotential for optimum crop performance.

No-tillage improves many critical soilproperties but some soils are still suscepti-ble to wheel and hoof compaction, no matterhow long they have been under no-tillage.

Machine performance is also improvedby the avoidance of mechanically inducedcompaction. Variably compacted soils dif-fer greatly in their strength and response tomechanical inputs. For example, this makesit difficult to achieve optimum performanceof seed drill openers. Openers may workwell in one condition or position on a drilland poorly or less well in others. A morehomogeneous soil condition over the fieldprovides greater machine precision. Soilresponses are more predictable and varyless from point to point. Avoiding soil com-paction diminishes the heterogeneity (vari-ability) of soil properties both within andbetween soil types, making them easier to


manage and more suitable for a wider rangeof crops under a no-tillage regime.

The effects of CTF on soil conditions

No-tillage farming systems may cause vary-ing amounts of soil disturbance. Initiallyno-tillage concentrated on avoiding generaltillage operations, but recent emphasis hasadded the importance of minimizing the dis-turbance created by the no-tillage tools (open-ers) themselves. Low-disturbance no-tillageis where drill and planter openers aim to dis-rupt the soil as little as possible – sufficientonly to sow the seed and place the fertilizer,but otherwise leaving the soil almost as if ithad not been drilled at all. Other forms ofno-tillage involve aggressive shank, hoe ortined openers that leave the surface, and oftendeeper layers, in a disturbed state resemblingthe effects of minimum or reduced tillage.

Defining low-disturbance no-tillage isdifficult. A general rule of thumb is that atleast 70% of the original surface residues

should remain undisturbed after passageof the drill. But, for openers operating at750 mm row spacing, 30% disturbanceallows 112 mm either side of each row to bedisturbed, whereas, at 150 mm spacing, only22.5 mm either side of the row is acceptable.

In general terms, the greater the compac-tion applied to the soil, the greater will be theneed for repair. No-tillage provides a largemeasure of remedial action by reducing thetraffic intensity, avoiding soil disturbanceand allowing the soil to restructure. However,removing the traffic altogether will allow thisto happen in greater measure and morequickly. Central to the creation and main-tenance of an improved soil structure is theminimization of disturbance, and, as we haveseen from the above, the more aggressive theopener, the more disturbance there will be.

Unlike randomly trafficked soils, wherethe openers may need to create a seedbed aswell as sow the seed, non-trafficked soilstend to retain their seedbeds from one seasonto the next, so that only seed and fertilizerplacement is required. From all points of

Controlled-traffic Farming 237

Fig. 16.1. A tractor-based controlled-traffic farming system showing drilling, spraying and harvesting.On this scale, all wheel tracks other than those used for chemical applications might be sown.

view, the less the disturbance created duringseeding within a no-tillage regime, the better,and CTF helps to make this possible. Wherecomparisons have been made between ran-dom trafficking and CTF, the research dataoften do not include details about the openerdesigns, and so the optimum no-tillage con-ditions for the trials may not always havebeen present, which may or may not haveaffected the comparisons.

Soil strength

The strength of soils is governed by a numberof factors, some of which are interrelated andall of which have an impact on no-tillage.Compacted soils are stronger and have greaterresistance to penetration than non-compactedsoils, particularly when their water contentsdiminish (Blackwell et al., 1985; Campbellet al., 1986; Gerik et al., 1987; Chamen et al.,1990, 1992; Dickson and Campbell, 1990;Carter et al., 1991; Unger, 1996; Radfordet al., 2000; Yavuzcan, 2000; Abu-Hamdeh,2003; Radford and Yule, 2003).

In a 10-year experiment, one particulartreatment subjected a moist (25–32% watercontent) Vertisol to a wheel load of 5 t inyear 1 and 3 t annually thereafter for 5 years(Radford and Yule, 2003). Tillage to controlweeds was used in the first 5 years of an ara-ble rotation. At the end of the initial 5 years,no-tillage and controlled traffic were appliedfor a further 5 years to these same plots.The greater shear strength persisted in the0–100 mm profile for over 3 years, while, ina treatment with repeated 5 t wheel loads inall of the first 5 years (compared with the 3 tafter year 1), strength effects to 100 mm per-sisted for nearly 5 years after no-tillage wasintroduced.

These data suggest that randomly traf-ficked soils may exhibit high levels of vari-ability in strength as a result of a history ofindiscriminate wheeling. Although thesedifferences may tend to diminish with timeunder a no-tillage regime, the natural ame-lioration in the top and most important fewcentimetres will tend to differ according tosoil type, opener design and newly appliedtraffic. Added to this will be a generalincrease in soil strength arising from repeated

wheel passes. On some soils this may not becompletely counteracted by structural impro-vements resulting from lack of disturbanceor by a greater concentration of organicmatter in the surface layers.

EFFECTS OF SOIL STRENGTH ON NUTRIENTS AND

SEEDLING GROWTH. Increased soil strengthreduces a crop’s ability to extract nutrientsand as a result some will be lost from thesoil system. With any particular soil, strengthvariation is dominated by changes in watercontent, but strength at a specific water con-tent is determined by its state of compact-ness. Denitrification caused by compactionis a source of nitrogen loss, and restrictedrooting may cause poor phosphorus uptake(Wolkowski, 1990, 1991). Potassium uptakeis primarily affected by aeration. Below anoxygen concentration of about 10%, uptakeis impaired.

Denitrification may lead to fertilizer losswith no-tillage in wet conditions (Torbertand Reeves, 1995). When the soil is dry,uptake of N can be compaction-impaired bylimiting root growth. This effect has been thecause of N loss, particularly under no-tillage,following N fertilization and heavy rainfall(Ball et al., 1999). Denitrification and meth-ane production were identified as one of themain constraints to the improved environ-mental performance of no-tillage comparedwith reduced tillage (King et al., 2004).King et al. attributed this to an increase inthe bulk density of the topsoil and to pooraeration.

Soil strength directly above emergingseedlings may also be an issue. Addae et al.(1991) suggested the following relationship:

Y = 90.4 – 3.58X

where:

Y = seedling emergence, percentageX = soil strength, kPa

The maximum force that a wheat seedlingcoleoptile can exert is around 30 g and onlywhen resistance is less than 25 g can 100%emergence be expected (Bouaziz et al., 1990).

238 W.C.T. Chamen

Compaction of the soil above an emergingseedling therefore reduces emergence,particularly if the soil is wet. Variation inthe time to emergence is also often associ-ated with soil strength variations (Brown,1997).

EFFECTS OF SOIL STRUCTURE ON SOIL STRENGTH.Increased soil strength can be attributed tochanges in soil structure. It is a readilyobservable fact that compacted non-shrinkingclay soils exhibit plasticity when moist andcloddiness when dry. They rarely displaythe friability and flow characteristics ofnon-compacted granular material. Conse-quently, randomly trafficked soils not onlyreveal large variations in penetration resis-tance, but they also react differently whendisturbed. In some areas they will flow and inothers they will smear or fracture into variablysized and often large aggregates. This is noteasy to deal with when designing an openerto work consistently within a given soil type ata given moisture content. It is even more dif-ficult when soil type changes across a givenfield. To overcome the problem of variablepenetration depth, electromechanical controlsystems for no-tillage drills have recentlybeen designed to cope with changes in soilstrength and go a long way towards over-coming the problem (see Chapter 13).

One of the outcomes of tillage to rem-edy compaction, in an attempt to create auniform but artificially structured seedbed,is interruption of natural soil structural-forming processes. This is despite the factthat the very mechanical processes beingemployed will themselves immediatelyrender that soil more susceptible to the nega-tive effects of random wheeling and othercompacting influences. Therefore, althoughtillage temporarily makes the operation ofseed drills relatively simple, it commits soilto a downward negative spiral of compactionand structural degradation and has neverbeen a long-term answer.

Cockcroft and Olsson (2000) suggestedthat no-tillage and zero traffic could notavoid the problem of hard setting on somesoils. Although biopores help the infiltrationof water and more organic matter improvesthe situation, drainage and root growth can

still be impaired. A sustainable solution hasyet to be found for these soils.

EFFECTS OF SOIL STRENGTH ON DRAUGHT FORCES

AND IMPLEMENT WEAR. Although no-tillageaims to minimize soil disturbance, the forcerequired to displace soil during sowing isstill directly proportional to its strength.Chamen et al. (1990) reported a 25% reduc-tion in energy requirement for no-tillage innon-trafficked compared with trafficked soil,despite a slightly greater depth of operation(56 mm in the non-trafficked compared with50 mm in the trafficked soil). This is similarto reported reductions in energy for tine till-age in trafficked and non-trafficked soil(Lamers et al., 1986).

A further consequence of lower soilstrength is proportional reductions in wearon soil-engaging components. Lower wearsaves on replacements and also saves onlabour and downtime to fit new components.

While in tilled soils and some untilledsoils it is often found that openers workingbehind wheels require replacement morefrequently than elsewhere, in other situationsthe reverse may be true. When operatingno-tillage drills in long-term pasture withgood load-bearing ability in New Zealand,often the surface disturbance resulting fromwheel slip by the tractor tyres loosens ratherthan compacts the soil and wear of openersin those wheel marks is reduced [Eds].

Soil structure

Avoiding vehicle-induced soil compactioncan have a major impact on the structure-related aspects of water and gas movementin and out of the soil. Much research has con-centrated on these characteristics. McQueenand Shepherd (2002) concluded that somesoils brought into cropping from permanentpasture could suffer from soil deformationcaused by traffic. Compaction, even onno-tillage soils, reduced water infiltration(Ankeny et al., 1990; Meek et al., 1990; Liet al., 2001), soil porosity, saturated hydraulicconductivity (Wagger and Denton, 1989), air-filled porosity and permeability (Blackwellet al., 1985; Campbell et al., 1986).


On the other hand, minimal-disturbanceno-tillage openers operating in silty soils inNew Zealand have been shown to leavemost indices of soil health (including soilstructure) in a similar state to the originalpermanent pasture. Even after 20 years ofcontinuous double cropping with no-tillageand random and repeated trafficking, therewas no obvious effect on such soils comparedwith their pasture equivalents (Anon., 2000;Ross et al., 2000, 2002a, b; Ross, 2001,2002) [Eds].

Both air capacity and available waterare primarily affected by bulk density,organic carbon and clay content, the latterbeing relatively more important in subsoils.Variability in air capacity and available wateris highly dependent on bulk density andsoil texture. In a clay loam, available waterhas been halved with an increase in bulkdensity from 1.4 g/cm3 to 1.75 g/cm3 (Hallet al., 1977).

Reduced infiltration due to traffic com-paction can increase runoff and erosion.Wang et al. (2003) measured a twofoldincrease in runoff on trafficked comparedwith non-trafficked no-tillage plots and anapproximate threefold increase in soil loss.

Environmental improvements associ-ated with non-compacted soils also relate togaseous losses to the atmosphere. Reducedair-filled porosity due to compaction leadsto denitrification in clay soils. Similarly,no-tillage and controlled traffic appear topreserve CH4 oxidation rates (Ball et al.,1999).

There is also evidence of improvedwater availability to crops on some non-trafficked, albeit shallow-tilled (100 mm)clay soils. Changes in matric potential at150 mm depth over a 48 h period showedlarge fluctuations on a trafficked soil com-pared with relatively small changes onnon-trafficked soil. The latter reinforces theimportance of promoting natural soil struc-ture through both no-tillage and controlledtraffic (Chamen and Longstaff, 1995).

Campbell et al. (1986) working on asandy clay loam found that, in the absenceof traffic, the soil could be reclassified frombeing unsuitable to being entirely suitablefor no-tillage.

The implications of CTF for no-tillageoperations

RESIDUES AND RESIDUE HANDLING. Residuesare a critical issue in no-tillage systemsbecause they are not incorporated into thesoil before the next crop is drilled. Indeed,many of the benefits of no-tillage accrue fromthis fact. It is preferable to leave the residuesin situ on the soil surface to decay slowlyand for both the residues themselves andtheir decayed products to be gradually incor-porated into the soil by fauna such as earth-worms. This is also advantageous in termsof nitrogen, which is often temporarilylocked up by rapid organic matter decom-position. Residue management prior toand during drilling is therefore particularlyimportant if the crop is to be sown withoutinterference or subsequent adverse effectson germination and seedling growth.

The additional precision afforded bycontrolled traffic (see next section) shouldallow crop residues to be manipulated andplaced more precisely, if required. For exam-ple, the tendency to use wider equipment isalready initiating the design of more accurateresidue placement methods by harvesters.Working from permanent wheel ways createdas part of carefully prescribed routes andwhere future sowing lines are predetermined,residues could specifically be placed toavoid the new crop row.

With random traffic systems, crop stub-bles and residues are flattened in an arbitraryway, resulting in their variable orientationto drill openers. Some openers do not per-form reliably in these conditions; while oth-ers not only perform reliably but they utilizerandom residues to control the seed micro-environment. Controlled traffic avoids ran-dom stubble trampling and its associatedvariability. It is possible, for example, todevelop the system where small grains havebeen stripped from straw that remains stand-ing following the harvester pass. Both manualand assisted-guidance methods could thenallow sowing between the standing strawrows and into soil that may only have a cov-ering of the chaff and light fraction (Fig. 16.2).

There will be additional effects on resi-dues from increased earthworm activity in

240 W.C.T. Chamen

non-trafficked soils. Radford et al. (2001)recorded an increase in earthworm numbersfrom 2 to 41/m2 when all compaction on amoist vertisol was avoided. Pangnakorn et al.(2003) found a favourable differential of 26%in numbers of earthworms in no-till com-pared with cultivated soils and an additional14% increase when traffic was removed.

Compaction restricts oxygen supply,nutrient intake and physical movement.Although the effect of additional earthwormactivity is unlikely to have a direct effect onthe sowing operation in terms of residues,the reverse is often true. Residues encourageearthworms and they in turn may improveseedling emergence, particularly in wet soils,primarily as a result of improved porosity.(Chaudry and Baker, 1988; Giles 1994).

Considering that there are increasinglevels of CO2 in the atmosphere and this

scenario is likely to continue, crop andweed residues and crop yields are likelyto increase (Prior et al., 2003). Improvedmanagement of residues will therefore be ofincreasing importance, not only to deal withthe quantity, but also to avoid a temporarylock-up of nutrients and longer-term exces-sive acidity in the surface layers. This issueremains to be dealt with adequately.

WEED CONTROL. Traditional cultivation sys-tems use a combination of cultural, chemicaland tillage methods to achieve weed control.Weeds are always a threat to the sustain-ability of cropping, and they continuouslyevolve to overcome any particular means ofcontrol. The most recent example of this isthe resistance of Lolium rigidum (annualryegrass) to glyphosate (Wakelin et al., 2004).Therefore, it can be argued that reducing thenumber of options for weed management isrisky; but there are positive aspects too, someof which are aided by CTF, the most impor-tant of which is minimizing soil disturbance.

There are several approaches thatimprove weed control without tillage. Oneof the few defendable objectives of tillage isto stimulate weed seed germination so thatthe offending seedlings can be killed by asubsequent tillage operation. In the absenceof such stimulation, the most widely prac-tised weed control measure is to blanketspray with either selective or non-selectiveherbicides. CTF will make this more effi-cient because a greater proportion of weedseeds are likely to germinate during theinter-crop period. Seeds lying on a friablesoil surface are more likely to germinatethrough intimate soil contact or by burial,either through their own activities (e.g. wildoats, Avena fatua) or external forces such asrainfall, frost, wind or the activities of soilfauna. After spraying, the aim is to avoidfurther weed seed germination, and crucialto the success of this is the minimization ofsoil disturbance by the no-tillage openers.

This approach has been effective inNew Zealand. Troublesome weeds such aswild turnip had forced many farmers to stopgrowing forage brassicas by conventionaltillage because of the difficulty in control-ling volunteer wild turnip plants, the seeds


Fig. 16.2. Soil and residue conditions followinggrain stripping. Global positioning systems (GPS)and other precision guidance methods allowsowing to take place between the rows in a CTFregime.

of which may remain dormant in undis-turbed soil for up to 40 years. Even vigorousno-tillage openers often disturbed sufficientsoil within the rows to create rows of theweeds where none had existed before drill-ing. But use of the disc version of wingedno-tillage openers or double disc openers,either of which minimizes surface distur-bance, avoids the problem [Eds].

After drilling, it may be possible to uti-lize the close precision of CTF to targetinter-row weeds that will either germinateas a function of their own activity (as des-cribed above) or be prompted to do so byshallow inter-row tillage with a light imple-ment. Inter-row flaming, steaming, mowingand non-selective herbicides can then beapplied where there is sufficient roombetween the rows. Vision guidance methodsfor doing this are now fast and reliable.

The efficiency of spray booms is likelyto be improved by CTF systems. Most CTFsystems use extended track widths and it isanticipated that future developments willprovide additional boom support even fur-ther from the boom centre. Improved stabilityreduces roll and allows booms to be posi-tioned closer to the crop or ground withoutfear of contact. The auto-guidance systemsgenerally associated with CTF also reduceboom yaw, a feature associated with man-ual overcorrection of steering. Reduction ofroll and yaw improve the application accu-racy while diminishing the risk of drift.

OPENER DESIGN AND PERFORMANCE. The mainimplication of CTF for no-tillage openerdesigns involves the general reduction in soilstrength in the absence of vehicle-inducedcompaction. This reduces the penetrationand draught forces required between wheeledand non-wheeled areas. Chamen et al.(1990) found that a triple disc openerpressed into non-trafficked no-tillage soilby rubber buffers penetrated too deeply. Asolution was to use a traditional single discopener designed for cultivated soils. Thus itmay be seen that no-tillage seeding on non-trafficked soils can be carried out with sig-nificantly lighter and less robust machines.

Non-trafficked soils tend to present amore friable seedbed regardless of the soil

moisture regime. This can have negative aswell as positive effects. The positive effectsare obvious and important, but hairpinningwith discs may be a greater problem withCTF because there is less soil resistance tothe vertical cutting of residues. Setting thediscs deeper is unattractive because draughtforces and soil disturbance are greatlyincreased. Other options include managingthe residues to avoid their presence in thesowing line (Fig. 16.2) and using openersthat do not create hairpinning or deliberatelyseparate the seed from contact with hair-pinned residues. The disc version of awinged opener places seeds to one side ofany hairpins that the central disc may create,and eliminates this problem. The more fria-ble nature of the soil under CTF will havelargely a neutral effect on hairpinning withthis opener [Eds].

Wide spacing of narrow tines workswell in dry conditions but becomes unac-ceptable in moist soils because of the largewedges of residue left as the tines eventuallyclear themselves (see Chapter 10). Punchplanters show promise if hairpinning canbe avoided, but their potential has been lim-ited by the high strength of trafficked soils.The greatest problems will be with moistclays, when fine soil and residues cling toevery part of the opener. Experience of theseconditions within a CTF regime is still lim-ited and further use and customized openerdevelopment are needed.

On a more general note, the more friableseedbed structure associated with CTFshould ensure that the firming devices ofseed openers operate more effectively. Assuggested by Baker and Mai (1982b) andAddae et al. (1991), firming should bearound or under the seed, not above it. WithCTF, a more homogeneous soil condition islikely to be presented to the opener andthere will therefore be less need for compro-mises in depth settings between individualopeners and less variation in seed covering.There will also be less wear, lower overalldraught and reduced power and tractiondemands.

Figure 16.3 shows how two disc-typeopeners on the same machine can performvery differently, depending on whether

242 W.C.T. Chamen

they are behind wheels or in between.In the absence of differential rutting fromwheels, the soil surface will also be smoo-ther. This reduces the potential for differ-ences in opener performance, particularlywhere they are mounted in gangs. Openersmounted individually on parallel linkageswill be less prone to depth variation whereruts are present, but a more level surfacewill still have a positive influence on theirperformance.

Consistent sowing depth is vital to avoidtoo shallow planting in dry conditions or toodeep in others, and Kirby (1993) noted thatthe time to emergence was extended as sow-ing depth increased. Heege (1993) foundthat, in the range of cereal seeding depthsfrom 25 to 45 mm, field emergence droppedfrom 82% when the depth varied by around6 mm, to 50% when the variation increasedto 20 mm. Heege and Kirby both foundthat rate of emergence affected subsequentgrowth, as did Benjamin (1990). They allsuggested that differences in date of emer-gence were perpetuated and even exacer-bated in subsequent growth. Although thesedifferences may not be large enough to cre-ate differences in yield, they do make it moredifficult to estimate crop growth stage forchemical applications. Additionally, thismeans that a larger proportion of the cropwill be treated at the wrong growth stageand, as a result, suffer a greater setback.

In summary, fewer differences in soilstrength and a more level surface will bothhelp to make sowing depth more consistent.

This minimizes crop emergence time andmakes subsequent management easier andmore effective.

The implications of CTF for soils and crops

AGRONOMY. Provided that severely com-pacted soils are loosened before introduc-ing CTF, it seems certain that the problemof poor initial crop growth and loss of nitro-gen through denitrification will be reduced,particularly in the early years of no-tillage.Improved initial growth will be promotedby the lack of a compacted surface layer andencourages crop root growth, which exploresand extracts nutrients from a greater pro-portion of the profile.

Australian farmers have found that rowcropping is a natural extension to controlledtraffic. This is possible because the positionof each crop row can be planned in advanceand achieved in practice with precisionguidance techniques.

Seed rates have often been increasedslightly with no-tillage, although rates ofseveral crops have been actually reducedwith advanced no-tillage openers (Bakeret al., 2001). Regardless, controlled trafficmakes seeding more reliable and works infavour of lowering seed rates because thesurface is more level and there is less com-paction variation across the drill width.Without compaction, many soils form a sta-ble fine crumb at the surface, which readilyaccepts seeds with minimal disturbance.This makes drill setting easier, reduces


Fig. 16.3. Performance of two closely adjacent openers on the same drill working in a moist clay soil.The opener was behind the tractor wheels in the left photo and the seed is clearly visible on the surface,while on the right it was operating correctly in less compacted soil.

irregularities in performance and avoidsthe need for increased ‘insurance’ seedrates.

A no-tillage farmer in the UK(Hollbrook, 1995) found that spring barleysown 3–4 mm deep was noticeably healthierthan the crop sown at 40–50 mm. Shallowsowing resulted in the first node emergingfrom the coleoptile when it was 20–30 mmabove ground rather than at the surface.This precluded the incidence of eyespot(Cercosporella) and subsequent weakness ofstraws, which often resulted in crop lodging.

Slugs (Deroceras reticulatum) have fre-quently been a problem with cropping sys-tems that retain surface residues, andparticularly those with cloddy seedbeds andsmeared and open sowing slots (Moens,1989). Slugs attack crops in two ways – belowground, where they eat the seeds, and aboveground, where they eat the young leaves.Openers that produce small clods mean thatslugs can access seeds more readily, whileopen or smeared sowing lines allow them tomove unhindered from one seed to the next.CTF has the potential to address these pro-blems through the avoidance of ‘cloddiness’and smeared sowing lines.

CROP YIELDS. Most research comparingtrafficked and non-trafficked soils has beenwith systems using cultivation, but work onno-till in Scotland found that, even withfairly modest wheel loads, no-tillage yieldswere reduced. This occurred in the earlyyears of no-tillage, but differences wereabsent by the fourth season, despite noactual reduction in bulk density on the traf-ficked soil (Campbell et al., 1986). In theUSA and in Argentina, soybean yields inno-tillage systems were reduced by between10% and 39% with repeated but often quitemodest wheel loads. Even where no-tillagehad been practised for 7 years it was stillpossible to reduce yields as a result ofnewly imposed wheel loads (Flowers andLal, 1998; Botta et al., 2004).

