Short‐Term Impact of Organic Fertilization and Seasonal Variations on Enzymes and Microbial Indices Under Rice–Wheat Rotation

Abstract

The impact of organic fertilization (OF) and seasonal variation on microbial indices was compared with chemical fertilization (CF) and integrated nutrient management (INM) practices under rice–wheat sequence. The field experiments conducted from 2011 to 2013, adopting a split‐plot design, showed that CF practices decreased the soil pH, microbial biomass carbon, and CO2 metabolic quotient but increased the percentage of microbial biomass C to soil organic carbon. Organic fertilization though enhanced the soil organic carbon but resulted in variable microbial responses. Under paddy soil, OF practices registered an increase in dehydrogenase, alkaline phosphatase (ALK), and fluorescein diacetate activity by 35, 169, and 22% in the first, second, and third crop cycle, respectively, compared with CF. However, the ratios of ALK and aryl sulfatase to microbial biomass carbon were higher (0.378 and 0.498, respectively) in INM‐practiced paddy soil compared to 0.364 and 0.447 in OF. Relatively higher soil enzymatic activity titers, basal respiration, microbial biomass carbon in winter wheat compared to summer paddy, indicated a more pronounced effect of season on soil microbial attributes than soil management practices. Though, organic manure could improve the soil quality in tropical agro‐ecosystems, compared to CF but their biannual application was not microbiologically beneficial beyond three rice–wheat crop cycles.