Yield and nitrogen response of lowland rice (Oryza sativaL.) toSesbania rostrataandAeschynomene afrasperagreen manure in different marginally productive soils in the Philippines

摘要

Organic-N fertilizers in the form of flood-tolerant, leguminous, stem-nodulatingSesbania rostrataandAeschynomene afrasperamay be useful alternatives to resource-poor rice farmers if applied as green manure. Therefore, the accumulation of N by these green manure species and their effect on the performance and yield of wetland rice (IR 64) was examined at four different sites in Luzon, Philippines. Soils deficient in N, P, and K were selected and compared with the fertile Maahas clay of the International Rice Research Institute (IRRI) at Los Baños. The green manure plants were grown under flooded conditions for 49 days in the wet season of 1987, chopped, and then ploughed in before transplanting rice seedlings. In a second experiment, the effect ofS. rostratagreen manure was studied under rainfed conditions. All green manure treatments were compared to an urea treatment (60 kg N ha−1) and an untreated control. Both legumes developed well, even on the marginally productive soils.S. rostrataaccumulated up to 190 kg N ha−1andA. afrasperaeven accumulated 196 kg N ha−1in the shoots. In all treatments, green manure increased grain yield significantly (P=0.05) over the untreated control, by 1.3–1.7 Mg ha−1. The yields were comparable to those obtained with 60 kg N ha−1of urea fertilizer.S. rostratacaused the highest grain yield, of 6.5 Mg ha−1on the Maahas clay soil of IRRI. The apparent release of exchangeable NH4+-N in the soils after green manuring and the rice grain yield response showed that both green manure species may provide sufficient available N throughout the development of IR 64 in the wet season. In the rainfed marginal soil site, green manure withS. rostrataproduced even higher rice grain yields than urea. Green manure therefore seems particularly attractive for poor farmers on marginally productive soils, at least as a temporary strategy to improve yield and yield