RANGE OF CROPS. Although we have con-centrated primarily on small-grain crop-ping, the introduction of CTF should makeit possible to grow a wider range of crops

with no-tillage. No-tillage establishment ofcotton, for example, was successful even inthe presence of wheel compaction. Lint yieldsfor no-tillage were only reduced in one yearout of three, while those for transplantedtomatoes, albeit with strip tillage, werecomparable at two sites in 2002. Strip tillagefor melons resulted in marginally loweryields than the traditional method, but, withboth tomatoes and melons, ‘cloddy’ soil con-ditions at planting/sowing were partly res-ponsible for the poorer crop performance. Avegetable producer in Australia growingtomatoes, zucchini, melons, onions andbroccoli predicted that CTF would allowhim to establish these crops with no-tillage.Potatoes have also been grown successfullywith deep mulches and no-tillage (Lamarca,1998; Mitchell et al., 2004a, b; Ziebarth,2003, personal communication).

The possible constraints on croppingwithin a no-tillage CTF regime arise from anumber of sources:

● Soil structure/crop interactions.● Inexperience and perception.● Machinery.

Because completely non-trafficked soil hasuntil recently been largely unknown withinfarming systems, it is difficult to predicthow some crops will react to these no-tillage conditions. Equally, there are veryfew data that might be used to determinewhether crops such as carrots, sugar beetand potatoes will perform adequately innon-trafficked, non-tilled soil.

The only way that this might be deter-mined is through the comparison of a num-ber of soil parameters, such as bulk density,penetration resistance and porosity. Forexample, does the bulk density of a givennon-trafficked non-tilled soil exceed that ofits cultivated counterpart for a particularcrop? In addition, within what soil environ-ment will a root crop perform equally tothat of the cultivated norm? Many of thesequestions remain unanswered. We shallalso have to be aware that considerable soildisturbance is often experienced duringthe harvest of root crops. Although thiswould at least partly interrupt the no-tillagecycle, it would still be advantageous for the

244 W.C.T. Chamen

remainder of the rotation and for establish-ment of the root crop. Controlled trafficwould also minimize the repair needed afterharvesting and ensure a quick and effectivereturn to no-tillage.

The crops that we can probably grownow under a CTF regime with a proven agro-nomy based on no-tillage include:

This range is necessarily more limited thanmentioned previously, and further techno-logical developments and in-field experi-ence are needed before more crops can beconsidered. However, given the characteris-tics of these crops and the typical climaticconditions under which they have beensuccessful, it would be quite rational toextrapolate to other crops and climates inlocations where CTF no-tillage farming hasnot been extensively attempted.

Making CTF Happen

Basic principles

There are several principles involved inCTF:

1. Forward planning.2. Matching of vehicle track widths.3. Matching of single (primary) or multi-ples of implement widths.4. Discipline.

These principles will be outlined in the fol-lowing sections, but far greater detail can befound in Tramline Farming Systems, pub-lished by the Department of Agriculture,Western Australia (Webb et al., 2000), inconjunction with the Grains Research andDevelopment Corporation.

Forward planning and machinerymatching

Planning is probably the most importantaspect of conversion to CTF, because itensures, amongst other things, that the costis kept to a minimum. Some farms may beable to convert within 12 months; othersmay require planning and change extendingover several years. In the context of thisbook, it is assumed that the end point oftransition is a no-tillage crop establishmentsystem, but the starting point could bemouldboard ploughing, secondary cultiva-tion and drilling. There must therefore bean initial commitment to a significantlylower input system. In some ways, changingfrom an extensive machinery system makesthe economics easier because the excessmachinery can be sold and appropriatelysized new or second-hand equipment pur-chased, probably at little additional cost. Itwill also entail a reduction in labour. Theeconomics, however, will be dominated bythe change to no-tillage rather than to CTF.If a minimum- or no-tillage system is alreadybeing used, the transition may have to beplanned more carefully and over a longertimescale because fewer costs will be lostfrom the system, but returns will still beimproved.

The width-matching process

The objective is to match all implementworking widths, on the one hand, andmachine track widths, on the other. Thepurpose is to minimize costs and number ofwheel tracks per unit area. The cost factormeans that most transitions will start withexamination of existing equipment to con-sider its adaptability. As an example, takea small farm growing grain crops with aminimum-tillage system that has a 3.5 mwide cultivator, a 5 m wide roll and a 3 mdrill; the cereal harvester is 6.1 m wide andchemicals are applied with 12 m booms.Tractors are on track widths varying from1.5 to 1.8 m and trailers have a track ofaround 1.8 m; the harvester is on 2.8 m. Ineffect, nothing matches up with anything in


● Wheat ● Barley● Oats ● Rye● Sorghum ● Millet● Oilseed rape ● Maize● Soybean ● Dry peas● Field beans ● Linseed● Dryland rice ● Cotton

terms of controlled traffic (Fig. 16.4, left).The tractor wheel track settings can, how-ever, be changed to 1.8 m (to match thetrailers) relatively easily.

Two challenges remain – the trackwidth of the harvester and the choice andwidth of no-tillage drill. If the 6.1 m har-vester is to be retained, the drill should be6 m wide (to ensure that the harvester gath-ers the entire crop on most occasions) andthe cost of this will need to be budgeted,with allowance made for the second-handvalue of the existing drill, cultivator and therolls (the economics of CTF will be studiedmore closely in a later section). It may alsobe possible to sell one tractor, but one of theremaining tractors must be capable of pull-ing the proposed replacement drill or a new(larger) tractor will have to be purchased.

The harvester track width cannot easilybe changed and these wheels will be theone set that extend outside the primary

track width. Their position, however, isknown and they will not necessarily causedamage every season because soils are oftendrier at this time (and therefore able towithstand more weight) than at sowing. Ifcompaction and surface rutting occur, theycan be repaired with a subsoiler having tinespositioned so that they loosen just the addi-tional width imposed by the harvester. A6 m system as described will create wheelways that cover around 16% of the area,depending on the width of the tyres used.Providing the wheel ways are well main-tained, it may be possible in the longer termto fit narrower tyres.

On a larger farm, an alternative mightbe to use a ‘twin-track’ CTF system. Thislargely eliminates the harvester problem,while maintaining wheel track settings moreor less as standard. Figure 16.5 shows thatthe system works by straddling the har-vester across adjacent passes of the primary

246 W.C.T. Chamen

Fig. 16.4. Placing all theequipment in the example arounda common centre line (left) showsthat it is only the harvester thathas a significantly different trackwidth. Available settings on thetractors will allow them to bealigned with the trailers, asindicated on the right, with onlythe cost of time.

Fig. 16.5. Twin-track CTF system,where the harvester straddles singletracks of adjacent pairs of tractor tracks.Primary implement width is determinedby the addition of the tractor andharvester track widths.

tracks. The primary implement width isdetermined from the simple addition of thecommon track width of the tractors, trailersand chemical application equipment, plusthe harvester track width. In the exampleabove, primary implement width would be:1.8 + 2.8 = 4.6 m. The harvester cuttingwidth can be any multiple of this; in thisinstance, the most practical would be 4.6 or9.2 m. The drilling width, however, canonly be odd multiples of the primary imple-ment width and this probably limits it to asingle multiple. Chemical applications canbe any multiple of the primary implementwidth if the primary tracks are used, e.g.4.6 m, 9.2 m, etc. If the chemical applicationequipment is on a wide axle and runs onthe harvester tracks (to improve the stabilityof the applicator), the width of the chemi-cal application equipment can only beeven multiples of the primary implementwidth.

Presently none of the implement widthsquoted above is standard, so some adjust-ment to the primary track width might beneeded even in a twin-track system. Forexample, if the primary track were narrowedto 1.7 m, this would correspond with avail-able harvester widths (9 m) and chemicalapplication equipment (18 m, 27 m, 36 m).Alternatively, the track settings could be2 m and 3 m, giving a primary implementwidth of 5 m. The harvester cutting widthshould be slightly wider than the calculated

width to ensure capture of the entire crop inall circumstances.

A further method of matching is toalign all field machinery on the same trackwidth as the harvester because, as previouslymentioned, this machine is difficult to alter.Unfortunately, the harvester is probably themachine with the widest track, and withcurrent designs this will mean a primarytrack width of around 3 m for all vehiclesand implements. This is common practicein Australia (Fig. 16.6), where there may beless need to drive on highways and whererural areas have relatively low populationdensities. In Europe and other parts of theworld with high population densities andoften-narrow roads, much greater difficul-ties are likely. However, because no-tillagereduces the number of field operations andfuture spray vehicles may have ‘on themove’ variable track widths, the extent ofthe problem should diminish considerably.It may only be the harvester and sowingmachine and associated tractor that havethe 3 m track setting on the road. The advan-tage of this system is that there are few con-straints in terms of primary implementwidths. With very wide machines, somemeans of extending the harvester’s unload-ing auger may be needed to ensure thatthe transport unit can be reached in theadjacent traffic lane.

A further alternative similar to ‘twin-track’ for smaller farms is for the harvester


Fig. 16.6. Example of an Australian system with a 9 m primary module and a 3 m primary track width(Webb et al., 2000).

to span between the same wheels of adjacenttractor passes, as shown in Fig. 16.7. Thebasis for this is:

This system potentially introduces alarge number of wheel tracks, but some ofthese may only be used once a year for cropsowing and most could be sown, asdescribed later.

So far, we have dealt primarily with thesystems used for small-grain crops, but theprinciples of no-tillage can be applied equallyto most other crops. Although little researchhas been done on no-tillage for vegetablecrops, improved potential may exist withinCTF systems, as discussed later.

Field layout and system management

Orientation and layout of controlled trafficwheel ways are all part of the planningprocess, and each individual area or blockof land needs to be considered independ-ently. Detailed field maps are an essentialpart of this planning, by measurements,historical records or aerial photographs.Topographic data are also valuable, parti-cularly on farms with significant slopes.Changes in soil type across a property arelikely to be of lesser significance than withrandom traffic systems, but it will still beuseful to know these boundaries, particu-larly with respect to drainage. With regardto drainage, it is essential that any installeddrainage systems are operating properly orproblems corrected before installing a CTFsystem. This is also true for soil structuralremediation. If inspection reveals a panlayer, fissuring of the profile should beattempted according to the guidelines sug-gested by Spoor et al. (2003).

The principal aspects to consider inany CTF layout are:

● Orientation of permanent wheel waysin relation to:■ length of run;■ slope and water movement;

248 W.C.T. Chamen

Fig. 16.7. A controlled traffic machinery system for small farms. The 1.5 m primary track width isspaced at 1.5 m intervals and thus any pair of wheel tracks can be used by all equipment other thanthe harvester.

Primary implement width = harvestertrack width

Primary track width = harvestertrackwidth/2

Harvester cutting width = harvestertrack width× 1.5

Chemical application width = any multi-ple ofprimaryimplementwidth

■ field shape and short rows;■ extraneous objects (trees, pylons,

ponds, etc.);■ field drainage system.

● Wheel-way management and fieldaccess.

Orientation of permanent wheel ways

In most situations the longest length of thearea being considered is chosen for the orien-tation because this improves field efficiencyby reducing the number of end turns. Thelength of run that this creates must also beconsidered in respect of any significant fieldslope. Although water infiltration on thesoil ‘beds’ is likely to be improved signifi-cantly compared with traditionally man-aged fields, water will still tend to run alongand erode the wheel ways, particularly ifthey run uninterrupted over long distancesand are orientated up and down slopes. InAustralia, where CTF is widely practisedand where rainfall events can be very heavy,orientation of operations has become moreflexible with CTF. Both up and down andacross the slope can work, whereas withrandom traffic across-slope or contour lay-outs predominate.

CTF orientation must also consider thepresence of any drainage system, and par-ticularly one that involves mole channels.The latter will run predominantly up anddown slopes and the aim with a controlledtraffic system is to run parallel to them. Thedanger with repeated wheeling across themole channels is that they may collapseprematurely. Running parallel to the moleswill mean crossing the drains themselves,but it is unlikely that these will be damaged,partly due to their depth but also becausethey are often backfilled with gravel. If thewheel ways run parallel to the mole chan-nels, although there is a danger that somewill be coincident with and may damagethem, the overall effect on the drainage sys-tem within a field is likely to be minimal.Running parallel will also ensure that themole channels can be redrawn withoutcomplete disruption of the wheel ways.

For more information on drainage systems,see Spoor (1994).

A similar approach is adopted with arow of pylons going across a field; in thiscase, they may be used for the orientationand as a line to set up the first wheel tracks.Unlucky indeed would be the farmerwho has both a drainage system and pylonswith completely different orientations! Thecompromise would have to be with thepylons. Experience with either drainagesystems or field ‘infrastructure’ is limited,because CTF has yet to be adopted in areaswhere these situations occur extensively.

Wheel-way management

The potential for wheel-way erosion can becountered in a number of ways. As a firstprinciple, the wheel ways need active man-agement from the outset; they cannot beallowed to sink or rut differentially. Theyshould be filled as required by drawing insoil from the surrounding area, particularlyin the early days of establishment, and par-ticularly if the soil has been deep-loosenedrecently. Within a tillage regime, these rec-ommendations could be met coincidentallyduring the creation of a false seedbed forweeds. However, in the context of no-tillage,a customized narrow unit (Fig. 16.8) mightbe used if rutting or plastic flow of soil outof the wheel ways has occurred. This imple-ment should not be used too frequently, how-ever, as the edges of the beds may becomerounded and cause uneven sowing depth.

If weed or erosion pressures on baresoil become unacceptable or, due to machin-ery constraints, the wheel tracks take up alarge proportion of the area, crop may beestablished within them (in general, thisapplies only to those tracks that will not beused after crop sowing). The roots of plantsestablished in these tracks will often explorelaterally and find their way into the maincrop bed. As a result and although they per-form less well, they do mature in unisonwith and add significantly to the main cropyield. This is not the case for sown wheelways that are used subsequently for cropmanagement. In these the plants are often


dwarfed by repeated wheeling and are lateto mature. Where wheel ways are sownwithin a narrowly spaced crop (300 mm orless), the row spacing may be altered slightly,as illustrated in Fig. 16.9. The openers willneed to be set very specifically to deal withthis situation and the wear rate on them islikely to be higher. To date there is limitedexperience with this technique and growerswill need to use some field experimenta-tion initially, but this technique has theadded advantage of temporarily markingthe wheel ways.

In some instances, further active man-agement of the wheel ways might be neededon slopes to ensure that water gatheredwithin them does not reach erosive potential.

This could be achieved by introducing diag-onal channels at regular intervals, whichdivert water into the beds alongside.

The second principle of wheel-waymanagement is to avoid water standing inor flowing along them. To a large extent, thefirst of these problems can be avoided byattending to active management, but lowspots in the field or areas of poor naturaldrainage can also create this situation. Ori-entation should aim to avoid low spots, butthis will not always be possible and an alter-native in the form of modifying the wheel-way edges, as described above, may need tobe introduced.

Wheel-way erosion may also be reducedby a buffer strip part-way downslope.

250 W.C.T. Chamen

Fig. 16.8. Rolling maintenance tool used to deal with plastic flow of soil out of the wheel ways. Thiswould not normally be used on more than an annual basis (J. Grant, 2001, personal communication).

Fig. 16.9. Example of how a cereal crop might be sown on a wheel way. The nominal 250 mmspacing is modified to 400/175 mm to encourage roots of the plants in the wheel way to access theadjacent bed.

This might also provide an area for benefi-cial insects and, if sited correctly, address‘short row’ issues.

Guidance systems

Fundamental to any controlled-traffic farm-ing system is a means of ensuring that thewheel ways are not only orientated but alsopositioned correctly at the outset. Tradition-ally, positioning has been achieved withmachine-mounted hardware that providesan adjacent parallel marking line offset bythe required distance. The driver then usesthis line on the next pass to position themachinery correctly. This works well withmodest machinery widths but, when theseapproach 10 m or more, the size, strengthand durability of the equipment become asignificant factor. Offset loads can also be aproblem if the marker engages with the soil,and maintenance costs can also be high. It isan even greater problem under no-tillagebecause the marker has to make a visibleline in untilled and often residue-coveredsoil, and this is difficult. Markers have rela-tively low precision and introduce errorsthat are cumulative pass to pass. An alter-native, but still with cumulative errors andpoor precision, is to place a closed-circuitvideo camera on the extremity of the imple-ment, with pictures relayed to a screen inthe driver’s cabin. This requires that thedriver continuously monitor the screen tokeep the machinery on course, as he or shewould with a marked line.

An increasingly available and attrac-tive alternative is electronic systems basedon a differential global positioning system(DGPS) using satellite signals. There is awide range of available costs, dependingupon the degree of accuracy delivered.With CTF systems, an accuracy of ± 3 cm isdesirable, with a peak error of ± 5 cm ifwide-row crop operations are planned.Such systems can also be coupled directlyto the vehicle’s steering to provide auto-steer capability for both straight-line andcurved parallel tracking. Automatic steer-ing allows drivers to concentrate on theimplement operation, relieves them of the

constant stress of driving to a mark and alsoavoids excessive steering corrections, whichcan adversely affect machinery operation. Afurther advantage, particularly with wideequipment, is that any pass can be driven inany sequence, because the positioning isabsolute, since it does not rely on a markfrom the previous pass. Drivers can skipevery other pass, for example. This makesturning at the end easier and has the addedadvantage that field completion can be atthe start point, which is normally the pointof field access.

It is also important to note that theimplement lateral offset feature found witha number of satellite guidance systems can-not be used with CTF. This feature compen-sates for an implement that does not trailcentrally behind the tractor by shifting thetractor appropriately on adjacent passes. Ifthis were used with CTF, it would move thevehicle off the permanent wheel ways. Anymisalignment in a CTF system must there-fore be dealt with physically on the tractoror implement and this can create a signifi-cant challenge on side slopes. Trailedequipment may need some wheel steer toovercome this problem.

Economics

There are a number of ways in which theeconomics of CTF systems can be assessedand all will give different answers. Everyproperty, circumstance and range of machin-ery will be unique and the economics ofchange will be very specific. The aim in thischapter, therefore, will be to establish theprinciples and the cost/revenue centresrather than entering into detailed cost ana-lyses that provide only a single hypotheticalsolution. This approach also concentrateson the transition from no-tillage seeding inthe presence of random traffic to a similarbut controlled traffic system.

Economics centre on:

● Planning and transition costs and theirtimescale.

● Fixed and variable costs of the CTFsystem employed.


● Change in output.● Management costs.

Transition costs and timescale forchange to CTF

Planning is the key to minimizing costs.And yet the cost of planning itself is diffi-cult to quantify. A typical consultancy feefor CTF conversion in Australia is aroundUS$75 per hour. There will, however, bemany growers who will study the subjectcarefully and put a plan together them-selves, the costs of which will be absorbedwithin normal overheads. But serious con-sideration should be given to employing theservices of experts to determine the mostefficient field layouts. Changing a layoutafter installation is not an attractive pro-position and is very wasteful of time andresources, as well as resulting in a loss inproductivity.

The planning process will involve tak-ing stock of existing farm equipment andhow much it can be applied within the newregime. A clear picture of the new CTF crop-ping and machinery regime needs to beclearly identified at this stage before transi-tion costs can be estimated. The transitioncosts fall into three main categories: (i) thoseassociated with changing the implements ormachines; (ii) those associated with chang-ing wheel-track settings; and (iii) thoseassociated with guidance:

1. Changing machinery might includebuying new, as well as discarding old equip-ment. If a change to no-tillage is being madeat the same time as adoption of CTF, theequipment requiring attention will be greater,but an opportunity exists to integrate thefull range rather than just parts. With CTF,the no-tillage drill will experience lowerpenetration and draught forces and as aresult there will be lower power demandson the tractor, so some longer-term savingsmay be possible. Centralization of the har-vester cutting platform may also be necessarybecause many are offset to assist unloading.The other main aspect to consider is the

matching of implement widths, on the onehand, and wheel-track settings, on the other.2. The cost of changing wheel tracks maybe in the range US$750 to US$4000 (Webbet al., 2000) and reflects considerable diver-sity in machine designs, axle configurationsand wheel equipment. This cost will alsovary considerably depending upon the typeof system adopted, for example single- ortwin-track, as described earlier. For single-track systems, the cost is likely to be greaterbecause all equipment will probably haveto be matched to the wider track setting ofthe harvester. Such conversions are nowavailable for some tractors, with total costsfor front and rear axles being in the regionof US$10,000. Most other equipment can bemodified locally or in the farm workshop.For twin-track systems, the costs may beconfined to the labour required to alter theposition of rims on centres or swappingwheels from side to side, for example.3. Costs for guidance systems can be as lit-tle as the time required to make up markerarms from existing farm equipment toaround US$50,000 for a satellite systemdelivering auto-steer with a mean offseterror of around ± 3 cm. The market andtherefore the cost structure for these satellite-based systems is changing rapidly and tosuch an extent that the full cost of the sys-tem may not necessarily be attributable onlyto conversion to CTF. Many farmers arenow purchasing these systems withinconventional practice as a means of improv-ing the accuracy of their operations, aswell as establishing tramlines for chemicalapplications.

Not only does the latter give greaterflexibility, but it also precludes the need toestablish marks within the crop. Tradition-ally these have been installed by specialequipment on the drill that leaves linesunsown at the required intervals.

To introduce CTF, an existing systemmight be upgraded from perhaps ± 25 cmmanual to ± 3 cm auto-steer. The additionalcost of this would be in the region ofUS$17,000.

The timescale for change will dependon the investment that has been calculated;

252 W.C.T. Chamen

the greater the investment, the shortershould be the timescale. This is because thegreatest benefits will only be realized whena complete CTF system is in place. Thesebenefits are dealt with in the section onoutputs.

Fixed and variable costs

Fixed costs are generally considered to beregular labour, machinery, rent and generaloverheads, while chemicals, seeds, fuel,wearing parts, contractors and casual labourare considered to be variable (Nix, 2001).With CTF, we would expect the mainimpact to be a lowering of fixed costs, andparticularly those related to labour andmachinery. The marginal labour benefitfrom CTF will be less than but additional tothe marginal labour benefit from changingto no-tillage in the first place.

Although it would be easy to attributeCTF with improvements in field efficiencydue to better guidance, this can now beachieved equally within conventional prac-tice using ‘tramline’ systems on drills orthrough satellite guidance, and is thereforenot considered as a CTF benefit. The mainimpact of CTF on labour in a no-tillagesystem will be a reduced demand duringdrilling, which could be slightly faster (con-ditions permitting) as a result of lowerdraught forces on the drill. Unless a contrac-tor is employed for this task, the farmer isonly likely to experience a timeliness benefitin the short term. In the longer term it maybe possible to increase the land farmed witha given labour force or lose some labourcosts if several are employed during drilling.

Changes in variable costs centre onseeds, fuel, wearing parts and chemicals, allof which should be reduced. Typically,power demands for drilling at any particu-lar speed are reduced by up to 25%, includ-ing the lower rolling resistance that can beattributed to working on the permanentwheel ways rather than on the crop bed.Due to the improved soil conditions, lowerseed rates may be possible with less risk,although this issue should also be handledby improving the drilling methodology

rather than relying on CTF alone to make upfor deficiencies in drilling equipment ortechnique. Savings on wearing parts are moredifficult to predict but will increase thelonger the soil is under no-tillage.

Chemical costs are likely to be reducedprincipally through greater precision andthe ability to inter-row band-spray with non-selective chemicals while simultaneouslyapplying selectively to the crop row. Altho-ugh such a system is not exclusive to CTF,the well-maintained wheel ways offer greaterpotential. If one considers that the cost ofprotection chemicals for wheat grown in atemperate region approaches 50% of thetotal cost of seed, fertilizer and spray (Nix,2001), then any saving on these chemicalsis likely to have significant cost implications.Equally, a reduction in chemical inputs,or at least input of less environmentallydamaging chemicals, is an added benefit.We may also presume that fertilizers appliedin a CTF regime will be more efficientlyutilized and, although this may not be a costsaving to the farm, it will result in animproved yield (discussed below) and alower risk of off-farm pollution of water-courses.

