EFFECTIVENESS OF SESBANIA-ROSTRATA AND PHASEOLUS-CALCARATUS AS GREEN MANURE FOR UPLAND RICE GROWN IN ACIDIC

Two field experiments on green manuring were conducted under upland ac idic soil (pH = 4.35) conditions with the following objectives: (1) to determine the influence of inoculation site, P fertilization, and lim ing on the biomass production, N content, N accumulation, and N availa bility of S. rostrata grown in an acidic soil, (2) to compare the effe ctiveness of S. rostrata, P calcaratus and urea as N sources for uplan d rice as affected by liming and N source-sowing time combination, and (3) to assess the effect of liming and N source-sowing time combinati on on % Ndff (N derived from the fertilizer), % Ndfs (N derived from s oil), % FNU (fertilizer N utilization), and FNY or fertilizer N yield (kg N ha(-1)) of upland rice grown in acidic soil. At 2 weeks after in corporating S. rostrata (95 days after lime application), liming signi ficantly increased N availability by more than 2-fold suggesting that the decomposition of S. rostrata by soil microflora was stimulated by lime. Liming, phosphorus application, and inoculation site improved si gnificantly the dry biomass production, N content and N accumulation o f S, rostrata; thus, enhancing its green manuring potential. Regardles s of liming, S. rostrata whether applied at 0 week or 2 weeks before s owing was superior to urea in improving grain and straw yields. P calc aratus when applied at 2 weeks before sowing also produced higher grai n yield than urea. Immediate sowing of upland rice after green manure incorporation did not affect negatively the growth and development of upland rice; hence, farmers could save at least 2 weeks in their cropp ing calendar. N source-sowing time combination had a highly significan t influence on % Ndff, % Ndfs, % FNU, N uptake, and fertilizer N yield of upland rice. However, only N uptake was influenced significantly b y liming. The rice plant obtained significantly higher % Ndfs from the soils treated with green manure than those treated with urea regardle ss of liming. The % FNU and % Ndff from the green manures were 11-37% and 9-25%, respectively. These values are much lower than those obtain ed under continuously flooded soil conditions possibly because of the differences in the organic matter decomposer populations and N loss me chanisms between sloping upland conditions and continuously flooded co nditions.