These field experiments determine the specific legume species that can best support the N requirement of rice and compared the yield of rice fertilized with field legumes as an organic fertilizer incorporated during the land preparation with that of rice fertilized with inorganic N. The yield responses of rice fertilized with Sesbania rostrate and mungbean were comparable to the yield of rice fertilized inorganic source at the rate of 45-30-30 kg NPK/ha. The result suggests that sesbania and mungbean as green manure have the potential of supplying nitrogen to lowland rain fed rice.