Biomass production, N accumulation, symbiotic effectiveness and mineralization of green manures in relation to yield of wetland grass
1989
Beri, V. | Meelu, O.P. | Khind, C.S. (Punjab Agricultural Univ., Ludhiana (India). Dept. of Soils)
A two year field experiment on Falehpur Sandy loam, Ludhiana, India to determine the effects of sesbania, cowpea clusterbean and sunn hemp as supplements for fertilizer nitrogen in wetland rice. The mean green and dry matter production of shoots of 60-day-old cowpea, sunn hemp, sesbania and clusterbean plants were 24 and 6.9, 21 and 5.4, 20 and 5.0, 17 and 3.8 t/ha respectively. Corresponding N additions through these green manures were 113, 110, 108 and 87 kg/ha respectively. Sesbania had the most nodules and their highest fresh weight per plant, followed by cowpea, sunn hemp and clusterbean. The symbiotic effectiveness of nodules at 15, 25, 35 and 55 days were 55-100, 60-95, 25-95 and 16-50 % in cowpea, sesbania, sunn hemp and clusterbean, respectively. All green manures decomposed rapidly and about 40 % of the added carbon was lost as CO2 in 7-15 days. The mineralization rate constant of green manures was 0.022-0.013/day. A peak in the formation of KCL-extractable NH4+-N from the soils amended with different green manures was observed between 7-15 days period. There was not much difference in the mineralization of N among different green manures. Green manures were found equally effective and resulted in significantly higher rice yield compared to fallow treatments. Rice yield with green manuring alone was comparable to 120 kg N/ha; green manuring with 60 kg N/ha resulted in yields equivalent to 180 kg N/ha. These results indicate a supplementation of 120 kg/ha of fertilizer N with green manuring in rice.
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