Nitrogen contribution to wetland rice by green manuring with Sesbania spp. in an alkaline soil

Summary Two annual species of Sesbania, S. aculeata and Sesbania sp. PL Se-17, were field evaluated as green manure for wetland rice in an alkaline soil. The two species were raised as a catch crop during summer in a wheat-rice rotation, and added as 24.7 and 20.8 t ha^–1 of green matter, 116 and 98 kg N ha^–1, respectively, after 45 days of growth. For the optimum green manuring effect on rice grain yield and N uptake, S. aculeata required 5 days of decomposition (after turning in and before rice transplantation), whereas no decomposition period was necessary for Sesbania sp. PL Se-17. The effect on grain yield and N uptake of rice was equivalent to an application of 122 and 78 kg ha^–1 of chemical N, for the two species, respectively. There was no residual effect of the green manuring on the soil N status after rice harvest.