sustainable soil

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SUSTAINABLESOIL

MANAGEMENT

ATTRA is the national sustainable agriculture information center funded by the USDAs Rural Business--Cooperative Service.

www.attra.ncat.org

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ATTRAis a project of the National Center for Appropriate Technology

Appropriate Technology Transfer for Rural Areas

Contents:

Part 1: Principles and Characteristics of Sustainable Soils..........................................................................

Introduction .......................................................................................................................................................The Living Soil: Texture and Structure ............................................................................................................The Living Soil: The Importance of Soil Organisms........................................................................................Organic Matter, Humus, and the Soil Foodweb...............................................................................................Soil Tilth and Organic Matter ............................................................................................................................Tillage, Organic Matter, and Plant Productivity ................................................................................................Fertilizer Amendments and Biologically Active Soils........................................................................................Conventional Fertilizers ....................................................................................................................................Topsoil Your Farms Capital ..........................................................................................................................Summary of Part I .............................................................................................................................................Summary of Sustainable Soil Management Principles ....................................................................................

Part II: Management Steps to Improve Soil Quality........................................................................................1. Assess Soil Health and Biological Activity on Your Farm............................................................................

2. Utilize Tools and Techniques to Build Soils.................................................................................................Animal Manure..........................................................................................................................................Compost ...................................................................................................................................................Cover Crops and Green Manures ............................................................................................................Humates ...................................................................................................................................................Reduced Tillage........................................................................................................................................Minimize Synthetic Nitrogen Use .............................................................................................................

3. Continue to Monitor......................................................................................................................................Part III. Examples of Successful Soil Builders (Farmer Profiles) ...................................................................References............................................................................................................................................................Additional Information Resources.....................................................................................................................

Abstract:This publication covers basic soil propertiesand management steps toward building and maintain-ing healthy soils. The publication is divided into threedistinct sections, each with its own purpose. Section 1deals with basic soil principles and provides an under-standing of living soils and how they work. In thissection you will find answers to why soil organismsand organic matter are important. Section 2 coversmanagement steps to build soil quality on your farm.The last section covers stories of farmers who have suc-cessfully built up their soil. The publication concludeswith a large resource section of other available informa-

tion.

By Preston Sullivan

NCAT Agriculture Specialist

September 2001
mailto:[email protected]?subject=Sustainable%20Soil%20Managementmailto:[email protected]?subject=Sustainable%20Soil%20Management


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Part I. Principles andCharacteristics of SustainableSoils

Introduction

What are some features of good soil? Anyfarmer will tell you that a good soil: feels soft and crumbles easily

drains well and warms up quickly in thespring

does not crust after planting

soaks up heavy rains with little runoff

stores moisture for drought periods

has few clods and no hardpan

resists erosion and nutrient loss

supports high populations of soil

organisms has a rich, earthy smell

does not require increasing inputs for highyields

produces healthy, high-quality crops (1).

All these criteria indicate a soil that functionseffectively today and will continue to producecrops long into the future. Thesecharacteristics can be built up throughmanagement practices that optimize the

processes found in native soils.

How does soil in its native conditionfunction? How do forests and nativegrasslands produce plants and animals in thecomplete absence of fertilizer and tillage?Understanding the principles by which nativesoils function can help farmers develop andmaintain productive and profitable soil bothnow and for future generations. The soil, theenvironment, and farm productivity benefitwhen the soils natural productivity is

managed in a sustainable way. Reliance onpurchased inputs declines year by year whileland value and income generation potentialincrease. Some of the things we spend moneyon can be done by the natural process itselffor little or nothing. Good soil management

The Living Soil: Texture andStructure

Soils are made up of four basic components:minerals, air, water, and organic matter. Inmost soils minerals represent around 45% ofthe total volume, water and air about 25%each, and organic matter from 2% to 5%.

The mineral portion consists of three distinctparticle sizes classified as sand, silt, or clay.Sand is the largest particle that can beconsidered soil.

Sand is largely the mineral quartz, thoughother minerals are also present. Quartzcontains no plant nutrients, and sand cannothold nutrientsthey leach out easily withrainfall. Silt particles are much smaller thansand but, like sand, silt is mostly quartz. Thesmallest of all the soil particles is clay. Clays

are quite different from sand or silt and mosttypes of clay contain appreciable amounts ofplant nutrients. Clay has a large surface arearesulting from the plate-like shape of theindividual particle. Sandy soils are lessproductive than silts, while soils containingclay are the most productive and usefertilizers most effectively.

Soil texturerefers to the relative portions ofsand, silt, and clay. A loam soil containsthese three types of soil particles in roughlyequal portions. A sandy loam is a mixturecontaining a larger amount of sand and asmaller amount of clay, while a clay loamcontains a larger amount of clay and asmaller amount of sand. These and othertexture designations are listed in Table 1.

produces crops and animals that arehealthier, less susceptible to disease, and moreproductive. To understand this better, letsstart with the basics.

Sustainable: capable of being maintained at

l ength w i thout i nterrupti on, w eakening, or

l osing in power or quali t y.



Another soil characteristicsoil structureisdistinct from soil texture. Structurerefers tothe clumping together or aggregation ofsand, silt, and clay particles into larger

secondary clusters. If you grab a handful ofsoil, good structure is apparent when the soilcrumbles easily in your hand. This is anindication that the sand, silt, and clayparticles are aggregated into granules orcrumbs.

Both texture and structure determine porespace for air and water circulation, erosionresistance, looseness, ease of tillage, and rootpenetration. While texture is related to theminerals in the soil and does not change with

agricultural activities, structure can beimproved or destroyed readily by choice andtiming of farm practices.

The Living Soil: The Importanceof Soil Organisms

An acre of living topsoil containsapproximately 900 pounds of earthworms,2,400 pounds of fungi, 1,500 pounds ofbacteria, 133 pounds of protozoa, 890 pounds

of arthropods and algae, and even smallmammals in some cases (2). Therefore, thesoil can be viewed as a living communityrather than an inert body. Soil organicmatter also contains dead organisms, plantmatter, and other organic materials in various

phases of decomposition. Humus, the dark-colored organic material in the final stages ofdecomposition, is relatively stable. Bothorganic matter and humus serve as a reser-voir of plant nutrients; they also help to buildsoil structure and provide other benefits.

The type of healthy living soil required tosupport humans now and far into the futurewill be balanced in nutrients and high inhumus with a high diversity of soilorganisms. It will produce healthy plantswith minimal weed, disease, and insectpressure. To accomplish this, we will workwiththe natural processes and optimize theirfunctions to sustain our farms.

Considering the natural landscape you mightwonder how native prairies and forests

function in the absence of tillage andfertilizers. These soils are tilled by soilorganisms, not by machinery. They arefertilized too, but the fertility is used againand again and never leaves the site. Nativesoils are covered with a layer of plant litterand/or growing plants throughout the year.Beneath the surface litter layer, a richcomplexity of soil organisms decompose plantresidue and dead roots, then release theirstored nutrients slowly over time. In fact,topsoil is the most biologically diverse part ofthe earth (3). Soil-dwelling organisms releasebound-up minerals, converting them intoplant-available forms that are then taken upby the plants growing on the site. Theorganisms recycle nutrients again and againfrom the death and decay of each newgeneration of plants.

There are many different types of creaturesthat live on or in the topsoil. Each has a roleto play. These organisms will work for the

farmers benefit if we simply manage for theirsurvival. Consequently, we may refer tothem as soil livestock. While a great varietyof organisms contribute to soil fertility, earth-worms, arthropods, and the variousmicroorganisms merit particular attention.

Table 1. Soil texture designations rangingfrom coarse to fine.

Texture Designation

Coarse-textured SandLoamy sandSandy loamFine sandy loam

LoamSilty loamSiltSilty clay loamClay loam

Fine-textured Clay



Figure 1. The soil is teeming with organisms that cycle nutrients from soil to plant and back again.

Earthworms

Earthworm burrows enhance waterinfiltration and soil aeration. Fields that aretilledby earthworm tunneling can absorb

water at a rate 4 to 10 times that of fieldslacking worm tunnels (4). This reduces waterrunoff, recharges groundwater, and helpsstore more soil water for dry spells. Verticalearthworm burrows pipe air deeper into thesoil, stimulating microbial nutrient cycling atthose deeper levels. When earthworms arepresent in high numbers, the tillage providedby their burrows can replace some expensivetillage work done by machinery.

Worms eat dead plant material left on top ofthe soil and redistribute the organic matterand nutrients throughout the topsoil layer.Nutrient-rich organic compounds line theirtunnels, which may remain in place for years

if not disturbed. During droughts thesetunnels allow for deep plant root penetrationinto subsoil regions of higher moisture con-tent. In addition to organic matter, wormsalso consume soil and soil microbes as theymove through the soil. The soil clusters theyexpel from their digestive tracts are known asworm casts orcastings. These range from thesize of a mustard seed to that of a sorghumseed, depending on the size of the worm.



