Soybean Residual Effects on a Subsequent Maize Crop

Maize (Zea mays 1.) grown after soybean (Glycine max 1. Merr.) consistently performs better than maize that follows itself (second year maize), irrespective of nitrogen fertilization. In previous studies of the soybean-maize rotation, there never has been an evaluation of the potentially different effects of soybean genotypes on following maize. A two-year, soybean maize rotation was initiated in Ames at 1988 with the first year planted to various soybean genotypes, a maize hybrid, and oat (Avena sativa 1.). These were followed in the second year by a single maize hybrid with 0, 80, 160, and 240 kg/ha N fertilization levels. Results are based on three repetitions of this cycle. Averaged over all years and N rates, maize after nodulated soybean and oat yielded 1270 and 1570 kg/ha, 16 and 20% respectively, more than second-year maize. Second-year maize was delayed in silking by 4 days. Though soybean returned 60 to 70 kg/ha of N to the soil in vegetative residue, there seemed to be no net N contribution from soybean to maize because soybean benefited maize less at zero N than did unharvested oat. Soybean evidently returns to the soil less N than is mineralized from soil organic matter during a cropping year. Prior soybean and oat both benefited maize even under the highest nitrogen fertilization rate. BSR 201 soybean benefited maize more than did the other soybean cultivars or oat. Averaged for years and the two highest N rates, BSR 201 benefited maize 680 kg/ha (ca 11 bu/A) more than all the other nodulated soybean genotypes averaged. The BSR 201 effect, however, was not consistent, occurring in two of the three years. Work is continuing using other BSR types