Crop rotations and manure versus agricultural chemicals in dryland grain production

A dryland experiment was initiated on Sharpsburg silty clay loam in 1975 to compare the value of beef feedlot manure and crop rotations with synthetic fertilizer and pesticides. A four-year crop rotation was compared with a corn monoculture. Experimental treatments included a rotation of corn-soybeans-corn-oats/clover with manure; the same rotation with synthetic fertilizer; the same rotation with herbicide and synthetic fertilizer; and continuous corn with herbicide, fertilizer, and insecticide. Yield differences among treatments were found in 1980 through 1983, particularly for corn grain yield. In 1980, a heat and drought stress year, yields of organically grown corn were significantly higher than those of continuous corn. In 1981, an excellent corn year, yields of organically grown corn were significantly lower than on the other treatments. In 1982, a short growing season, yields of continuous corn were significantly lower than on the other treatments. In 1983, again a heat and drought stress year, yields of continuous corn were significantly less than on the other treatments. Soybean yields were comparable for all treatments in 1980 and 1981. Organically grown soybeans yielded significantly less grain than both the other treatments in 1982 and 1983. Oat grain yields were similar for all treatments in 1981, 1982, and 1983. Soil pH, organic matter, P, K, and total N were significantly higher with the organic treatment than with the other treatments in 1980 through 1983.