Abstract
Field investigations were carried out on a sandy loam soil (Typic Ustochrept) to study the yield response of rice to green manuring with Sesbania aculeata, Vigna sinensis (common cowpea), and Crotalaria juncea (Sann hemp) grown for 40, 50, and 60 days between harvesting of wheat and transplanting of paddy with a view to improving the N economy for rice and increasing the productivity of a rice-wheat cropping system. Nitrogen accumulation in tops of Crotalaria at 40, 50, and 60 days after planting (DAP) was 84, 98, and 101 kg ha-1, respectively, which were higher than the corresponding values in cowpea and Sesbania. Mean rice yield response with green manuring at 60 kg N ha-1 was 2.6 t ha-1. Rice yields obtained at 60 kg N ha-1 with green manuring of either Crotalaria or cowpea or Sesbania incorporated at 40 or 50 or 60 DAP were higher than yields obtained at 120 kg N ha-1 without green manuring, indicating a substitution of 60 kg N ha-1 for rice. Highest agronomic efficiency of green manure N (rice grain response kg-1 N added through green manure) was recorded in the green manure crop 40 DAP and lowest at 60 DAP. The residual effects of green manuring can under some conditions significantly increase the yield of wheat grown after rice due to an increase in organic content of the soil. Studies thus reveal that incorporation of a green manure crop (Crotalaria or cowpea or Sesbania) even at 40 DAP, one day before transplanting of paddy, results in a saving of 60 kg N ha-1 for paddy and higher productivity of a rice-wheat cropping system.