Change in output

Reviewing research undertaken over thepast 30–40 years on soil compaction with17 different crops showed that yields underCTF in both tilled and non-tilled conditionshad increased in the range 9–16% comparedwith random traffic. The less extensive dataquoted for no-tillage systems suggest a moremodest level of improvement; a safe figuremay be around 10%. Soil type, culturalpractices, crop rotations and the percentagearea of land taken up by permanent wheeltracks will obviously moderate these per-centages, and the crop row spacing will fur-ther influence the effect. To determine whathappens in practice, each individual caseneeds to be considered and the followingsuggests an approach that might be taken.

Taking the 8 m system considered ear-lier and a close-spaced row crop such as


wheat (250 mm in this case), the followingis assumed to apply:

Assuming that crop yield is improved by10% only on the non-trafficked area andthat the harvester will have wheels around750 mm wide, the number of rows affectedby wheels will be 3 × 2 × 4 = 24 rows out of atotal of 96. There will be no improvement inyield on these rows and therefore the netimprovement will be 7.5%. This is actuallya conservative estimate because conventionalsystems usually have tramlines where atleast two rows will be missing within a24 m width.

In-field management costs

The main ongoing management cost to sus-tain field operations is likely to be that asso-ciated with the permanent wheel ways. Asindicated earlier, a customized small imple-ment (Fig. 16.8) may suffice for this task,but within a no-tillage regime this representsan additional pass, usually carried out afterharvest. Experience suggests that this maybe needed in the early years of conversionand when any operation has to be carriedout in wet conditions. In some instances,this may only be needed on the chemicalapplication wheel ways.

Summary of costs and returns

Table 16.1 provides an overview of theaspects considered in the foregoing text andattempts to quantify a number of the vari-ables. As stressed earlier and confirmed byUri (2000), the variables are so numerousthat any fully calculated example involvingconservation or no-tillage systems will onlyprovide a specific solution unique to a par-ticular situation. It is better, therefore, to

have the tools and a procedure to calculaterather than to give a single answer.

The magnitude of these costs can beput into context by examining some of thebenefits. A world price for wheat of US$100/tand an average yield of 4 t/ha increased by7.5% on 500 ha, equates to an additionalincome of US$15,000 per annum. At 2001prices, a 20% reduction in tractor size from134 kW would give a saving of aroundUS$17,000. The net benefit from these twoitems on 500 ha is US$32,000 at the end ofthe first year.

Detailed analyses on a regional basis areoffered by a number of authors and thereader is referred to these specific studies forfurther information. Gaffney and Wilson(2003), for example, suggest a net benefit ofUS$15–25/ha for a change to CTF within ano-tillage regime on a vertisol in Queensland,while Mason et al. (1995) for the same sce-nario in the South Burnett of Australia sug-gest a net improvement of US$75/ha.

Summary of Controlled-trafficFarming as a Complementary

Practice to No-tillage

1. Controlled-traffic farming (CTF) is acrop production system in which the cropzone and traffic lanes are distinctly andpermanently separated. In practice, itrequires:

a. use of the same wheel tracks for allfield operations;b. all machines to have the samewheel-track setting;c. all implements to have a particularspan or multiple of it.

2. CTF relies on good guidance systems toinstall and keep the permanent wheel waysin the same place from year to year. The mainsystems used to do this are:

a. physical markers, which provide ameans of positioning the next pass,which, if integrated with seeding, maybe used to introduce guide rows forlater use;b. closed-circuit television (CCTV)video cameras with an associated dis-play in the driver’s cabin;

254 W.C.T. Chamen

Primary implement width = 8 mPrimary track width = 3 mChemicals applied at 24 m widthTwo out of every three primary tracks

are sown

c. differential global positioning sys-tems using satellites;d. automatic steering controlled bythe guidance system.

3. CTF should liberate the full potentialof no-tillage seeding by avoiding soilcompaction damage in the cropping zone.This is likely to result in:

a. improved crop yields from theoutset;b. better nutrient use efficiencyachieved through greater root proli-feration;c. improved soil porosity, which pro-vides better water infiltration, drainageand gaseous exchange;d. reduced threat of denitrification,particularly in the presence of organicresidues;

e. lower draught forces and wear onseed openers;f. reduced labour and fuel inputs,particularly during seeding operations;g. lower power demand for drilling,allowing a smaller tractor to be used fora given output;h. more reliable and consistent opera-tion of seed openers in a wider range ofconditions and soils;i. the potential for a wider range ofcrops to be grown with no-tillage.

4. In other situations, many of theseadvantages will come from the change tono-tillage, which reduces, but seldom elim-inates, the additional gains to be had fromCTF. In most cases, combining CTF andno-tillage achieves a greater potential fromno-tillage [Eds].


Factor/variable Costs, US$ Savings/benefits, %

Consultancy for CTF field layout 75/hDrill price (from Uri, 2000) 6,400 11DGPS guidance with ± 25 cm pass-to-pass accuracy 2,400a

DGPS guidance upgrade from ± 25 cm to ± 3 cm accuracyc 15,400b

DGPS guidance to ± 3 cm with automatic steeringc 5,400–10,200Axle conversions to 3 m:

Tractors – per tractor with full warranty 750–4,000Drill, chasers or trailers, per item 5,000–7,000Self-propelled chemical applicators with full warranty 17–25d

(Not needed if tractor mounted. Also, many NorthAmerican special-purpose vehicles are now availablewith 3 m axles)

5d

Lower-power tractor for hauling drill 20Labour 15

20Variable costs: 10

SeedFuel 3/ha 7.5Wearing parts – soil-engaging elementsChemicalsWheel-way maintenance

Crop yield

aAdditional cost to the ± 25 cm system, i.e. total cost would be 6400 + 2400 = US$8800.bAdditional cost to the ± 3 cm system, i.e. total cost would be 8800 + 15,400 = US$24,200.cThis option has an annual US$1330 correction signal fee.dTractor power or labour reduction, not both – see ‘Fixed and variable costs’ in main text.

Table 16.1. Factors and variables that impact on the economics of changing from a random traffic to acontrolled traffic no-tillage seeding system, their likely magnitude and level following transition.

5. CTF allows farmers to anticipate greaterlevels of precision in all operations so thatthey may:

a. increase the flexibility and effec-tiveness of weed control;b. spray the crop row and inter-rowindependently;c. use non-selective chemicals in theinter-row;d. perhaps position and manage resi-dues to allow their manipulation togreater benefit.

6. The cost of converting to CTF need notbe great, providing it is carefully designedand part of the forward-planning process. Ifproperly planned, the benefits are likely tofar outweigh the costs.7. There are a number of ways that CTFcan be achieved and all will vary in terms

of cost. Field layout is a particularly impor-tant aspect because it needs to account forfield drainage, slope, operating efficiencyand permanent obstacles.8. Permanent wheel tracks within a CTFregime need to be managed to ensure opti-mum performance. Management is likely toinclude:

a. regular infilling, preferably as anintegral part of normal field operations;b. engineering their drainage downslopes and in low areas;c. sowing with crop in particular cir-cumstances and in a particular way.

9. Additional environmental benefits canbe achieved by no-tillage in combinationwith CTF.

256 W.C.T. Chamen

17 Reduced Environmental Emissionsand Carbon Sequestration

Don C. Reicosky and Keith E. Saxton

While tillage agriculture contributessignificant greenhouse gases detrimental

to the atmosphere, no-tillage agriculture willreduce them by both storing new SOM and

reducing the oxidation of existing SOM.

Introduction

Agriculture affects the condition of theenvironment in many ways, includingimpacts on global warming through theproduction of ‘greenhouse gases’, such asCO2 (Robertson et al., 2000). In 2004, theUS Environmental Protection Agency (EPA)estimated that agriculture contributedapproximately 7% of the US greenhousegas emissions (in carbon equivalents, CE),primarily as methane (CH4) and nitrousoxide (N2O). While agriculture represents asmall but relevant source of greenhouse gasemissions, it has the potential, with newpractices, to also act as a sink by storing andsequestering CO2 from the atmosphere inthe form of soil carbon (Lal, 1999). Esti-mates of the potential for agriculturalconservation practices to enhance soil car-bon storage range from 154 to 368 millionmetric tons (MMTCE), which compare tothe 345 MMTCE of reduction proposed forthe USA under the Kyoto Protocol (Lalet al., 1998). Thus, agricultural systems can

be manipulated for the dual benefits ofreducing greenhouse gas emissions andenhancing carbon sequestration. The influ-ence of agricultural production systems ongreenhouse gas generation and emission isof interest as it may affect potential globalclimate change. Agricultural ecosystems canplay a significant role in production andconsumption of greenhouse gases, specific-ally, CO2.

Conservation tillage reduces the extent,frequency and magnitude of mechanical dis-turbance caused by the mouldboard plough,reduces the air-filled macropores and slowsthe rate of carbon oxidation. Any effort todecrease tillage intensity and maximize resi-due return should result in carbon seques-tration for enhanced environmental quality.

Tillage-induced Carbon DioxideEmissions

Tillage or soil preparation has been an inte-gral part of traditional agricultural produc-tion. Tillage is also a principal agentresulting in soil perturbation and subse-quent modification of the soil structurewith soil degradation. Intensive tillage canadversely affect soil structure and causeexcessive breakdown of aggregates, leading


to potential soil movement via erosion.Intensive tillage causes soil degradationthrough carbon loss and tillage-inducedgreenhouse gas emissions, mainly CO2,which have an impact on productive capa-city and environmental quality.

Intensive tillage decreases soil carbon.The large gaseous losses of soil carbon fol-lowing mouldboard ploughing comparedwith relatively small losses with no-tillagehave shown why crop production systemsusing mouldboard ploughing have resultedin decreased SOM and why no-tillage ordirect-seeding crop production systems arestopping or reversing that trend (Reicoskyand Lindstrom, 1993). Reversing the trendof decreased soil carbon with less tillageintensity will be beneficial to agriculture aswell as the global population through bettercontrol of the global carbon balance(Reicosky, 1998).

Emission measurements

The tillage studies reported in this chapterwere conducted in west central Minnesota,USA, on rich soils high in soil organic car-bon (Reicosky and Lindstrom, 1993, 1995;Reicosky, 1997, 1998). The CO2 flux fromthe tilled surfaces in these studies was mea-sured using a large, portable chamber,described by Reicosky (1990) and Reicoskyet al. (1990), in the same manner asdescribed by Reicosky and Lindstrom (1993)and Reicosky (1997, 1998). Measurements ofCO2 flux were generally initiated within1 minute after the tillage pass and contin-ued for various times. The CO2 flux from thesoil surface was measured using the large,portable chamber described by Reicosky andLindstrom (1993).

Briefly, the chamber, with mixing fansrunning, was placed over the tilled surfaceor the no-tilled surface, the chamber low-ered and data collected for 1 s intervals for atotal of 60 s to determine the rate of CO2 andwater vapour increases inside the chamber.The chamber was then raised, calculationscompleted and the results stored on com-puter floppy disk.

The data included the time, plot identi-fication, solar radiation, photosyntheticallyactive radiation, air temperature, wet bulbtemperature, output of the infrared gasanalyser measuring CO2 and water vapourconcentrations in the same airstream. Afterthe appropriate lag and mixing times, datafor a 30 s calculation window were selectedto convert the volume concentrations ofwater vapour and CO2 to a mass basis andthen regressed as a function of time usinglinear and quadratic equations to estimatethe gas fluxes. These fluxes represent therate of CO2 and water vapour increasewithin the chamber from a unit horizontalland area as differentiated from a soil sur-face basis caused by differences in soilroughness. Only treatment differences inrespect of tillage methods, tillage type orexperimental objectives are described, withthe results.

Tillage and residue effects

Recent studies, involving the dynamicchamber described above, various tillagemethods and associated incorporation ofresidues in the field, indicated major car-bon losses immediately following intensivetillage (Reicosky and Lindstrom, 1993, 1995).The mouldboard plough had the roughestsoil surface, the highest initial CO2 flux andmaintained the highest flux throughout the19-day study. High initial CO2 fluxes weremore closely related to the depth of soil dis-turbance that resulted in a rougher surfaceand larger voids than to residue incorpora-tion. Lower CO2 fluxes were caused by till-age associated with low soil disturbanceand small voids, with no-tillage having theleast amount of CO2 loss during 19 days.

The large gaseous losses of soil carbonfollowing mouldboard ploughing (MP)compared with relatively small losses withno-tillage (NT) or direct seeding haveshown why crop production systems usingmouldboard ploughing have decreasedSOM and why no-tillage or direct-seedingcrop production systems are stoppingor reversing that trend. The short-term


cumulative CO2 loss was related to the soilvolume disturbed by the tillage tools. LowerCO2 fluxes were caused by tillage asso-ciated with low soil disturbance and smallvoids, with no-tillage having the leastamount of CO2 loss during 19 days. Simi-larly, Ellert and Janzen (1999) used a singlepass with a heavy-duty cultivator that wasrelatively shallow and a small dynamicchamber to show that fluxes from 0.6 hoursafter tillage were two- to fourfold above thepre-tillage values and rapidly declinedwithin 24 hours of cultivation. They con-cluded that short-term influences on tillageand soil carbon loss were small undersemi-arid conditions, in agreement withFranzluebbers et al. (1995a, b).

On the other hand, Reicosky andLindstrom (1993) concluded that intensivetillage methods, especially mouldboardploughing to 0.25 m deep, affected this ini-tial soil flux differently and suggested thatimproved soil management techniques canminimize the agricultural impact on globalCO2 increase. Reicosky (2001b) furtherdemonstrated the effects of secondary till-age methods and post-tillage compaction indecreasing the tillage-induced flux. Appa-rently, severe soil compaction decreasedporosity and limited the CO2 flux afterplough tillage to that of the no-tillagetreatment.

This concept was further exploredwhen Reicosky (1998) determined theimpact of strip tillage methods on CO2 lossafter five different strip tillage tools wereused in row-crop production and no-tillage.The highest CO2 fluxes were from mould-board plough and subsoil shank tillage.Fluxes from both slowly declined as the soildried. The least CO2 flux was measuredfrom the no-tillage treatment. The otherforms of strip tillage were intermediate,with only a small amount of CO2 detectedimmediately after the tillage operation.These results suggested that the CO2 fluxesappeared to be directly and linearly relatedto the volume of soil disturbed. Intensivetillage fractured a larger depth and volumeof soil and increased aggregate surface areaavailable for gas exchange, which contrib-uted to the vertical gas flux. Narrower and

shallower soil disturbance caused less CO2

loss, suggesting that the volume of soil dis-turbed must be minimized to reduce carbonloss and the impact on soil and air quality.The results also suggest that the environ-mental benefits and carbon storage of striptillage compared with broad-area tillageneed to be considered in soil managementdecisions.

Reicosky (1997) reported that averageshort-term CO2 losses 5 hours after the useof four conservation tillage tools were only31% of that of the mouldboard plough. Themouldboard plough lost 13.8 times as muchCO2 as the soil area not tilled, while differ-ent conservation tillage tools lost an averageof only 4.3 times. The benefits of residueson the soil surface to minimize erosion andsmaller CO2 loss following conservationtillage tools are significant and suggestprogress in developing conservation tillagetools that can enhance soil carbon manage-ment. Conservation tillage reduces the extent,frequency and magnitude of mechanical dis-turbance caused by the mouldboard ploughand reduces the large air-filled soil pores toslow the rate of gas exchange and carbonoxidation.

Reicosky et al. (2002) have shown thatremoval of maize stover as silage for 30years of continuous maize, compared withreturning the residue and removing only thegrain, resulted in no difference in the soilcarbon content after 30 years of mouldboardploughing. Fertility level had no observableeffect on CO2 losses. The tillage-inducedCO2 flux data represented the cumulativegas exchange for 24 h for all treatments.

The pre-tillage CO2 flux from the samearea not tilled averaged 0.29 g CO2/m2/h forthe high-fertility plots at the start of mea-surements. This contrasts with the largestcumulative flux after tillage of 45 g CO2/m2/h on a low-fertility grain plot. The CO2

flux showed a relatively large initial fluximmediately after tillage and then rapidlydecreased 4 to 5 hours after tillage. The CO2

flux decrease continued as the soil lost CO2

and dried out to 24 hours, when valueswere lower but still substantially higherthan those from the no-tillage treatment.The flux 24 h after tillage on the same plots

Reduced Environmental Emissions 259

above was approximately 3 g CO2/m2/h,considerably higher than the pre-tillagevalue.

The temporal trend was similar for alltreatments, suggesting that the physicalrelease controlled the flux rather than theimposed experimental treatments. The con-sistency of the C : N ratio across all fourtreatments suggests little effect of residueremoval or addition and that mouldboardploughing masked the effects of residueremoval as silage or grain removal andabove-ground stover returned. Intensivetillage with the mouldboard plough over-shadowed any residue management aspectsand resulted in essentially the same lowercarbon content at the end of 30 years. Theresults suggest that intensive tillage with amouldboard plough may overshadow anybeneficial effect of residue management(return or removal) that might be consi-dered in a cropping system.

Strip tillage and no-tillage effects onCO2 loss

The impact of broad-area tillage on soil car-bon and CO2 loss suggests possible improve-ments with mulch between the rows and lessintensive strip tillage to prepare a narrowseedbed, as well as no-tillage. Reicosky(1998) quantified short-term tillage-inducedCO2 loss after the use of strip tillage toolsand no-tillage. Various strip tillage tools,spaced at 76 cm, were used and gas exchangemeasured with a large portable chamber.Gas exchange was measured regularly for6 hours and then at 24 and 48 hours.No-tillage had the lowest CO2 flux duringthe study and mouldboard ploughing hadthe highest immediately after tillage, whichdeclined as the soil dried. Other forms ofstrip tillage had an initial flush related totillage intensity, which was intermediatebetween these extremes, with both the5 and 24 hour cumulative losses relatedto the soil volume disturbed by the till-age tool.

Reducing the volume of soil disturbedby tillage should enhance soil and airquality by increasing soil carbon content.

These results suggest that soil and environ-mental benefits of strip tillage should beconsidered in soil management decisions.Limited tillage can be beneficial and domuch to improve soil and air quality, mini-mize runoff to enhance water quality andminimize the greenhouse effect. The energysavings represent an additional economicbenefit associated with less disturbance ofthe soil. The results suggest environmentalbenefits of strip tillage over broad-area till-age, which need to be considered whenmaking soil management decisions.

The CO2 flux as a function of time foreach tillage method for the first 5 hoursshowed that mouldboard ploughing had thehighest flux, which was as large as 35 gCO2/m2/h and then rapidly declined to 6 gCO2/m2/h 5 hours after tillage. The secondlargest CO2 flux was 16 g CO2/m2/h follow-ing subsoil shanks, which also slowlydeclined. The least CO2 flux was measuredfrom the no-tillage treatment, with an aver-age flux of 0.2 g CO2/m2/h for the 5 hourperiod. Other forms of strip tillage wereintermediate and only a small amount ofCO2 was detected immediately after sometillage operations, which ranged from 3 to8 g CO2/m2/h and gradually declined toapproach no-tillage values within 5 hours.These results suggest a direct relationshipbetween the magnitude of the CO2 flux thatappears to be related to the volume of soildisturbed.

The cumulative CO2 losses calculatedby integrating the flux as a function of timefor both 5 and 24 h periods showed similartrends. The values for 24 hours may be sub-ject to error due to the long time betweenthe last two measurements and tillage-induced drying, which may have causedthe tilled treatments to dry out faster thanthe no-tillage treatments. The cumulativeflux for the first 5 hours after tillage formouldboard ploughing was 59.8 g CO2/m2,decreasing to 31.7 g CO2/m2 for the subsoilshank to a low of 1.4 g CO2/m2 for the no-tillage treatment. The strip tillage methodshad slightly more CO2 loss than no-tillage.Similarly, the cumulative data for the24 h period reflect the same trend, the max-imum release by mouldboard ploughing,


159.7 g CO2/m2, decreasing to 7.2 g CO2/m2

for no-tillage. The other forms of strip tillagewere intermediate between these, whichparalleled the 5 hour data. The results sug-gest that cumulative CO2 loss was directlyrelated to the soil volume disturbed by thetillage tool. The narrower and shallowersoil disturbance caused less CO2 loss.

The cross-sectional areas of the soil dis-turbed by the tillage were estimated fromfield measurements drawn to scale, usinggraphical techniques. The drawings werethen cut out and run through an area meter.The cumulative CO2 fluxes for 24 hourswere then plotted as a function of these soilareas disturbed and showed a nearly linearrelationship between the 24 hour cumulativeCO2 flux and the soil volume disturbed bytillage. These results suggest that intensivetillage fractured a larger depth and volumeof soil and increased aggregate surface areaavailable for gas exchange. This increasedsoil porosity and area for gas exchange con-tributed to the vertical flux, which was lar-gest following mouldboard ploughing.

The results of short-term CO2 loss fromthe strip tillage study for row crops suggestthat, to minimize the impact of tillage onsoil and air quality, the volume of soil dis-turbed must be minimized. Tilling the soilvolume necessary to get an effective seed-bed and leaving the remainder of the soilprotected and undisturbed to conservewater and carbon to minimize soil erosionand CO2 loss should be the preferred stra-tegy. Limited tillage can be beneficial anddo much to improve soil and air quality,minimize runoff to enhance water qualityand minimize the greenhouse effect. Theenergy savings represent an additional eco-nomic benefit associated with less distur-bance of the soil (West and Marland, 2002;Lal, 2004). The results suggest that theenvironmental benefits of strip tillage overbroad-area tillage need to be consideredwhen making soil and residue manage-ment decisions.

The concept that each soil has a finitecarbon storage capacity is being revisited.This has important implications for soilproductivity and the potential of using soilto enhance soil carbon storage and reduce

greenhouse gases in the atmosphere. Mostagricultural and degraded soils can providesignificant potential sinks for atmosphericCO2. However, soil carbon accumulationdoes not continue to increase with timewith increasing carbon inputs but reachesan upper limit or carbon saturation level,which governs the ultimate limit of the soilcarbon sink (Goh, 2004). The relationbetween no-tillage and conservation tillagein the way they affect soil carbon stocks isopen to further debate and definition ofcarbon pools.

The relationship between tillage-induced changes in soil structure and sub-sequent effect on carbon loss was reviewedby Six et al. (2002) within the framework ofa newly proposed soil C-saturation concept.They differentiated SOM that is protectedagainst decomposition by various mecha-nisms from that which is not protected anddiscussed implications of changes in landmanagement for processes that affected car-bon release. This new model defined a soilC-saturation capacity, or a maximum soilcarbon storage potential, determined by thephysicochemical properties of the soil, andwas differentiated from models that sug-gested soil carbon stocks increased linearlywith carbon inputs. Presumably, thiscarbon saturation capacity will be soil-,climate- and management-specific. Thiscauses a change in the thinking about car-bon sequestration and that a soil-dependentnatural limit may exist in both natural andmanaged systems.

Superimposed on this analysis is therole of glomalin, a sticky substance pro-duced by fungal hyphae that helps glue soilaggregates together (Nichols and Wright,2004). No-tillage is one management prac-tice that has been successful in increasingthe hyphal fungi that produce glomalin.The next researchable challenge will be todetermine if the carbon saturation andglomalin over the entire profile in no-tillageand conservation tillage systems are sub-stantially different. Presumably with lesstillage-induced breakdown of soil aggre-gates, no-tillage may have an advantageover other forms of conservation tillage. Thefinal answer awaits further research.


Carbon Sequestration UsingNo-tillage

Conservation agriculture is receiving muchglobal focus as an alternative to the use ofconventional tillage systems and as a meansto sequester soil organic carbon (SOC)(Follett, 2001; Garcia-Torres et al., 2001).Conservation agriculture can work undermany situations and is cost-effective from alabour standpoint. More importantly, thepractices that sequester soil organic carboncontribute to environmental quality and thedevelopment of a sustainable agriculturalsystem. Tillage or other practices that des-troy SOM or cause loss and result in a netdecrease in soil organic carbon do not resultin a sustainable agriculture. Sustainableagricultural systems involve those culturalpractices that increase productivity whileenhancing carbon sequestration. Crop resi-due management, conservation tillage(especially no-tillage), efficient manage-ment of nutrients, precision farming, effi-cient management of water and restorationof degraded soils all contribute to asustainable agriculture.

