Changes in microbial biomass and activity in relation to shifting cultivation and horticultural practices in subtropical evergreen forest ecosystem of north-east India

The present study conducted in the Nokrek biosphere reserve (BR) of Meghalaya in north-east India aimed at analyzing the impact of human activities such as shifting agriculture ('Jhum') and horticultural practices on temporal and spatial changes in microbial biomass and dehydrogenase and urease activities in soil. Microbial biomass-C (MBC) and -N(MBN) as well as dehydrogenase and urease activities were significantly (P < 0.01) greater in the soils of the undisturbed forest ecosystem in core zone of the BR than the soils under various land use practices in the buffer zone of the BR. The microbial biomass-N in the surface soil layer (0-10 cm) was maximum (285.4 μg g-1) in the undisturbed core zone and minimum (75.1 μg g−1) in the 1-year-old jhum fallow, which was subjected to intense human activities. Similarly, dehydrogenase (TPF released = 0.70 μg g−1 24 h−1) and urease activities (NH4 released = 31.56 μg 100 g−1 6 h−1) were maximum in the undisturbed core zone and minimum (TPF released = 0.37 μg g−1 24 h−1 and NH4 released = 10.78 μg 100 g−1 6 h−1, respectively) in the 1-year-old jhum fallow. Thus, human activities in the buffer zone of the BR were responsible for significant reduction in both microbial biomass-N and enzyme activities. Both these properties showed recovery during regrowth of vegetation on jhum fallows. Microbial biomass-N and enzyme activities declined significantly (P < 0.01) with increasing soil depth at all the sites. Seasonal variations in both microbial biomass-N and enzyme activities at all sites were also significant (P < 0.01) with peak in autumn and trough in winter.