Use of Tillage in Organic Farming Systems: The Basics

This article includes information about the use of tillage in organic farming systems. It provides an overview of how tillage fits within the organic standards and organic farming systems. It defines types of tillage, introduces tillage equipment, provides a summary of pros and cons associated with tillage practices, and gives examples of primary and secondary tillage and no-till applications. 

• I. Overview of Tillage and Organic Management
• II. Organic Certification and Tillage
• III. What is Tillage?
• IV. Types of Mechanical Tillage and Tools
• V. Pros and Cons of Tillage
• VI. Primary and Secondary Tillage and No-Till Options
• VII. Tillage Glossary
• VIII. Tillage Resources
• IX. References

I. Overview of Tillage and Organic Management

Heavy reliance on tillage for weed control has been cited as a weakness in organic systems. However, from an organic matter and soil structure perspective, there is plenty of evidence that organic farming systems typically perform as well or better than conventional, herbicide-intensive systems with less soil disturbance. This is because importation of organic inputs such as manures and composts, recycling of on-farm organic matter, and well-designed crop rotations (including cover crops and perennial forages), tend to offset the negative influences of tillage on soil structure and organic matter. These negative consequences can include loss of organic matter, increased soil strength, reduced infiltration rates, compaction, and increased erosion.

Experienced organic farmers minimize the negative consequences of tillage through careful consideration of the timing of tillage, equipment operation, soil conditions, and the crop rotation in which tillage practices are applied. Certain crops, like root vegetables, that involve intensive soil disturbance during harvest and return little crop residue can be rotated with crops that involve less soil disturbance and return more crop residue.

Beginning farmers have much to learn about the art and science behind effective tillage practices. Policy makers need to appreciate when and where organic farming can provide desired ecological services, including carbon sequestration, despite tillage intensity that is often higher than in conventional systems. Increased collaboration between agroecologists, agricultural engineers, and experienced farmers will lead the way to better tillage systems that allow more consistent benefit from strategic tillage in the context of well-planned cropping systems while minimizing negative side effects.

Three points to remember are:

• Implement selection and setup have a significant influence on success.
• Tractor size and speed influences tool performance.
• Practitioner skill is a key ingredient to success!

II. Organic Certification and Tillage

The National Organic Program final rule (United States Deptartment of Agriculture [USDA], 2000) Certified organic farmers must document the tillage practices and procedures performed as part of their Organic System Plans [NOP section §205.201(a)(1)]. Hand weeding and mechanical cultivation are among the allowed weed control measures [NOP section §205.206(c)(4)]. Farm records must document the frequency of tillage applications. This can be done in a number of ways; an organized and easy-to-use system should be adopted by the producer for documenting tillage, rotation, and amendment history (in addition to other information required by the NOP standard) for each field. When reviewing a producer's farm plan, the organic inspector will consider whether tillage practices are being used in ways that maintains or improves the physical, chemical, and biological condition of the soil and that minimize soil erosion [NOP section §205.203(a)].

III. What is Tillage?

Tillage is mechanical modification of soil structure. Tillage tools modify soil structure through a wide range of soil–tool interactions, including: cutting, milling, crushing, beating, and rebound.

Figure credit: Joel Gruver, Western Illinois University. Adapted from Gajri, P. R., V. K. Arora, and S. S. Prihar. 1999. Tillage for sustainable cropping. Food Products Press, Binghampton, NY.

The outcome of soil–tool interactions varies with respect to both the characteristics of the tillage operation, such as depth, width, speed, and form of soil-engaging action, and the characteristics of the soil that is being tilled, such as texture, structure, moisture, friability, and plasticity.

Tillage tools subject soil structure to mechanical stresses such as compression, shear, and tension. When the applied stresses exceed soil strength, soil structure fails, either by crumbling along planes of weakness, if the soil is in a friable state, or by deforming, if the soil is in a plastic state.