Kern and Johnson (1993) calculatedthat conversion of 76% of the croplandplanted in the USA to conservation tillagecould sequester as much as 286 to 468MMTCE over 30 years and concluded thatUS agriculture could become a net sink forcarbon. Lal (1997) provided a global esti-mate for carbon sequestration from conver-sion of conventional to conservation tillagethat was as high as 4900 MMTCE by 2020.Combining economics of fuel cost reduc-tions and environmental benefits derivedby converting to conservation tillage arepositive first steps for agriculture towardsdecreasing carbon emissions into theatmosphere.

Soil tillage practices are of particularsignificance for the carbon status of soilsbecause they affect carbon dynamics direc-tly and indirectly. Tillage practices thatinvert or considerably disturb the surfacesoil reduce soil organic carbon by increas-ing decomposition and mineralization ofbiomass due to increased aeration and mix-ing plant residues into the soil, exposing

previously protected soil organic carbon insoil aggregates to soil fauna, and by increas-ing losses due to soil erosion (Lal, 1984,1989; Dick et al., 1986a, b; Blevens andFrye, 1993; Tisdall, 1996). Conversely,long-term no-tillage or reduced tillage sys-tems increase soil organic carbon content ofthe soil surface layer as a result of variousinteracting factors, such as increased resi-due return, less mixing and soil distur-bance, higher soil moisture content, reducedsurface soil temperature, proliferation of rootgrowth and biological activity and decreasedrisks of soil erosion (Lal, 1989; Havlin et al.,1990; Logan et al., 1991; Blevens and Frye,1993; Lal et al., 1994a, b).

Cambardella and Elliott (1992) observedfor a loam soil that the soil organic car-bon content in the 0 to 20 cm depth was 3.1,3.5, 3.7 and 4.2 kg/m2 for bare fallow,stubble mulch, no-tillage and native sod,respectively. They observed that tillagepractices can lead to losses of 40% or moreof the total soil organic carbon during aperiod of 60 years. Edwards et al. (1992)observed that conversion from mouldboardplough tillage to no-tillage increased soilorganic carbon content in the 0 to 10 cmlayer from 10 g/kg to 15.5 g/kg in 10 years,an increase of 56%. Lal et al. (1998) stated:

A summary of the available literatureindicates that the soil organic carbonsequestration potential of conversion toconservation tillage ranges from 0.1 to0.5 metric tons ha−1 yr−1 for humid temper-ate regions and from 0.05 to 0.2 metric tonsha−1 yr−1 for semi arid and tropical regions.

They further estimated that the soil organiccarbon increase may continue over a periodof 25 to 50 years, depending on soil proper-ties, climate conditions and management.

Carbon sequestration in the soil hasbenefits beyond removal of CO2 from theatmosphere. No-tillage cropping reducesfossil fuel use, reduces soil erosion andenhances soil fertility and water-holdingcapacity. Beneficial effects of conservationtillage on soil organic carbon content,however, may be short-lived if the soil isploughed, even after a long time under con-servation tillage (Gilley and Doran, 1997;


Stockfisch et al., 1999). Stockfisch et al.(1999) concluded that organic matter strati-fication and accumulation as a result oflong-term minimum tillage were com-pletely lost by a single application of inver-sion tillage in the course of a relatively mildwinter. Tillage accentuates carbon oxida-tion by increasing soil aeration and soil res-idue contact, and accelerates soil erosion byincreasing exposure to wind and rain(Grant, 1997). Several experiments in NorthAmerica have shown more soil organiccarbon content in soils under conservationtillage compared with plough-tillage seedbeds (Doran, 1980; Doran et al., 1987;Rasmussen and Rohde, 1988; Havlin et al.,1990; Tracy et al., 1990; Kern and Johnson,1993; Lafond et al., 1994; Reicosky et al.,1995).

Similar to the merits of no-tillagereported in North America, Brazil andArgentina (Lal, 2000; Sa et al., 2001), sev-eral studies have reported a high potentialfor soil organic carbon sequestration inEuropean soils. In an analysis of 17European tillage experiments, Smith et al.(1998) found that the average increase ofsoil organic carbon, with a change fromconventional tillage to no-tillage, was 0.73 ±0.39% per year and that soil organic carbonmay reach a new equilibrium in approxi-mately 50 to 100 years. Analysis of somelong-term experiments in Canada (Dumanskiet al., 1998) indicated that soil organic car-bon can be sequestered for 25 to 30 years ata rate of 50 to 75 g carbon/m2/year, depend-ing on the soil type in well-fertilizedCherozem and Luvisol soils cropped con-tinuously to cereals and hay. Analysis ofthese Canadian experiments focused oncrop rotations, as opposed to tillage, and isunique in that it considered rates of carbonsequestration with regard to soil type.

On a global basis, West and Post (2002)suggested that soil carbon sequestrationrates with a change to no-tillage practicescan be expected to have a delayed response,reach a peak sequestration rate in 5 to 10years, and then decline to nearly 0 in 15 to20 years, based on regression analysis. Thisagrees with a review by Lal et al. (1998),based on results from Franzluebbers and

Arshad (1996) showing that there may belittle or no increase in soil organic carbon inthe first 2 to 5 years after a change in manage-ment practice, followed by a large increase inthe next 5 to 10 years. Campbell et al. (2001)concluded that wheat rotation systems inCanada will reach an equilibrium, follow-ing a change to no-tillage, after 15 to 20years, provided average weather conditionsremained constant. Lal et al. (1998) esti-mated that rates of carbon sequestrationmay continue over a period of 25 to 50years. The different estimates of carbonsequestration may be expected partlybased on different rotations and rotationdiversity.

Nitrogen Emissions

Cropping systems and nitrogen fertilizationaffect plant biomass production, partiallycontrolling input of organic carbon to theSOM stocks. Agriculture alters the terres-trial nitrogen cycle as well. Through nitro-gen fertilization, annual cropping,monocropping and improper water man-agement, nitrogen is more prone to beinglost to both ground- or surface water and theatmosphere. N2O, a common emission fromagricultural soils, is a potent greenhouse gas(310 times more potent than CO2), whichhas increased its atmospheric concentrationby 15% during the past two centuries(Mosier et al., 1998). Reductions can beachieved through improved nitrogen man-agement, as well as with irrigation watermanagement, because N2O is generatedunder both aerobic conditions (where nitri-fication occurs) and anaerobic conditions(where denitrification occurs) in the soil.

Due to the tightly coupled cycles of car-bon and nitrogen, changes in rates of carbonsequestration and terrestrial ecosystems willdirectly affect nitrogen turnover processesin the soils and biosphere–atmosphereexchange of gaseous nitrogenous compounds.Some data suggest that increasing N2O emis-sions may be closely linked to increasingsoil carbon sequestration (Mosier et al.,1991; Vinther, 1992; McKenzie et al., 1998;


Robertson et al., 2000). If no-tillage is a trulyviable management practice, it must miti-gate the overall impact of no-tillage adop-tion by reducing the net global warmingpotential determined by the fluxes of all thegreenhouse gases, including N2O and CH4.

Six et al. (2004) assessed potentialglobal warming mitigation with the adop-tion of no-tillage in temperate regions, bycompiling all available data reporting dif-ferences in fluxes of soil-derived C, N2Oand CH4 between conventional tillage andno-tillage systems. Their analysis indicatedthat, at least for the first decade, switchingfrom conventional tillage to no-tillagewould generate enhanced N2O emissionsfor humid environments and somewhatlower emissions for dry environments,which would offset some of the potentialcarbon sequestration gains; and that, after20 years, N2O emissions would return to ordrop below conventional tillage fluxes.They found that N2O emissions, with a highglobal warming potential, drive much of thetrend in net global warming potential, sug-gesting that improved nitrogen manage-ment is essential to realize the full benefitsfrom carbon storage in the soil for the pur-poses of global warming mitigation. Theysuggested caution in the promotion ofno-tillage agriculture to reduce greenhousegas emissions and that the total radiativeforcing needs additional considerationbeyond just the benefit of carbon sequestra-tion. They suggested that it is critical toinvestigate the long-term as well as short-term effects of various nitrogen manage-ment strategies for long-term reduction ofN2O fluxes under no-tillage conditions.These results suggest the need for morebasic research on N2O emissions during thetransition from conventional tillage tono-tillage and after equilibrium conditionshave been achieved to adequately quantifythe carbon-offsetting effects in globalwarming potential.

In Brazil, most, but not all, studiesindicate that the introduction of zone till-age increases SOM (Bayer et al., 2000a, b;Sa et al., 2001). Sisti et al. (2004) evalu-ated changes in soil carbon in a 13-yearstudy comparing three different cropping

rotations under zone tillage and conserva-tion tillage in a clayey Oxisol soil sampledto 100 cm. They found that, under a con-tinuous sequence of winter wheat and sum-mer soybean, the stock of soil carbon to100 cm under zone tillage was not signifi-cantly different from that under conserva-tion tillage. However, in rotations with avetch crop, soil carbon stocks were signifi-cantly higher under zone tillage than underconservation tillage. They concluded thatthe contribution of nitrogen fixation by thelegume crop was the principal factorresponsible for the observed carbon accu-mulation in the soil under zone tillage. Theresults demonstrate the role of diverse croprotations, especially including legumessupplying organic nitrogen under zone till-age, in the accumulation of soil carbon. Thedynamic nature of the carbon : nitrogenratio may require additional organic nitrogento increase carbon sequestration at depth.Sisti et al. (2004) found that much of thenitrogen gain was at depths below theplough layer, suggesting that most of theaccumulated soil carbon was derived fromcrop root residues.

Further work in Brazil reflects theimportance of soil and plant managementeffects on soil carbon and nitrogen losses to1 m depth (Diekow et al., 2004). They eva-luated carbon and nitrogen losses dur-ing a period of conventional cultivation thatfollowed on native grassland and 17-yearno-tillage cereal- and legume-based croppingsystems with different nitrogen fertilizationlevels to increase carbon and nitrogen stocks.With nitrogen fertilization, the carbon andnitrogen stocks of the oat/maize rotationwere steady with time. However, theyfound increased carbon and nitrogen stocksdue to higher residue input in the legume-based cropping systems. The long-termno-tillage legume-based cropping systemsand nitrogen fertilization improved soil car-bon and nitrogen stocks of the previ-ously cultivated land to the original valuesof the native grassland. Nitrogen and legumeresidues in a rotation were more effective forbuilding soil carbon stocks than inorganicnitrogen from fertilizer applied to the grasscrop in the rotation. In addition, legume


nitrogen does not require the cost of usingfossil fuel to manufacture nitrogen ferti-lizer. The dominant soil change took placein the surface layer; however, deeper layerswere important for carbon and nitrogenstorage, which leads to improved soil andenvironmental quality.

The literature holds considerable evi-dence that intensive tillage decreases soilcarbon and supports the increased adoptionof new and improved forms of conservationtillage or direct seeding to preserve orincrease SOM (Reicosky et al., 1995; Paulet al., 1997; Lal et al., 1998). Based on thesoil carbon losses with intensive agricul-ture, reversing the decreasing soil carbontrend with less tillage intensity should bebeneficial to agriculture and the global pop-ulation by gaining better control of theglobal carbon balance (Houghton et al.,1983; Schlesinger, 1985). The environmen-tal and economic benefits of conservationtillage and direct seeding demand their con-sideration in the development of improvedmanagement practices for sustainable pro-duction. However, the benefits of no-tillagefor soil organic carbon sequestration may besoil- or site-specific, and the improvementof soil organic carbon may be inconsistenton fine-textured and poorly drained soils(Wander et al., 1998). Six et al. (2004) indi-cated a strong time dependency in thegreenhouse gas (GHG) mitigation potentialof no-tillage agriculture, demonstrating thatgreenhouse gas mitigation by adoption ofno-tillage is much more variable and com-plex than previously considered.

Policy of Carbon Credits

The increase in greenhouse gas concentra-tions in the atmosphere is a global problemthat requires a global solution (Kimbleet al., 2002; Lal, 2002). Concern about nega-tive effects of climate warming resultingfrom increased levels of greenhouse gasesin the atmosphere has led nations to estab-lish international goals and policies forreductions of these emissions. Initial targetsfor reductions are stated in the Kyoto

Protocol of the United Nations FrameworkConvention on Climate Change, whichallows trading credits that represent veri-fied emission reductions and removal ofgreenhouse gases from the atmospheres(United Nations Framework Convention onClimate Change Secretariat, 1997).

Emissions trading may make it possibleto achieve reductions in net greenhouse gasemissions for far less cost than withouttrading (Dudek et al., 1997). Storing carbonin soils using conservation agriculturetechniques can help offset greenhouse gasemissions while providing numerous envi-ronmental benefits, such as increasing siteproductivity, increasing water infiltrationand maintaining soil flora and fauna diversity(Lal et al., 1998; Lal, 2002). Storing carbonin forests may also provide environmentalbenefits resulting from increased numbersof mature trees contributing to carbonsequestration (Row et al., 1996). While car-bon is a key player for agriculture in solvingthe problem of global warming, a criticalcaveat is that other greenhouse gaseschange with changes in land use, includingCH4 and N2O. We must look at the netglobal warming potential, not only for car-bon in future trades but global warmingpotential credits, rather than carbon creditsalone.

As interest in soil carbon sequestrationgrows and international carbon tradingmarkets are developed, it is important thatappropriate policies be developed that willprevent the exploitation of soil organiccarbon and at the same time replace the lostcarbon and establish its value (Walsh,2002). Policies are needed that will encour-age the sequestration of carbon for all envi-ronmental benefits that will evolve (Kimbleet al., 2002). Making carbon a commoditynecessitates determining its market valueand doing so with rational criteria.

Both farmers and society will benefitfrom sequestering carbon. Enhanced soilquality benefits farmers, but farmers andsociety in general benefit from erosion con-trol, reduced siltation of reservoirs andwaterways, improved air and water qualityand biodegradation of pollutants and chem-icals. Farmers need to be compensated for


the societal benefits of carbon sequestrationand the mechanisms that develop willallow for carbon trading and maintainingproperty rights. One important criterion indeveloping the system is the measurementand verification of the carbon options forsequestration that must be developed andthe importance of making policymakersaware of these procedures and the technicaldifficulties. The use of international carboncredit market mechanisms is intended tohelp meet the challenge of climate changeand future carbon constraints, which enablesustainable development and at the lowestsocial cost.

Carbon credit accounting systems mustbe transparent, consistent, comparable,complete, accurate and verifiable (IPCC,2000). Other attributes for a successful sys-tem include global participation and mar-ket liquidity, linking of different tradingschemes, low transaction costs and rewardsfor early actions to voluntarily reduce emis-sions before regulatory mandates are putin place. Characterizing the relationshipsbetween soil carbon and water quality, airquality and all the other environmentalbenefits should be an easy sell to get socialacceptance of this type of agriculture. Thelargest impediment is the educational pro-cesses directed at the policymakers andfood-consuming public, which require fur-ther enhancement.

A growing number of organizationsaround the world are implementing volun-tary projects that are climate-beneficial as ameans to improve efficiency and reduceoperating costs and risk. Businesses andinstitutions throughout the world are realiz-ing that the benefits of good environmentalmanagement far outweigh the cost, bothnow and in the future, of good corporatemanagement, which includes strategies toreduce greenhouse gas emissions, riskexposure and costs and to enhance overallcompetitive operations. Multinational orga-nizations are participating in carbon energycredit trading markets in order to avoidfuture compliance costs and to protect theirglobal franchise in the face of increasingconcern over global warming (Walsh, 2002).In the evolution towards a global economy

and as concerns over global environmentalimpacts increase, CO2 emission managementwill become a factor in the planning andoperations of industrial and governmententities all over the world, creating chal-lenges and opportunities for those who areable to recognize and capitalize on them.

The global ecosystem services pro-vided by farmers and other landownerscould provide a source of carbon-emissioncredits to be sold to carbon emitters andhence provide an additional source ofincome for farmers, particularly no-tillagefarmers. Trade in carbon credits has thepotential to make conservation agriculturemore profitable and enhance the environ-ment at the same time. The potential forcarbon credits has attracted considerableattention of farmers and likely buyers of thecarbon credits. However, it is difficult tostay fully informed about developingcarbon credits because of their technicalcomplexity and the pace of development onthis subject. Rules for trading in carboncredits are not yet agreed upon, but inter-national dialogue is under way to develop aworkable system and rules for trading. Thenumber of organizations working on deve-loping a carbon trading system suggests thatsome type of international mechanism willevolve and that carbon credit trading willbecome a reality.

Information is rapidly becoming avail-able on publicly traded carbon credits;however, little information is available onprivately traded contracts. A great deal ofuncertainty exists at this time as to whichcompanies will emerge as reliable sourcesof high-quality information and entities thatcan handle trading in a fair and reliablemanner. Potential suppliers and buyers ofcarbon credits are urged to proceed withcaution because many of the issues central tocarbon credit markets and trade are yet to beclarified. We must convince policymakers,environmentalists and industrialists thatsoil carbon sequestration is an additionalimportant benefit of adopting improvedand recommended conservation agricul-tural production systems. This optionstands on its own, regardless of the threat ofglobal climate change from fossil fuels.


Conservation agricultural practices(especially no-tillage) can help to mitigateglobal warming by reducing carbon emis-sions from agricultural land and by seques-tering carbon in the soil through regulatory,market incentive and voluntary or educa-tional means (Lal, 2002). Public policy canencourage adoption of these practices.For the present, there is a degree of uncer-tainty for investors and potential investorsin forest-related carbon sinks over the spe-cific rules that will apply to implementa-tion of the sinks provisions of the KyotoProtocol. Investors and potential investorsin carbon sinks need to be aware that thereis uncertainty at the international level.Administration and transaction costs couldplay a key role in determining the successof any carbon credit trading system. Costsin these areas are expected to be minimizedthrough improved techniques and servicesfor measuring and reporting sequesteredcarbon, private-sector consultants, econo-mies of scale and the emergence of marketmechanisms and strategies such as carbonpooling or aggregating. There are risksinvolved in selling carbon credits in advanceof any formalized international trading sys-tem and those participating in early tradingneed to clarify responsibilities and obliga-tions. However, care should be taken in thedesign of these policies to ensure theirsuccess, to avoid unintended adverse eco-nomic and environmental consequencesand to provide maximum social benefit.

Summary of Reduced EnvironmentalEmissions and Carbon Sequestration

While we learn more about soil carbonemissions, soil carbon storage and theircentral roles in environmental benefits, wemust understand the secondary environ-mental benefits of no-tillage and what theymean to sustainable production agriculture.Understanding these environmental benefitsdirectly related to soil carbon and getting theconservation practices implemented on theland will hasten the development of har-mony between humans and nature whileincreasing production of food, fibre andbiofuels.

Reducing soil carbon emissions andincreasing soil carbon storage can increaseinfiltration, increase fertility, decreasewind and water erosion, minimize com-paction, enhance water quality, impedepesticide movement and enhance environ-mental quality. Increased levels of green-house gases in the atmosphere require allnations to establish international andnational goals and policies for reductions.Accepting the challenges of maintainingfood security by incorporating carbon stor-age in conservation planning demonstratesconcern for our global resources and ourwillingness to work in harmony withnature. This concern presents a positiverole for no-tillage, which will have a majorimpact on global sustainability and ourfuture quality of life.


18 Some Economic Comparisons

C. John Baker

The long-term economics of no-tillage willbe determined more by maximizing cropperformance and net cash returns than by

minimizing the inputs costs.

In this chapter we look at some economiccomparisons of tillage versus no-tillage.But, no matter how the comparisons areanalysed, in the end, crop yield will affectthe results at least as much as input costs.

Comparisons between different levelsof no-tillage are also important. For exam-ple, a relatively inexpensive no-tillage drillcosting half as much as a more advancedalternative will only need to cause a 4–5%reduction in crop yield to become a badinvestment.

But the most common comparison isbetween no-tillage and tillage. Opinionsabound about whether it is cheaper to useno-tillage or tillage. Comparisons are oftenmisleading for the following reasons:

1. Farmers who consider changing fromtillage to no-tillage often compare the costof engaging a no-tillage contractor (customdriller) with the cost of undertaking theirown tillage. Many only include direct costs(such as fuel) as the cost of undertaking till-age since they already own the equipment,which they consider has already been paidfor. The real issue is not apparent untilthese farmers have to replace their worn-out

tillage equipment. None the less, we attemptto analyse this situation by comparing thecost of used tillage equipment with usedno-tillage equipment.2. Understandably, even if farmers aredetermined to make a switch to no-tillage,they will often keep their tillage equipmentfor a few years as a form of insurance – ‘incase no-tillage does not work out’ – whilealso paying for a no-tillage contractor. Thus,for a period, they are paying twice, but notby as much as they might imagine, asshown later by the analyses.3. Many comparisons penalize no-tillageby imposing expected reductions in cropyields and/or increases in seeding and/orfertilizer rates for the first few years. This nolonger applies when using modern no-tillageequipment and methodologies. Recent expe-rience has repeatedly shown that usingadvanced no-tillage machinery and systemswill produce crop yields at least comparableto tillage in year 1, and probably significantlybetter with time. Seeding rates of some cropsand pastures have actually been reduced, notincreased – some by up to 50%. On the otherhand, if lower technology no-tillage systemsand equipment are used, temporary yieldreductions may well be applicable.4. Economic comparisons should, but sel-dom do, factor in no-tillage reductions inlabour, tractor numbers, tractor hours, fuel


use and depreciation. One US farmer, forexample, using modern no-tillage methods,recently reported that he now usesmore fuel to harvest his crops than to growthem – an unheard-of scenario using con-ventional tillage (D. Wolf, 2005, personalcommunication).5. Tractors often clock only one-quarter ofthe annual hours using no-tillage comparedwith tillage and thus last considerablylonger. Therefore, the annual depreciation,interest and insurance costs can be reducedand machinery replacement intervalslengthened.6. Some farmers already have a perma-nent labour force and no alternative func-tion for that labour when the demand atseeding is reduced; thus there is seeminglylittle to be gained by adopting no-tillage. Onthe other hand, enterprising farmers haveused the freed-up time to increase the areacropped each year. The economics of thisare hard to factor into any analysis.7. The amount of capital recovered fromthe sale of second-hand tillage equipmentwill diminish as no-tillage increases in pop-ularity. The market for second-hand tillageequipment will shrink and this has cer-tainly been a factor for some farmers whenmaking the change.

So how do the figures stack up on bothsides of tillage versus no-tillage? We provideanswers to this question from two perspec-tives. The first was to examine four possiblescenarios of ownership (C.J. Baker, 2000,unpublished data). We use the costs ofequipment in New Zealand because thatcountry has some of the more expensiveand capable no-tillage options available, aswell as cheaper alternatives. The secondanalysis was to review the results of chargesmade by a contractor in England to a clientover two seasons. The first season (2002/03)was for tillage and minimum tillage. Thesecond season (2003/04) was for no-tillage(J. Alexander, 2004, personal communication).

In both analyses we assume that cropyields are the same for both tillage and no-tillage. Such an assumption is only realisticif advanced (and usually more expensive)no-tillage equipment is used. If less advanced

(cheaper) no-tillage equipment is used, it islikely that crop yields will be depressedbelow tillage, which will add an effectiveadditional cost to the no-tillage. The com-parisons quoted below may therefore requireadjustment for less advanced equipment.

Obviously the actual figures will requireadjustment for other countries and years.But readers are encouraged to change theinput data to those applying locally andrecalculate the figures. In most cases therelative values will remain approximatelythe same, regardless of how the actualfigures change over time and location.

New Zealand Comparisons

● Scenario A: Economics of using a till-age contractor or a no-tillage contractor.

● Scenario B: Economics of purchasingnew tillage or new no-tillage equipment.

