CROP AND SOIL SCIENCES
Cover Crops and Conservation Tillage for Soil Erosion Control on Cropland
The Erosion Problem
Before the introduction of terracing, contour farming, strip tillage, minimum-tillage or no-till crop production, soil losses from tilled and cultivated cropland in Pennsylvania amounted to 9 to 13 tons per acre each year. Because only 4 to 5 tons of soil is produced annually from parent materials, the annual net loss was 5 to 8 tons.
Soil erosion is a natural process that is greatly accelerated by human activity, specifically when vegetation is destroyed or plant residues buried through tillage. At present, the Pennsylvania Clean Streams Law requires growers who till the soil to have conservation plans. Growers who receive USDA benefits are also required to have a conservation compliance plan that should have been fully implemented by 1995. Such plans are intended not only to reduce soil erosion and protect water quality, but also to retain long term soil productivity.
Practices such as contour strip cropping, diversions, grassed waterways, and cropland terraces, promoted during the 1940s and 1950s, reduced soil losses by 50% or more. With the arrival of 2,4-D in 1946 and the rapid adoption of herbicides for weed control in the fifties and sixties, it became possible in the seventies and eighties to control weeds with less tillage. Some crops, such as corn and soybean are now grown without any tillage at all. Because of the plant residues left on the soil surface in no-till, reductions in soil losses of 90% or more are not unusual compared to those of conventional tillage.
Even with such practices, however, many farmers may not be able to grow as much corn or soybean as they would like and still satisfy their conservation compliance plan. An alternative soil-conserving practice is to use a permanent living groundcover into which corn, soybean, small grains, and forages can be planted using minimum-or no-tillage cropping practices. Research on crownvetch as a living mulch has been conducted at Penn State since 1975, and its use for this purpose may be the ultimate soil conservation practice of this century. Further research has shown that birdsfoot trefoil also can be used. These cover crops prevent surface water runoff from ever getting started, virtually eliminating soil erosion and nutrient and pesticide runoff from even the steepest slopes. At the same time, farmers still have the freedom to grow the crops they want in the amount desired with equipment designed for large fields.