The Effects of Green Manure (Sesbania rostrata) on the Growth and Yield of Rice

Green manuring with an $N_2$-fixing legume crop can meet a substantial portion of rice N requirement and provide organic matter to wetland rice soils to maintain soil fertility. Organic-N fertilizers in the form of flood-tolerant, leguminous, stem-nodulating Sesbania rostrata can be useful alternatives to resource-poor rice farmers if applied as green manure. Therefore, the accumulation of fixed N by this green manure, their effect on the performance and yield of rice was examined. Firstly, root and/or stem nodulation, nitrogen fixation (acetylene-reducing activity), growth and N accumulation of S. rostrata as affected by inoculation site were studied in a pot experiment. The growth and N accumulation of S. rostrata in stem inoculation treatment was the highest. Therefore, stem inoculation method was used for growing S. rostrata to incorporate into the rice soils for the second experiment. In the second experiment, the effects of S. rostrata green manure application on the growth and yield of rice were studied. Green manure treatments (2 and 4 plants $pot^-1$) were compared to urea treatments (40 and 80 kg N $ha^-1$) and no application treatment. Green manure treatments increased dry matter weight and grain weight of rice significantly over urea and no application treatments. All green manure treatments increased N uptake of the plant. It can be concluded that incorporation of green manure legumes can add large amount of biologically fixed N to rice soils. The effective utilization of biomass produced by the stem-nodulating S. rostrata could be an economically viable component of integrated nutrient management for increasing the yield components and yield of rice per unit area