● Scenario C: Economics of retaining usedtillage equipment or purchasing eithernew or used no-tillage equipment.

● Scenario D: Economics of retainingused tillage equipment or engaging ano-tillage contractor.

Assumptions

1. Farmed area 300 hectares – 150 hec-tares cropped twice annually. (The croppedarea could increase substantially withno-tillage but this is not included.)2. With no-tillage, glyphosate, slug baitand chlorpyrifos are used in spring forweed and pest control.3. For tillage, glyphosate is applied priorto spring ploughing (at a lighter rate than forno-tillage) but is omitted for autumn sowing.4. All values are shown in 2004 NewZealand dollars.

Scenario A: Economics of using a tillagecontractor or a no-tillage contractor

Establishing 150 hectares of spring wheat(Table 18.1), followed by 150 hectares ofautumn forage crop (Table 18.2). Table 18.3summarizes the pre-tax costs.

Economic Comparisons 269

CONCLUSIONS

1. On a contractor basis, costs (andtherefore gross margins) for the year favourno-tillage by $16,500 or $55/ha.2. Even if glyphosate is omitted from till-age in the spring (at $55/ha), the comparison

still favours no-tillage by $8250 per year or$27.50/ha for the whole year.3. No allowance has been made in thisanalysis for the benefits of establishingautumn crops or pasture using advancedno-tillage methods immediately afterharvest, nor for the additional spring utili-zation of land that comes from no-tillage.These factors alone can be valued at anadditional $440/ha in favour of no-tillage(W.R. Ritchie, 2003, unpublished data).

NOTES

1. When sowing brassicas, peas or otherbroadleaved crops in spring, the chlorpyrifoscost for no-tillage can be reduced to $8/ha,which reduces the per-hectare cost ofno-tillage in spring to $213/ha (overall cost$140/ha), increasing the overall differencebetween the two to $87/ha in favour ofadvanced no-tillage.2. Contract tillage varies by district from$250/ha to $500/ha. The conservative lowerfigure was used.3. Contract no-tillage with advancedequipment varies from $100/ha to $150/ha,depending on contour, size of field, etc. Theconservative lower figure was used.4. If using cheaper no-tillage equipment,drilling costs will be reduced, but cropyields are likely to be reduced by more thanthe saving in costs.5. Herbicides and pesticides are oftenunnecessary in autumn with no-tillage.Some or all may be necessary in othersituations, in which case their cost atreduced application rates should be addedto no-tillage.6. Autumn tillage in New Zealand (NZ)usually involves minimum tillage.

Scenario B: Economics of purchasing newtillage or new no-tillage equipment

Establishing 150 hectares of spring wheat fol-lowed by 150 hectares of autumn forage crop.The capital costs associated with purchasingall new equipment are shown in Table 18.4.The annual pre-tax operating costs of the twosystems are shown in Table 18.5.

270 C.J. Baker

Item Tillage No-tillage

Glyphosate (includingapplication)

$55/haa $65/ha

Chlorpyrifos (appliedwith glyphosate)

$40/hab

Slug bait (appliedwith drill)

$40/ha

Contractor $250/ha $100/haSeed and fertilizer Same SameTotal $305/ha $245/haCrop yield Same Same× 150 hectares $45,750 $36,750

aGlyphosate is applied at a lower rate for tillage.bThe chlorpyrifos cost would reduce to $8/ha whenthere was lighter pest pressure.

Table 18.1. Spring cropping using contractors.


GlyphosateChlorpyrifosSlug baitContractor $150/ha $100/haSeed and fertilizer Same SameTotal $150/ha $100/haCrop yield Same Same× 150 hectares $22,500 $15,000

Table 18.2. Autumn cropping using contractors.

Tillage No-tillage

Costs $68,250 $51,750Costs/ha $227/ha $172/haDifference (in favour

of no-tillage)$16,500($55/ha)

Table 18.3. Summary of total annual pre-tax costs.

CONCLUSIONS

1. The capital cost of advanced no-tillageequipment was very similar to new tillageequipment.2. With new equipment, annual savingsin operating costs of approximately $18,000per year ($61/ha) will be achieved by pur-chasing advanced no-tillage equipmentrather than tillage equipment.

NOTES

1. Depreciation was calculated on astraight-line basis as:

Tillage tractors: Annual depreciation =new price minus trade-in price (50%of new price) divided by service life(10 years).

No-tillage tractor: Annual depreciation =new price minus trade-in price (50%



1 × 170 hp tractor $170,0001 × 120 hp tractor $120,0001 × 80 hp tractor $80,000Sprayer $6,000 $6,000Plough (5 furrow) $28,000Power harrow (3 m) $23,000Roller $6,000Leveller $3,000Drill $34,000 $120,000Total capital cost $300,000 $296,000Difference Negligible

Table 18.4. Pre-tax capital costs of purchased new equipment.


Depreciation1

(tractors) $10,000 $4,250(other equipment) $2,500 $3,150

Interest2 (9%) on average investment $20,250 $19,980Maintenance3 (tractors @ 5%/year) $10,000 $8,500Maintenance3 (soil-engaging equipment @ 7%/year) $6,580 $8,400Maintenance3 (non-soil-engaging equipment @ 3%/year) $180 $180Fuel

(50 l/ha spring tillage) @ 65c/l $4,875(25 l/ha autumn tillage) @ 65c/l $2,438(15 l/ha spring and autumn no-tillage) @ 65c/l $2,925

Labour(4 h/ha spring tillage) @ $15/h $9,000(2 h/ha autumn tillage) @ $15/h $4,500(1 h/ha spring and autumn no-tillage) @ $15/h $4,500

Total annual operating cost $70,323 $51,885Cost per hectare $234 $172Difference (in favour of no-tillage) $18,438

(or $61/ha)

1,2,3 See ‘Notes’ on pp. 271–272.

Table 18.5. Annual pre-tax operating costs of new equipment.

of new price) divided by service life(20 years).

All other equipment: Annual deprecia-tion = new price minus trade-in price(50% of new price) divided by ser-vice life (20 years).

2. Interest was calculated on the averageinvestment (new price plus trade-in pricedivided by 2) × 0.09.3. Maintenance was from published data(Bainer et al., 1955).4. Actual total cost of labour will probablybe closer to $20/hour if allowance is madefor downtime, travel, maintenance, etc.

Scenario C: Economics of retaining usedtillage equipment or purchasing either new

or used no-tillage equipment

Establishing 150 hectares of spring wheatfollowed by 150 hectares of autumn for-age crop. The capital costs associatedwith purchasing new or used no-tillage

equipment, compared with retaining own-ership of used tillage equipment, areshown in Table 18.6. The annual pre-taxoperating costs of new or used no-tillageequipment versus used tillage equipmentare shown in Table 18.7.

CONCLUSION. Capital costs are virtuallyhalved by owning second-hand equip-ment (tillage or no-tillage) comparedwith new equipment. Some $95,000–$97,500 in capital cost is saved by pur-chasing second-hand tillage or no-tillageequipment.

NOTE

1. The value of used equipment wasassumed to be two-thirds of its new valueand the equipment is halfway through itsservice life. The trade in value remains at50% of the new value at the end of itsservice life.

272 C.J. Baker

ItemTillage(used)1

No-tillage(new)

No-tillage(used)1

1 × 170 hp tractor $170,000 $114,0001 × 120 hp tractor (3300 h) $80,0001 × 80 hp tractor (3300 h) $54,000Sprayer $4,500 $6,000 $4,500Plough (5 furrow, used) $19,000Power harrow (3 m, used) $15,500Roller (used) $4,500Leveller (used) $4,500Conventional drill (used) $23,000No-tillage drill $120,000 $80,000Total capital cost $205,000 $296,000 $198,500Difference (in favour of usedequipment – see Scenario B above)

$95,000 $97,500

Table 18.6. Pre-tax capital costs of new no-tillage and used tillage and no-tillageequipment.

CONCLUSIONS

1. Annual costs of owning and operatingused tillage equipment ($59,228/year) wereapproximately $11,000 lower than fornew tillage equipment ($70,323/year –Scenario B).2. The annual costs of owning and operat-ing used tillage equipment ($59,228/year)were approximately $7000 (or $24/ha)greater than owning and operating newadvanced no-tillage equipment ($51,885/year) and approximately $14,000 (or$46/ha) greater than used advanced no-tillage equipment.

NOTES

1. Depreciation was calculated on astraight-line basis as follows:

Tillage tractors: Annual depreciation =used price minus trade-in price

(50% of new price) divided byremaining service life (5 years).

No-tillage tractor: Annual deprecia-tion = new or used price minustrade-in price (50% of new price)divided by remaining service life (20years for new or 10 years for used).

All other equipment: Annual deprecia-tion = new or used price minustrade-in price (50% of new price)divided by remaining service life(20 years for new or 10 years forused).

2. Interest was calculated on the averageinvestment (used or new price plus trade-inprice divided by 2) × 0.09.3. Maintenance was from published data(Bainer et al., 1955).4. The maintenance costs shown for usedequipment are conservative because main-tenance could be expected to increase withage of machines.


Item Tillage (used) No-tillage (new) No-tillage (used)

Depreciation1 (tractors) $6,800 $4,250 $2,900Depreciation1 (other equipment) $2,100 $3,150 $2,150Interest2 @ 9% (tractors and equipment) $15,975 $19,980 $15,592Maintenance3 (tractors @ 5% new

price/year)$10,000 $8,500 $8,500

Maintenance3 (soil-engaging equipment@ 7% new price/year)

$3,360 $8,400 $8,400

Maintenance3 (non-soil-engagingequipment @ 3% new price/year)

$180 $180 $180

Fuel(50 l/ha spring tillage) @ 65c/l $4,875(25 l/ha autumn tillage) @ 65c/l $2,438(15 l/ha spring and autumn no-tillage)

@ 65c/l$2,925 $2,925

Labour(4 h/ha spring tillage) @ $15/h $9,000(2 h/ha autumn tillage) @ $15/h $4,500(1 h/ha spring and autumn no-tillage)

@ $15/h$4,500 $4,500

Total annual operating cost $59,228 $51,885 $45,147Cost per hectare $197 $173 $150Difference (in favour of no-tillage) $7,343

(or $24/ha)$14,081

(or $46/ha)

1,2,3 See ‘Notes’ on p. 273.

Table 18.7. Annual pre-tax operating costs of new and used no-tillage and used tillage equipment.

Scenario D: Economics of retaining usedtillage equipment or engaging a no-tillage

contractor

Establishing 150 hectares of spring wheat fol-lowed by 150 hectares of autumn forage crop.The annual pre-tax costs of operating usedtillage equipment versus hiring a no-tillagecontractor are shown in Table 18.8.

CONCLUSION

1. Ownership of used tillage equipment wasmore expensive (by approximately $15,000per year or $52/ha) than engaging a contractorwith advanced no-tillage equipment.

Summary and conclusions

The A–D scenarios outlined above aresummarized in Table 18.9.

General conclusions

1. It made little difference whether suchcomparisons were made between new orused equipment, hiring contractors, orcombinations of these options. No-tillagewas less expensive than tillage for allsituations.2. For 150 hectares cropped twice per year,it was cheaper to use advanced no-tillageequipment in any form than to use any formof tillage ($7000–$18,000/year, or $24–$61/hectare).3. The smallest difference was ownershipof used tillage versus ownership of newno-tillage equipment ($24/ha).4. The largest difference was ownershipof new tillage versus ownership of newno-tillage equipment ($61/ha).5. All other comparisons result in anapproximate $50/ha saving using no-tillage.6. Hiring a no-tillage contractor withadvanced equipment is most often accompa-nied by a high level of specialist expertise.7. The only valid economic argument fornot adopting advanced no-tillage is if afarmer does not have access to an advancedno-tillage drill. Substandard crop yieldswill be likely, if not a regular occurrence,with less advanced no-tillage equipment.Tillage is more forgiving of substandardequipment.8. If a farmer chooses to continueownership of the used tillage equipmentwhile hiring a no-tillage contractor withadvanced equipment on a trial basis (asensible practice), the costs of deprecia-tion and interest on the tillage equipmentwill remain although it is not being used($80/hectare, Scenario C). Since the use of

274 C.J. Baker


Annual operatingcosts of used tillageequipment (fromScenario C)

$59,228

Glyphosate in spring(from Scenario A)

$8,250

Annual cost ofcontractor includingglyphosate andpesticides (fromScenario A)

$51,750

Totals $67,478 $51,750Cost per hectare $225 $172Difference (in favour

of no-tillage)$15,728($52/ha)

Table 18.8. Costs of used tillage equipmentversus hiring a no-tillage contractor.

Tillage($/year)

Tillage($/ha)

No-tillage($/year)

No-tillage($/ha)

Differences

Scenario $/year $/ha

Scenario A (contractors) 68,250 227 51,750 172 16,500 55Scenario B (own new equipment) 70,323 234 51,885 173 18,438 61Scenario C (own used equipment) 59,228 197 45,145–51,885 150–173 7,343–14,081 24–47Scenario D (own used equipment

versus contractor)67,478 225 51,750 172 15,728 53

Table 18.9. Summary of Scenarios A–D.

a no-tillage contractor is less than a tillageoption ($53/ha, Scenario D), the netcost of trying out advanced no-tillage for ayear will be about $27/ha ($80–$53),which is a modest price to pay with theprospect of saving $24–61/ha/year forevery year thereafter with the adoption ofno-tillage.

European Comparisons

In these comparisons, an English tillagecontractor provided the following figuresfor a client who cropped 404 hectares (1000acres) per year. The tillage and minimum-tillage figures were actual charges madeto the farmer in previous years. Theadvanced no-tillage figures were quotationsfor 2004.

Two scenarios are compared: plough-based tillage versus no-tillage, and minimumtillage versus no-tillage. The tillage andminimum-tillage programmes are outlined in

Tables 18.10 and 18.11 and are consideredtypical for many English properties.

The no-tillage quote was for anadvanced and more expensive no-tillagedrill (which would assure crop productionwith at least equal yield to the tillage sys-tems), as reflected in the higher per-hectare charge rate. As with the NewZealand comparison, substituting a lessadvanced no-tillage drill for the advancedno-tillage drill might have had the poten-tial to reduce the costs of no-tillage butit also had the potential to reduce theno-tillage crop yield.

Scenario (A) Comparison of no-tillage withfull plough-based tillage

Establishing cereal grain on a 404 hectare(1000 acre) farm using a plough-basedtillage system, compared with advancedno-tillage (contractor charges). Comparativecosts are shown in Table 18.10.


Cost/ha Area Total

Tillage machinesSubsoiler, with packer roller £31.75 404 £12,827.00Ploughing £36.00 404 £14,544.00‘Cultipress’ £14.20 404 £5,736.80Rolling £10.75 404 £4,343.00Power harrow £25.60 200 £5,120.00Fertilizing £7.50 404 £3,030.00Combination conventional drill £29.75 304 £9,044.00Cultivator-drill £30.00 100 £3,000.00Spraying £7.00 404 £2,828.00Total £60,472.80

No-tillage machinesAdvanced no-tillage drill £55.00 404 £22,220.00Spraying £7.00 404 £2,828.00Total £25,048.00

Difference £35,424.80Difference per hectare £87.68/ha

Table 18.10. Comparison of tillage and no-tillage costs in England.

Scenario (B) Comparison of no-tillage withminimum tillage

Establishing cereal grain on a 404 hectare(1000 acre) farm using a minimum-tillagesystem, compared with advanced no-tillage(contractor charges). Comparative costsare shown in Table 18.11.

Conclusions

1. On a contractor basis, minimum tillagewas cheaper than tillage by £29/ha.2. On a contractor basis, advanced no-tillage was cheaper than plough-basedtillage by £87/ha.3. On a contractor basis, advanced no-tillage was cheaper than minimum tillageby £58/ha.4. These comparisons may not have beenvalid if less advanced no-tillage machineshad been used.5. Comparisons between tillage, minimumtillage and no-tillage are machine-dependent,since no-tillage drill designs have the poten-tial to influence crop yields markedly.

Summary of Some EconomicComparisons

1. The most common economic compari-son is between no-tillage and tillage but suchcomparisons are often misleading for anyone of a number of reasons and assumptions.2. Several possible scenarios provide eco-nomic examples of tillage versus no-tillage,but the items and figures will requirechanging for other countries and years.3. Machine costs involved with changingfrom a tillage to a no-tillage system are amajor consideration.4. Maintaining ownership of tillage mach-ines for a period after beginning no-tillageadds some costs to the transition but may bea comforting and affordable choice for manyfarmers.5. Economics of using a tillage contractoror a no-tillage contractor favours using ano-tillage contractor.6. Economics of purchasing new tillage ornew advanced no-tillage equipment showedsimilar capital costs in either case but signi-ficantly lower operating costs for no-tillage.7. Economics of retaining used tillageequipment or purchasing either new or usedno-tillage equipment showed that capitalcosts are virtually halved by owning second-hand equipment (tillage or no-tillage),compared with new equipment, but againoperating costs are in favour of no-tillage.8. Economics of retaining used tillageequipment or engaging a no-tillage contractorshowed that ownership of used tillage equip-ment was more expensive than hiring a con-tractor with advanced no-tillage equipment.9. It made little difference whether com-parisons were made between new or usedequipment, hiring contractors, or combina-tions of these options. No-tillage was lessexpensive than tillage for all situations.10. Hiring a no-tillage contractor with adv-anced equipment is most often accompaniedwith a high level of specialist expertise.11. A US farmer who recently converted fromtillage to no-tillage reports a ‘win–win’ situa-tion with advanced no-tillage equipment. Hehas not only recorded his best crop yieldsever with no-tillage, but he now also uses lessfuel to grow his crops than to harvest them.

276 C.J. Baker

Cost/ha Area Total

Minimum-till machinesSubsoiler, with

packer roller£31.75 202 £6,413.50

Tillage train £35.00 404 £14,140.00‘Cultipress’ £14.20 404 £5,736.80Rolling £10.75 404 £4,343.00Fertilizing £7.50 404 £3,030.00Cultivator-drill £30.00 404 £12,120.00Spraying £7.00 404 £2,828.00Total £48,611.30

No-tillage machinesAdvanced

no-tillage drill£55.00 404 £22,220.00

Spraying £7.00 404 £2,828.00Total £25,048.00

Difference £23,563.30Difference per

hectare£58.32/ha

Table 18.11. Comparison of minimum tillage andno-tillage costs in England.

19 Procedures for Development andTechnology Transfer

C. John Baker

Measuring the mechanical performance ofno-tillage machines is far less important than

measuring their biological performance.

One of the distinguishing aspects of experi-ments conducted with agricultural tillagemachines is that there are very few commonexperimental techniques and standardizedinstruments that can be universally applied.The designs and functions of most agricul-tural machines are quite diverse; thus thetechniques used to evaluate them are tailor-made for specific purposes and to answerspecific questions.

This situation contrasts with experi-ments with plants, for example, in which themost common procedure is to grow plants inpots or plots of soil, each with a designatedtreatment. Since all plants perform essen-tially the same functions of utilizing thesun’s energy to convert nutrients from thesoil, atmosphere and water into biomass,there is a high degree of commonality of plantexperiments.

In the study of no-tillage drills, plan-ters and openers, design scientists havesought knowledge not only about resultingplant growth, using well-established experi-mental procedures, but also about theirmechanical performance and, perhaps mostimportantly, about the interactions between

infinite design variations of the machinecomponents, the soil, surface residues, pestsand the plants.

Described here are some of the experi-mental procedures and techniques used bythe authors and their colleagues to gain know-ledge about the functions and performanceof no-tillage components and subsequentlyto develop new no-tillage technologies,designs and practices. Many of the tech-niques developed are specific to no-tillagebut should be useful to others pursuingsimilar investigations. Some were uniqueexperiments, while others followed well-established common procedures.

This is not an attempt to provide acomprehensive review of all techniquesused by scientists in this field, althoughthe results of much relevant work by awide range of scientists are reported else-where in this book. The technique descrip-tions and instrumentation given hereare restricted to those used or devised bythe authors. We explain how many of theexperiments were conducted in somedetail because they were designed to add-ress a variety of questions about how plantsand soil interact with no-tillage machines,and because there were no known method-ologies for those purposes available at thetime.


The techniques and procedures des-cribed examined the following subjects:

1. Plant responses to no-tillage openers incontrolled conditions.2. The micro-environment within andsurrounding no-tillage seed slots.3. Soil compaction and disturbance byno-tillage openers.4. Locating seeds in the soil.5. Seed travel within no-tillage openers.6. Drag on a disc opener.7. Accelerated wear tests of no-tillageopeners.8. The effects of fertilizer banding.9. Prototype drills and managementstrategies.

Plant Responses to No-tillageOpeners in Controlled Conditions

It is often assumed that most seeds will ger-minate and grow satisfactorily if sown intomoist soil followed by favourable climaticconditions. Unfortunately, under no-tillagethis assumption is not always correct. Earlyexperience with no-tillage had suggested that,as the soil and climatic conditions becameless favourable, seed, seedling and plant per-formance often suffered more than whereseeds were sown into tilled seedbeds.

Thus, it became important to develop afundamental procedure to evaluate the bio-logical performance of different no-tillageopeners under controlled conditions. Theaim was to create a facility where scientistscould put stress on the no-tillage system bysuperimposing unfavourable soil moistureconditions followed by unfavourable climaticconditions without the risk of interventionby unpredictable weather.

Sowing seeds in the field was consideredtoo impractical and imprecise to control thesoil moisture and climate. Conventional‘rainout’ shelters, which involve largemovable transparent canopies covering sev-eral plots of soil, were expensive and wouldhave limited the experiments to one site.This contrasted with tillage experiments,where the soil beneath a ‘rainout’ shelter

can be re-tilled several times to repeat sev-eral experiments on the same site.

The scientists also did not have theconvenience of being able to place seeds indisturbed soils that had been prepared inpots or trays so that they could later betransported into glasshouses or other artifi-cially controlled climate laboratories. Forno-tillage experiments, the soils had to havebeen truly undisturbed for at least 12 months,and preferably longer, and to remain thisway throughout the experiments.

A new technique was developed totransport untilled soil in bins to an indoorclimatically controlled facility. This involvedremoving large 2.0 m × 0.7 m × 0.2 m blocksof soil weighing approximately 0.5 t fromthe field in an undisturbed state, control-ling pre-drilling soil moisture content, drill-ing with openers arranged to duplicate theirperformance on a field drill or planter andthen controlling the post-drilling climate andsoil moisture content for the duration of theexperiment (Baker, 1969a, 1976a, b).

Rectangular steel bins were constructedwith both ends open. The front end of eachbin was able to be attached to the rear of astirrup-shaped soil cutter, which was itselfattached to and pulled through the soil by atractor (Fig. 19.1). The horizontal blade ofthe cutter was hollow, with exit ports drilledalong its rearmost edge. Water was pumpedinto the hollow blade during extraction ofthe 0.5 t soil blocks to create a thin slurry onthe underside of each soil block and thustemporarily lubricate it as it slid along eachof the 2 metre bins. The base of each bin waslined with a veneer of stainless steel to assistthis process.

In practice, it was found that 2 m wasabout the maximum slice length that a200 mm deep undisturbed soil slab couldbe expected to slide without becoming com-pressed and perhaps buckled. Increasingthe depth beyond 200 mm may have permit-ted longer blocks to be extracted, but suchbins would have been difficult to handlebecause of their added weight and length.

Although a 200 mm soil depth couldnot be expected to sustain plant growth forlong periods before roots reached the stain-less steel bases, all of the studies that utilized

278 C.J. Baker

these bins concentrated on the germinationand seedling emergence phases of crop pro-duction, since these were considered to bethe most critical phases obstructing reliableno-tillage. It was also considered that machineinfluences on plant growth were likely to begreatest at the germination and emergencephases and thereafter would be of less influ-ence than other factors, such as weather, soiland management effects.

