Direct and Residual Effects of Organic Sources on Rice Productivity and Soil Quality of Vertisols

A field experiment was conducted on a Vertisol (Typic Pellustert) of the Directorate of Rice Research farm, Hyderabad for three years (2001–02 to 2003–04) to study the influence of organic sources (paddy straw, dhaincha) in combination with chemical fertilizers on productivity and soil quality in irrigated rice-rice system. In the first year, incorporation of green gram only resulted in a significant yield increase of 13% over inorganic fertilizers. From second year onwards, all the organics caused a significant increase of 23–39% in grain yield of rice over fertilizers alone; the treatment where green gram was added, recorded the maximum increase in the grain yield. Residual effect of organics was observed after two years of application. Organic sources improved the soil physical (bulk density and penetration resistance), fertility (soil organic carbon and available Nand K) and biological (soil respiration) parameters over inorganic fertilizers alone. Green gram with moderate C/N ratio and high lignin content (green gram) performed better than wide (straw) and narrow (dhaincha) C/N ratio sources with low lignin content.