The soluble nutrient content of worm casts isconsiderably higher than that of the originalsoil (see Table 2). A good population ofearthworms can process 20,000 pounds oftopsoil per yearwith turnover rates as highas 200 tons per acre having been reported insome exceptional cases (5). Earthworms also

secrete a plant growth stimulant. Reportedincreases in plant growth following earth-worm activity may be partially attributed tothis substance, not just to improved soilquality.

Earthworms thrive where there is no tillage.Generally, the less tillage the better, and theshallower the tillage the better. Worm num-bers can be reduced by as much as 90% bydeep and frequent tillage (7). Tillage reducesearthworm populations by drying the soil,burying the plant residue they feed on, and

making the soil more likely to freeze. Tillagealso destroys vertical worm burrows and cankill and cut up the worms themselves.Worms are dormant in the hot part of thesummer and in the cold of winter. Youngworms emerge in spring and fallthey aremost active just when farmers are likely to betilling the soil. Table 3 shows the effect oftillage and cropping practices on earthwormnumbers.

Table 2. Selected nutrient analyses of wormcasts compared to those of the surrounding soil.

Nutrient Worm casts Soil

Lbs/ac Lbs/acCarbon 171,000 78,500Nitrogen 10,720 7000

Phosphorus 280 40Potassium 900 140

From Graff (6). Soil had 4% organic matter.

As a rule, earthworm numbers can beincreased by reducing or eliminating tillage(especially fall tillage), not using a moldboardplow, reducing residue particle size (using astraw chopper on the combine), addinganimal manure, and growing green manurecrops. It is beneficial to leave as much surface

residue as possible year-round. Croppingsystems that typically have the most earth-worms are (in descending order) perennialcool-season grass grazed rotationally, warm-season perennial grass grazed rotationally,and annual croplands using no-till. Ridge-tilland strip tillage will generally have moreearthworms than clean tillage involvingplowing and disking. Cool season grassrotationally grazed is highest because itprovides an undisturbed (no-tillage)environment plus abundant organic matter

from the grass roots and fallen grass litter.Generally speaking, worms want their foodon top and they want to be left alone.

Earthworms prefer a near-neutral soil pH,moist soil conditions, and plenty of plantresidue on the soil surface. They are sensitiveto certain pesticides and some incorporatedfertilizers. Carbamate insecticides, includingFuradan, Sevin, and Temik, are harmful toearthworms, notes worm biologist CliveEdwards of Ohio State University (4). Some

insecticides in the organophosphate familyare mildly toxic to earthworms, whilesynthetic pyrethroids are harmless to them(4). Most herbicides have little effect onworms except for the triazines, such asAtrazine, which are moderately toxic. Also,anhydrous ammonia kills earthworms in theinjection zone because it dries the soil andtemporarily increases the pH there. Highrates of ammonium-based fertilizers are alsoharmful.

For more information on managing earth-worms, order The Farmers EarthwormHandbook: Managing Your UndergroundMoneymakers, by David Ernst. Ernsts bookcontains details on what earthworms need tolive, how to increase worm numbers, theeffects of tillage, manure, and livestockmanagement on earthworms, how 193chemicals affect earthworms, and more. Seethe Additional Information Resources

Table 3. Effect of crop management onearthworm populations.

Crop Management Worms/foot2

Corn Plow 1Corn No-till 2Soybean Plow 6Soybean No-till 14Bluegrass/clover --- 39Dairy pasture --- 33

From Kladivko (8).



section of this publication for orderinginformation. Also visit the earthworm web-sites listed in that section.

Arthropods

In addition to earthworms, there are manyother species of soil organisms that can beseen by the naked eye. Among them aresowbugs, millipedes, centipedes, slugs, snails,and springtails. These are the primarydecomposers. Their role is to eat and shredthe large particles of plant and animal

residues. Some bury residue, bringing it intocontact with other soil organisms that furtherdecompose it. Some members of this groupprey on smaller soil organisms. Thespringtails are small insects that eat mostlyfungi. Their waste is rich in plant nutrientsreleased after other fungi and bacteriadecompose it. Also of interest are dungbeetles, which play a valuable role inrecycling manure and reducing livestockintestinal parasites and flies.

Bacteria

Bacteria are the most numerous type of soilorganism: every gram of soil contains at leasta million of these tiny one-celled organisms.There are many different species of bacteria,each with its own role in the soilenvironment. One of the major benefitsbacteria provide for plants is in makingnutrients available to them. Some speciesrelease nitrogen, sulfur, phosphorus, and

trace elements from organic matter. Othersbreak down soil minerals, releasingpotassium, phosphorus, magnesium, calcium,and iron. Still other species make and releaseplant growth hormones, which stimulate rootgrowth.

Several species of bacteria transform nitrogenfrom a gas in the air to forms available forplant use and from these forms back to a gas

again. A few species of bacteria fix nitrogenin the roots of legumes while others fixnitrogen independently of plant association.Bacteria are responsible for convertingnitrogen from ammonium to nitrate and backagain depending on certain soil conditions.Other benefits to plants provided by various

species of bacteria include increasing thesolubility of nutrients, improving soilstructure, fighting root diseases, anddetoxifying soil.

Fungi

Fungi come in many different species, sizes,and shapes in soil. Some species appear asthread-like colonies, while others are one-celled yeasts. Slime molds and mushroomsare also fungi. Many fungi aid plants by

breaking down organic matter or by releasingnutrients from soil minerals. Fungi aregenerally quick to colonize larger pieces oforganic matter and begin the decompositionprocess. Some fungi produce planthormones, while others produce antibioticsincluding penicillin. There are even species offungi that trap harmful plant-parasiticnematodes.

The mycorrhizae (my-cor-ry-zee) are fungi

that live either on or in plant roots and act toextend the reach of root hairs into the soil.Mycorrhizae increase the uptake of waterand nutrients, especially phosphorus. Theyare particularly important in degraded orless fertile soils. Roots colonized bymycorrhizae are less likely to be penetratedby root-feeding nematodes, since the pestcannot pierce the thick fungal network.Mycorrhizae also produce hormones andantibiotics, which enhance root growth andprovide disease suppression. The fungi

benefit from plant association by takingnutrients and carbohydrates from the plantroots they live in.

Actinomycetes

Actinomycetes (ac-tin-o-my-cetes) arethread-like bacteria that look like fungi.While not as numerous as bacteria, they tooperform vital roles in the soil. Like the

As a rule, earthworm numbers can be

increased by reducing or eliminating

tillage.



bacteria, they help decompose organic matterinto humus, releasing nutrients. They alsoproduce antibiotics to fight diseases of roots.Many of these same antibiotics are used totreat human diseases. Actinomycetes areresponsible for the sweet, earthy smell noticedwhenever a biologically active soil is tilled.

Algae

Many different species of algae live in theupper half-inch of the soil. Unlike most othersoil organisms, algae produce their own foodthrough photosynthesis. They appear as agreenish film on the soil surface following asaturating rain. Algae improve soil structureby producing slimy substances that glue soiltogether into water-stable aggregates. Somespecies of algae (the blue-greens) can fix their

own nitrogen, some of which is later releasedto plant roots.

Protozoa

Protozoa are free-living microorganisms thatcrawl or swim in the water between soilparticles. Many soil protozoa are predatory,eating other microbes. One of the mostcommon is an amoeba that eats bacteria. Byeating and digesting bacteria, protozoa speedup the cycling of nitrogen from the bacteria,

making it more available to plants.

Nematodes

Nematodes are abundant in most soils, andonly a few species are harmful to plants. Theharmless species eat decaying plant litter,bacteria, fungi, algae, protozoa, and othernematodes. Like other soil predators, nema-todes speed the rate of nutrient cycling.

Soil organisms and soil quality

All these organismsfrom the tiny bacteriaup to the large earthworms and insectsinteract with one another in a multitude ofways in the soil ecosystem. Organisms notdirectly involved in decomposing plantwastes may feed on each other or each

others waste products or the othersubstances they release. Among thesubstances released by the various microbesare vitamins, amino acids, sugars, antibiotics,gums, and waxes.

Roots can also release into the soil varioussubstances that stimulate soil microbes. Thesesubstances serve as food for select organisms.Some scientists and practitioners theorize thatplants use this means to stimulate the specificpopulation of microorganisms capable ofreleasing or otherwise producing the kind of

nutrition needed by the plants.

Research on life in the soil has determinedthat there are ideal ratios for certain keyorganisms in highly productive soils (9). TheSoil Foodweb Lab, located in Oregon, testssoils and makes fertility recommendationsthat are based on this understanding. Theirgoal is to alter the makeup of the soilmicrobial community so it resembles that of ahighly fertile and productive soil. There areseveral different ways to accomplish this goal,depending on the situation. For more on theSoil Foodweb Lab see the AdditionalInformation Resources section of thispublication.