When soil is too moist—wetter than the “plastic limit”—tillage causes smearing and creates clods that may last for the rest of the growing season. Winter freezing and thawing will generally break down clods.

Many tillage operations are designed to loosen and homogenize soil—increase macroporosity and structural uniformity—within the zone of tillage, but some tillage operations are intended to shape or firm soil. Some of the effects of tillage are intentional—see the tillage objectives listed in Section V for example—whereas other effects are unintentional, such as the formation of a plowpan, increased susceptibility to compaction, and erosion.

IV. Types of Mechanical Tillage and Tools

 

Table 1. Types and purpose of tillage, and implements used.

Type of tillage	Purpose	Implements
Primary tillage	Create a soil condition from which a seed bed can be prepared using secondary tillage implements. Soil disturbance is generally >6 inches deep. Primary tillage is necessary when existing soil conditions inhibit the effectiveness of secondary tools.	Moldboard and disk plows invert the soil in a plow layer, resulting in the burial of most crop residues. Aggressive tine tools—such as chisel plows, rippers, and subsoilers—fracture, but do not invert soil and retain more residue cover. Aggressive PTO-powered tools such as spaders and rotary tillers can be used for primary tillage. An acceptable seed bed can sometimes be prepared in only one pass.
Secondary tillage	Seed bed preparation—may involve pulverizing, leveling, and/or residue sizing and burial. Soil preparation is traditionally full-field but can be concentrated in row zones.	Tillage tools used for seed bed preparation are generally referred to as harrows. Most harrows are draft implements with gangs of tines, disks, rolling baskets, or combinations. Powered harrows, such as rotovators, rod weeders, and reciprocating harrows, are also used for seed bed preparation and can accomplish more in one pass than draft tools. Sweeps are used to push residues aside for conservation planting.
Cultivation	Mechanical management of weeds and residues.	Directed vs. blind cultivation equipment: Directed (row crop) cultivators are used to undercut or dislodge weeds growing between crops planted on wide rows (generally >2 feet). Soil may be thrown into the row. Shields are sometimes used to prevent burial of the crop. Blind cultivation is mostly used preemergent or shortly after the emergence of wide row crops, but is also sometimes used in narrow row or broadcast crops.
Land shaping	Important for vegetable production systems and fields using conservation practices.	Listers/ridge builders come in a variety of shapes and sizes and build beds (rows or ridges) 6 to 10 inches high, 30 or 40 inches apart, separated by a furrow (interrow). Bedshapers form vegetable beds, often 6 to 8 inches high, with pairs of heavy discs. Wider and lower (<6 inches) beds are often formed prior to the planting of vegetable crops, especially under plasticulture.
Conservation tillage	Conservation tillage practices maintain a minimum of 30% of crop residue on the soil surface or at least 1,000 lb/ac (1,100 kg/ha) of small grain residue on the surface during the critical soil erosion period.	No-till, strip-till, ridge-till, and mulch-till rely on a combination of chisels, strip tillers, and specialized planters.
Planters/ Transplanters	Open soil, insert seeds or set transplants, and firm soil. Goal is to achieve good soil–seed or soil–root contact and desired depth and spacing of placement.	Planters are used to plant wide rows, usually 20 to 40 inches (50 to 100 cm); seed is singulated. Drills are used to plant rows that are close together, usually 6 to 10 inches apart (15 to 30 cm); seed flow rate is controlled but seed is not singulated. Transplanters are important for vegetable production systems.
Tools to manage surface residue	A variety of tools are used for residue management, mulching, killing cover crops, and distributing materials on the soil surface.	Roller–crimpers and undercutters are important tools used to kill mature cover crops. Mowers and flail choppers are used to control standing biomass by cutting it into pieces small enough to distribute as mulch or incorporate with primary tillage. Chain harrows can be used to spread out residues and manure, incorporate seed, and level the soil surface.

V. Pros and Cons of Tillage

On the positive side, tillage has been part of most agricultural systems throughout history because tillage can be used to achieve many agronomic objectives.

