UTILIZING LEGUME CROPPING SYSTEMS TO REDUCE NITROGEN-FERTILIZER REQUIREMENTS FOR CONSERVATION-TILLED CORN

The need to reduce production costs has promoted a renewed interest in using legumes as a source of N for non-leguminous summer crops. Development of legume cropping systems which will permit reseeding of winter cover-crop legumes is a promising approach to reducing legume establishment costs. Field studies were conducted in Alabama for 4 yr on Wynnville sandy loam and Dothan fine-sandy loam soils (fine-loamy, siliceous, thermic, Glossic Fragiudults and Plinthic Paleudults, respectively) to determine the effects of both cash crop and winter cover-crop legumes in cropping systems on N fertilizer requirements of corn (Zea mays L.) grown in a conservation-tillage system. On the Wynnville soil, soybean (Glycine max L. Merr.) was more effective in providing early season N, and clover (Trifolium incarnatum L.) in providing late-season N. The system with both soybean and clover resulted in an even more effective contribution of N to corn grain yield, and a higher yield level than that of continuous corn regardless of N fertilizer rate. On the Dothan soil, the benefits of cropping systems were not as pronounced, and the responses were eliminated by N fertilization, suggesting increased yields were due to N and not to a rotation effect. On both soils, in years of adequate and inadequate rainfall, the reseeding crimson clover system, in combination with a soybean-corn rotation consistently produced the highest yields of the systems studied, and provided a 68 to 159 kg N ha-1 fertilizer equivalent for corn.