ROLE OF MICROBIAL BIOMASS IN SOIL NUTRIENT DYNAMICS ALONG A JHUM CYCLE GRADIENT

Abstract

The impact of shifting cultivation (jhum) on soil physicochemical properties and soil microbial biomass at lowland areas (< 260 m asl) of Arunachal Pradesh, north-east India was investigated by comparing fields under three-, five- and 10-yearjhum cycle systems. The pH of the top 0 to 10 cm soil increased after the burn, but gradually decreased during cropping phase. The soil moisture content declined sharply after burning and slowly recovered with time to a level
comparable to a mature forest of the locality. C and N concentrations decreased slightly during cropping but recovered with increasing periods of jhum cycling. Microbial biomass C and N were low in soils after burning but increased diereafter. Contribution of microbial biomass to soil organic C was greater in 10-yearjhum cycle system while their contribution to total Kjeldahl-N was greater in three-year cycle system. Longer fallow periods favoured greater improvement in humus and some nutrients. A jhum cycle of three to five years, now prevalent in the region, is considered short. Soil nutrient depletion was more in three-year jhum cycle systems.