The benefits of tillage include:

• Soil conditioning—the modification of soil structure to favor agronomic processes such as soil–seed contact, root proliferation, water infiltration, and soil warming;
• Weed and pest suppression—direct termination or disruption of weed and pest life cycles;
• Residue management—movement, orientation, or sizing of residues to minimize the negative effects of crop or cover crop residues and promote beneficial effects;
• Incorporation and mixing—placement or redistribution of substances such as fertilizers, manures, seeds, and residues, sometimes from a less favorable location to a more favorable spatial distribution;
• Segregation—consolidation of rocks, root clumps, soil crumb sizes, and so forth;
• Land forming—changing the shape of the soil surface; the simplest variant is probably leveling; ridging, roughening and furrowing are also examples; and
• Stimulation of nutrient release—achieved by aeration and mixing; note this can be a disbenefit when not synchronized with crop uptake.

More specific tillage objectives include seed bed formation, stale seed bed formation, compaction alleviation, fracturing of soil crusts, severing and/or dessication of weeds, maceration of biofumigant cover crops, stimulation of soil biology, and harvesting of root crops.

Figure credit: George Wadsworth, Potash Development Association.

Negative effects of tillage include:

• Compaction of soil below the depth of tillage (formation of a tillage pan);
• Crusting of soil when soil pulverization is followed by rain, stimulating weed seed germination and inhibiting crop emergence;
• Increased susceptibility to water and wind erosion associated with residue removal and soil loosening;
• Accelerated decomposition of organic matter, which is undesirable from a long-term perspective;
• Cost of equipment purchase and operation;
• Energy cost of tillage operations;
• Labor and temporal obligations; and
• Alteration of the soil foodweb, shifting populations away from larger, longer-lived organisms to smaller, shorter-lived organisms.

Figure credit: Ontario Ministry of Agriculture, Food and Rural Affairs. 2008. No-till: Making it work. Best Management Practices Series BMP11E. Government of Ontario, Canada. (Available online at: http://www.omafra.gov.on.ca/english/environment/bmp/no-till.htm) (verified 14 Jan 2009). ©2008 Queen's Printer for Ontario. Adapted by Joel Gruver, Western Illinois University.

Figure credit: Saginaw Valley Research Farm, Michigan State University.

To get the most from any tillage operation, be clear about the purpose. Before you till, make sure to:

• Ask yourself if tillage is needed and, if so, what is the best implement to achieve the purpose?
• Avoid tillage when the soil is too wet or too dry (tillage over-pulverizes soil that is too dry). If using a moldboard plow or other inversion implement, make sure not to bring subsoil to the surface.
• Vary the depth and type of tillage to minimize hardpan formation. Relieve hardpan by using a chisel plow in future crop rows or beds, and plow when moderately dry so that the implement effectively fractures the hard layer.
• Retain as much surface residue (cover crops, etc.) as practical for the crop grown, existing weed pressure, and other conditions.
• In general, cultivate shallowly, no deeper than needed to control the weeds.

VI. Primary and Secondary Tillage and No-Till Options

Many organic farmers use more tillage operations than their conventional neighbors. This includes the number of trips across the field and the diversity of tillage operations. Farmers moving through a multicrop rotation will use different techniques based on crop needs. Small direct-seeded crops call for more aggressive secondary tillage and a fine seedbed than do transplanted crops. Multiple cultivations are desirable before planting broadcast or blanket-seeded crops that cannot be mechanically weeded after crop emergence, whereas crops seeded in rows are amenable to postemergence cultivation, mulching, and strip tillage.

Typically, primary tillage operations are determined by the sequence of crops and desired crop planting dates. Before farmers prepare the seedbed they must first kill or incorporate any cover crops, green manures, or amendments. The timing and types of secondary tillage operations used are determined by weed pressure, climate conditions, field status, and crop characteristics. Interest in conservation practices that skip whole-field, preplant tillage, and that substitute mulch or surface residues for weed control, is growing. These techniques are best suited for large-seeded and transplanted crops. Moving from a mulched crop to one that requires a clean seedbed can be difficult in some situations.