The soil remained in its bin throughouteach experiment. Bins were transported fromthe field to the laboratory using heavy lift-ing equipment on a tractor (Fig. 19.2). Themoisture content of the soil in each bin wasmanipulated either by covering each binwith clear plastic and leaving it to air-dry orby irrigating it from above by sprinkler orfrom below by placing the perforated binsin shallow troughs containing a predeter-mined quantity of water.

Two processes were used to drill theseundisturbed blocks of soil with a variety ofno-tillage openers. Where measurements ofthe drilling process itself were to be made ormultiple openers were to be tested in eachbin, five bins were placed end to end on theraised bed of a ‘tillage bin’ arrangement,which also had a tool carrier on a moving

gantry that straddled the line of bins andcould be moved forwards or backwards atinfinitely variable speeds from 0 to 8 km/h(0 to 5 mph) (Fig. 19.3).

Where drilling took place indoors, theopeners on test were usually arranged at150 mm row spacing with three rows to abin. This resulted in 200 mm of clearancebetween the outside rows and the edges ofthe bins. The slightly larger distance in thiszone was to avoid soil disturbance at the binedges. All openers were mounted on paralleldrag arms attached to a subframe. The verticalangle was variable to alter the opener pitchfor any geometrical arrangement. Downforcewas applied by adding weights to indivi-dual openers and draught forces were mea-sured by a load cell mounted within thedrag arm attachment subframe.

Mounting openers on parallel armsand applying downforce by application ofweights were not a true duplication of com-mon field practice. Weights ensured thatthe downforce applied to any one openerremained constant regardless of its positionin the vertical plane. This seldom happensin practice. But the objective was to removemost ancillary functional differences betweenopeners and their modes of operation to

Development and Technology Transfer 279

Fig. 19.1. A stirrup-shaped soil cutter with bin attached for extracting undisturbed soil blocks(from Baker, 1969a).

evaluate differences associated with theiractions in the soil and the shape of the slotsthey created.

Individual seeds were metered by a modi-fied vacuum seeder designed by Copp (1961).

As drilling was usually conducted at slowspeeds, a visual count was made of theseeds entering the soil by observing them asthey passed down a clear plastic deliverytube at bench height. In this manner, the

280 C.J. Baker

Fig. 19.2. A filled soil bin being transported.

Fig. 19.3. The ‘tillage bin’ with soil bins arranged end to end ready for drilling (from Baker, 1969a).

exact number of seeds sown was known tomake accurate counts of germination per-centages. With the ‘tillage bin’ elevated tobench height, this allowed instrumentationto be inserted from beneath or beside thesoil to monitor variables such as verticaland/or lateral soil forces resulting from thepassage of individual openers.

It was occasionally necessary to testopeners operating on actual field drills. Inthis case, the open-ended steel bins were leftembedded in the soil after pulling them inwith a tractor and the stirrup-shaped cutter.A field drill was then operated over themwhile they were in situ, taking care to avoidcontact with the steel side walls of the bins.The soil bins could then be removed to con-trolled climate facilities.

The ‘tillage bin’ facility successfullyallowed an accurate measure of how differ-ent shapes of no-tillage openers and slotsrespond to different soil conditions in termsof their abilities to promote satisfactory seedgermination and seedling emergence. Almostall previous no-tillage experiments had usedfield conditions reporting successful estab-lishment, but the results may have been asmuch a function of favourable conditionsas of mechanical performance. While fieldexperiments served to demonstrate thatno-tillage seeding could work, there was aneed to identify and eliminate the causes offailures. This required precise control to beexercised over the seeding conditions.

The tillage bin facility, because of itsmoving gantry, was also used for a varietyof other related experiments. Among thesewere a study of spray droplet dissipationin pasture (Collins, 1970; see Chapter 12),monitoring of seed spacing from precisionspacing planters (Ritchie and Cox, 1981;Ritchie, 1982; Carter, 1986; see Chapter 8)and the transplanting of cabbage seedlingsinto untilled soil (Pellow, 1992).

The micro-environment within andsurrounding no-tillage seed slots

To learn the environmental requirementsof seeds and seedlings within the seed slot,the following variables were tested to define

the effects of opener designs: (i) soil moistureregime within the slot; (ii) soil-air humiditywithin the slot; (iii) soil oxygen within andaround the slot; and (iv) soil temperaturewithin the slot.

No attempt was made in these experi-ments to monitor the presence of allelo-pathic substances from decaying residue orother root material in the slot, since thiswas being well researched by Lynch andothers at the time (Lynch, 1977, 1978;Lynch et al., 1980). However, later experi-ments on wet soils by the authors and theircolleagues added knowledge about theseeffects and how they might be avoidedthrough opener design (see Chapter 7).

Soil moisture regime within the slot

Most non-destructive devices for measuringthe liquid water content of soil sample areasonably large soil volume. This is neces-sary to average the variations inherent insmall soil volumes. The slot zone left by ano-tillage opener represents a relatively smallvolume of soil, which has made monitor-ing of liquid-phase moisture particularlydifficult.

Gypsum blocks and most other physicalabsorption-based devices work best at thewet, low-tension, end of the moisture range,which made them unsuitable for experimentswith dry soils. Early designs of dew-pointpsychrometers were tried, but the steeptemperature gradients at or near the soilsurface made them unreliable. Eventually,recourse was had to destructive gravimetricsampling, in which miniature cores ofsoil (20 mm diameter × 10 mm deep) wereremoved from the slot zone and oven-driedto provide a measurement of the liquid-phase soil moisture content on a differentialweight basis. More sophisticated instrumentshave become available since these experi-ments were conducted.

The research showed that the liquid-phase water content of the soil in andaround contrasting slot shapes did notgreatly differ, at least in the short term, evenwhen there were marked differences in seed-ling emergence between openers in other-wise relatively dry soils. While this at first


seemed anomalous, it was decided thatexhaustive testing of further alternativedevices for measuring liquid-phase soil waterwas not justified. Rather, attention shiftedto the measurement of slot humidity, orvapour-phase soil water.

Soil-air humidity within the slot

Soil physics shows that the atmosphere (air)in soil macropores and voids forms an equi-librium water vapour pressure with the liq-uid water contained in the surrounding soilpores. At a given temperature, the vapour-phase water in these soil spaces representssoil-air humidity. Since soil temperature atseeding depth does not change rapidly andis easily measured, soil humidity becamea reasonably reliable way to measure thewater-vapour pressure of the soil atmosphere.

Choudhary (1979) first monitored soil-air humidity within no-tillage slots using anaspirator to slowly draw quantities of airfrom the slot and pass these through a dew-point hygrometer for a direct reading of therelative humidity of the air sample. Whilethis method produced interesting figures,the scientists were conscious that the removalof air from the slot inevitably resulted in itsbeing replaced with air drawn predomi-nantly from the atmosphere above the soilsurface. Thus, the slot air samples only partlyreflected the humidity within the slot.

The accuracy of the method relied onthe removal rate of the slot air and the diffu-sion resistance of the slot cover, which con-trolled the rate that atmospheric air replacedthat being removed. A high diffusion resis-tance of the slot cover, for example, mightresult in the removed slot air sample beingreplaced by additional slot air from furtherdown the slot, while a low diffusion resis-tance might contain a larger proportion ofatmospheric air. As it turned out, this diffu-sion resistance was later identified as animportant variable in seed/seedling survival,but in the meantime a method was foundthat sampled the relative humidity in situwithout removing air from the slot.

A modified direct-reading humidityprobe was inserted into the slot and allowedto equilibrate with the undisturbed slot

atmosphere for at least 2 minutes. The probeselected was originally designed to monitorrelative humidity between sheets of news-print. As such it was flat and thin in shape.The point was removed and a small piece offibreglass filter material was wrapped overthe end to prevent soil from falling into thesensitive probe. The filter was left behindin the soil when the probe was withdrawnand was not reused. Figure 19.4 shows ahumidity probe being inserted into a dryno-tilled soil that is contained within aclimate-controlled room.

This method yielded a direct reading ofrelative humidity, approximating what theseeds experienced in the slot. The informa-tion gathered with this technique had far-reaching consequences. The experimentsshowed that no-tilled seeds could germi-nate in a high-humidity slot atmosphere,i.e. without access to substantial amounts ofliquid-phase water, a fact that was later con-firmed by Martin and Thrailkill (1993) andWuest (2002).

More importantly, subsurface seedlingscould survive beneath the soil for severalweeks if the slot atmosphere was main-tained at or near 100% relative humidity.The latter observation was shown to be afunction of the diffusion resistance of theslot cover and the humidity gradient betweenthe slot air and the ambient air outside theslot. Slot cover was itself a function of slotshape, the presence of surface residues overthe slot and the design of the opener.

Being able to monitor slot atmospherehumidity was one thing, but being able tocontrol and vary that humidity for the pur-poses of experimentation was quite anothermatter. Even rain-protection covers werenot satisfactory since they were unable toalter the ambient humidity of the day. Uti-lizing a multi-room controlled-climate faci-lity, the 0.5 t blocks of soil in their steel binswere moved after drilling into climate-control rooms in groups of three. Each roomhad an artificial climate in which the tem-perature, humidity, light intensity, lightspectrum, day length, nutrients and, if nec-essary, wind speed and direction could becontrolled. In this way, the effects of highand low ambient humidity levels and/or

282 C.J. Baker

temperatures were varied and the effectson the establishing seedlings measured (seeChapter 6).

Soil oxygen within and around the slot

The main consequence of a no-tilled soilbecoming very wet after drilling is restric-tion of oxygen supply to the germinatingseeds and embryonic roots. In a tilled soil,there is much artificial loosening, whichexaggerates the oxygen regime around theseeds for a time. In an untilled soil, seedsrely almost entirely on the ability of the soilto remain adequately oxygenated in its nat-ural state. To test a range of opener designsto provide varying oxygen conditions withwet soil conditions, variables of oxygen diffu-sion rates, earthworms, infiltration and soiltemperatures were considered.

Several scientists have described anoxygen-diffusion measurement techniqueinvolving pushing a small platinum elec-trode into the soil and measuring the cur-rent passing between this electrode and areference electrode. The current has theeffect of reducing electro-reducible material,in this case oxygen, at the platinum surface.The size of the current is governed by the

rate of oxygen diffusion from within the soilto the surface of the electrode and thus givesan indication of the oxygen diffusion rate(ODR) within the soil.

Most scientists agree that the ODRvalues obtained with platinum electrodes areonly an approximation of what a root mightexperience, but the technique provides arelative measure of the difference between arange of soil conditions. The advantages arethat it is cheap, non-destructive, quick, easyand capable of sampling very small zones ofsoil in the vicinity of the slot.

Chaudhry (1985) sampled ODR in agrid pattern around the basal area of a rangeof slots in a wet soil and used a computerprogram to draw iso-ODR lines reflectingthe contrasting oxygen regimes generatedby the passage of no-tillage openers and thepresence or absence of surface residues andearthworms (see Chapter 7).

Earthworm activity was a likely con-tributor to the soil slot oxygen status. Mai(1978), Chaudhry (1985) and Giles (1994)monitored the numbers of earthwormspresent in the general plot soil and thosearound a seed slot. Cylindrical cores of soilcentred on the slot were extracted and earth-worms counted and weighed. Chaudhry also


Fig. 19.4. Sampling soil humidity in the field.

monitored earthworm activity on the soilsurface by estimating the percentage of agiven area of soil that was covered withearthworm casts. He termed this the ‘castingindex’.

Water infiltration into the slot zone wasanother potential factor in providing oxygenexchange. Relative infiltration rates weremonitored by rectangular metal boxes (infil-trometers) inserted into the soil surfacecentred on the slot (Chaudhry, 1985; Bakeret al., 1987).

Exhaustive temperature comparisonswere made by Baker (1976a) within a rangeof slot configurations. Temperature is rela-tively easy to measure in small discrete zonesusing miniature thermometers or electronicthermocouples. Short-term readings were bysimple mercury thermometers, while thermo-couples were used for continuous readings,such as diurnal ambient fluctuations.

Soil Compaction and Disturbanceby No-tillage Openers

It had long been thought that a logical resultof no-tillage openers operating in untilledsoils would be progressive compaction andrestricted root growth in the slot zone. There-fore, several studies centred on monitoringthese aspects. The parameters measuredwere: (i) soil strength; (ii) instantaneous soilpressure (stress); (iii) instantaneous andpermanent soil displacement; (iv) soil bulkdensity; and (v) smearing.

Soil strength

Soil strength is traditionally assessed bymeasuring the force required to push aprobe (penetrometer) into the soil. To moreclosely resemble the actions of a root, theprobe ends are usually conical in shape sothat the force dissipation is radial as wellas longitudinal. Such probes, however, areusually designed to sample reasonably largevolumes of soil and, because of the naturalheterogeneity of soil, repetitive samplingwith a single probe is common.

To get the benefits of multiple soilprobing within the confines of the slot zone,a miniature multi-point penetrometer wasdesigned (Dixon, 1972; Baker, 1976a; Bakerand Mai, 1982b). This device consisted of20 1 mm diameter stainless steel probesmounted in a common horizontal press barin such a way that the vertical position ofeach probe with respect to the bar could beadjusted and clamped individually. Thepress bar could be angled at any desiredposition from horizontal to vertical andwas attached to a threaded shaft that actedas the thrust mechanism, together with asensitive ring-shaped force-measuring device(known as a ‘proving ring’). Two differentdisplacement-measuring devices have beenused to monitor the changes in diameter ofthe ring. Initially, a micrometer sufficed,but in later tests a displacement transducerwas substituted to facilitate recorded results.The multi-point penetrometer is shown inFig. 19.5.

Because soil tends to flow as a plasticbody to a limited extent for several secondsafter a rigid probe is inserted, it was neces-sary to insert the probes at a predeterminedand constant speed and to read the forceapplied at a standard time interval afterthe probe penetration had been stopped atthe desired depth (when plastic flow hadceased). The probes were inserted at a con-stant speed of penetration by rotating thethreaded shaft at a constant speed, using aslow-speed electric motor drive, which wasimmediately disconnected upon reaching thedesired depth, and then waiting 10 secondsbefore reading the gauge.

To accommodate the irregularities of thesoil surfaces, the press bar was positionedparallel to the chosen surface and each probewas slipped through the bar until it lightlycontacted the soil surface, then clamped inthat position. Care was taken to ensure thatan equal number of probes on each side ofthe central threaded shaft contacted the soilto ensure, as nearly as possible, symmetryof forces about the central point when all ofthe probes were pushed into the soil. Eventhen, a single probe would occasionallycontact a stone, greatly distorting the sym-metry, and the readings were discarded.

284 C.J. Baker

Using the tillage bin facility previouslydescribed, the multi-point penetrometerwas inserted from a number of directions:(i) from above the ground to test soil strengthvertically downwards at the base of slots(Baker and Mai, 1982b); (ii) from the sideperpendicular to the side walls of slots (Mai,1978; Baker and Mai, 1982b); (iii) frombeneath the bins pushing upwards to mea-sure the resistance of slot cover to shoot

emergence (Choudhary, 1979); and (iv) per-pendicular to the cross-sectional end facesof soil blocks in their bins to test the soilstrength in a grid pattern surrounding across-section of the slots (Mitchell, 1983).

The penetrometer was not usable in thefield as its high sensitivity required a verystable base from which to derive the pene-tration force. This could only realisticallybe provided by the tillage bin supported on


Fig. 19.5. A multi-point penetrometer attached to a ‘proving ring’ force-measuring device (from Bakerand Mai, 1982a).

a concrete floor. Even then, a person pressingon one of the bins could cause the penetro-meter reading to deflect.

Instantaneous soil pressure (stress)

As the opener passes through the soil, pres-sures are created to move the soil aside, withmultiple potential consequences from com-paction to smearing. These pressures weremeasured using a specially designed dia-phragm pressure pad (Mai, 1978). A smalllength of 9.5 mm diameter brass tube had arubber diaphragm attached to one end. Theother end had a sensitive electronic miniaturepressure transducer attached. The tube wasfilled with water to act as a non-compressibleliquid and a small bleed screw was used toexpel all air. These tubes were insertedthrough holes in the side walls and base of thesteel bins into close-fitting pre-bored holesin the soil so as to position the rubber dia-phragm in intimate contact with soil a set dis-tance (as close as 10 mm) from the expectedpathway of a no-tillage opener to be tested.

Since each opener travelled a well-controlled pathway on the tillage bin tram-way, it was possible to very accuratelypredetermine the side position of the soil-stress devices. The depth of penetration ofeach opener was somewhat less predictable,despite common ground-gauging wheelsbeing used with each opener, because theground surface of each bin did not finishexactly the same distance from the base ofits steel bin during the field extraction pro-cess. Thus, somewhat more latitude wasallowed for vertical positioning.

Even so, the water-filled tubes wereused to protect the expensive miniature pres-sure transducers in the event of mechanicalcontact with a passing opener. The brasstubes and their rubber diaphragms wereconsidered expendable in the event of anaccident. The expensive pressure transduc-ers were not. Figure 19.6 shows one suchtube. In this manner, the contrasting instan-taneous soil stresses created by a range ofpassing openers in an untilled soil weremonitored and reported (Baker and Mai,1982a).

286 C.J. Baker

Fig. 19.6. A soil pressure measuring tube (from Baker, 1969a).

Instantaneous and permanent soildisplacement

This was measured by placing small verticalprobes in the soil at predetermined distancesfrom the anticipated pathway of an openerto be tested in the soil bins on the tillage bin(Mai, 1978). A light non-stretchable threadwas attached at one end to each probe andat the other end to a small electronic dis-placement transducer, which recorded boththe instantaneous horizontal displacementof the soil as the opener passed and thepermanent displacement after it had passed.The displacement data gave a measureof the direction in which an opener dis-placed the soil, as well as the plasticity ofthe soil and how it had responded to themechanical action of that particular opener.

Soil bulk density

This was measured by extracting small soilcores (10 mm × 10 mm) from the slot zonesin a location and pattern required by thespecific experiment (Mai, 1978; Chaudhry,1985). The cores were weighed and a standardprocedure was used to calculate soil bulkdensity as the weight per unit volume of soil.

Smearing and compaction

This was a difficult parameter to accuratelyquantify, since smearing, in particular, wasoften confined to a layer less than 1 mmthick. It was determined that smearing inany case only affected root growth when itwas allowed to dry and become a crust.Other environmental parameters determineslot drying, as previously described. Thus, noeffort was made to develop a direct method toaccurately quantify smears. It appeared thatthe difference between a smear and a com-pacted layer was only a matter of thickness.

Locating Seeds in the Soil

Three aspects of seed position within the soilwere considered important to the design of

no-tillage seed drills and planters (Ritchie,1982): (i) seed spacing along the row; (ii)seed depth; and (iii) lateral position of theseed relative to the centre line of the slot.

Seed spacing

Measuring seed spacing is relatively simple.At least, it is if no account is taken of seedbounce in the slot and other soil factors,such as cloddiness. Accurate measurementcan be achieved by simulated drilling, whichinvolves moving a seeder over a sticky plateor paper so that the seeds dropped from theseeder are immediately fixed on the paperas the machine moves forward. The tillagebin and moving gantry described earlier wereideal for this function (Ritchie, 1982; Carter,1986). Seed spacing can also be determineddirectly by measuring the distance along thesurface of the soil between emerged seed-lings. The latter method takes no account ofdisplacement of shoots from the originalpositions of the seeds (by, for example, weav-ing around soil clods or stones) or of failureof seeds to germinate or of seedlings toemerge.

Seed depth

Measuring seeding depth is a deceptivelydifficult problem. For obvious reasons, theposition of seeds in the vertical plane in thesoil can only be determined after they havebeen sown, unlike horizontal seed spacing,which can be simulated on sticky paper with-out the opener having to penetrate the soil.

The problem is that when scientistsexcavate the soil to find individual seeds, itis almost inevitable that other seeds in thevicinity will be disturbed. In recent years,scientists have used one of four approaches:

Manual excavation (Hadfield, 1993;Thompson, 1993)

Despite the disadvantages, careful excavationof the soil in the field to expose individualseeds is still the most common method.This method has the problem that inherent


errors are difficult to quantify and correct.With tilled soils, the seeds are approachedfrom above, but, because of the lack of dis-turbance and the relative stability of someuntilled soils and slots, it is sometimes pos-sible to cut a trench alongside and approachthe seeds from the side, which reduces therisk of disturbing other seeds.

Scoop sampling

A semi-cylindrical horizontal core of undis-turbed soil, which centres on a drilled row,is removed with a specially shaped scoop,and then carefully split open on a bench ina laboratory to expose the seeds (Baker,1976a). This technique can only be usedwith untilled soils because tilled soils aretoo friable and the cores collapse. It is some-what more accurate than manual excavationfrom above because the seeds are approachedfrom the side. It is also more convenient thanfield sampling from the side because theoperator works mostly at bench height andthe soil samples can be laid on their sideson the bench. The technique removes rela-tively short lengths of row at a time, andtransports these to a laboratory. It is moretime-consuming than other methods. It ismore useful for locating and counting seedsand seedlings in a given length of row thanfor accurately recording their positions rela-tive to the soil surface.

Tracing down seedlings

After emergence of seedlings, careful tracingdown from the emerged shoots to the seedposition will establish the original positionof sown seeds within the soil (Stibbe et al.,1980; Pidgeon, 1981; Allam and Weins, 1982;Choudhary et al., 1985). This procedure hasbeen mechanized for automatic recording toprovide measurements for relatively largenumbers of seedlings. But, because it onlymeasures the emerged seedlings, it fails torecord any position for non-emerged seeds.Since identifying disadvantaged seeds wasone of the more obvious aims of locatingthem in the soil for no-tillage studies, thetechnique has had limited application.

X-ray imagery of seeds

By coating seeds with red lead oxide (acommon bird repellent) prior to sowing,images of the seeds can be recorded byX-raying samples of soil removed from thefield in metal boxes using a veterinary X-rayfacility (Campbell, 1985; Choudhary et al.,1985; Praat, 1988; Campbell and Baker,1989; D. de Kantzow, 1985, 1993, personalcommunication). Both aluminium and steelare suitable for the boxes, as X-rays readilypass through these metals without an image.The technique is non-injurious to the seeds(they will germinate after X-raying) and itpositively identifies seeds beneath the soilwithout disturbing them. It is also largelyunaffected by soil type, moisture content ororganic matter levels, but it is best suited tolarge seeds and relatively small numbers ofsamples because it is time-consuming andrelatively expensive.

X-rays are derived from a point sourceon the X-ray machine; thus, as the X-raysscan a sample, a parallax error is created atall positions except those directly beneath thepoint source. This parallax error increasestowards the extremities of the sample andaffects the accuracy of quantifying the dis-tances between individual seeds or betweenseeds and the surface of the soil. Campbell(1985) derived a mathematical correctionfor this error. He also used a strip of leadsoldering wire to indicate the position ofthe soil surface in the X-rays. Figure 19.7shows pea seeds coated with lead oxideX-rayed beneath the soil after seeding.

Lateral position of seeds relative to thecentre line of the slot

As with seed depth, manually locating thelateral position of seeds after they have beendrilled presents problems arising from thepossibility of inadvertently displacing thembefore their positions can be recorded. Bothscoop sampling and X-ray imagery were usedon the few occasions this parameter wasstudied.

To date, no totally satisfactory methodhas been devised to positively, cheaply

288 C.J. Baker

and repeatably identify the final three-dimensional position of seeds in the soil.Perhaps this accounts for why most design-ers of furrow openers and seed drills seem tosatisfy themselves with defining how welltheir openers follow the ground surface,with the implied assumption that final seedplacement is solely related to this capability.

Seed Travel within No-tillage Openers

The pathway seeds are required to travelthrough and from no-tillage openers is oftenmore tortuous and less predictable thanwith simpler openers for tilled soils. Thus,it has been important to monitor seed traveland to analyse the causes of blockage ordisruption to the flow.

