Long-term effects of integrated nutrient management on productivity and soil properties of rice (Oryza sativa)-rice cropping system in coastal Odisha

A long-term experiment was initiated in 1983–84 and continued for 31 years on integrated nutrient management (INM) in rice (Oryza sativa L.)-rice cropping system at Bhubaneswar, Odisha. The study was conducted on sandy loams under irrigated conditions in a permanently laid out plot in randomized block design with 12 treatments and 4 replications. Application of 50% recommended dose of chemical fertilizers (RDF) coupled with 50% recommended N through green manuring of azolla or through FYM to rainy season (kharif) rice followed by supply of 100% RDF through chemical fertilizers to summer rice resulted in higher system yield of 9.07 and 8.75 t/ha/year respectively. This INM treatment was also most sustainable and improved the physico-chemical properties of the soil with respect to bulk density, soil organic carbon, available NPK, microbial biomass carbon and soil nutrient balance. Reduction in RDF by 100, 50 and 25% without supplementing any organic manure reduced system yield by about 52, 23 and 10%, respectively compared to RDF. Reduction in yield due to supplementation of 25 and 50% N through organic sources was to the tune of 10% during initial five years, and the yield gap between RDF and INM practices narrowed down with passage of time. Yield advantage due to supplementation of N through green manuring was noticed after 10 years, whereas that of FYM after 15 years. On the other hand, no yield advantage was observed with supplementation of 25% N through paddy straw even after 31 years. Application of 50% RDF through fertilizers along with 50% recommended N through green manuring of azolla to rainy season (kharif) rice followed by supply of RDF through fertilizers to summer rice recorded the highest system gross returns 1, 11, 870 and net returns 65, 644 with the highest benefit: cost ratio 2.42.