Because we cannot see most of the creaturesliving in the soil and may not take time toobserve the ones we can see, it is easy toforget about them. See Table 4 for estimatesof typical amounts of various organismsfound in fertile soil. There are many websites

that provide in-depth information on soilorganisms. Look for a list of these websites inthe Additional Information Resourcessection. Many of these sites have colorphotographs of soil organisms and describetheir benefits to soil fertility and plant

growth.

Research on life in the soil has determined thatthere are ideal ratios for certain key organisms in

productive soils.



Organic Matter, Humus, and theSoil Foodweb

Understanding the role that soil organismsplay is critical to sustainable soil management.Based on that understanding, focus can bedirected toward strategies that build both thenumbers and the diversity of soil organisms.Like cattle and other farm animals, soil live-stock require proper feed. That feed comes inthe form of organic matter.

Organic matter and humus are terms thatdescribe somewhat different but relatedthings. Organic matter refers to the fractionof the soil that is composed of both livingorganisms and once-living residues in variousstages of decomposition. Humus is only asmall portion of the organic matter. It is theend product of organic matter decom-position and is relatively stable. Furtherdecomposition of humus occurs very slowlyin both agricultural and natural settings. In

natural systems, a balance is reached betweenthe amount of humus formation and theamount of humus decay (11). This balancealso occurs in most agricultural soils, butoften at a much lower level of soil humus.Humus contributes to well-structured soilthat, in turn, produces high-quality plants. Itis clear that management of organic matterand humus is essential to sustaining thewhole soil ecosystem.

Like cattle and other farm animals,soil livestock require proper feed.

The benefits of a topsoil rich in organic matterand humus are many. They include: rapiddecomposition of crop residues, granulationof soil into water-stable aggregates, decreasedcrusting and clodding, improved internaldrainage, better water infiltration, andincreased water and nutrient holding

capacity. Improvements in the soils physicalstructure facilitate easier tillage, increased soilwater storage capacity, reduced erosion,better formation and harvesting of root crops,and deeper, more prolific plant root systems.

Soil organic matter can be compared to abank account for plant nutrients. Soilcontaining 4% organic matter in the top 7inches has 80,000 pounds of organic matterper acre. That 80,000 pounds of organicmatter will contain about 5.25% nitrogen,

amounting to 4,200 pounds of nitrogen peracre. Assuming a 5% release rate during thegrowing season, the organic matter couldsupply 210 pounds of nitrogen to a crop.However, if the organic matter is allowed todegrade and lose nitrogen, purchasedfertilizer will be necessary to prop up cropyields.

All the soil organisms mentioned previously,except algae, depend on organic matter astheir food source. Therefore, to maintaintheir populations, organic matter must berenewed from plants growing on the soil, orfrom animal manure, compost, or othermaterials imported from off site. When soillivestock are fed, fertility is built up in the soiland the soil will feed the plants.

Ultimately, building organic matter andhumus levels in the soil is a matter ofmanaging the soils living organismssomething akin to wildlife management oranimal husbandry. This entails working tomaintain favorable conditions of moisture,temperature, nutrient status, pH, andaeration. It also involves providing a steadyfood source of raw organic material.

Table 4. Weights of soil organisms in the top7 inches of fertile soil.

Organism Pounds of liveweight/acre

Bacteria 1000Actinomycetes 1000Molds 2000Algae 100

Protozoa 200Nematodes 50Insects 100Worms 1000Plant roots 2000

From: Bollen (10).

Ultimately, building organic matter andhumus in the soil is a matter of managing

the soil's living organisms.



Soil Tilth and Organic Matter

A soil that drains well, does not crust, takesin water rapidly, and does not make clods issaid to have good tilth. Tilth is the physicalcondition of the soil as it relates to tillage ease,seedbed quality, easy seedling emergence,

and deep root penetration. Good tilth isdependent on aggregationthe processwhereby individual soil particles are joinedinto clusters or aggregates.

Aggregates form in soils when individual soilparticles are oriented and brought togetherthrough the physical forces of wetting anddrying or freezing and thawing. Weakelectrical forces from calcium and magnesiumhold soil particles together when the soildries. When these aggregates become wet

again, however, their stability is challengedand they may break apart. Aggregates canalso be held together by plant roots, earth-worm activity, and by flue-like productsproduced by soil microorganisms. Earth-worm-created aggregates are stable once theycome out of the worm. An aggregate formedby physical forces can be bound together byfine root hairs or threads produced by fungi.Aggregates can also become stabilized

Figure 2. Microbial byproducts glue soil particles into water-stable aggregates.

(remain intact when wet) through the by-products of organic matter decomposition byfungi and bacteriachiefly gums, waxes, andother glue-like substances. These by-productscement the soil particles together, formingwater-stable aggregates (Figure 2). Theaggregate is then strong enough to hold

together when wethence the term water-stable.

USDA soil microbiologist Sara Wright namedthe glue that holds aggregates togetherglomalinafter the Glomales group ofcommon root-dwelling fungi (12). Thesefungi secrete a gooey protein known asglomalin through their hair-like filaments, orhyphae. When Wright measured glomalin insoil aggregates she found levels as high as 2%of their total weight in eastern U.S. soils. Soil

aggregates from the west and midwest hadlower levels of glomalin. She found thattillage tends to lower glomalin levels. Higherglomalin levels and higher aggregation werefound in no-till corn plots than in tilled plots(12). Wright has a brochure describingglomalin and how it benefits soil, entitledGlomalin, a Manageable Soil Glue. To orderthis brochure see the Additional InformationResources section of this publication.



A well-aggregated soil allows for increasedwater entry, increased air flow, and in-creased water-holding capacity (13). Plantroots occupy a larger volume of well-aggre-gated soil, high in organic matter; as com-pared to a finely pulverized and dispersedsoil, low in organic matter. Roots, earth-

worms, and soil arthropods can pass moreeasily through a well-aggregated soil (14).Aggregated soils also prevent crusting of thesoil surface. Finally, well-aggregated soils aremore erosion resistant, because aggregatesare much heavier than their particle compo-nents. For a good example of the effect oforganic matter additions on aggregation, asshown by subsequent increase in water entryinto the soil, see Table 5.

Table 5. Water entry into the soil after 1 hour

Manure Rate Tons/acre Inches of water0 1.28 1.916 2.7

Boyle, et al. (13).

The opposite of aggregation is dispersion. Ina dispersed soil, each individual soil particleis free to blow away with the wind or washaway with overland flow of water.

Clay soils with poor aggregation tend to besticky when wet, and cloddy when dry. Ifthe clay particles in these soils can be aggre-gated together, better aeration and waterinfiltration will result. Sandy soils can benefitfrom aggregation by having a small amountof dispersed clay that tends to stick betweenthe sand particles and slow the excess down-ward movement of water.

Crusting is a common problem on soils thatare poorly aggregated. Crusting resultschiefly from the impact of falling raindrops.Rainfall causes clay particles on the soilsurface to disperse and clog the poresimmediately beneath the surface. Followingdrying, a sealed soil surface results in whichmost of the pore space has been drasticallyreduced due to clogging from dispersed clayparticles. Subsequent rainfall is much morelikely to run off than to flow into the soil(Figure 3).

Figure 3. Effects of aggregation on water andair entry into the soil.Derived from: Land Stewardship ProjectMonitoring Toolbox (15).



Since raindrops start crusting, any manage-ment practices that protect the soil from thisimpact will decrease crusting and increasewater flow into the soil. Mulches and covercrops serve this purpose well, as do no-tillpractices, which allow the accumulation ofsurface residue. Also, a well-aggregated soil

will resist crusting because the water-stableaggregates are less likely to break apart whena raindrop hits them.

Long-term grass production produces thebest-aggregated soils (16). A grass sodextends a mass of fine roots throughout thetopsoil, contributing to the physical processesthat help form aggregates. Roots continuallyremove water from soil microsites, providinglocal wetting and drying effects that promoteaggregation. Fine root hairs also bind soil

aggregates together.

Roots also produce food for soilmicroorganisms and earthworms, which, inturn, generate compounds that bind soilparticles into water-stable aggregates. Inaddition, perennial grass sods provideprotection from raindrops and erosion. Thus,a perennial cover creates a combination ofconditions optimal for the creation andmaintenance of well-aggregated soil.

Conversely, cropping sequences that involveannual plants and extensive cultivationprovide less vegetative cover and organicmatter, and usually result in a rapid declinein soil aggregation. For more information on

aggregation, see the soil quality informationsheet entitled Aggregate Stabilityat the SoilQuality Institutes homepage .From there, click on Soil Quality InformationSheets, then click on Aggregate Stability.

