Comparative assessment of organic, inorganic and integrated management practices in rice (Oryza sativa)-based cropping system in acid soil of Assam

A field experiment was conducted from 2008–09 to 2014–15 under All India Coordinated Research Project on Integrated Farming System at Assam Agricultural University, Jorhat, Assam, to evaluate the effect of organic (alone), inorganic (alone) and integrated nutrient management on soil properties and productivity of rainfed winter rice (Oryza sativa L.)-toria [Brassica rapa subsp. Dichotoma (Roxb.) Honalt]-blackgram [Vigna mungo (L.) Hepper] system. The highest rice-equivalent yield (8.91 t/ha) was recorded with the application of 100% NPK through organic sources plus intercropping with wheat (Triticum aestivum L.) during the winter (rabi) season and okra [Abelmoschus esculentus (L.) Moench] during the summer. Application of 100% recommended dose of fertilizer (RDF) through FYM, vermicompost and mustard seed-cake in the rice during the rainy (kharif) season, followed by toria + wheat during rabi and blackgram + okra during the summer season resulted in the maximum average uptake of N, P and K (95.5, 20.1 and 84.9 kg/ha respectively). Bacteria, fungi and Actinomycetes counts as well as microbial biomass carbon in soil were the highest (253 × 10⁴, 137 × 10⁴, 195 × 10⁴ and 163.95 μg/g respectively) in the organic management having 100% supply of nutrients through ¹/₃ FYM + ¹/₃ vermicompost + ¹/₃ mustard seed cake (MSC) along with 3.5 kg/ha each of Azospirillum/Azotobacter and phosphate-solubilizing bacteria. The highest dehydrogenase, phosphatase and urease activity in soil was also observed in the same treatment. Full dose of NPK through organic sources to rice-toria-blackgram sequence intercropping with wheat during the winter (rabi) and okra during the summer registered the highest earthworm count (25 numbers per m³).