1 the ‘what’ and ‘why’ of no-tillage farming · 2010-06-29 · 1 the ‘what’ and...

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

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biol

ogic

alris

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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.


1 the ‘what’ and ‘why’ of no-tillage farming · 2010-06-29 · 1 the ‘what’ and...

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