Residual nitrogen from Sesbania rostrata and inorganic fertilizer in rice-tobacco sequential cropping

The study was undertaken to determine the direct effect of Sesbania rostrata (green manure) and inorganic N fertilizer on rainfed lowland rice and their residual N to succeeding flue-cured tobacco, identifying the economic benefits derived from green manuring and inorganic N fertilization in a rice-tobacco sequential cropping. Flue-cured tobacco (cv Coker 254) at three levels of N (0, 40 and 80 kg N/ha) was planted after transplanted rice at four levels of N (0, 40, 80 and 120 kg N/ha) with and without green manure. A combined analysis of variance using strip plot design was used. Sesbania rostrata (green manure) accumulated 101 kg N/ha and dry matter production of 4.9 t/ha. There was a significant interaction between green manuring and N level on dry matter production, number of productive tillers and grain yield but not on plant height, N concentration of straw and grain and N uptake. Green manure in combination with 40 kg N ha-1 had similar yield with the application of 80 kg/ha inorganic N fertilizer. The increase in grain yield with green manure regardless of N level was associated with greater number of productive tillers and high dry matter yield. The N level applied to tobacco significantly affected yield, plant height, leaf area, specific leaf weight, nitrogen uptake and nicotine except the number of harvested leaves and reducing sugar content. Cured leaf yield, height, leaf area and nicotine content increased with N level. On the other hand, specific leaf weight and grade index decreased with N level. Yields of tobacco from residual N of S. rostrata and S. rostrata plus inorganic N applied to rice were greater than those with inorganic N. The slightly higher yield in S. rostrata alone than in S. rostrata plus inorganic N, however was not slightly different. There was a slight contribution of N from S. rostrata as indicated by the higher cured leaf yield when green manure was applied. The requirement for optimum yield of tobacco despite the green manure and inorganic N applied to the previous rice crop is about 40 kg N/ha