• Watch a video about incorporating cover crops and compost with a soil spader from Vegetable Farmers and their Sustainable Tillage Practices featuring Jean-Paul Cortens and Jody Bolluyt, Roxbury Farm, Kinderhook, NY.

This series of photographs was taken on a vegetable farm in Illinois after a heavy rain. (a) Beds were prepared with a spader. A spader had been used one month prior to incorporate a rye cover crop. A flamer will be used 1–2 weeks later before lettuce is transplanted into the bed (b). Hand weeding may be called for before the crop shades the bed (b, c) if weed pressure is high. If weed control is adequate, then lettuce can be cut for harvest and allowed to regrow for a second cutting (d). Figure credit: Michelle Wander, University of Illinois.

Organic farmers typically use a variety of tillage tools for similiar jobs because changes in weather and crop and/or weed growth rates can force them to change strategies with short notice. Owning or having access to multiple tractors and/or implements that are easy to attach and detach helps growers save needed time.

VII. Tillage Glossary

• Bulk density—the mass of dry soil divided by the bulk volume. Bulk density is not an absolute indicator of compaction because root limiting density varies with texture. Root extension is generally limited by bulk densities >1. 6 g/cm³ in silt loam soils; 1.6 g/cm³ is unlikely to be limiting in sandy soils and is severely limiting in clayey soils.
• Cultivation—shallow tillage intended to manage weeds. Can be blind (not guided by crop position) or directed (row crop cultivation—designed to minimize disruption of crop rows). Traditional cultivation equipment does not function well with high residues but high-residue options exist. Actions include undercutting, vibration, and rolling. Can be draft or PTO powered.
• Conservation tillage—any tillage system that maintains 30 percent or more of the soil surface covered with plant residues after planting. Where soil erosion by wind is the primary concern, any system that maintains at least 1,000 pounds per acre of flat, small grain residue equivalent on the surface throughout the critical wind erosion period.
• Conventional tillage (intensive tillage)—full width tillage that disturbs all of the soil surface and is performed prior to and/or during planting. Less than 15 percent of the soil is covered with residue after planting, or less than 500 pounds per acre of small grain residue equivalent throughout the critical wind erosion period. Generally involves inversion of a plow layer or multiple field operations with non-inversion tools. Weed control is accomplished with crop protection products and/or cultivation.
• Critical erosion period—period of the year when most of the erosion of unprotected fields can be expected to occur.
• Crusting—surface compaction resulting from raindrop impact, particle detachment, and size-sorting, leaving the finest soil particles concentrated at the surface. Impedes infiltration, gas exchange, and seedling emergence.
• Dead furrow—a narrow strip of soil (the width of a plow share) that has its plow layer excavated in the process of moldboard plowing but does not get filled in because it is on the outer edge of a field or a “land”. Secondary tillage generally does not completely fill in a dead furrow, leaving a depression and often a zone of low fertility because of topsoil removal. Crops tend to yield poorly when planted in a dead furrow.
• Disks—rolling circular blades that have straight or fluted edges and are intended to cut residues, pulverize soil structure, and/or level the soil surface. Disks are often mounted in groups (gangs) of parallel blades. In a tandem disk harrow, leading and following disk gangs are mounted with opposite angles such that soil is first moved out and then back in. The amount of soil movement caused by disks is related to the angle of the disks, the down pressure on the disks, the design of the blade (straight or fluted), and the speed at which the disks are pulled. Single disks (coulters) designed to cut residues often precede other ground engaging tools in equipment designed for high residue conditions. Disks are often arranged and used to shape beds.
• Draft—power required to pull a draft tillage tool such as a plow or disk a specified distance.
• Draft implement—an implement that requires force to be dragged through the soil.
• Inversion tillage—in contrast with noninversion tillage, inversion tillage flips over a layer (often 6–12”) of soil, burying surface residues (and associated weed seeds, spores, and insect larva and eggs) in the process. The result is a surface with minimal residues that can be easily managed using traditional secondary tillage equipment, but is susceptible to erosion. The moldboard plow is the standard inversion tillage implement. Disk plows also perform inversion tillage.
• Lands—in the context of one way plowing, lands are rectangular sections of a larger field that are plowed one at a time. To start out, a ridge is formed in the center of a land and then plowing occurs around and around this ridge until the land is complete. The purpose of plowing in lands is to minimize running time, that is, time moving between areas to be plowed.
• Minimum till (reduced till)—tillage system that does not involve soil inversion and maintains a high level of surface residue.
• Moldboard plow—traditional primary tillage tool consisting of the following key ground engaging parts: the plow share (slices the soil horizontally), the moldboard (lifts and rolls the soil, bringing about inversion), the landside (transfers the sideways thrust), and the coulter (slices the soil vertically). The coulter is essential if plowing sod or soil with significant residues. The moldboard plow is often the best tool for breaking sod.