Farming practices can be geared to conserveand promote soil aggregation. Because thebinding substances are themselves susceptible

to microbial degradation, organic matterneeds to be replenished to maintain microbialpopulations and overall aggregated soilstatus. Practices should conserve aggregatesonce they are formed, by minimizing factorsthat degrade and destroy aggregation. Somefactors that destroy or degrade soil

aggregates are:

bare soil surface exposed to the impact ofraindrops

removal of organic matter through cropproduction and harvest without return oforganic matter to the soil

excessive tillage working the soil when it is too wet or too

dry use of anhydrous ammonia, which speeds

up decomposition of organic matter

excess nitrogen fertilization allowing the build-up of excess sodium

from irrigation or sodium-containingfertilizers

Tillage, Organic Matter, and PlantProductivity

Several factors affect the level of organicmatter that can be maintained in a soil.Among these are organic matter additions,

moisture, temperature, tillage, nitrogen levels,cropping, and fertilization. The level oforganic matter present in the soil is a directfunction of how much organic material isbeing produced or added to the soil versusthe rate of decomposition. The objectives ofthis balancing act entail slowing the speed oforganic matter decomposition, whileincreasing the supply of organic materialsproduced on site and/or the addition oforganic matter from off site.

Moisture and temperature also profoundlyaffect soil organic matter levels. High rainfalland temperature promote rapid plantgrowth, but these conditions are alsofavorable to rapid organic matterdecomposition and loss. Low rainfall or lowtemperatures slow both plant growth andorganic matter decomposition. The nativeMidwest prairie soils originally had a highamount of organic matter from the

The best-aggregated soils are

those that have been in long-term

grass production.



continuous growth and decomposition ofperennial grasses, combined with a moderatetemperature that did not allow for rapiddecomposition of organic matter. The moistand hot tropical areas may appear lushbecause of rapid plant growth, but soils inthese areas are low in nutrients. Rapid

decomposition of organic matter returnsnutrients back to the soil, where they arealmost immediately taken up by rapidlygrowing plants.

Tillage can be beneficial or harmful to abiologically active soil, depending on whattype of tillage is used and when it is done.Tillage affects both erosion rate and soilorganic matter decomposition rate. Tillagecan reduce the organic matter level in crop-lands below 1%, rendering them biologically

dead. Clean tillage involving moldboardplowing and disking breaks down soilaggregates and leaves the soil prone toerosion from wind and water. The mold-board plow can bury crop residue and topsoilto a depth of 14 inches. At this depth, theoxygen level in the soil is so low thatdecomposition cannot proceed adequately.Surface-dwelling decomposer organismssuddenly find themselves suffocated andsoon die. Crop residues that were originallyon the surface but now have been turned

under will putrefy in the oxygen-deprivedzone. This rotting activity may give a putridsmell to the soil. Furthermore, the top fewinches of the field are now often coveredwith subsoil having very little organic mattercontent and therefore limited ability tosupport productive crop growth.

The topsoil is where the biological activityhappensits where the oxygen is. Thatswhy a fence post rots off at the surface. Interms of organic matter, tillage is similar toopening the air vents on a wood-burningstove; adding organic matter is like addingwood to the stove. Ideally, organic matterdecomposition should proceed as an efficientburn of the woodto release nutrients andcarbohydrates to the soil organisms andcreate stable humus. Shallow tillage incor-porates residue and speeds the decomposi-tion of organic matter by adding oxygenthat microbes need to become more active.

In cold climates with a long dormantseason, light tillage of a heavy residue may bebeneficial; in warmer climates it is hardenough to maintain organic matter levelswithout any tillage.

As indicated in Figure 4, moldboard

plowing causes the fastest decline oforganic matter, no-till the least. The plowlays the soil up on its side, increasing thesurface area exposed to oxygen. The otherthree types of tillage are intermediate in theirability to foster organic matter decomposi-tion. Oxygen is the key factor here. Themoldboard plow increases the soil surfacearea, allowing more air into the soil andspeeding the decomposition rate. Thehorizontal line on Figure 4 represents thereplenishment of organic matter provided by

wheat stubble. With the moldboard plow,more than the entire organic mattercontribution from the wheat straw is gonewithin only 19 days following tillage. Finally,the passage of heavy equipment increasescompaction in the wheel tracks, and sometillage implements themselves compact thesoil further, removing oxygen and increasingthe chance that deeply buried residues willputrefy.

Tillage also reduces the rate of water entryinto the soil by removal of ground cover anddestruction of aggregates resulting incompaction and crusting. Table 6 showsthree different tillage methods and how theyaffect water entry into the soil. Notice thedirect relationship between tillage type,ground cover, and water infiltration. No-tillhas more than three times the waterinfiltration of the moldboard-plowed soil.Additionally, no-till fields will have higheraggregation from the organic matter

Table 6. Tillage effects on water infiltration and groundcover.

Water Infiltration Ground Cover

mm/minute PercentNo-till 2.7 48Chisel Plow 1.3 27Moldboard Plow 0.8 12

From Boyle, et al. 1989 (13).



decomposition on site. The surface mulchtypical of no-till fields acts as a protectiveskin for the soil. This soil skin reduces theimpact of raindrops and buffers the soil from

temperature extremes as well as reducingwater evaporation.

Both no-till and reduced-tillage systemsprovide benefits to the soil. The advantagesof a no-till system include superior soilconservation, moisture conservation, reducedwater runoff, long-term buildup of organicmatter, and increased water infiltration. Asoil managed without tillage relies on soilorganisms to take over the job of plantresidue incorporation formerly done bytillage. On the down side, no-till can foster areliance on herbicides to control weeds andcan lead to soil compaction from the traffic ofheavy equipment.

Pioneering development work on chemical-free no-till farming is proceeding at severalresearch stations in the eastern U.S. and onfarms. Pennsylvania farmer Steve Groff hasbeen farming no-till with minimal or no

herbicides for several years. Groff growscover crops extensively in his crop fields,rolling them down in the spring using a10-foot rolling stalk chopper. This rolling

chopper kills the rye or vetch cover crop andcreates a nice no-till mulch into which heplants a variety of vegetables and grain crops.After several years of no-till production, hissoils are mellow and easy to plant into. Grofffarms 175 acres of vegetables, alfalfa, andgrain crops on his Cedar Meadow Farm.Learn more about his operation in the FarmerProfilessection of this publication, by visitinghis website, or by ordering his video (seeAdditional Information Resources section).

Other conservation tillage systems includeridge tillage, minimum tillage, zone tillage,and reduced tillage, each possessing some ofthe advantages of both conventional till andno-till. These systems represent intermediatetillage systems, allowing more flexibility thana no-till or conventional till system might.They are more beneficial to soil organismsthan a conventional clean-tillage system ofmoldboard plowing and discing.

Figure 4. Organic matter losses after various tillage practices (17).



Adding manure and compost is a recognizedmeans for improving soil organic matter andhumus levels. In their absence, perennialgrass is the only crop that can regenerate andincrease soil humus (18). Cool-season grassesbuild soil organic matter faster than warm-season grasses because they are growing

much longer during a given year (18). Whenthe soil is warm enough for soil organisms todecompose organic matter, cool-season grassis growing. While growing, it is producingorganic matter and cycling minerals from thedecomposing organic matter in the soil. Inother words, there is a net gain of organicmatter because the cool-season grass isproducing organic matter faster than it isbeing used up. With warm-season grasses,organic matter production during thegrowing season can be slowed during the

long dormant season from fall through earlyspring. During the beginning and end of thisdormant period the soil is still biologicallyactive, yet no grass growth is proceeding (18).Some net accumulation of organic matter canoccur under warm-season grasses, however.In a Texas study, switchgrass (a warm-seasongrass) grown for 4 years increased soil carboncontent from 1.1% to 1.5% in the top 12inches of soil (19). In hot and moist regions, acropping rotation that includes several yearsof pasture will be most beneficial.

Effect of Nitrogen on Organic Matter

Excessive nitrogen applications stimulateincreased microbial activity, which in turnspeeds organic matter decomposition. Theextra nitrogen narrows the ratio of carbon tonitrogen in the soil. Native or uncultivatedsoils have approximately 12 parts of carbonto each part of nitrogen, or a C:N ratio of12:1. At this ratio, populations of decay

bacteria are kept at a stable level (20), sinceadditional growth in their population islimited by a lack of nitrogen. When largeamounts of inorganic nitrogen are added, theC:N ratio is reduced, which allows thepopulations of decay organisms to explode asthey decompose more organic matter withthe now abundant nitrogen. While soilbacteria can efficiently use moderateapplications of inorganic nitrogen

accompanied by organic amendments(carbon), excess nitrogen results indecomposition of existing organic matter at arapid rate. Eventually, soil carbon contentmay be reduced to a level where the bacterialpopulations are on a starvation diet. Withlittle carbon available, bacterial populations

shrink and less of the free soil nitrogen isabsorbed. Thereafter, applied nitrogen,rather than being cycled through microbialorganisms and re-released to plants slowlyover time, becomes subject to leaching. Thiscan greatly reduce the efficiency of fertiliza-tion and lead to environmental problems.

To minimize the fast decomposition of soilorganic matter, carbon should be added withnitrogen. Typical carbon sourcessuch asgreen manures, animal manure andcompostserve this purpose well.Amendments containing too high a carbon tonitrogen ratio (25:1 or more) can tip thebalance the other way, resulting in nitrogenbeing tied up in an unavailable form. Soilorganisms consume all the nitrogen in aneffort to decompose the abundant carbon;tied up in the soil organisms, nitrogenremains unavailable for plant uptake. Assoon as a soil microorganism dies anddecomposes, its nitrogen is consumed byanother soil organism until the balancebetween carbon and nitrogen is achievedagain.

