Corn (Zea mays L.) is a widely grown crop in the USA that responds positively to crop rotation. This study compares yields of corn grown in continuous monoculture with that of a (i) 2-yr soybean [Glycine max (L.) Merr.]-corn rotation; (ii) a 4-yr soybean-grain sorghum [Sorghum bicolor (L.) Moench]-oat + clover [Avena sativa L. interseeded with 80% Melilotus officinalis (L.) Lam., 20% Trifolium pratense]-corn rotation; and (iii) a 4-yr oat + clover-grain sorghum-soybean-corn rotation. Interactions between crop rotation and N rate were also determined. The study was conducted for 4 yr on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll). Continuous corn produced less grain (5.5 mg ha-1 yr-1) than corn grown in rotation (7.6 Mg ha-1 yr-1 average). Corn following a legume in rotation produced maximum grain yield with 90 kg N ha-1, while continuous corn required at least 180 kg N ha-1, while continuous corn required at least 180 kg N ha-1 for maximum yield. Corn following oat + clover produced maximum yield in a year of above-average precipitation, but this rotation was vulnerable to soil-water deficits. In 3 of 4 yr, corn following soybean in a 4-yr rotation produced more grain than other rotations.
