The definition of conservation tillage adopted for this book is the definition given by the Conservation Technology Information Center :
“[Conservation tillage is] any tillage and planting system that covers 30 percent or more of the soil surface with crop residue, after planting, to reduce soil erosion by water. Where soil erosion by wind is the primary concern, any system that maintains at least 1000 pounds per acre of flat, small grain residue equivalent on the surface throughout the critical wind erosion period.”
By this definition, conservation tillage is any tillage practice that builds up crop residues on the soil surface to minimize the impact of water and wind erosion. The 30 percent residue benchmark for water erosion and the 1,000 pounds per acre benchmark for wind erosion are minimum requirements. There are a number of conservation tillage practices [6, 31]:
- No-till: The soil is undisturbed by tillage during the entire year. Crop residues left on the soil surface may be disturbed in strips up to one-third of the row width for planting or drilling seed. Other common terms for no-till include direct seeding, slot planting and zero-till.
- In-row subsoiling: The soil surface and residue are left undisturbed except for strips up to one-third of the row width. Within these strips, soil below the surface is disturbed or loosened using deep-tillage implements. In-row subsoiling is non-inversion tillage. Other names for in-row subsoiling include ripping, row-till and slot-till. Depending on the type of tillage shank used, names for this practice also include paratill or terra-till.
- Strip-till: Strip-till, also called zone tillage, retains a number of the benefits of no-till, but disturbs the row or zone using tillage practices only where the next crop will be planted. The space between the rows is covered with residue. Strip-till improves the seedbed environment, disturbing the soil only in a narrow zone up to 6–8 inches wide and 6–8 inches deep. This tillage practice is commonly done concurrently with planting and can be combined with in-row subsoiling to break up compacted soil layers [18, 20].
- Ridge-till: Specialized planters and cultivators are used to form and retain permanent ridges on which cash crops are grown. Crops are planted on the top of the ridge after removing residue, which is left between ridges. Cultivation is used to form and maintain ridges, and to manage weeds.
The use of conservation tillage requires the management of crop residues on the soil surface. Crop residues, a renewable resource, play a key role in conservation tillage. When crop residues are properly managed they protect soil resources; enhance soil quality; restore degraded ecosystems; improve nutrient cycling; increase water conservation and availability; enhance pest suppression, for example weed and nematode suppression; reduce runoff and leaching of nutrients off-site; and sustain and enhance crop productivity and profitability .
The Natural Resources Conservation Service (NRCS) in the Southeast provides these additional considerations that deal primarily with management of crop residues or other residues :
- Uniformly distribute loose residue in the field. Do not burn residue. A minimum of 30 percent coverage is needed to prevent erosion. Coverage of 50 percent or greater is recommended to conserve soil moisture and increase organic matter.
- Use planters and drills that can plant through untilled residues or into a tilled seedbed prepared using approved implements. Do not disturb more than one-third of the row width when planting or fertilizing.
- Equip combines and harvesting equipment with spreaders that are capable of spreading residue over 80 percent of the header width. The header is the part of the combine that harvests the crop. Limit removal of residue from baling or grazing to retain the recommended amount of residue on the soil surface.
Conservation tillage can be combined with other practices to enhance the soil benefits provided from reducing tillage and increasing soil-surface coverage. Complementary practices include cover crops; crop rotations that optimize biomass production; planting practices that adjust plant populations, such as alter-row spacing to manage residue; and integrated pest management and crop nutrient management that take account of the increased residue on the soil surface . Many of these practices are already used on agricultural lands in the Southeast, as evidenced in Table 1.1. It is the bundling of these types of practices that form the basis of conservation tillage systems.