The ability of legumes to supply nitrogen to succeeding crops has been recognized for many years. The actual amount of 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, farmers need to know how much nitrogen fertilizer they should apply when the crop 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.