Crop rotation is reported to increase seed yield of soybean [Glycine max (L.) Merr.], but rotation effects are less pronounced than for cereal crops. This study compares yield of soybean grown in continuous monoculture with that of soybean grown (i) in a 2-yr rotation with corn [Zea mays L.]; (ii) in a 2-yr rotation with grain sorghum [Sorghum bicolor (L.) Moench]; (iii) in a 4-yr grain sorghum-oat + clover [Avena sativa (L.) + 80% Melilotus officinalis (L.) Lam., 20% Trifolium pratense]-corn-soybean rotation; and (iv) in a 4-yr corn-oat + clover-grain sorghum-soybean rotation. Interactions between crop rotation and fertilizer N rate were also determined. The study was conducted for 4 yr on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll) near Mead, NE. Continuous soybean produced less seed (2.4 Mg ha-1) than soybean in rotation (2.7 Mg ha-1 average). Rotations in which soybean followed sorghum in rotation produced higher seed yield (2.8 Mg ha-1) than soybean following corn (2.6 Mg ha-1), mainly because soybean following sorghum responded positively to N applications, while soybean following corn did not.
