Nineteen-Year Assessment of Nutrient Management on Soil Microbiological and Enzymatic Activities of Inceptisols in Rice-Wheat System

The soil biological properties and productivity of the rice-wheat system were examined after the long-term (19 years) application of chemical fertilizers (100% N, 100% NP, 100% NPK, and 150% NPK) alone and in combination with organic manures (100% NPK+Straw Incorporation (SI), 100% NPK+Green manure (GM), 100% NPK+Farmyard manure (FYM)). The integrated use of inorganic fertilizers and organic manure enhanced rice and wheat grain production by 5-20% and 12-15%, respectively, compared to balanced inorganic fertilization, and by 115% and 250% over the control (without fertilization). Long-term use of 100% NPK+FYM significantly improved the viable count of aerobic bacteria, fungi, actinobacteria, P-solubilizer, pseudomonads, free-living N-fixers, nitrate reducers, and ammonia oxidizers over the unfertilized control. Integrated usage of chemical fertilizer and organic manure increased the activity of soil enzymes such as dehydrogenase, alkaline phosphatase, urease, and protease. Significant relationships were found between the productivity of rice and wheat and soil biological factors such as soil microbial population (P-solubilizer, free-living N-fixer, pseudomonas, aerobic bacteria) and soil enzyme activities (dehydrogenase activity and microbial biomass carbon). The results showed that long-term application of chemical fertilizer and organic manure increased rice-wheat productivity via improving soil microbiological properties and biological functioning.