Rotational vs. Nitrogen-Fixing Influence of Soybean on Corn Grain and Silage Yield and Nitrogen Use

Abstract

Corn (Zea mays L.) grain yields generally are higher when planted following soybean [Glycine max. (L.) Merr.] as opposed to continuous corn. Many factors have been hypothesized to explain this phenomenon, including enhanced N availability following soybean. The purpose of this study was to separate the N 2 -fixing contribution from the rotational effect of soybean on corn yield using nodulating and non-nodulating soybean and to determine whether increased rates of N fertilizer could compensate for a previous crop of soybean. A field experiment was conducted for 4 yr (1991-1994) at Arlington, WI, on a Plano silt loam soil (fine-silty, mixed, mesic Typic Argiudolls). Corn, nodulating soybean, and non-nodulating soybean were planted in 1991 and 1992 and corn was planted in all plots in 1993 and 1994. In 1992 and 1993, three N rates of 0, 80, and 160 lb/acre were applied to both corn and soybean plots. Corn for grain and silage, without added N, preceded by either nodulating or non-nodulating soybean, outyielded continuous corn by an average of 46 bu/acre and 2.1 tons/acre, respectively. Nitrogen removal in corn grain and silage increased following nodulating and non-nodulating soybean as compared with continuous corn. Continuous corn yield with 80 lb N/acre was the same as corn following nodulating or non-nodulating soybean without added N, but 160 lb N/acre did not compensate for the crop rotation effect. Second year corn grain and silage yields following soybean averaged 15 bu/acre and 0.9 tons/acre greater, respectively, than continuous corn and the addition of 160 lb N/acre compensated for the previous crop advantage. When corn was planted the third year after soybean, the influence of previous crop was still present, but the rotation benefits to corn disappeared with added N. The results of this study demonstrate that a corn-soybean rotation enhances corn yields, however the N 2 -fixing ability of nodulating soybean does not appear to be responsible for the observed rotation effect.