Evaluation of Rice-Rice System on Grain Yield, Chemical, and Biological Properties of an Acid Inceptisols

Abstract

Soil microbial population, microbial biomass carbon (MBC), enzyme activities, available nitrogen (N), phosphorus (P) and potassium (K) contents were evaluated in an acidic Inceptisols (udic Ustochrept) after five crop cycles of rice-rice system, fertilized with mineral fertilizer alone or in combination with farmyard manure (FYM). The studied long-term manured treatments included 100% N, 100% NP, 100% NPK, 100% NPK+FYM (5 t ha-1) and an unmanured control. Soils of fertilized plots showed a higher microbial activity in terms of microbial population, MBC and enzymic activities than those under unfertilized control which exihibited a fall from the initial value of the experiment. The microbial activity in the fertilized plots decreased in the order of NPK+FYM > NP > N > NPK. Lower activity in 100% NPK than 100% NP demonstrated the negative impact of K and higher activity in 100% NP treatment than 100% N showed the positive impact of P on microbial activity. Between N and P, the effect of former was more pronounced than that of the latter. Highest activity in 100% NPK+FYM treatment was due to the high positive effect of FYM that overrode the negative effect of K. Highest soil organic matter with favourable pH and available N, P and K were recorded under integrated use of FYM and chemical fertilizers. Continuously unmanured soils showed a very low levels of available N, P and K where N and P levels measured lower values than the initial levels. The soils with higher microbial activity recorded higher yield and were more sustainable.