Variation of functional diversity of soil microbial community in sub-humid tropical rice-rice cropping system under long-term organic and inorganic fertilization

Abstract

Soil microbial communities play an essential role in maintaining soil fertility and considered as ecolog-ical indicators to evaluate soil health. In the present study, long-term effects of organic and inorganicfertilizers on functional diversity of soil microbial communities, and their correlation with soil organiccarbon, microbial biomass and activities, were observed under sub-humid tropical rice-rice croppingsystem. This experiment comprises six treatments viz. control (plots without application of chemicalfertilizers and farm yard manure), nitrogen (N at the rate of 60 & 80 kg ha−1in wet and dry seasons, respec-tively), nitrogen + phosphorus + potassium (NPK), farm yard manure (FYM), FYM + N and FYM + NPK. Theresults indicated that pH of the soil under the treatments decreased from its initial value, whereas totalorganic carbon increased in FYM-treated plots. Microbial biomass carbon and nitrogen in FYM + NPK wereincreased by 50.0 and 46.4%, respectively as compared to control treatment. Carbon and nitrogen miner-alization; and soil enzyme activities were significantly (p ≤ 0.05) higher in FYM + NPK over control. Theaverage well color development (AWCD) values derived from Biolog®eco-plates followed the order ofFYM + N > FYM > FYM + NPK > NPK > N > Control. Shannon index was greater (p ≤ 0.05) in FYM-treated soilas compared to control and chemical treated soil. Principal component analysis (PCA) indicates a clearseparation of the cluster of treatments with FYM application (FYM and FYM + NPK) and treatments with-out FYM (N and NPK). Shannon index was significantly correlated with available phosphorus (p ≤ 0.002)and carbon mineralization (p ≤ 0.015). Biplot analysis suggested that polymer and amino acid utilizingmicrobes were dominant, irrespective of all treatments. These results revealed that continuous applica-tion of nitrogen fertilizer alone has responded a shift in soil microbial community in the long run anddecreased the functional diversity of microbes. However, application of FYM either alone, or in combina-tion with chemical fertilizers, could restore soil fertility. Moreover, the information generated from thisexperiment though Biolog®may be the first particularly with reference to the dominance of polymer andamino acid utilizing microbes, irrespective of treatments under long-term fertilized paddy soil.