Synchrony between Legume Nitrogen Release and Corn Demand in the Upper Midwest
- James K. Stute and
- Joshua L. Posner
If 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 teachable 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.
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