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 5.2). 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 multicomponent 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).
Strip-till is a conservation tillage system that was developed for row crops grown in heavy, poorly drained cool soils (See Figure 5.3). 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.
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 5.4). 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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