Soil Tillage in Organic Farming Systems
Conservation Tillage Systems
The term conservation tillage represents a broad spectrum of tillage systems. These systems are based on the idea that tillage can be limited to the area around the plant and does not have to disturb the entire field. Several conservation tillage systems—no-till, strip till, and ridge till—fit this concept. Among these tillage practices, no-till has a greater potential in sequestering more carbon into the soil than other conservation tillage methods.
No-till is a procedure whereby a crop is planted directly into the soil with no primary or secondary tillage since harvest of the previous crop (See Figure 6.1). The no-till system loosens the soil only in a very narrow and shallow area immediately around the seed zone. In its simplest form, no-till planting is a one-pass operation accomplished with a multi-component implement that slices through surface residue and the top three or four inches of soil, drops seeds into the slot, and squeezes the slot back together over and around the seed, leaving little or no visible evidence that the crop has been planted. This localized disturbance is typically accomplished with a conservation planter (for row crops) or seed drill (for narrow-seeded crops). This system represents the most extreme change from conventional tillage and is most effective in preventing soil erosion and building organic matter.
Strip-till is a conservation tillage system that was developed for row crops grown in heavy, poorly drained cool soils (See Figure 6.2). Strip-till removes the residue from the row area, allowing sunlight to hit the soil surface to warm the soil to increase soil evaporation. As with ridge planting, planting with strip-till takes place in the residue free strips. Strip tillage is designed for row crops in which only a 9 to 12 inch (23 to 30 cm) wide strip is tilled and planted and the ground between rows is left undisturbed. The depth of tillage varies but can vary from 8 to 16 inches (20 to 41 cm) deep, depending on the implement used. This “vertical tillage” approach promotes deeper root growth and water movement.
Benefits of Strip Till
One benefit of strip-till, compared to no-till, is accelerated soil warming and drying of the immediate seedbed area that results from removing residue and disturbing the soil in the berm. Thus, strip-till can have a significant impact on soil temperature, particularly in poorly drained soils and when soil moisture conditions remain relatively near field capacity. In traditional no-till, where planting is done into a narrow slot, harvest can be delayed by as much as two to three weeks in some areas.
Disadvantages of Strip Till
Weeds and weed seeds in the inter-row spaces that would otherwise be buried in a conventional broadcast tillage are not disturbed or displaced in a strip-tillage system, causing increased weed densities early in the season.
Timing of Strip-Till
Strip-till is most effectively accomplished when the soil in the vertical zone that is to be tilled is relatively dry, but not so dry that the strip-till implement brings up large soil clods or bends under the high resistance that can exist in very dry conditions.
A variety of strip-till implements have been developed and are now used for different cropping systems. These implements tend to be either PTO-powered rotary tillers that have been used primarily in vegetable fields or ground-driven shank-coulter tiller implements that have been most commonly and widely used in row crops like corn, soybeans, cotton, sorghum, and sunflower. A shank-coulter tiller (See Figure 6.3) uses a front disk coulter with a depth wheel that cuts through crop residue and vegetation, followed by a subsoiling shank that operates to a depth of about 14 inches (36 cm). A double set of fluted coulters mixes and chops the soil, followed by a clod-crushing basket. When strip tilling in cover crop residue, the coulter should be positioned as far forward of the shank as possible and centered on the shank. This allows the coulter to operate in firm soil enabling it to cut residue ahead of the shank.
Real Time Kinetic Guidance
Strip-till can be implemented without precision guidance tools but most farmers suggest that dollars spent on the most-precise level of accuracy, such as RTK (Real Time Kinetic) guidance, is worth the investment. Effort should be made to plant the crop into the center of tilled strips. RTK guidance technology with sub-inch accuracy helps match up last fall’s tillage and this spring’s planting operations.
Ridge-till is a method of preparing the seedbed and planting on a ridge formed during cultivation of the previous year’s crop (See Figure 6.4). The permanent raised beds are flat and generally 12 to 24 inches (30 to 61 cm) wide and four to six inches (10 to 15 cm) high. Residue-covered areas between the rows alternate with residue-free strips in the row area. Ridges are maintained year-to-year with a cultivator, making ridge plant well suited to continuous row crops like corn, soybeans, cotton, sorghum, and sunflower. Rows remain in the same place each year, and any crop residue on the ridges at planting is pushed between the rows.
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