Fertilizer Amendments andBiologically Active Soils

What are the soil mineral conditions thatfoster biologically active soils? Drawing fromthe work of Dr. William Albrecht (1888 to1974), agronomist at the University ofMissouri, we learn that balance is the key.Albrecht advocated bringing soil nutrientsinto a balance so that none were in excess ordeficient. Albrechts theory (also called base-saturation theory) is used to guide lime andfertilizer application by measuring and

Excessive nitrogen stimulates increasedmicrobial activity, which in turn speedsorganic matter decomposition.



evaluating the ratios of positively chargednutrients (bases) held in the soil. Positivelycharged bases include calcium, magnesium,potassium, sodium, ammonium nitrogen, andseveral trace minerals. When optimum ratiosof bases exist, the soil is believed to supporthigh biological activity, have optimal physical

properties (water intake and aggregation)and become resistant to leaching. Plantsgrowing on such a soil are also balanced inmineral levels and are considered to benutritious to humans and animals alike. Basesaturation percentages that Albrechtsresearch showed to be optimal for the growthof most crops are:

Calcium 6070%Magnesium 1020%Potassium 25%

Sodium 0.53%Other bases 5%

According to Albrecht, fertilizer and limeapplications should be made at rates that willbring soil mineral percentages into this idealrange. This approach will shift the soil pHautomatically into a desirable range withoutcreating nutrient imbalances. The basesaturation theory also takes into account theeffect one nutrient may have on another andavoids undesirable interactions. For example,

phosphorus is known to tie up zinc.

The Albrecht system of soil evaluationcontrasts with the approach used by manystate laboratories, often called thesufficiency method. Sufficiency theoryplaces little to no value on nutrient ratios,and lime recommendations are typicallybased on pH measurements alone. While inmany circumstances base saturation andsufficiency methods will produce identicalsoil recommendations and similar results,

significant differences can occur on a numberof soils. For example, suppose we tested acornfield and found a soil pH of 5.5 and basesaturation for magnesium at 20% andcalcium at 40%. Base saturation theorywould call for liming with a high-calciumlime to raise the % base saturation of calcium;the pH would rise accordingly. Sufficiency

theory would not specify high-calcium limeand the grower might choose, instead, ahigh-magnesium dolomite lime that wouldraise the pH but worsen the balance ofnutrients in the soil. Another way to look atthese two theories is that the base saturationtheory does not concern itself with pH to any

great extent but rather with the proportionalamounts of bases. The pH will be correctwhen the levels of bases are correct.

Albrechts ideas have found their way ontolarge numbers of American farms and intothe programs of several agricultural consult-ing companies. Neal Kinsey, a soil fertilityconsultant in Charleston, MO, is a majorproponent of the Albrecht approach. Kinseywas a student under Albrecht and is one ofthe leading authorities on the base-saturation

method. He teaches a short course on theAlbrecht system and provides a soil analysisservice (21). His book, Hands On Agronomy,is widely recognized as a highly practicalguide to the Albrecht system. For moreinformation on the Albrecht theory requestthe ATTRA publication on Albrecht andReams Fertility Management Systems.

Several firmsmany providing backupfertilizer and amendment productsoffer abiological-farming program based on theAlbrecht theory. Typically these firms offerbroad-based soil analysis and recommendbalanced fertilizer materials consideredfriendly to soil organisms. They avoid the useof some common fertilizers and amendmentssuch as dolomite lime, potassium chloride,anhydrous ammonia, and oxide forms oftrace elements because they are consideredharmful to soil life. The publicationHow toGet Started in Biological Farmingpresents sucha program. See the Additional Information

Resources section for ordering information.For names of companies offering consultingand products, order the ATTRA publicationsAlternative Soil Testing Laboratories andSources for Organic Fertilizers andAmendments. Both of these are also availableon the ATTRA web site located at .
http://www.attra.org/http://www.attra.org/http://www.attra.org/http://www.attra.org/



Conventional Fertilizers

Commercial fertilizer can be a valuableresource to farmers in transition to a moresustainable system and can help meetnutrient needs during times of high cropnutrient demand, or when weather

conditions result in slow nutrient release fromorganic resources. Commercial fertilizershave the advantage of supplying plants withimmediately available forms of nutrients.They are often less expensive and less bulkyto apply than many natural fertilizers.

Not all conventional fertilizers are alike.Many appear harmless to soil livestock but afew are problematic. Anhydrous ammoniacontains approximately 82% nitrogen and isapplied subsurface as a gas. Anhydrousspeeds the decomposition of organic matterin the soil, leaving the soil more compact as aresult. The addition of anhydrous causesincreased acidity in the soil, requiring 148pounds of lime to neutralize 100 pounds ofanhydrous ammonia or 1.8 pounds of limefor every pound of nitrogen contained in theanhydrous (22). Anhydrous ammoniainitially kills many soil microorganisms in theapplication zone. Bacteria and actinomycetesrecover within one to two weeks to levels

higher than those prior to treatment (23).Soil fungi, however, may take seven weeks torecover. During the recovery time, bacteriaare stimulated to grow more, and decomposemore organic matter, by the high soil nitrogencontent. As a result, their numbers increaseafter anhydrous applications, then decline asavailable soil organic matter is depleted.Farmers commonly report that the long-termuse of synthetic fertilizers, especiallyanhydrous ammonia, leads to soil compac-tion and poor tilth (23). When bacterial

populations and soil organic matter decrease,aggregation declines because existing gluesthat stick soil particles together are degradedand no other glues are being produced.

Potassium chloride (KCl) (0-0-60 and 0-0-50),also known as muriate of potash, containsapproximately 50 or 60% potassium and47.5% chloride (24). Muriate of potash ismade by refining potassium chloride ore,

which is a mixture of potassium and sodiumsalts and clay from the brines of dying lakesand seas. The potential harmful effects fromKCl can be surmised from the salt concentra-tion of the material. Table 7 shows that,pound for pound, KCl is surpassed only bytable salt on the salt index. Additionally,

some plants such as tobacco, potatoes,peaches, and some legumes are especiallysensitive to chloride. High rates of KCl mustbe avoided on such crops. Potassium sulfate,potassium nitrate, sul-po-mag, or organicsources of potassium may be considered asalternatives to KCl for fertilization.

Sodium nitrate, also known as Chileannitrate, or nitrate of soda, is another high-saltfertilizer. Because of the relatively lownitrogen content of sodium nitrate, a high

amount of sodium is added to the soil whennormal applications of nitrogen are madewith this material. The concern is thatexcessive sodium acts as a dispersant of soilparticles, degrading aggregation. The saltindex for KCl and sodium nitrate can be seenin Table 7.

Top$oil Your Farm$ Capital

Topsoil is the capital reserve of every farm.Ever since mankind started agriculture,erosion of topsoil has been the single largestthreat to a soils productivityand,consequently, to farm profitability. This isstill true today. In the U.S., the average acreof cropland is eroding at a rate of 7 tons peryear (2). To sustain agriculture means tosustain soil resources because thats the

source of a farmers livelihood.

The major productivity costs to the farmassociated with soil erosion come from thereplacement of lost nutrients and reducedwater holding ability, accounting for 50 to75% of productivity loss (2). Soil that isremoved by erosion typically contains aboutthree times more nutrients than the soil leftbehind and is 1.5 to 5 times richer in organic

Protecting soil from erosion is the firststep toward a sustainable agriculture.



matter (2). This organic matter loss not onlyresults in reduced water holding capacityand degraded soil aggregation, but also lossof plant nutrients, which must then bereplaced with nutrient amendments.

Five tons of topsoil (the so-called tolerancelevel) can easily contain 100 pounds ofnitrogen, 60 pounds of phosphate, 45 poundsof potash, 2 pounds of calcium, 10 pounds ofmagnesium, and 8 pounds of sulfur. Table 8shows the effect of slight, moderate, andsevere erosion on organic matter, soil

phosphorus level, and plant-available wateron a silt loam soil in Indiana (25).

When erosion by water and wind occurs at arate of 7.6 tons/acre/year it costs $40 peracre each year to replace the lost nutrients asfertilizer and around $17/acre/year to pumpwell irrigation water to replace the soil waterholding capacity of that lost soil (26). Thetotal cost of soil and water lost annually fromU.S. cropland amounts to an on-site produc-tivity loss of approximately $27 billion eachyear (2).

