The ability of legumes to supply nitrogen to succeeding crops has been recognized for many years. The amount of actual N available will depend on the amount of N in the alfalfa and its availability, and any additional soil N that may be released due to the growth of the legume. From a practical standpoint, however, it is not the amount of N added to the system that is of primary importance. Much more important is the amount of N not needed by the com when the com is grown following the legume. This approach, commonly called the nitrogen fertilizer replacement value, integrates the N directly made available from the legume with the nitrogen provided from other sources, such as the stimulation of easily-released soil N, into a single value. From the Wisconsin perspective and for this paper, although we use the term nitrogen fertilizer replacement value and legume nitrogen credit interchangeably, we actually are referring to the fertilizer replacement value.