All of the techniques adopted by theauthors have involved use of video cameraand slow replay facilities. Ritchie (1982)studied discharge of seeds from precisionsingulation seeders, together with a range ofdelivery tubes, by videotaping the seeds asthey fell. He calculated the delay timesbetween passage of successive seeds past agrid and the resulting potential variations

in horizontal spacing along the row. Thevideo was then replayed on a frame-by-frame basis against a background grid cali-brated on both a time and distance basis.Figure 19.8 shows seed ejection being mon-itored in this manner using the tillage binmoving gantry as the source of seedermovement.

One study of seeds within the disc ver-sion of a winged opener involved substitut-ing a clear Plexiglas disc for the normalsteel disc on the opener and videotaping theseed pathway through the transparent disc.This opener is somewhat unique in thatmuch of the internal pathway for the seedsinvolves a three-sided tube in close proxi-mity to a revolving disc. The rotation of thedisc forms one wall of this delivery tubeand moves continuously. Scientists wantedto study the influence of this moving walland the geometric shape of the stationarywalls on seed drop and ejection from theopener. Figure 19.9 shows the seed flowingthrough such an opener.

To date, no satisfactory technique hasbeen found for viewing seeds as they emergefrom an opener beneath the soil, althoughknowledge of such action would assistgreatly in designing openers with improved


Fig. 19.7. Pea seeds coated with lead oxide X-rayed beneath the soil after seeding(from Campbell and Baker, 1989).

seed ejection and depth control qualities.The advent of endoscopes and laparoscopesappeals as a possibility, but dust collectionon the lens while operating beneath thesoil would seem to be inevitable, and

continuous dust removal, by, for example, asmall jet of air, might interfere with the seedejection process itself. None the less, thereis potential for innovative design in the pur-suit of this objective.

290 C.J. Baker

Fig. 19.8. The ejection of seeds from a no-tillage opener being filmed on video. Four individual maizeseeds can be seen dropping from the precision seeder at the centre right of the photograph.

Fig. 19.9. Seed flow being monitored through a clear Plexiglas disc.

Drag on a Disc Opener

The disc version of winged openers, in par-ticular, operates on the principle of a cen-tral vertical disc with a number of othercomponents rubbing on it, creating a dragon the disc, resisting turning. Contact betweenthe disc and some of these components, e.g.the left- and right-hand side blades and scra-pers, is essential to the residue-handlingand seed-placement functions of theopener. So, too, is continued and uninter-rupted rotation of the disc. Thus, it becameimportant to be able to quantify the magni-tude of the various torsional drag forcesopposing continuous rotation of the disc sothat those that are unnecessary might beeliminated and those that are useful couldbe minimized.

The method adopted consisted of des-igning a special test stand in which a singleopener was mounted in such a way as toallow each of the components contributingto torsional drag to be individually attachedand removed without otherwise affectingthe function of the opener (Javed, 1992).The test stand with opener attached waspulled through a range of test soils at a con-stant and known ground speed. The disc

had a modified motorcycle disc brake ass-embly attached to it, which was capable ofstopping the disc, resulting in 100% discslip in the soil. The force required to achieveany intermediate and predetermined degreeof braking of the disc was recorded by anelectronic force transducer mounted betweenthe disc brake assembly and the frame of thetest stand. The speed of the disc, in revolu-tions per minute, was indicated by a tacho-meter and was directly proportional to discslip in the soil at any given forward speed.Figure 19.10 shows the disc drag test standand opener.

The free disc, i.e. without any torsionallydragging components attached, was firstbraked down to a predetermined speed,representing a set amount of disc slip in thesoil. Then each of the components thoughtto cause torsional drag was added to theopener individually and measurements weretaken of the residual braking found neces-sary to achieve the same set amount of discslip. The difference between this and theoriginal reading represented the torsionaldrag on the disc attributable to the addedcomponent. Variability of the soil that pro-vided the tractive forces driving the discrequired that a large number of recordings


Fig. 19.10. A test stand for monitoring disc drag of a no-tillage opener.

be made to develop accuracy. These weremade using a high-speed electronic datalogger, which recorded some 10,000 indi-vidual readings per test.

Accelerated Wear Tests ofNo-tillage Openers

The disc version of the winged opener wasquite different from other seed drill openersfor either tilled or untilled seedbeds. Thus,little was known about the relative wear ratesof its essential components, although Bakerand Badger (1979) had studied aspects of wearon earlier simple winged openers. The twomost important areas of wear on this openerwere considered to be the soil-to-metal wearon the outside of the side blades and theirwings and the metal-to-metal wear betweenthese side blades and the rotating disc.

Indeed, it had not yet been determinedwhether the side blades actually rubbed onthe disc (metal-to-metal contact) or wereheld fractionally clear of the disc by a finefilm of soil passing between the two compo-nents, in which case the contact would resultin metal-to-soil-to-metal wear. The questionof possible contact between the side bladesand the disc was important because, if therewas no direct contact, it would allow theside blades to be manufactured from mate-rial of considerably greater wear resistance.If there was direct contact, hard side bladesmight have eroded the discs themselves,which would have been unacceptable.

A technique was developed to examineboth questions (Brown, 1982; Brown andBaker, 1985). A single opener was assem-bled in such a manner as to electrically iso-late the side blades from the disc. It wasthen operated in the soil with leads con-nected to both the disc and side bladesthrough a 12-volt battery to complete a cir-cuit if the two made electrical contact andmonitored by a meter or resistance lightbulb. In the soils tested, a thin film of soilcontinually isolated the blades from the disc.Subsequent field experience confirmed thatthe hardness of blades had no effect on thelife and integrity of the face of the disc, andthat the abrasion patterns on both the disc

and insides of the blades are consistentwith metal-to-soil-to-metal wear.

None the less, the thin film of soil wearsboth components at this interface. A furthertechnique was developed to accelerate weartesting of alternative strategies for prolong-ing the life of the side blades. The openerwas modified so that the axle of the disccould be powered, causing it to rotate whenthe opener was stationary. The modifiedopener was arranged so that the base of thedisc and blades were immersed in an openbox of crushed (and, in one case, slurried)soil at normal sowing depth. The side bladeswere held against the disc with springs tosimulate the forces experienced in the fieldif the opener was proceeding forwards. Thetest stand was left to run continuously inthis manner for extended periods so as tomonitor the pattern of wear at the interfacebetween the blades and the disc. Figure 19.11shows the accelerated wear box and testopener.

Where normal field wear patterns onthe outside of the blades and wings werebeing studied (soil-to-metal wear), there wasno substitute for continuous field drilling.By definition, the openers were required toexperience continuously undisturbed soil;thus, re-drilling the same area repeatedlywas not an option. In one test, a single-rowdrill was constructed and 16 hectares ofundisturbed land were drilled in singlerows. The opener covered some 500 km,which was equivalent to 225 hectares ofcontinuous drilling with a 4.5 metre (15foot) wide drill. Wear of the various bladetreatments was measured both dimensionallyand as weight loss (Brown, 1982; Brownand Baker, 1985).

Effects of Fertilizer Bandingin the Slot

A number of experiments were conductedto determine the most appropriate positionto place fertilizer separately from seed.Apart from the more common field experi-mentation techniques (which are notdescribed in detail here), a number of

292 C.J. Baker

specialized experimental facilities weredeveloped.

Horizontal, vertical or diagonal separa-tion directions were compared using modi-fied disc-version winged openers withside-blade combinations as follows:

1. The side blades were on opposite sidesof the disc and of equal length (horizontalseparation).2. The side blades were on opposite sidesof the disc but the fertilizer blade was20 mm longer (diagonal separation).3. One side blade was extended below thedisc to create a deep band beneath and toone side of the seed (deep banding).4. A short and a long side blade were bothpositioned on the same side of the disc (ver-tical separation).

Crop performance and seed damagewere compared with field trials of thesecombinations. The horizontal option per-formed better than the diagonal or verticaloptions in all respects (see Chapter 9). Thiswas fortunate, because the vertical optionwould have been difficult to implement ona field scale because the placement of twoblades on one side of the disc would havebeen a difficult engineering task for other

than experimental purposes. Figure 9.4(Chapter 9) shows the experimental verticalplacement opener.

Surprisingly, the extended diagonaloption did not seem to interfere with theability of the opener to handle surface resi-dues, but it did cause undesirable wear pat-terns on the inside edges of the bladesbecause each blade contacted the disc in thegullet zone for approximately half of thetime, whereas contact was continuous ifabove the gullets. Longer blades also resultedin an increase in torsional drag on the discbecause of the extended contact zonebetween the two. Since there was no benefitfor the longer, more complicated, fertilizerblades, the option was not pursued.

Afzal (1981) studied vertical versushorizontal placement of fertilizer relative toseed without using an opener by extractingsmall blocks of undisturbed soil from thefield and placing these in pots and boxes.For vertical placement, he bored smallholes vertically into the soil, placed a pre-weighed amount of fertilizer in the base ofthe hole and replaced a known quantity ofloose, tamped soil on top.

For horizontal separation he repeatedthe process described above but bored the


Fig. 19.11. An accelerated wear box for testing a no-tillage opener.

vertical hole only to the seeding depth andcovered the seeds with the plug of undis-turbed soil. He then bored a horizontal holefrom the side of the pot or box to positionthe fertilizer a predetermined distance frombut at the same height as the seed. This holewas also closed using a plug of undisturbedsoil, but in this case without surface residues.

Prototype Drills and ManagementStrategies

As part of the logical development of a newfield technology, laboratory developmentseventually need to be tested on a field scale.With seed drills and planters, this can onlybe partially achieved using small experi-mental machines. For example, one of themost important functions of no-tillage drillsis the ability to handle surface residues. Asingle-row experimental machine mightsuggest how well an opener would performthis task, but only a machine with multipleopeners would experience interactions ofadjacent openers over a field with variableresidue amounts and configurations. Thus,it is important to observe opener and drillperformance on a field scale along withmonitoring component wear and durability.

It is also necessary to compare differentopener design performances on a field basis,but only after testing their biological perfor-mance in controlled laboratory conditions.When laboratory details are complete, appro-priate field comparisons are possible usinga test machine with several openers.

Operation in the field offers opportuni-ties to monitor farmer reaction to the newtechnologies and to learn from farmers theconstraints imposed by their managementsystems. It also allows the scientists, workingwith innovative farmers, to evolve new man-agement strategies based on the increasedcapabilities of no-tillage and related emerg-ing new technologies.

The development sequence involvestesting: (i) single-row test drills; (ii) univer-sal toolbars for field-testing several differentdesigns of openers at the same time;(iii) plot-sized field drills and planters; and

(iv) field-scale prototype drills and a drill-ing service for farmers.

Single-row test drills

A range of single-row drill designs wereconstructed for three objectives. First, theywere a facility to test the mechanical perfor-mance of prototype openers in a field soil.Usually, the scope of such tests was focusedon quantifying the mechanical functioningin different soil or residue conditions.Occasionally, as previously described, theymay be used to drill an extended area foraccelerated wear tests.

Generally, these single-row test drillsconsist of an opener rigidly mounted in asubframe attached to a tractor three-pointlinkage, with the downforce provided byremovable ballast. In this manner, the trac-tor three-point linkage acted as the articu-lating drag arms for the opener, althoughthe geometries of such linkages were seldomadjustable to form a perfect parallelogram.Within the limited range of vertical move-ment required of the test machines whenthe opener was in the ground, the tractorlinkages were considered acceptable.

Secondly, single-row units were usedfor seeding purposes, at which time simpleseed and fertilizer distribution systems wereadded to the basic machines. These simpledrilling units offered field experience forverifying the laboratory biological perfor-mance of seed and fertilizer placement.

Thirdly, they became a convenient,although limited, machine to demonstratethe new opener capabilities to farmer groupswithout the need to transport heavy multi-row machines to the field. But developerslearned that, even with the aid of beingable to see how each opener operated on thesingle-row demonstration drills, few obser-vers were able to visualize the capabilitiesof a full-sized multi-row drill operating inthe same circumstances. Consequently, thesingle-row demonstration concept playedonly a minor role in the wider technologytransfer process, but was important in theengineering development process.

294 C.J. Baker

The single-row no-tillage drill conceptwas extended to become a commerciallyavailable machine as a plot drill for experi-mental stations; as a commercial drill forestablishing edible shrubs by no-tillage onsteep and erodible land; and as a commercialdrill for small farmers in developing nations.The adaptability was further enhanced withthe provision of a wheeled front steeringframe to ensure that the wing angle on theopener remained correct and to facilitateturning corners when draught animals wereused. A platform was added to the rear toallow an operator to step on or off to act asthe downforce ballast. Figures 19.12, 19.13and 19.14 illustrate several single-row testmachines used to test and/or demonstratethe disc version of winger openers.

Simultaneous field testing of severalopener designs

It is difficult to conduct a valid test of con-trasting openers on a field scale without theability to control the soil and climatic con-ditions. Almost invariably, such tests revealthe dominance of one opener over othersbeing compared in that particular set of

conditions, only to have the order altered indifferent conditions. The field conditionsmust be carefully identified under whichany one opener is dominant, to learn thestrengths and weaknesses of contrastingdesigns.

Often several parameters may vary,making it very difficult to isolate the rea-sons for one or more openers being superiorfor that particular set of conditions, withoutresults from laboratory experiments thatprovide the biological capabilities of variousno-tillage openers. And, unless the openersrequire very similar toolbar controls or areself-controlled, a single setting of height,down-pressure or speed may not be appro-priate to all openers, biasing the resultstowards those openers that benefit mostfrom the test settings.

It is interesting that, when people areasked to comment on the pros and cons ofvarious no-tillage machines, many believethat such judgements cannot be made untilseveral machines are lined up beside eachother and tested in the same field. This seem-ingly obvious answer, however, is flawedbecause such field tests do not usually iden-tify, let alone isolate, the individual causalprocesses of any differences that do arise. It


Fig. 19.12. A commercially available single-row no-tillage drill.

is doubtful if any scientifically useful pur-pose has ever been served by field compari-sons of multiple no-tillage machines.

Field toolbars are useful as an interme-diate stage in the engineering field testingand development of prototype openers before

any are considered sufficiently promisingto incorporate into either a multi-row drillor planter, or even a self-contained single-row drill.

Figure 19.15 shows a universal fieldtoolbar for evaluating a variety of openers,

296 C.J. Baker

Fig. 19.13. An early single-row demonstration unit.

Fig. 19.14. A single-row machine for testing the residue-handling capability of a no-tillage opener.

as designed by the University of NewEngland, NSW, Australia (J. Scott, 1992,personal communication).

Plot-sized field drills and planters

Once the capabilities of an opener, e.g. thedisc version of winged openers, are pub-lished or made public, it is common thatother research organizations will design andconstruct plot-sized drills and plantersequipped solely with these openers to sowtest plots and fields for evaluation. In gen-eral, most designs of the plot machines havebeen an attempt to duplicate the mechanicalarrangements of commercial field machinesas faithfully as possible while at the sametime incorporating facilities to more accu-rately monitor seed and fertilizer applica-tion rates, clean the product boxes betweenplots and adjust various mechanical options.These machines are made convenient to beeasily transported to remote plots or farmfield demonstrations. Such plot-sized drillshave been an important intermediate stageof development before full-sized field proto-type machines are contemplated. Figure 19.16

shows a selection of typical plot drills basedon the disc version of winged openers.

Several designs of plot drills were usedfor plant-breeding purposes where plot sizeswere small and the quantity of seed avail-able was limited. Innovative mechanismswere introduced to delay release of the seedfrom the front gang of openers so that boththe front and rear gangs began and endedseeding on the plot edges.

Field-scale prototype drills and a drillingservice for farmers

The ultimate objective of any seed drilldevelopment programme is to produce afield-capable machine that can prove itselfin normal commercial operation. One of theproblems in developing effective no-tillagedrills was that the drilling requirementswere largely unknown and highly variablein this new style of farming, and few userscould identify the causes of success or fail-ure. Thus, field demonstration and provingtook on a new dimension.

At first, a prototype drill was trans-ported to a series of farmers’ properties whowere willing to try it on their farms, but this


Fig. 19.15. An example of a universal plot seed drill.

often required modifying the hitches andhydraulic fittings each time a new farmerand tractor was involved. The problem ofthe incompatibility of hydraulic couplingswas at first solved by equipping the testdrill with a self-contained hydraulic systemoperated by a stationary petrol enginemounted on the drill itself, but this did notsolve the other problems outlined above. Itwas also difficult to find a serious commit-ment from farmers to manage the no-tilledcrops in a manner to provide reliable data

on production and economics useful forfield analyses.

A successful example of prototype testingand evaluation was a fully self-containedtractor, drill and truck developed and trans-ported around New Zealand (Ritchie andBaker, 1987). That country offered a widevariety of agricultural enterprises, micro-climates, farming systems and soil typesrepresentative of many of the agricultures ofthe world within a convenient travellingdistance.

298 C.J. Baker

Fig. 19.16. Several plot drills based on the disc version of the winged opener.

A charge was made to the farmers toboth fund the operation and involve theparticipating farmers in a more committedand meaningful way. Thus, what was stillprimarily a field testing operation for thescientists also became a contract drillingservice for the farmers (‘custom drilling’)and a highly effective technology transferprocess for both parties. Over a 10-yearperiod, during which three generations ofprototype drills were utilized, this fielddrilling operation was used on approxi-mately 200 separate fields on over 100different properties, many of which weredrilled for a number of successive years.Figure 19.17 shows the self-contained fieldoperational machine.

While the primary purpose of this pro-totype drilling operation was to provide vitalfield performance information for the origi-nating scientists and function as a technol-ogy transfer medium, the operation becamethe cornerstone for development and evalua-tion of new and innovative farm managementtechniques and strategies. And cooperatingscientists and consultants used the oppor-tunity as the means to introduce drought-tolerant pasture species into existingdryland grasslands by other scientists (Barr,1986; Ritchie, 1986a, b; Milne and Fraser,1990; Milne et al., 1993).

Summary of Drill Development andTechnology Transfer

1. There are few known or standardizedexperimental procedures for objectivelyevaluating no-tillage technologies.2. The study of no-tillage drills, plantersand openers requires developing knowledgeabout experimental procedures, mechanicalperformance and resulting plant growth.3. Removing large soil blocks from thefield in an undisturbed state to a climati-cally controlled environment is a usefulmethod to control soil moisture, drill withopeners to simulate field performance andcontrol post-drilling climate.4. Environmental requirements of seedsand seedlings within the seed slot involvesstudying such variables as: (i) soil moistureregime within the slot; (ii) soil-air humiditywithin the slot; (iii) soil oxygen within andaround the slot; and (iv) soil temperaturewithin the slot.5. Soil disturbance by drill openersrequires monitoring the parameters of:(i) soil strength; (ii) instantaneous soil pres-sure (stress); (iii) instantaneous and perma-nent soil displacement; (iv) soil bulk density;and (v) smearing.6. Important aspects of seed positionwithin the soil after drilling are: (i) seed


Fig. 19.17. A fully self-contained drilling machine for field testing and on-farm demonstrations.

spacing along the row; (ii) seed depth; and(iii) lateral position of the seed relative tothe centre line of the slot.7. The pathway seeds travel from meteringto and through successful no-tillage openersis often more tortuous and less predictablethan with simpler openers for tilled soils.8. It is important to quantify the drag forcesopposing rotation of disc openers to elimi-nate those that are unnecessary and minimizethose that are useful.9. Normal field wear of all drill compo-nents (blades, wings, discs, bearings, etc.)

must be studied with continuous field drill-ing in undisturbed soil.10. Adding components to openers for fer-tilizer placement may cause undesirablewear patterns or interfere with the ability ofthe opener to handle surface residues.11. Field toolbars with multiple openersare useful to field-test prototype openers.12. The ultimate objective of any seed drilldevelopment programme is to produce afield-capable machine that can prove itselfin the normal commercial operation forwhich it is intended.

300 C.J. Baker

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Index

Page numbers in bold refer to figures in the text; those in italics refer to tables or boxes

acetic acid 94, 162allelopathy 23, 163ammonia, loss from soils 126ammonium hydroxide (‘aqua’) 125–126, 131,

132animal-drawn equipment

knife roller 141–143planters 212, 213

animal/crop systems, integrated 134, 169–171animals, treading damage 170–171, 234Argentine stem weevil 231, 233Asia

obstacles to technical development 221‘poverty square’ 220small-scale no-tillage 213–225

‘auto-casting’ 57–58automatic down force control (ADF) 111Avena fatua see oats, wildAvena strigosa see oats, blackThe Awakening (Bevin) 5

bacteria, root 22‘Baker boot’ 52–53, 54, 182band spraying 176–180

equipment 180–183Bangladesh 216, 220, 221, 224barley crops

fertilizer placement 128–129seed slot cover 64, 66straw residues 97wet soils 90, 91

bed planters 219, 222, 224beds, permanent 224benefits of no-tillage 11–12

carbon emissions and sequestration19–20

crop production 13–19energy inputs 17–19nutrient cycling 17soil erosion 15–16soil organic matter 14, 15, 265–267soil quality 16–17soil water 15

Bevin, Alsiter 5bio-channels 8, 118, 162biofuels 18Borlaug, Norman 2brassicas 170, 270

fertilizer placement 128–129seed metering 113–114seeding depth 101

Brazil 209, 264broadcasting see surface broadcastingbullocks 221

Cajanus cajan 145‘Cambridge’ roller 67canola crops 121, 123–124, 229carbon

seedling content 129–130soil see soil organic carbon

carbon cycle 18

317

carbon dioxide (CO2)emission measurements 258emissions 18, 19–20, 257–261

carbon equivalents (CE) 18carbon sequestration 18, 19, 262–263

benefits 265–267carbon trading 19–20, 265–267cash cropping 185cation exchange capacity (CEC) 17Cercosporella 244cereal production, world 2chaff 139, 140, 146chemical fallow (chem fallow) 3chemical ploughing 3chlorpyrifos 231, 232, 233, 269, 270CIMMYT (International Centre for the

Improvement of Maize andWheat) 216–217, 222, 224

clay soils 87–88closed-circuit television (CCTV) 254clover 175

red 100–101, 116combine harvester 57–58

straw spreading 139, 140compaction see soil compactioncompressed-air 109–110, 116conservation agriculture

definition 3, 11principles of 12–13

conservation tillage 3contractor, no-tillage 31, 269–270, 274controlled-traffic farming (CTF)

benefits of 236–237, 255constraints 244definition 236economics 251–254, 255field layout/system management 248–249implications for no-tillage

operations 240–244implications for soils and crops 244–245machine-implement matching 245–248planning 245principles 245wheel ways 249–251

costs 7, 9capital 270–273, 276operating 273pasture renovation 179–180see also economic comparisons

cotton 4, 244cover, broadcast seed 57–58

see also slot coveringcover-crops, killing 138, 145crop failures 7, 163, 164crop ranges 244–245crop residues see residue handling; residuescrop rotations 170

legume-based 264–5rice–wheat 219

crop yields 7, 9, 13, 268, 276comparison of disc-type openers 165controlled-traffic farming 244, 253–254and fertilizer placement 126–132machine impacts 31–32, 234–235transition phase 13, 226–227

crusting 85CTF see controlled-traffic farming

decomposition, residues 94, 118, 143–144seed toxicity 22, 94, 162–163

definitions in no-tillage 3–4deflecting devices 69–71denitrification 238depreciation 269, 271–272, 273depth bands 103depth-gauging 101–103, 166Deroceras reticulatum see slugsdiammonium phosphate (DAP) fertilizer 128,

