Green manure legume crops can often meet much of the nitrogen (N) demand of a crop. There may be, however, an asynchrony between N mineralization from green manures and crop N uptake, resulting in substantial nitrogen loss through leaching or denitrification. In our research, we hypothesize that the synchrony between N mineralization and crop N uptake can be improved by manipulating the termination date of the hairy vetch (Vicia villosa) and the sowing date of the corn (Zea mays) in the spring. This will regulate the quality and quantity of the N in the vetch, the rate of N mineralization from the vetch residues, and the relative rate of N uptake in the corn. Field experiments have been implemented that will evaluate three vetch termination dates on soil N availability and corn N uptake. In addition, the effects of the C/N ratio of the hairy vetch residues on N uptake by the corn will also be considered. We anticipate that these experiments will provide help provide management guidelines to improve the N-use efficiency of green manure systems and reduce nitrogen pollution.