• Mulch till—full-width tillage involving one or more tillage trips that disturbs all of the soil surface, and is done prior to and/or during planting, but leaves residues concentrated at the soil surface. Tillage tools such as chisels, field cultivators, disks, sweeps, or blades are used. Weed control is accomplished with crop protection products and/or cultivation.
• No till (zero tillage, direct drilling, or transplanting)—tillage system that maintains residues (even in row) and plants through these residues using specially designed equipment.
• Plastic limit (PL)—the soil moisture content where soil starts to exhibit plastic behavior. As a general rule, a soil is at its plastic limit when a 3 mm diameter soil worm/sausage can first be formed. Soils in which the plastic limit is drier than field capacity have a narrow window of workability. Soils in which the plastic limit is wetter than field capacity have a broader window of workability and are better suited for agriculture that involves tillage.
• Plow pan—compacted layer immediately below the depth of regular tillage. Moldboard plows, disks, and rotary tillers are notorious for creating plow pans.
• Point—the leading edge of a stiff tine. The shape of a point impacts its ability to penetrate and how much lifting and soil disturbance it causes. The front of a plow share is also called a point.
• Primary tillage—tillage used to break or fracture soil for a depth of six or more inches. Primary tillage implements vary in their ability to penetrate high-strength soils and cut through plant residues. Examples include moldboard plows, heavy disks, spading machines, heavy rotary tillers, chisel plows, and subsoilers.
• PTO-powered tillage—in contrast with draft powered tillage implements, such as the moldboard plow, and ground driven rotary tillage, such as the rotary hoe, PTO-powered tillage implements have a greater capacity to pulverize and mix soil structure in one pass because they receive rotary power from a tractor. Rotary tillers, spading machines, rotary harrows, and reciprocating harrows are examples of PTO-powered tillage.
• Puddling—tillage designed to disrupt aggregates and disperse clay, creating an impermeable layer that will perch water. Puddling is a tillage objective in flooded rice systems, but is undesirable in other production systems.
• Ridge till—tillage system that uses cultivation to build or rebuild ridges during the early part of the growing season, and then plants the next crop on ridges that have had the top sliced off during the planting process.
• Rollers—rolling tools that press soil, increasing its density or firmness (e.g., cultipacker), or scarify the soil surface (e.g., Lilliston rolling baskets used for cultivation).
• Roller–crimpers—rolling tools used to knock down and—ideally—kill mature cover crops.
• Secondary tillage—tillage used (generally following primary tillage) to pulverize, level, and/or condition soil less than six inches deep to prepare or “fit” a seed bed.
• Spading machine—a PTO-powered rotary tillage tool that has large flat blades (spades) arranged in sets of 3 on a rotor. Rotary and recipricating spaders are described above. For rotary versions, the spades plunge into the soil, lift the dug soil and then tip to drop off the soil. The system is efficient in power use and gentle on soil structure but requires a complex and thus expensive machine. Normal forward operating speeds are slow (less than 1.5 mph). The degree of soil pulverization achieved depends on the ratio of rotor speed to forward speed, the magnitude of the speeds (rotor and forward), shape and arrangement of the spades, and the positioning of the back flap (upon which the soil will rebound). Spading machines are primarily used in preparing soil for vegetable production and are most widely used and manufactured in Europe.
• Spring tooth plow—acts a lot like a chisel plow but allows shanks to spring back when sufficient resistance is met (such as when striking a rock).
• Strip till/Zone till—tillage system that maintains residues between rows but relocates residues out of the planting row (up to 1/3 of the row spacing) and may involve deep loosening in the row.
• Subsoiling—tillage designed to fracture deep, compacted layers; may or may not be in-row.
• Sweeps—wings that extend out from tines on cultivation equipment to undercut weeds and lift soil causing rapid dessication.
• Tilth—a holistic term referring to favorable soil physical properties for agriculture. Soils with "good tilth" are friable, can be tilled with less draft, and allow tillage objectives to be easily achieved. Similar terms include describing the soil as “mellow”, having good “condition”, or “works like a garden”.
• Tines—straight or curved, stiff or flexible, and varying with respect to angle of soil contact, tines modify soil structure by a range of processes, including, cutting, lifting, and vibration, that transfer draft energy to the soil through the tine. Stiff tines are often referred to as shanks. Tines generally do not create significant down pressure and thus do not compact the soil below the depth of tillage. Flexible tines vibrate as they are pulled through soil and this vibration contributes to the shattering of soil structure.
• Traction—resistance to wheel or track slippage; allows draft to be applied to a pulled implement.
• Vertical tillage—deep tillage designed to create vertical zones of fractured soil (generally in row) that promote more extensive rooting.

