In search of alternative fertilizers for sustainable agriculture: the sesbania option

Biofertilization with Sesbania rostrata improved the grain yield of rainfed lowland rice by about 1.8 t/ha over that of the control. The same yield level was obtained by the 60 kg N/ha treatment (about 3 bags of urea/ha). Therefore, S. rostrata biofertilization could substitute effectively for 60 kg N/ha applied as urea for rainfed lowland rice. In an upland rice-corn cropping pattern, inoculated S. rostrata resulted in a grain yield equivalent to the application rate of 46 kg N/ha as ammonium sulfate. Under acidic conditions and using the same N rate (60 kg N/ha), the biofertilizers (S. rostrata and P. calcaratus) produced 2.7 times and 1.2 times higher grain yield than that of urea in unlimed and limed soils, respectively. These results implied that in the absence of liming, the biofertilizers can supply the rice plants with essential nutrient elements (probably Ca and Mg) which cannot be supplied by chemical nitrogenous fertilizers. In a corn-corn cropping sequence, the performance of the biofertilizers was comparable with that of the 50 kg N/ha treatment applied as urea. During the dry season, the effectiveness index of the biofertilizer was higher than that of the wet season. However, during the wet season, the combination of urea + biofertilizer showed a marked increase in effectiveness index over the biofertilizer alone. When S. rostrata was intercropped with corn and either the whole plants or the leaves alone were incorporated into corn furrows, the effectiveness index (127 percent) was much higher than that of urea (100 percent). In an on-farm verification trial, the net income from the experimental cropping pattern (S. rostrata-corn-corn) was 50.9 percent higher than that from the farmer's cropping pattern (corn-corn-corn). The average marginal benefit cost ratio (MBCR) was 3.03:1, indicating that for every peso of added investment in the S. rostrata-corn-corn cropping pattern, a net return of two pesos and three centavos was obtained. Since the MBCR requirements for a technology to be economically profitable is only 2:1, S. rostrata biofertilization may be considered economically viable for corn production