GRAIN-YIELD RESPONSES IN RICE TO 8 TROPICAL GREEN MANURES

Eight legume species were evaluated as substitutes for fertilizer N fo r wet season (WS) rice in the Philippines. The above-ground biomass of Sesbania cannabina accumulated mean maximum N (84-199 kg ha-1) and in digo accumulated the least N (8-84 kg ha-1) in 30-60 days. Mungbean an d cowpea, which produced grain and crop residue, are potential dual-pu rpose grain and green manure species. Regardless of species, mean rice grain yield from green manures was 4.0 t ha-1 in 1984 and 4.6 t ha-1 in 1985, comparable with 4.1 t ha-1 from 50 kg fertilizer N in 1984 an d 4.7 t ha-1 from 105 kg fertilizer N ha-1 in 1985. In both years, 60- day Sesbania and Crotalaria accumulated N in excess of the rice crop r equirement. Residual effects from green manures on dry season (DS) ric e were not significant in 1984 but were significant from Sesbania gree n manure in 1985. Soil organic C and total N were also significantly h igher after Sesbania and Crotalaria than after other green manures or fertilizer N treatments.