Joel Gruver, Western Illinois University
Michelle Wander, University of Illinois
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.
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:
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)].
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.
|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.
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:
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:
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:
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.
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.
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: http://www.conservationinformation.org/ (verified 16 Dec 2008).
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: http://www.sare.org/publications/naf.htm) (verified 16 Dec 2008).
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: http://www.sare.org/publications/steel/index.htm) (verified 11 Dec 2008).
"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.
This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.