VIII. Tillage Resources

The biological farmer: A complete guide to the sustainable & profitable biological system of farming. G. Zimmer. 2000. Acres U.S.A., Austin, TX.

Very readable comprehensive guide to ecological farming by a successful organic farmer, consultant, and founder of Midwest BioAg. Chapter 17 discusses tillage specifically. Zimmer recommends the use of rotary tillers to shallowly incorporate green manures.

Building soils for better crops, 3rd ed. F. Magdoff and H. Van Es. 2009. Building soils for better crops. 3rd ed. Sustainable Agriculture Network Handbook Series Book 2. National Agricultural Laboratory, Beltsville, MD. (Available online at: http://www.sare.org/publications/bsbc/bsbc.pdf) (verified 10 March 2010).

This book provides a comprehensive discussion of sustainable soil management.

Conservation technology information center [Online]. Conservation Technology Information Center, West Lafayette, IN. Available at: https://www.ctic.org/ (verified 27 Jan 2020).

The CTIC website provides access to Partners (a quarterly publication discussing conservation tillage) and results of the National Crop Residue Management Survey (annual county-by-county tillage practice statistics).

Conservation tillage systems and management: Crop residue management with no-till, ridge-till, and mulch-till, 2nd ed. MidWest Plan Service. 2000. Iowa State University, Ames.

Easy to read and handy for reference, this book (the work of more than 60 university and industry specialists) explains the major benefits of conservation tillage. Supplementing descriptions are 199 color drawings and photographs, plus 72 tables with color highlights. Twenty-nine chapters cover all aspects of conservation tillage. Appendices describe tillage implements and offer rainfall and temperature data maps.

From the soil up. D. Schrieffer. 2000. Acres U.S.A., Austin, TX.; and Agriculture in transition. D. Schrieffer. 2000. Acres U.S.A., Austin, TX.

“Eminently readable, still available, and still the best book relating tillage systems to the management of soil aeration, water and the decay of residues” - David Patriquin referring to From the Soil Up.

Green fields forever: The conservation tillage revolution in America. C. E. Little. 1987. Island Press, Washington, DC.

Very readable history of conservation tillage through the mid-80s.

