Synchrony between Legume Nitrogen Release and Corn Demand in the Upper Midwest

Abstract

AbstractIf legume cover crops are to be an effective, environmentally sound N source for corn (Zea mays L.), there must be a synchrony between legume N release and corn demand. A field study was conducted in Wisconsin during 1991 and 1992 that measured the release of legume N throughout the growing season using mesh bags, and compared resultant levels of soil mineral N following legume incorporation to those following fertilizer N applied at the recommended rate (179 kg N ha−1) and a control (no cover crop, no fertilizer) in a conventional tillage (CT) system. Corn N uptake during the growing season was also measured to determine if legume N could meet uptake demands. Hairy vetch (Vicia villosa Roth) and red clover (Trifolium pratense L.) residues decomposed rapidly, releasing half of their N within 4 wk after burial, while very little N was released after 10 wk (corresponding to corn silking). Soil tests indicated an increase in mineral N levels corresponding to legume N release, similar to those following an application of 179 kg ha−1 fertilizer N, occurring before the period of rapid N uptake by corn. Mean corn grain yields of 11.25 Mg ha−1 in 1991 and 10.89 Mg ha−1 in 1992 following the legumes were similar to those produced with 179 kg ha−1 fertilizer N, indicating that, in addition to releasing N in synchrony with the uptake pattern of corn, legumes released N in adequate amounts for corn production. Finally, postharvest levels of potentially leachable soil NO3‐N following the legumes were similar to or less than when following fertilizer. Therefore, legume cover crops can be an effective N source for corn in the Upper Midwest.