Farmers interested in reducing or eliminating the use of synthetic nitrogen (N) fertilizers from their cropping systems often use the N₂ fixing capabilities of legume green manure crops in their rotations. The dynamics of N mineralization in the soil after a legume crop are complex and are influenced by many environmental factors. For optimum performance, N-supplying legume crops must decompose sufficiently, and at the appropriate time, to contribute adequate amounts of plant-available N to a subsequent N-consuming crop, such as corn. The objectives of this project were to 1) determine the N fertilizer replacement value of two legumes, alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.), when they were intercropped with oats (Avena sativa L.) and incorporated into the soil in the fall or in the spring preceding a corn (Zea mays L.) crop; and 2) quantify the net N mineralization potential of soil amended with alfalfa and red clover residues during the corn phase of a two-year cropping sequence.