Water erosion gets started when fallingrainwater collides with bare ground

detaching soil particles from the parent soilbody. After enough water builds up on the



soil surface, following detachment, overlandwater flow transports suspended soil down-slope (Figure 5). Suspended soil in the runoffwater abrades and detaches additional soilparticles as the water travels overland.Preventing detachment is the most effectivepoint of erosion control because it keeps the

soil in place. Other erosion control practicesseek to slow soil particle transport and causesoil to be deposited before it reaches streams.These methods are less effective at protectingthe quality of soil within the field.Commonly implemented practices to slowsoil transport include terraces and diversions.Terraces, diversions, and many other erosioncontrolpractices are largely unnecessary ifthe ground stays covered year-round. For

erosion prevention, a high percentage ofground cover is a good indicator of success,while bare ground is an early warningindicator for a high risk of erosion (27).Muddy runoff water and gullies are too-late indicators. The soil has already erodedby the time it shows up as muddy water and

its too late to save soil already suspended inthe water.

Protecting the soil from erosion is thefirststep toward a sustainable agriculture. Sincewater erosion is initiated by raindrop impacton bare soil, any management practice thatprotects the soil from raindrop impact willdecrease erosion and increase water entryinto the soil. Mulches, cover crops, and crop

Figure 5. Raindrops falling on bare ground initiate erosion.Drawing from Cropland monitoring guide (27).



residues serve this purpose well.Additionally, well-aggregated soils resistcrusting because water-stable aggregates areless likely to break apart when the raindrophits them. Adequate organic matter withhigh soil biological activity leads to high soilaggregation.

Many studies have shown that cropping

systems that maintain soil-protecting plantcanopy or residue cover have the least soilerosion. This is universally true. Long-termcropping studies begun in 1888 at theUniversity of Missouri provide dramaticevidence of this concept. Gantzer andcolleagues (28) examined the effects of acentury of cropping on soil erosion. Theycompared depth of topsoil remaining after100 years of cropping (Table 9). As the tableshows, the cropping system that maintainedthe highest amount of permanent ground

cover (timothy grass) had the greatestamount of topsoil left.

The researchers commented that subsoil hadbeen mixed with topsoil in the continuouscorn plots from plowing, making the real

topsoil depth less than was apparent. Inreality, all the topsoil was lost from thecontinuous corn plots in only 100 years. Therotation lost about half the topsoil over 100years. How can we feed future generationswith this type of farming practice?

In a study of many different soil types in eachof the major climatic zones of the U.S.,researchers showed dramatic differences insoil erosion when comparing row crops toperennial sods. Row crops consisted ofcotton or corn, and sod crops were bluegrassor bermuda grass. On average the row cropseroded over 50 times more soil than did theperennial sod crops. The two primaryinfluencing factors are ground cover andtillage. The results are shown in Table 10.

So, how long do fields have before the topsoilis gone? This depends on where in thecountry the field is located. Some soilsnaturally have a very thick topsoil whileother soils have a thin topsoil over rock orgravel. Roughly 8 tons/acre/year soilerosion loss amounts to the thickness of adime spread over an acre. Twenty dimesstack up to 1-inch high. So a landscape withan 8-ton erosion rate would lose an inch oftopsoil about every 20 years. On a soil with athick topsoil, this amount is barely detectablewithin a persons lifetime and may not benoticed. Soils with naturally thin topsoils ortopsoils that have been previously eroded canbe transformed from productive to degradedwithin a generation.

Table 9. Topsoil depth remaining after 100 yearsof different cropping practices.

Crop Sequence Inches of topsoil remaining

Continuous Corn 7.76-year rotation* 12.2Continuous timothygrass

17.4

*Corn, oats, wheat, clover, timothy, timothyFrom: Gantzer, C.J. et al. (28).



Forward-thinking researcher Wes Jackson, ofthe Land Institute, waxes eloquent abouthow tillage is engrained in human cultureever since we began farming. Beating ourswords into plowshares surely embodies thetriumph of good over evil. Someone whocreates something new is said to have

plowed new ground. Yet the plowsharemay well have destroyed more options forfuture generations than the sword (30).

Tillage for the production of annual crops isthe major problem in agriculture, causing soilerosion and the loss of soil quality. Anyagricultural practice that creates andmaintains bare ground is inherently lesssustainable than practices that keep theground covered throughout the year. WesJackson has spent much of his career

developing perennial grain crops andcropping systems that mimic the naturalprairie. Perennial grain crops do not requiretillage to establish year after year, and theground is left covered. Ultimately, this is thefuture of grain production and trulyrepresents a new vision for how we producefood. The greatest research need inagriculture today is breeding work to developperennial crops that will replace annualcrops requiring tillage. Farming practicesusing annual crops in ways that mimic

perennial systems, such as no-till and covercrops, are our best alternative until perennialsystems are developed.

Summaryof Part I

Soil management involves stewardship of thesoil livestock herd. The primary factorsaffecting organic matter content, build-up,and decomposition rate in soils are: oxygencontent, nitrogen content, moisture content,temperature, and the addition and removal

of organic materials. All these factors worktogether all the time. Any one can limit theothers. These are the factors that affect thehealth and reproductive rate of organicmatter decomposer organisms. Managersneed to be aware of these factors whenmaking decisions about their soils. Lets takethem one at a time.

Increasing oxygenspeeds decomposition oforganic matter. Tillage is the primary wayextra oxygen enters the soil. Texture alsoplays a role, with sandy soils having moreaeration than heavy clay soils. Nitrogencontentis influenced by fertilizer additions.Excess nitrogen without the addition of

carbon speeds the decomposition of organicmatter. Moisture contentaffects decomposi-tion rates. Soil microbial populations aremost active over cycles of wetting anddrying. Their populations increase followingwetting as the soil dries out. After the soilbecomes dry, their activity diminishes. Justlike humans, soil organisms are profoundlyaffected by temperature. Their activity ishighest within a band of optimumtemperature, above and below which theiractivity is diminished.

Adding organicmatterprovides more food formicrobes. To achieve an increase of soilorganic matter, additions must be higherthan removals. Over a given year, underaverage conditions, 60 to 70 percent of thecarbon contained in organic residues addedto soil is lost as carbon dioxide (20). Five toten percent is assimilated into the organismsthat decomposed the organic residues andthe rest becomes newhumus. It takesdecades for new humus to develop into stablehumus, which imparts the nutrient-holdingcharacteristics humus is known for (20). Theend result of adding a ton of residue wouldbe 400 to 700 pounds of new humus. Onepercent organic matter weighs 20,000pounds per acre. A 7-inch depth of topsoilover an acre weighs 2 million pounds.Building organic matter is a slow process!

It is more feasible to stabilize and maintainthe humus present, before it is lost, than to

try to rebuild it. The value of humus is notfully realized until it is severely depleted (20).If your soils are high in humus now, workhard to preserve what you have. The forma-tion of new humus is essential to maintainingold humus and the decomposition of raworganic matter has many benefits of its own.Increased aeration caused by tillage coupled



with the absence of organic carbon infertilizer materials has caused greater than50% decline in native humus levels on manyU.S. farms (20).

Appropriate mineral nutrition needs to bepresent for soil organisms and plants to

prosper. Adequate levels of calcium,magnesium, potassium, phosphorus,sodium, and the trace elements should bepresent, but not in excess. The cation balancetheory of soil management helps guidedecision-making toward achieving optimumlevels of these nutrients in the soil. Severalbooks have been written on balancing soilmineral levels, and several consulting firmsprovide soil analysis and fertility recommen-dation services based on this theory.

Commercial fertilizers have their place in asustainable agriculture. Some appear harm-less to soil livestock and provide nutrients attimes of high nutrient demand from crops.Anhydrous ammonia and potassium chloridecause problems, however. As noted above,anhydrous kills soil organisms in the injectionzone. Bacteria and actinomycetes recoverwithin a few weeks, but fungi take longer.The increase in bacteria, fed by high availablenitrogen from the anhydrous, speeds thedecomposition of organic matter. Potassiumchloride has a high salt index, and someplants and soil organisms are sensitive tochloride.

Topsoil is the farmers capital. Sustainingagriculture means sustaining the soilresource. Maintaining ground cover in theform of cover crops, mulch, or crop residuefor as much of the annual season as possibleachieves the goal of sustaining the soilresource. Any time the soil is tilled and left

bare it is susceptible to erosion. Even smallamounts of soil erosion are harmful overtime. It is not easy to seethe effects oferosion over a human lifetime, and thereforeerosion may go unnoticed. Tillage forproduction of annual crops has created mostof the erosion associated with agriculture.Perennial grain crops not requiring tillageprovide a promising alternative for

drastically improving the sustainability offuture grain production.

