Soil Conservation

Strip or alley cropping grows alternate strips of different crops in the same field. For example, rows of annual cultivated crops such as corn or potatoes, which have the most potential to cause erosion because of frequent plowing, are rotated with small grains such as oats that allow less erosion, and also with dense perennial grasses and legumes such as lespedeza and clover, which provide the best erosion control because the soil is not disturbed very often.

A combination of contouring and strip cropping provides relatively efficient erosion control and water conservation. Both contour and strip crops can be planted with shrubs and trees, known as windbreaks or shelter-belts, that form perennial, physical barriers to control wind erosion. In addition, shrubs and trees produce litter that increases soil cover, while helping to accumulate soil upslope to eventually develop terraces, and stabilizing the soil with their root systems.

Protective cover cropping and conservation tillage are systems of reduced or no-tillage that leave crop debris covering at least 30% of the soil surface. Crop residues on the surface decompose more slowly than those that are plowed into the soil, and they release nitrogen more uniformly and allow plants to use it more efficiently. Crop residues also reduce wind velocity at the surface, trap eroding soil, and slow down surface and subsurface runoff of water. Residues also attract earthworms to the surface, whose burrows act as drains for the percolation of runoff water during heavy rains. Crop residues also provide insulation that lowers spring and summer soil temperatures, and increases soil moisture by reducing evaporation. In areas that are more productive under irrigation, conservation tillage reduces water requirements by one-third to one-half, compared with conventionally tilled areas.

Degrees of conservation tillage range from no-till, in which the soil is not plowed and seeds are planted by a drilling technique, to varying degrees of tillage. However, during tillage the soil is not completely turned, as it would be if a moldboard plow was used. Weeds and pest insects are controlled using herbicides and insecticides, respectively. Conservation tillage eliminates the need to let fields lie fallow (unplanted) for a year to "rest." Fallow acreage is somewhat prone to soil erosion and to becoming dominated by intruding vegetation.

Another cover approach can provide temporary erosion control, such as that needed at construction sites. When certain chemical substances known as polymers are added to the soil, they form aggregates with the soil particles. These additives have no toxic effect, but stabilize the soil to provide temporary erosion control until a longer-lived plant cover can be established.