Horsedrawn tillage tools. L. R. Miller. 2003. Small Farmer's Journal, Sisters, OR.

Comprehensive collection of information on the art of horse-powered tillage using plows, discs, harrows, harrow carts, rollers, culti-packers, single row cultivators, and straddle row cultivators. 368 pages with over 1,000 illustrations.

The new American farmer: Profiles of agricultural innovation, 2nd ed. V. Berton. (ed.) 2005. Sustainable Agriculture Network, Beltsville, MD. (Availabe online at: https://www.sare.org/Learning-Center/Books/The-New-American-Farmer-2nd-E...) (verified 27 Jan 2020).

The NAF presents highly readable profiles of 60+ farmers/ranchers representing every state in the US and 2 territories. Lots of practical information about tillage systems can be found by searching the document for terms related to tillage.

Resource management: Soil. Revised ed. B. Davies, D. Eagle, and B. Finney. 2001. Farming Press, Tonbridge, UK.

This book is a practical guide to the principles and practices of good soil husbandry (with several chapters on tillage) written by British authors with a wealth of on-farm experience. Some content is specific to England but most is broadly relevant.

The roller/crimper gallery [Online]. Rodale Institute, Kutztown, PA. Available at: http://www.newfarm.org/depts/notill/roller_gallery/ (verified 16 Dec 2008).

Soil dynamics in tillage and traction. W. R. Gill and G. E. V. Berg. 1967. Agricultural handbook No. 316. Agricultural Research Service, USDA, Washington, DC.

Classic discussion of tillage from an ag engineering perspective.

Focus is on no-till and soil quality benefits.

Steel in the field: A farmers guide to weed management tools. G. Bowman. (ed.) 1997. Sustainable agriculture network handbook series book 2. National Agricultural Laboratory, Beltsville, MD. (Available online at: https://www.sare.org/Learning-Center/Books/Steel-in-the-Field (verified 27 Jan 2020).

"Steel in the Field" shows how today's implements and techniques can control weeds while reducing or eliminating herbicides. In practical language, Steel in the Field presents what farmers and researchers have learned in the last 20 years about cutting weed-control costs through improved cultivation tools, cover crops and new cropping rotations.

Stubble over the soil: The vital role of plant residue in soil management to improve soil quality. C. Crovetto. 1996. American Society of Agronomy, Madison, WI.; and No tillage: The relationship between no tillage, crop residues, plants and soil nutrition. C. Crovetto. 2006. Conservation Technology Information Center, West Lafayette, IN.

Pioneering no-till farmer/agronomist in Chile describes his experiences with no-till in two books which are an interesting mix of agronomic science and practical observations.

Tillage. F. Buckingham. 1993. Fundamentals of machine operation series. John Deere Publishing, Davenport, IA.

Very readable and highly illustrated presentation of practical information about tillage practices used for agronomic crop production.

Tillage equipment pocket identification guide. USDA–NRCS, Washington, DC. (Available online at: http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_007135.pdf (verified 16 Dec 2008).

This graphics rich publication is designed to help NRCS staff recognize general categories of tillage systems and the equipment used for primary tillage, secondary tillage, manure/fertilizer incorporation and combination tools.

IX. References

• Gajri, P. R., V. K. Arora, and S. S. Prihar. 1999. Tillage for sustainable cropping. Food Products Press, Binghampton, NY.
• Ontario Ministry of Agriculture, Food and Rural Affairs. 2008. No-till: Making it work. Best Management Practices Series BMP11E. Government of Ontario, Canada. (Available online at: http://www.omafra.gov.on.ca/english/environment/bmp/no-till.htm) (verified 14 Jan 2009).
• United States Department of Agriculture. 2000. National organic program: Final rule. Codified at 7 C.F.R., part 205. (Available online at: http://www.ecfr.gov/cgi-bin/text-idx?SID=a6a0935ddf00e166695f4c2138bd58d...) (verified 21 Jan 2009).