Grass and legume cover crop decomposition rates in no-tillage

Legume cover crops used as no-tillage mulches can reduce soil erosion and potentially contribute supplemental nitrogen to a subsequent crop. The decomposition rate of a chemically-killed legume may affect the availability of this additional nitrogen. Three legumes: hairy vetch (Vicia villosa), crimson clover (Trifolium incarnatum), Austrian winter pea (Pisum sativum), and wheat (Triticum aestivum) were compared as winter cover crops with no-tillage corn receiving 0, 56, 112, 168, or 224 kg N ha^-1. Nylon bags containing each cover type were placed on the soil surface and decomposition rates determined from weight, carbon, and nitrogen loss from the bags over a 16-week period. The experiment consisted of a main plot of five N rates and sub-plot of each winter cover crop. Nitrogen and carbon contents of the cover crops and rate of N fertilization affected mulch decomposition. Mulch decomposition was distinctly different for both years. Carbon and weight losses were greater for wheat residues than the legume residues in 1985, while in 1986 all cover crop residues had similar carbon and weight losses. Hairy vetch vetch had greater N losses over time at all N rates when compared to the other residues. Analysis of yield response curves indicated that legume mulches contributed up to 154 kg N ha^-1.