Evaluation of organic nutrient-management practices in rice (Oryza sativa)-tomato (Lycopersicum esculentum)-okra (Abelmoschus esculentus) system under irrigated conditions

A field experiment was conducted during 2005–06 to 2012–13 on organic nutrient management in rice (Oryza sativa L.)-tomato (Lycopersicum esculentum L.)-okra (Abelmoschus esculentus L.) cropping system under irrigated conditions in a sandy loam soil having pH 5.9 and organic carbon 0.76% at Chiplima, Odisha. Eight treatments comprising 5 organic, 2 integrated and 1 inorganic approach of nutrient management were evaluated with 3 replications. Organic source of nutrient supply reduced the system yield by 5.5–12.7% compared to the inorganic source in the first year. However, the mean system yield of ‘conversion period’ (first 3 cropping system cycles) with organic treatment comprising supply of one-third N each through farmyard manure (FYM), green manuring of dhaincha (Sesbania cannabina) or vermicompost and neem oilcake + Azospirillum or Azotobacter + phosphorus solubilizing bacteria (PSB) was at par with inorganic and integrated approach. The mean system yield from fourth to eighth cropping system cycles (‘after conversion period’) with organic source of nutrient supply, i.e. FYM + green manuring or vermicompost + neem oilcake + Azospirillum or Azotobacter + PSB was significantly higher (12%) than that of with inorganic source of nutrient supply, i.e. 100% NPK + ZnSO₄ @ 25 kg/ha to rice and 100% NPK + gypsum @ 110 kg/ha + borax @ 10 kg/ha + ammonium molybdate @ 0.8 kg/ha to both tomato and okra. The organic nutrient-management package increased the soil organic carbon and available N, P and K at the end of eighth cropping system cycle over the initial and the buildup was maximum in the soil applied with one-third N each through FYM, dhaincha/vermicompost and neem oilcake + Azospirillum/Azotobacter + PSB. The microbial population in terms of colony-forming units increased in a higher rate in soils with organic nutrient-supply system (bacteria 32.4 to 37.1%, fungi 30.2 to 34.4% and actinomycetes 29.3 to 35.9%) compared to the inorganic source of nutrient supply system (bacteria 11.2%, fungi 5.5% and actinomycetes 11.3%) after eighth cropping system cycle over initial status. The microbial biomass carbon of the soils with organic sources of nutrient supply was enhanced considerably (53.4% to 61.8%) over the initial level (104.7 to 118.2 μg C/g).