Summary of Sustainable SoilManagement Principles

Soil livestock cycle nutrients and

provide many other benefits

Organic matter is the food for the soillivestock herd

The soil should be covered to protect itfrom erosion and temperature extremes

Tillage speeds the decomposition oforganic matter

Excess nitrogen speeds the decompositionof organic matter; insufficient nitrogenslows down organic matter decomposi-tion and starves plants

Moldboard plowing speeds the decompo-sition of organic matter, destroys earth-worm habitat, and increases erosion

To build soil organic matter, the produc-tion or addition of organic matter mustexceed the decomposition of organic

matter

Soil fertility levels need to be withinacceptable ranges before a soil-buildingprogram is begun

Part II. Management Steps toImprove Soil Quality

1. Assess Soil Health and BiologicalActivity on Your Farm

A basic soil audit is the first and sometimesthe only monitoring tool used to assesschanges in the soil. Unfortunately, thestandard soil test done to determine nutrientlevels (P, K, Ca, Mg, etc.) provides noinformation on soil biology and physicalproperties. Yet, most of the farmer-recog-nized criteria for healthy soils (see p. 2)



include, or are created by, soil organisms andsoil physical properties. A betterappreciation of these biological and physicalsoil properties, and how they affect soilmanagement and productivity, has resultedin the adoption of several new soil healthassessment techniques, which are discussed

below.

The USDA Soil Quality Test KitThe USDA Soil Quality Institute provides aSoil Quality Test Kit Guide developed by Dr.John Doran and associates at the AgriculturalResearch Services office in Lincoln,Nebraska. Designed for field use, the kitallows the measurement of water infiltration,water holding capacity, bulk density, pH, soilnitrate, salt concentration, aggregate stability,earthworm numbers, and soil respiration.

Components necessary to build a kit includemany items commonly availablesuch aspop bottles, flat-bladed knives, a gardentrowel, and plastic wrap. Also necessary todo the tests is some equipment that is not asreadily available, such as hypodermicneedles, latex tubing, a soil thermometer, anelectrical conductivity meter, filter paper, andan EC calibration standard. The Soil QualityTest Kit Guide can be ordered from theUSDA through the Soil Quality Instituteswebpage . The 88-pageon-line version of the guide is available inAdobe Acrobat Reader format through theabove web page and may be printed out. Asummary of the tests is also available fromthe web page. To order a paper version, seethe Soil Quality Institute reference underAdditional Information Resources, below.

A greatly simplified and quick soil qualityassessment is available at the Soil Quality

Institutes web page as well, by clicking onGetting to Know your Soil,near the bottomof the homepage. This simplified methodinvolves digging a hole and making someobservations. Here are a few of the proce-dures shown at this website: Dig a hole 4 to6 inches below the last tillage depth andobserve how hard the digging is. Inspectplant roots for lots of branching and fine root

hairs or a balled-up condition. A lack offineroot hairs indicates oxygen deprivation,while sideways growth indicates a hardpan.The process goes on to assess earthworms,soil smell, and aggregation. Another usefulhands-on procedure for assessing pasturesoils is available from the ATTRA publication

entitled Assessing the Pasture Soil Resource.

Early Warning Monitoring for CroplandsA cropland monitoring guide has beenpublished by the Center for HolisticManagement (27). The guide contains a setof soil health indicators that are measurablein the field. No fancy equipment is needed tomake the assessments described in thismonitoring guide. In fact, all the equipmentis cheap and locally available for almost anyfarm. Simple measurements can help

determine the health of croplands in terms ofthe effectiveness of the nutrient cycle andwater cycle, and the diversity of some soilorganisms. Assessments of living organisms,aggregation, water infiltration, ground cover,and earthworms can be made using thisguide. The monitoring guide is easy to readand understand, and comes with a field sheetto record observations. It is available for $12from the Savory Center for HolisticManagement (see Resources section).

Direct Assessment of Soil HealthSome quick ways to identify a healthy soilinclude feeling it and smelling it. Grab ahandful and take a whiff. Does it have anearthy smell? Is it a loose, crumbly soil withsome earthworms present? Dr. Ray Weil, soilscientist at the University of Maryland,describes how he would make a quick evalu-ation of a soils health in just 5 minutes (31).

Look at the surface and see if it is

crusted, which tells somethingabout tillage practices used, organicmatter, and structure. Push a soilprobe down to 12 inches, lift outsome soil and feel its texture. If aplow pan were present it wouldhave been felt with the probe. Turnover a shovelful of soil to look forearthworms and smell for actino-mycetes, which are microorganisms



that help compost and stabilizedecaying organic matter. Theiractivity leaves a fresh earthy smellin the soil.

Two more easy observations are to count thenumber of soil organisms in a square foot ofsurface crop residue and to pour a pint of

water on the soil and record the time it takesto sink in. Comparisons can be made usingthese simple observations along with RayWeils evaluation above to determine howfarm practices affect soil quality. Some of thesoil quality assessment systems discussedabove utilize these and other observationsand provide recordkeeping sheets to recordyour observations on.

A simple erosion demonstration

This simple procedure demonstrates the valueof ground cover. Tape a white piece of papernear the end of a 3-foot-long stick. Hold thestick in one hand so as to have the paper endwithin 1 inch of a bare soil surface (see Figure6). Now pour a pint of water onto the baresoil within 23 inches of the white paper andobserve the soil accumulation on the whitepaper. Tape another piece of white paper tothe stick and repeat the operation, this timeover soil with 100% ground cover, andobserve the accumulation of soil on the

paper. Compare the two pieces of paper. Thissimple test shows how effective ground covercan be at preventing soil particles fromdetaching from the soil surface.

2. Utilize Tools and Techniques to BuildSoil

Can a cover crop be worked into your rota-tion? How about a high-residue crop orperennial sod? Are there economical sources

of organic materials or manure in your area?Are there ways to reduce tillage and nitrogenfertilizer? Where feasible, bulky organicamendments may be added to supply bothorganic matter and plant nutrients. It isparticularly useful to account for nutrientswhere organic fertilizers and amendmentsare utilized. Start with a soil test and anutrient analysis of the material you areapplying. Knowing the amount of nutrients

Figure 6. Simple erosion test.Drawing from Cropland monitoring guide (27).

needed by the crop guides the amount ofamendment applied and can lead to signifi-cant reductions in fertilizer purchase. Thenutrient composition of organic materials canbe variable, which is all the more reason todetermine the amount you have with appro-priate testing. In addition to containing themajor plant nutrients, organic fertilizers cansupply many essential micronutrients. Propercalibration of the spreading equipment isimportant to ensure accurate applicationrates.

Animal Manure

Manure is an excellent soil amendment,providing both organic matter and nutrients.The amount of organic matter and nitrogenin animal manure depends on feedconsumed, type of bedding used (if any), andwhether the manure is applied as a solid orliquid. Typical rates for dairy manure wouldbe 10 to 30 tons per acre or 4,000 to 11,000gallons of liquid for corn. At these rates the



crop would get between 50 and 150 poundsof available nitrogen per acre. Additionally,lots of carbon would be added to the soil,resulting in no loss of soil organic matter.High crop residues grown from this manureapplication and left on the soil would alsocontribute organic matter.

However, a common problem with usingmanure as a crop nutrient source is thatapplication rates are usually based on thenitrogen needs of the crop. Because somemanures have about as much phosphorus asthey do nitrogen, this often leads to buildupof soil phosphorus. A classic example ischicken litter applied to crops that requirehigh nitrogen levels, such as pasture grassesand corn. Broiler litter, for example, containsapproximately 50 pounds of nitrogen and

phosphorus and about 40 pounds ofpotassium per ton. Since an establishedfescue pasture needs twice as much nitrogenas it does phosphorus, a common fertilizerapplication would be about 50 pounds of

nitrogen and 30 pounds of phosphorus per

acre. If a ton of poultry litter were applied tosupply the nitrogen needs of the fescue, anover-application of phosphorus would resultbecause the litter has about the same levels ofnitrogen and phosphorus. Several years oflitter application to meet nitrogen needs canbuild soil phosphorus up to excessive levels.One easy answer to this dilemma is to adjustthe manure rate to meet the phosphorusneeds of the crop and to supply theadditional nitrogen with fertilizer or alegume cover crop. On some farms this may

mean that more manure is being producedthan can be safely used on the farm. In thiscase, farmers may need to find a way toprocess and sell (or barter) this excessmanure to get it off the farm.

Compost

Composting farm manure and other organicmaterials is an excellent way to stabilize their

nutrient content. Composted manure is alsoeasier to handle, less bulky, and bettersmelling than raw manure. A significantportion of raw-manure nutrients are inunstable, soluble forms. Such unstable formsare more likely to run off if surface-applied,or to leach if tilled into the soil. Compost is

not as good a source of readily available plantnutrients as raw manure. But compostreleases its nutrients slowly, therebyminimizing losses. Quality compost containsmore humus than its raw componentsbecause primary decomposition has occurredduring the composting process. However, itdoes not contribute as much of the stickygums and waxes that aggregate soil particlestogether as does raw manure, because thesesubstances are also released during theprimary decomposition phase. Unlike

manure, compost can be used at almost anyrate without burning plants. In fact, somegreenhouse potting mixes contain 20 to 30%compost. Compost (like manure) should beanalyzed by a laboratory to determine thenutrient value of a particular batch andensure that it is being used effectively toproduce healthy crops and soil, and notexcessively so that it contributes to waterpollution.