129dibblers (hand-jabbers) 205–206differential global positioning system

(DGPS) 251costs 255

diquat 2disc-drilling 3disc-type openers

angled 29, 41–43, 145–146, 191comparison of function 28, 29, 163,

164–166controlled-traffic farming 242–243double disc 59

angled 41–43, 94, 126offset 35, 36seed placement problems 105, 106slanted 40small-scale drills/planters 208unequal size 35–37

downforces 165, 166residue handling 105, 150–155

hairpinning 146–147, 207, 212scrapers 156, 157simple design 59triple disc 37–40, 59, 97, 128, 190, 191wet soil operation 86, 92, 94, 95

discsdrag measurement 291–292seed flick 105, 106small-scale planters 207

disease 7–8, 22, 163disease control 228downforce 157–158, 191

control mechanisms 106–113, 116, 166disc-type openers 165, 166

318 Index

large-scale drills/planters 190–195power till opener 46–47range 166re-establishing 194–195small no-tillage planters 206–207variables 190vibrating openers 50–51

drag arms 111–112, 157–158options for attachment 191–194parallelogram 112–113, 182, 194stagger arrangement 157–158stress loadings 195

drainage 7, 227, 249draught requirements

large-scale no-tillage equipment 190, 191small-scale no-tillage equipment 211–212and soil strength 239

drillage 3drilling 9, 233

dry soils 77–83wet soils 85–89, 105, 106

drills 13–14, 100cost–benefits of advanced 31–32, 234–235,

268, 275, 276downforce application 106–113, 190–195drag arms 111–112, 157–158, 191–194, 195matching to power 198–200operating width 185–186, 187–188, 246pasture renovation 182–183power requirements 189, 190, 191product storage/metering 200–202prototypes 294–299reduced-till 222, 223risk of functioning 26selection 9speed of operation 189spray booms 202surface-following 101, 106–113, 108, 114,

186–189transport 195–198, 199for two-wheeled tractors 222see also openers; planters

dry soilsfield experience 84moisture loss 74–75seed germination 76–77seedling emergence 80–83seedling survival 77–80slot covering 66, 83–84V-shaped slots 37

‘dust mulch’ 75

earthworms 6, 9, 17, 22, 227channels 118effects of absence 92, 94and slot disturbance 162

soil aeration 95, 96, 283–284and surface residues 89–90, 97tolerance of smearing/compaction 94wet soils 87, 88, 89–92, 95, 96

economic comparisons (no-tillage/tillage) 30–31controlled-traffic farming 251–254, 255cost–benefits of advanced

machinery 234–235, 268, 275, 276Europe 275–276levels of no-tillage 268misleading factors 268–269New Zealand 269–275summary 276

economic risk 29–32energy use 17–19

carbon equivalents (CE) 18fuel 6, 18–19, 268–269, 271

environmental sustainability wheel 15experimental techniques/procedures

disc drag measurement 291–292fertilizer banding assessment 292–294opener accelerated wear test 292, 293plant responses to no-tillage 278–281prototype drills and management

strategies 294–299seed placement assessment 287–288seed travel within openers 289–290slot microenvironment

assessment 281–284soil compaction/disturbance 284–287

expertise, availability 9, 274eyespot 244

fallowing, chemical 174–175farmers

benefits of soil carbon storage 265–266perceptions of no-tillage 21, 185–186valuation of forage crops 168–169

Faulkner, Edward 5fertilizer

soil nitrogen losses 126, 263–265storage hoppers 200–202toxicity to seeds 24, 29, 119–120, 129

fertilizer placement 5, 8, 9, 23, 118–119,232–233

banding 120–121, 128–132, 133, 163seed-fertilizer distance 131, 132vertical versus horizontal 121–126

broadcasting 118, 119, 120, 126–128,232–233

comparisons of drill/openers 28, 29, 165costs 228, 276crop yields 126–132disc-type openers 40, 126experimental studies 292–294metering devices 210–211

Index 319

pastures 119, 179–180‘skip-row’ method 128–129, 129–130, 163small-scale no-tillage 208winged opener, disc-version 55, 56,

121–123, 125–126fescue, tall (Festuca arundinacea) 173–174field appearance 9field layout 248–249flail mower 144–145forage crops 168–169

see also pastures‘fuçador’ plough 212fuel use 6, 18–19, 268–269, 271fungal hyphae 261furrowers 49–50

Gaeumannomyces graminis see take-allgas-over-oil systems 109, 110–111, 116gauge wheels 101–104, 116, 189gauge/press wheels 55, 56, 68, 103, 189genetically modified crops 3germination see seed germinationglobal positioning systems (GPS) 240, 241, 251,

252costs 252, 255

glomalin 261Glycine max see soybeanglyphosate 2, 180, 231, 232

costs of use 270crop resistance 3timing of use 269

grassesfertilizer placement 119, 179–180residues 90seed metering 113–114, 183see also pastures

grazing 134, 170–171‘green bridge’ concept 22Green Fields Forever (Little) 1greenhouse gases 257

contribution of agriculture 257nitrous oxide 263–264trading of credits 265–267see also carbon dioxide (CO2)

‘Ground Hog’ 231guidance systems 240, 241, 251, 254–255

costs 252, 255

hand-jab planters 205–206‘happy seeder’ 219, 220, 225harrows

slot covering 69, 70, 71‘straw’ 139–140

herbicides 2, 8, 27, 29, 138

band spraying of pastures 176–183costs of use 270factors in effectiveness 27, 29planning use 232selection 227timing of use 269

hillsides 16, 42, 165, 201, 212hoe-type openers 43–46, 59

bounce 105–106downforce requirements 191fertilizer placement 130, 131pasture renovation 176, 177residue handling 45–46, 145–146seed placement 105–106seedling survival 78slot covering 68, 69–71soil disturbance 105wet soils 86–87, 91, 92, 93, 94–95, 97, 98

hoppers, product 201–202

India 216, 220infiltration 6, 17, 162

measurement 284wet soils 97–98

inputsenergy 17–19, 268–269, 271reduction 13

insecticides 201–202integrated animal/crop systems 134, 169–171inverted-T-shaped slots 35, 51–56

biological risk 28covering 161depth control 103dry soils 84humidity loss 63, 64, 79micro-environment 23pasture renovation 182–183pressing 83principle of 51retention of gases 126seed germination 77seed–fertilizer separation 121, 122seedling survival 78–79soil-to-seed contact 162wet soils 87–89, 90, 91, 92, 97, 98

irrigation requirements 6

kale 66‘knee-action farming’ principle 230knife rollers 141–145Kyoto Protocol 265

labour requirements 6, 269leaching 17

320 Index

fertilizer placement continued

legumescrop rotations 264–265pastures 180seed metering 113–114

lentils 214leveller 231lime application 230, 231Little, Charles 1Lolium perenne see ryegrassLolium rigidum see ryegrass, annuallucerne 65, 66, 180lupin (Lupinus angustifolius) 4, 66, 100, 116

machine ‘tailing’ 42machinery 7

cost–benefits of advanced designs 31–32,234–235, 268, 275, 276

functioning of 26–27impacts on crop yields 31–32purchase costs 270–273tillage

depreciation 269, 271–272, 273retention of used 272–273, 274–275sale of used 269

service wear 7, 165, 239, 292, 293width-matching 245–248see also types of machinery and equipment

macropores 63, 87, 88, 118, 162maize

fertilizer placement 119, 120, 127–128slot cover 65, 66

managementoperator skills 229–230pest/disease control 228planning 230–234post-seeding 230prototype strategies 294–299seeding rate 228–229site selection/preparation 226–227soil fertility 228, 231weed control 227–228

Medicago sativa see lucernemelons 244methane 238, 264, 265Mexico 219, 224micro-environment, seed slot 28, 29, 161,

281–284mineralization 118–119, 128minimum tillage 3, 186, 275–276moisture-vapour potential captivity

(MVPC) 63–64mole channels 249monsoons 215, 219montmorillonite 87–88mouldboard ploughing 16

and carbon dioxide emissions 19, 258–259

see also tillage (conventional)mud, shedding from wheels 104mulches 79–80

dust 75and soil humidity 75see also residues

mulching, vertical 149, 158mungbean 224MVPC see moisture-vapour potential captivity

narrow-row crops 160Nepal 216, 221nitrogen 6

availability to crops 8, 118biological fixation 175losses from soils 17, 126, 238, 263–265seedling content after fertilization 129–130

no-tillagedefinitions 4terminology 3–4

nutrient availability 118–119, 238–239nutrient cycling 17nutrient stress 23

oatsblack 143–144wild 241

openers 34accelerated wear tests 292, 293bounce 105–106, 116clearance between adjacent 156–158,

188–189comparisons 28, 59, 164–166controlled-traffic farming 242–243depth-gauging devices 101–103derivation from tillage machines 39–40design challenges 208downforce mechanisms 106–113, 116furrowers 49–50herbicide application 181, 182horizontal slot creation 51–56minimum disturbance 159–160optimal performance requirements 99pasture renovation 175–176, 176–177raising and lowering 195–196residue handling 145–158, 162–163

hairpinning 146–147, 207, 212, 242risk-assessment of designs 28seed travel, measurement 289–290small-scale no-tillage 208–209soil disturbance 4–5, 105, 159–163,

237–238surface following 26, 101, 108, 186–189and surface smoothness 227tined 208–209, 212

Index 321

vertical slot creation 35–51vertical travel 116vibrating 50–51see also types of openers, e.g. disc-type

openers; hoe-type openersoperator

small-scale no-tillage machinery 211–212skills 7, 8–9, 166, 229–230

origins of no-tillage 2overdrilling 4, 175, 176, 177, 178oxygen diffusion

experimental measurement 283–284soils 95, 96

paraquat 2, 29, 180pastures 134–135, 171–183

fertilizer placement 119, 179–180high-altitude 49, 50improved 168new no-tillage 7, 233permanent 169renewal 171–175renovation 175–183residue-handling 134–135value to farmers 168–169

pea 81, 270penetration forces 165penetrometer, multi-point 284–286permanent wilting point (PWP) 63, 75pesticides

application/handling 8, 201–202costs 270timing of use 269

pests 7–8, 9, 13, 22, 163control 228, 231, 232, 233, 269, 270

phosphorus, soil 7, 8, 238pigeon pea 145planning 230–234, 245plant density 229plant ownership 9, 272–273, 274–275planters

animal-drawn 212, 213hand-jab 205–206precision 100punch (star-wheel) 217–219small-scale no-tillage 206–212tractor selection 198–200see also drills

plastic slot cover 79–80Ploughman’s Folly (Faulkner) 5pollution 7, 8post-seeding management 230potassic super-phosphate 125potassium, soil 7, 238poverty, Asia 215

power requirementslarge-scale drill/planter 189, 190, 191small-scale no-tillage machinery 211–212

power tillers 46–49adaptation for small-scale

no-tillage 212–213residue handling 47, 145, 150seeding depth 105stone damage 48–49wet soils 87, 91, 92, 93, 95

precision seeders 100, 115press wheels 39, 55, 56, 68–69, 72, 103, 189

angled 71, 72semi-pneumatic tyres 103–104

product storage/metering 200–202profitability, and weather variations 25punch planters 56–57, 59, 217–219

hand-jab 205–206operation in wet soils 90, 91, 93–94, 97, 98

‘rabi’ seed drills 216, 217, 221radish, fodder 128–129rainfall 25

and seedling emergence 82–83, 96monsoons 215, 219

relative humidity (RH)direct measurement 282soil/slot 63–65, 161

residue farming, defined 3–4residue handling (micro-management) 26,

145–158, 159–160comparisons of drills/openers 28, 29, 164disc-type openers 105, 146–147, 150–155,

207, 212hairpinning into slot 94, 105, 146–147,

162–163, 164, 207, 212, 242hoe/shank-type openers 45–46pasture species 134–135power till opener 47, 145removing from over slot 161scrapers/deflectors 156, 157small planters 212spacing of adjacent openers 156–158winged opener (disc-version) 55–56

residuesand carbon dioxide fluxes 259–260controlled-traffic farming 240–241coverage levels 4decomposition 22, 94, 118, 143–144

seed toxicity 22, 94, 162–163and earthworms 89–90, 97field-scale management 138–145, 159‘long flat’ 136–137management planning 230, 233–234micro-management see residue handlingpastures 174

322 Index

openers continued

‘rational retention’ 214removal/burning 134, 138, 214rooted anchored/standing 134–136and seed delivery 115in small-scale no-tillage 140–145and soil erosion 16, 25and soil temperatures 135, 161‘trash’ 9, 134wet soils 90–91

‘retired’ land 171Rhizoctonia 22rice

dry-seeded 219zero-tilled 214–215, 216

rice–wheat rotations 219ridge and furrow planting 219ridge tillage 4risk 163

biological 7–8, 21–24, 163chemical 27–29comparison of openers 28, 29, 164conventional tillage 230economic 29–32management 231perception of 21physical 24–27

rollersknife 141–145spiral-caged 69, 71

rollingherbicide application 181–182slot covering 67–68

root systems 8, 77–78rotary tillage 46row cleaners 147row spacing 165

pasture/forage species 172–173, 174runoff 15–16ryegrass

annual 241dry soils 82pastures 173–174residues 90

safety, human/biological 2scrapers, disc-cleaning 156, 157seed, storage hoppers 201–202seed bounce 106, 117‘seed burn’ 24, 29, 119–120, 129seed covering see slot coveringseed delivery 114–116seed drills see drillsseed flick 105, 106seed germination 23, 76–77

and fertilizer placement 125minimum-disturbance slot 161–162

and slot cover 64–65, 66and soil humidity 75, 76–77

seed metering 99–100, 113–116large-scale no-tillage machinery 200–201pasture species 113–114, 183precision 100, 115, 205singulation 209small-scale no-tillage 209–210

seed placementopener capabilities 99power till openers 46surface broadcasting 28, 57–58, 90, 91, 92,

95, 96seed quality 23–24seed size

and metering 113–114and seedling emergence 64–65

seed spacing 100measurement 287

seed–soil contact 76–77, 83–84, 162seeding depth

comparison of drills/openers 28controlled-traffic farming 243experimental measurement 287–288maintaining consistency of 101–106pasture species 182and seedling emergence 100–101

seeding openers see openersseeding rate 228–229, 268

calculation 229controlled-traffic farming 243–244

seedling emergencecomparison of disc-type openers 164–165dry soils 80–83and fertilizer placement 121–126, 131, 132and residues 90and seeding depth 100–101, 116and slot cover 64–65, 66, 162wet soils 90–93

seedling survivalpasture renovation 176–177and slot cover 162and slot shape 77–80and soil moisture 282–283

seedlingsphysiological stress 23, 24twisted 233

‘set-aside’ areas 5, 171shank-type openers see hoe-type openerssite selection 226–227‘skip-row’ planting 128–129, 163slot covering 99

artificial materials 79–80classification 60–63, 72–73comparison of drill/opener designs 28, 164deflecting 69–70folding 71–72

Index 323

and humidity loss 63–65loose (tilled) soil 61–63, 71, 72minimum disturbance slots 160–161pasture renovation 176, 177pressing 68–69, 83–84rolling 67–68scuffing/harrowing 69, 70, 71and seed size 64–65and seedling emergence 64–65, 66self-closure 106squeezing 39, 67V-shaped slots 38–39, 64, 66

slot shapeshorizontal 51–56micro-environment 28, 29, 161, 281–284pasture renovation 176–177and seed germination 76–77and seedling emergence 80–83and seedling survival 77–80and soil humidity 63–65, 79, 161vertical 35–51see also individual slot shapes

slugs 22, 233, 244control 232, 233, 269, 270

small-scale no-tillageAsia 213–215benefits 204characteristics 204machinery

adapted from power tillers 212–213animal-drawn 212, 213for four-wheeled tractors 216–219power requirements/ease of

operation 211–212row-type planters 206–212for two-wheeled tractors 220–225

residue management 140–145smearing 85, 86, 87, 94, 162

comparison of disc-type openers 164experimental assessment 287

snow 135society, benefits of soil carbon storage

265–266sod-seeding 4soil aeration 6, 92, 95, 96, 283–284soil bulk density, measurement 287soil compaction 16, 86

animal treading 171comparison of disc-type openers 164experimental assessment 284–287historical 5in and around slot 37, 38, 85, 162tolerance of earthworms 94traffic-induced 239–240

soil conservation 12–13soil damage 170–171

soil displacement, experimentalmeasurement 287

soil erosion 6, 15–16, 25, 163soil fertility management 228, 231soil organic carbon (SOC) 5, 12–13, 19

benefits of increases 265–267gaseous losses 258–260increases in no-tillage 5, 14–15, 262–263,

265–266soil storage capacity 261

soil organic matter 6, 15, 128soil pressure, instantaneous 286soil quality 16–17soil strength 8

controlled-traffic farming 237–238experimental assessment 284–286and nutrient availability 238–239V-shaped slots 37, 38

soil structure 6, 9and controlled-traffic farming 239–240and soil strength 239tillage 17

soil temperatures 6–7, 25, 135, 161soil type 87–88soil water/moisture 6, 15, 79, 161

experimental measurement 282–283infiltration 6, 17, 97–98, 162liquid-phase 76, 77losses 74–75, 79and seed germination 75–76, 125and slot covering 63–65, 66and soil fauna 22soil water-holding capacity 6, 15vapour-phase 75–76, 164

soil–seed contact 76–77, 83–84, 162soil/slot disturbance 4–5, 105, 237–238

comparison of disc-type openers 163,164–166

effects 160–163maximum 160, 162minimum 159–160, 208

soybean 4, 105, 106, 131speed of operation 43

comparison of disc-type openers 164large-scale machinery 186, 189small-scale no-tillage machinery 211

spring barley 244springs, drill/planter 106–109‘stale’ seedbed 4star-wheel (punch) planters 217–219steering, automatic 251stone damage 48–49stover, lying 136–137straw

chopping 139, 147–149cutting in place 149–153hairpinning by openers 146

324 Index

slot covering continued

lying 136–137rooted/standing stubble 135–136spreading 138–140vertical mulching 149wet versus dry 155–156

stress, physiological 23, 24strip tillage 4, 46–49, 63, 160, 161, 212–213,

244, 264and carbon dioxide fluxes 259, 260–261drills 217, 218on permanent beds 224residue handling 145small-scale no-tillage 222–225

stubble 135–136stubble trampling 240subsoiling 5, 231surface broadcasting

fertilizer 118, 119, 120, 126–128, 232–233seed 28, 57–58, 90, 91, 92, 95, 96

surface following 8, 26, 101, 108–109comparison of drills/openers 28, 113, 114downforce control 106–113, 116large-scale machinery 186–189

surface smoothness 227sustainability wheel 15sustainable farming 4, 11

tailings see chafftake-all 22technology, transitional 221terminology, no-tillage 3–4tillage (conventional) 1, 34

carbon dioxide emissions 19, 257–261costs 30–31crop fertilizer response 118crop rotations 170fertilizer placement 124history of 165, 226–227mechanisms of soil carbon loss 262, 263objectives 1–2‘recreational’ 8risk 230seed covering 61–63susceptibility to treading damage 170in wet soils 89

tilled soilsfertilizer placement 126–128moisture loss 74–75seedling survival 77–78structure 17

time flexibility 6time saving 6, 7tined openers 208–209, 212toolbars

four-wheeled tractors 216two-wheeled tractors 221–222

towing configurations 195–198, 199toxicity 22–23

fertilizer–seed 24, 29, 119–120, 129residue decomposition 22, 94, 162–163

tractors 7four-wheeled 216–219implement width-matching 245–248matching with drills/planters 198–200two-wheeled 220–225

traffic 195–198, 238trafficability 7, 24–25transition to no-tillage 9, 13, 226–227, 264treading damage 170–171, 231Trifolium pratense see clover, redTriticum aestivum see wheat‘turbo disc’ 37turnips, summer 170‘twin-track’ CTF system 246–247tyres, semi-pneumatic (zero pressure) 85,

103–104, 116

U-shaped slots 40–51angled disc-type openers 41–43hoe/shank-type openers 43–46humidity loss 63, 64, 79pressing 83risk assessment 28seed–soil contact 76–77seedling emergence 80–83seedling survival 78, 79wet soils 86–87, 91, 97, 98

undersowing/underdrilling 4urea fertilizer 125–126, 131, 132

V-shaped slots 35–40covering 38–39, 65humidity loss 63, 64, 79pasture renovation 176, 177pressing 83–84risk assessment 28seedling emergence 80, 81seedling survival 77, 79slanted 40soil–seed contact 76, 162wet soils 37, 38, 86, 89, 90, 91, 93, 94, 97,

98vertical mulching 149, 158vibrating openers 50–51

walking beams 104, 116, 189water quality 27water table, rising 96wear tests, accelerated 292, 293weather 24–26, 27

Index 325

weed control 13, 227–228chemical 27, 29, 138controlled-traffic farming 241–242mechanical 2, 5, 145zero-tilled rice 216see also herbicides

weeds 7pastures 173–174shift in dominant species 8, 227–228vigour 27, 28

weights, as downforce 111, 206–207wet soils

drilling 37, 38, 85–89, 105, 106dry soils that become wet 89–93infiltration 97–98opener performance 93–98residue management 90–91slot cover 66

wheatbed-planting 219dry soils 80–81economic risk of no-tillage

production 31–32fertilizer placement 129, 130, 131, 132seeding depth 100slot cover 66

wheel ways, permanent 249–251, 256wheels

combined press/gauge 55, 56, 103, 189configurations 195–198depth-gauging 101–103mud shedding 104press 39, 55, 56, 68–69, 71–72, 189semi-pneumatic tyres 85, 103–104, 116

width, operating 185–186, 187–188width matching 245–248wildlife 135wilting point, permanent (PWP) 63, 75wind erosion 16windrows, spreading 138–140winged (inverted-T) openers 51–53

‘Baker boot’ 52–53, 54, 182bounce 105–106disc version 29, 53–56, 59, 128, 163, 242

herbicide application 181, 182seeding depth 101

double/triple-shoot 53, 54downforce and draught requirements 190,

191drag arms 112–113fertilizer placement 55, 56, 121–123,

125–126pasture renovation 176–177, 182–183small-scale design 217wet soil function 87–90, 91, 93, 94, 95, 97,

98wireworms 22

X-ray imagery 288, 289

Yacqui Valley, Mexico 219

Zea mays see maizezero tillage 4zone tillage see strip tillage

326 Index

CABI Head OfficeNosworthy Way, Wallingford, Oxfordshire, OX10 8DE, UK

CABI North American Office 875 Massachusetts Avenue, 7th Floor, Cambridge, MA 02139, USA

Cover photograph: "The ultimate in time-saving that only no-tillage

can provide - sowing a new crop as the existing crop is being harvested,

while retaining maximum residue cover throughout".

C. J. Baker, K. E. Saxton, W. R. Ritchie, W. C. T. Chamen,D. C. Reicosky, F. Ribeiro, S. E. Justice and P. R. Hobbs

This book is a much-expanded and updated edition of a previous volume, published in 1996 as

‘No-tillage Seeding: Science and Practice’. The base objective remains to describe in lay terms, a

range of international experiments designed to examine the causes of successes and failures in

no-tillage. It summarizes the advantages and disadvantages of no-tillage in general, but takes the

view that the case for widespread adoption of no-tillage has already been made by others. The

authors have been involved in designing new equipment, but the new edition is notless promotional

of any particular product but does highlight the pros and cons of a range of features and options.

Topics added or covered in more detail in the second edition include:� soil carbon and how its retention or sequestration interacts with tillage and no-tillage

� controlled traffic farming as an adjunct to no-tillage� a comparison of the performance of generic no-tillage opener designs

� the role of banding fertilizer in no-tillage� the economics of no-tillage

� small-scale equipment used by poorer farmers� forage cropping by no-tillage

� a method for risk assessment of different levels of machine sophistication

The book represents a major resource for practitioners and academics in agronomy, soil science

and agricultural engineering.

From reviews of the first edition:“…will be a useful addition to many libraries…interested in no-tillage techniques.”

Agricultural Science

“Did the authors achieve their aims? I believe they have done so admirably.”

New Zealand Journal of Agricultural Research

ISBN 1 84593 116 5 (CABI) 92-5-105389-8 (FAO)

2nd Edition


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Download - No-tillage Seeding in Conservation AgricultureNo-tillage farming in Asia 213 Summary of No-tillage Drill and Planter Design – Small-scale Machines 225 15 Managing a No-tillage Seeding

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