For legumes to be considered effective N sources for succeeding crops, they must supply sufficient N and they must release the legume N to fill the demand. Ideally, any N containing material (fertilizer, plant, or animal manure) must be able to produce a large pool of mineral N before the period of rapid N uptake by a crop. If the mineral N pool in soil is produced too early, it can potentially be lost to leaching and/or denitrification. If released too late, it will not benefit the crop, and poses a potential threat to groundwater quality via leaching. This may be a particular problem for winter wheat if the wheat is planted soon after the alfalfa is killed or if the wheat is no-till planted (Kelling et al., 2000). The synchrony of nitrogen released from legumes with crop demand for N has been a concern even with crops such as corn, where N uptake can occur throughout the summer (Stute and Posner, 1995). Using mesh bags, these researchers found that 50% of the N from clover or vetch residue was not yet released by 1 June after spring burial. Since uptake of N by wheat generally precedes this time period, the residue decomposition and crop N need may be out of synchrony. This concern was found to be real with spring wheat no-till planted following spring alfalfa kill in Manitoba where the delayed N release resulted in significantly reduced grain yields in two out of five site years (Mohr et al., 1999).