Swine manure application to nodulating and nonnodulating soybean

Manure has traditionally been applied to corn (Zea mays L.), but as livestock operations expand, there are not always sufficient corn acres to minimize the environmental impact of the manure load. Our objective was to evaluate soybean [Glycine max (L.) Merr.] as a reasonable alternative crop to receive manure applications. Impact of manure applications on soybean was measured by evaluating seed yield, N accumulation, and soil NO₃-N at six locations in southern Minnesota in 1996 and 1997. Whole-plot treatments included a control, five liquid swine (Sus scrofa) manure rates (100, 200, 300, 400, and 500 kg N ha^-1), and four NH₄NO₃ rates (84, 168, 252, and 336 kg N ha^-1). Split-plot treatments were two soybean isolines (a segregating row of an Altona x Chippewa with rj1 gene cross), one nodulating and one nonnodulating isoline. Maximum seed yield (2.3 Mg ha^-1) was obtained for the nodulating isoline regardless of manure or fertilizer treatment. Average N accumulation in the nodulating isoline with manure treatment was about 202 kg N ha^-1. This was about 11 kg N ha^-1 greater than the nodulating isollne with fertilizer treatment. There were no adverse agronomic effects of applying manure to soybean. At N applications greater titan plant N accumulation, postharvest soil NO₃-N (0-120 cm) ranged from 80 to 158 kg N ha^-1. Manure applied to soybean at available N rates equal to or less than the amount of N accumulated in the crop appeared to be agronomically and environmentally sound.