Composting also reduces the bulk of raw

organic materialsespecially manures,which often have a high moisture content.However, while less bulky and easier tohandle, composts can be expensive to buy.On-farm composting cuts costs dramatically,compared with buying compost. For morecomprehensive information on composting atthe farm or the municipal level, request theATTRA publication entitled On-FarmComposting Resource List.

Cover Crops and Green Manures

Many types of plants can be grown as covercrops. Some of the more common onesinclude: rye, buckwheat, hairy vetch, crimsonclover, subterranean clover, red clover, sweetclover, cowpeas, millet, and forage sorghums.Each of these plants has advantages over theothers and differs in its area of adaptability.Cover crops can maintain or increase soilorganic matter if they are allowed to grow

A common problem with using manure as acrop nutrient source is that application rates areusually based on the nitrogen needs of the crop.



long enough to produce high herbage. Alltoo often, people get in a hurry and take outa good cover crop just a week or two before ithas reached its full potential. Hairy vetch orcrimson clover can yield up to 2.5 tons peracre if allowed to go to 25% bloom stage. Amixture of rye and hairy vetch can produce

even more.

In addition to organic matter benefits, legumecover crops provide considerable nitrogen forcrops that follow them. Consequently, thenitrogen rate can be reduced following aproductive legume cover crop taken out atthe correct time. For example, corn grownfollowing 2 tons of hairy vetch shouldproduce high yields of grain with only half ofthe normal nitrogen rate.

When small grains such as rye are used ascover crops and allowed to reach theflowering stage, additional nitrogen may berequired to help offset the nitrogen tie-upcaused by the high carbon addition of the ryeresidue. The same would be true of any high-carbon amendment, such as sawdust orwheat straw. Cover crops also suppressweeds, help break pest cycles, and throughtheir pollen and nectar provide food sourcesfor beneficial insects and honeybees. Theycan also cycle other soil nutrients, makingthem available to subsequent crops as thegreen manure decomposes. For moreinformation on cover crops, request ATTRAsOverview of Cover Crops and Green Manures.This publication is comprehensive andprovides many references to other availableresources on growing cover crops.

Humates

Humates and humic acid derivatives are a

diverse family of products, generally obtainedfrom various forms of oxidized coal.Coal-derived humus is essentially the same ashumus extracts from soil, but there has beena reluctance in some circles to accept it as aworthwhile soil additive. In part, this stemsfrom a belief that only humus derived fromrecently decayed organic matter is beneficial.It is also true that the production and

recycling of organic matter in the soil cannotbe replaced by coal-derived humus.However, while sugars, gums, waxes andsimilar materials derived from fresh organic-matter decay play a vital role in both soilmicrobiology and structure, they are nothumus. Only a small portion of the organic

matter added to the soil will ever beconverted to humus. Most will return to theatmosphere as carbon dioxide as it decays.

Some studies have shown positive effects ofhumates, while other studies have shown nosuch effects. Generally, the consensus is thatthey work well in soils with low organicmatter. In small amounts they do notproduce positive results on soils already highin organic matter; at high rates they may tieup soil nutrients.

There are many humate products on themarket. They are not all the same. Humateproducts should be evaluated in a small testplot for cost effectiveness before using themon a large scale. Salespeople sometimes makeexaggerated claims for their products.ATTRA can provide more information onhumates upon request.

Reduced Tillage

While tillage has become common to manyproduction systems, its effects on the soil canbe counter-productive. Tillage smoothes thesoil surface and destroys natural soil aggrega-tions and earthworm channels. Porosity andwater infiltration are decreased followingmost tillage operations. Plow pans maydevelop in many situations, particularly ifsoils are plowed with heavy equipment orwhen the soil is wet. Tilled soils have muchhigher erosion rates than soils left covered

with crop residue.

Because of all the problems associated withconventional tillage operations, acreageunder reduced tillage systems is increasing onthe American landscape. Any tillage systemthat leaves in excess of 30% surface residue isconsidered a conservation tillagesystem byUSDA (32). Conservation tillage includes



no-till, zero-till, ridge-till, zone-till, and somevariations of chisel plowing and disking.These conservation till strategies andtechniques allow for establishing crops intothe previous crops residues, which arepurposely left on the soil surface. Theprincipal benefits of conservation tillage are

reduced soil erosion and improved waterretention in the soil, resulting in moredrought resistance. Additional benefits thatmany conservation tillage systems provideinclude reduced fuel consumption, flexibilityin planting and harvesting, reduced laborrequirements, and improved soil tilth. Two ofthe most common conservation tillagesystems are ridge tillage and no-till.

Ridge tillage is a form of conservation tillagethat uses specialized planters and cultivators

to maintain permanent ridges on which rowcrops are grown. After harvest, crop residueis left until planting time. To plant the nextcrop, the planter places the seed in the top ofthe ridge after pushing residue out of the wayand slicing off the surface of the ridge top.Ridges are re-formed during the lastcultivation of the crop.

Often, a band of herbicide is applied to theridge top during planting. With bandedherbicide applications, two cultivations aregenerally used: one to loosen the soil andanother to create the ridge later in the season.No cultivation may be necessary if theherbicide is applied by broadcasting ratherthan banding. Because ridge tillage relies oncultivation to control weeds and reformridges, this system allows farmers to furtherreduce their dependence on herbicides,compared with either conventional till orstrict no-till systems.

Maintenance of the ridges is key to successfulridge tillage systems. The equipment mustaccurately reshape the ridge, clean awaycrop residue, plant in the ridge center, andleave a viable seedbed. Not only does theridge-tillage cultivator remove weeds, it alsobuilds up the ridge. Harvesting in ridgedfields may require tall, narrow dual wheelsfitted to the combine. This modification

permits the combine to straddle several rows,leaving the ridges undisturbed. Similarly,grain trucks and wagons cannot be drivenrandomly through the field. Maintenance ofthe ridge becomes a consideration for eachprocess.

Conventional no-till methods have beencriticized for a heavy reliance on chemicalherbicides for weed control. Additionally,no-till farming requires careful managementand expensive machinery for someapplications. In many cases, the springtemperature of untilled soil is lower than thatof tilled soil. This lower temperature canslow germination of early-planted corn ordelay planting dates. Also, increased insectand rodent pest problems have beenreported. On the positive side, no-till

methods offer excellent soil erosionprevention and decreased trips across thefield. On well-drained soils that warmadequately in the spring, no-till has providedthe same or better yields as compared toconventional till.

A recent equipment introduction into theno-till arena is the so-called no-tillcultivator. These cultivators permitcultivation in heavy residue and provide anon-chemical option to post-emergentherbicide applications. Farmers have theoption to band herbicide in the row and usethe no-till cultivator to clean the middles as away to reduce herbicide use. ATTRA canprovide a number of resource contacts oncultural methods, equipment, andmanagement for designing a conservation tillcropping system.

Minimize Synthetic Nitrogen Use

If at all possible, add carbon with nitrogensources. Animal manure is a good way toadd both carbon and nitrogen. Growinglegumes as a green manure or rotation cropis another way. When nitrogen fertilizer isused, try to do it at a time when a heavy cropresidue is going onto the soil, too. Forexample, a rotation of corn, beans, andwheat would do well with nitrogen added



after the corn residue was rolled down orlightly tilled in. Spring-planted soybeanswould require no nitrogen. A small amountof nitrogen could be applied in the fall for thewheat. Following the wheat crop, a legumewinter-annual cover crop could be planted.In the spring, when the cover crop is taken

out, nitrogen rates for the corn would bereduced to account for the nitrogen in thelegume. Avoid continual hay cropsaccompanied by high nitrogen fertilization.The continual removal of hay accompaniedby high nitrogen speeds the decomposition ofsoil organic matter. Heavy fertilization ofsilage crops, where all the crop residue isremoved (especially when accompanied bytillage), speeds soil decline and organicmatter depletion.

3.Continue to Monitor for Indicators ofSuccess or Failure

As you experiment with new practices andamendments, continue to monitor the soil forchanges using some of the tools discussedabove in the Assessing Soil Health andBiological Activity section. Several of thesemonitoring guides have data sheets you canuse in the field to record data, and use forfuture comparison after changes are made tothe farming practices. Review the principles

of sustainable soil management and findways to apply them in your operation. If thethought of pulling everything together seemsoverwhelming, start with only one or twonew practices and build on them. Seekadditional motivation by reading the nextsection on people who have successfully builttheir soils.

Part III. Examples of SuccessfulSoil Builders (Farmer Profiles)

Steve Groff: Steve and his family producevegetables, alfalfa and grain crops on 175acres in Lancaster County, Pennsylvania.When Steve took over operation of the familyfarm 15 years ago, his number one concernwas eliminating soil erosion. Consequently,he began using cover crops extensively in hiscrop fields. In order to transform his greencover crop into no-till mulch, Steve uses a 10-

foot Buffalo rolling stalk chopper. Under thehitch-mounted frame, the stalk chopper hastwo sets of rollers running in tandem. Theserollers can be adjusted for light or aggressiveaction and set for continuous coverage. Stevesays the machine can be run up to 8 miles anhour and does a good

sustainable soil

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