INFLUENCE OF GREEN MANURING WITH SESBANIA-ROSTRATA AND AESCHYNOMENE AFRASPERA OF UREA ON DYNAMICS AND UPTAKE OF NUTRIENTS BY WETLAND RICE

Nutrient concentrations in the soil and crop uptake from incorporated green manure and urea in flooded rice was studied in field experiments . Release of plant-available nitrogen (NH4+-N) from green manure was s lightly delayed compared with that from prilled urea (PU) because Sesb ania rostrata L. and Aeschynomene afraspera L. released the N graduall y after their decomposition, whereas N became available immediately af ter PU application. Exchangeable NH4+-N concentration in soil peaked a t 163 mg kg(-1) in the transplanted rice (TPR) and 198 mg kg(-1) in br oadcast-seeded rice (BSR) at 0 and 1 week after PU application, Broadc ast-seeded rice depleted NH4+-N faster than did TPR because of the cro p's vigorous growth in the former during the early stage, Soil solutio n NH4+-N followed a similar trend to that of soil NH4+-N. Incorporatio n of S. rostrata and A. afraspera increased the concentration of P, K, Fe2+ and Mn2+ in soil solution more than did the application of PU, However, zinc concentration decreased in all treatments. Both PU and g reen manure increased the N status of the rice plants and enhanced the uptake of P, K, Fe, Mn and Zn by the rice crop, This suggests that ap plication of green manures improves the uptake of these nutrients by t he crop. The highest apparent N recovery was obtained with PU followed by green manure.