SOIL DEGRADATION AFFECTS MICROBIAL BIOMASS CARBON AND DEHYDOGENASE ACTIVITY IN HUMID TROPICAL HILLY FOREST SOILSS.C. TIWARV, S.S. SOROKHAIBAMI, M.S. DKHAR AND R.R. MISHRA
Deforestation for expansion of shifting cultivation and selective logging is the cause of reduced fertility and degradation of hilly forest soils in humid tropical regions of North Eastern India. Studies were conducted by measuring microbial biomass carbon (Cmic) and dehydrogenase (DHA) enzyme activity along with selected physico-chemical properties (bulk density, total organic carbon, pH, and moisture content) to assess microbial activity and fertility level of two soil ecosystems namely., degraded forest (DF) and slightly degraded forest (SDF) soils as compared to a naturally undegraded forest (UDF) soil at 0-20 cm and 20-40 cm soil depths. The C decreased by 20% in SDF and 50% in DF for both soil depths as compared to UDF which had a maximum of 259 mg C g-1 dry soil at 0-20 cm and 137 mg Cg-1 dry soil at 20-40 cm following forest soil disturbance for selective logging and shifting cultivation. DHA also decreased by 25% in SDF site and 40% in DF site for both soil depths as compared to the UDF which had a maximum activity of 112 mg TPF gl dry soil 24 h1. The DHA and C were higher at the surface layer than the subsurface layer in all the three sites. There was statistically significant (p=0.05; 0.01) correlation among microbial biomass carbon, dehydrogenase activity, soil moisture content (SMC), pH and Co content in DF and SDF sites. Analysis of variance of data showed that microbial biomass carbon content, bulk density (BD), pH and total organic carbon varied significantly (p=0.05) in all the three sites. However, dehydrogenase activity and soil moisture content did not vary significantly (p=0.05) among three sites. Microbial biomass carbon being most responsive to forest and soil degradation than dehydrogenase may be used as an indicator of microbial activity and soil fertility in hilly forest soils of humid tropics.
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