An incubation study was carried out during 2009-2010 in net house at BHU, Varanasi on alluvial soils, to investigation the consequences of enriching the soil with different organic amendments viz. FYM, sludge, poultry manure, fresh cow dung and Lantana Camera on microbial inhabitant, CO₂ evolution, Soil microbial biomass carbon (SMBC) and C: N ratio of soil at 15,30 and 45 days of incubation (DAI).The results indicated a significant rise in microbial inhabitant, CO₂ evolution, Soil microbial biomass carbon (SMBC) and C: N ratio. Microbial inhabitant under the sludge application (45 DAI) was significantly higher than that gained under other organic materials, while CO₂ evolution, SMBC and C: N ratio was significantly higher under FYM application (45 DAI).Highest soil respiration was reported with FYM followed by sludge and fresh cow dung with increasing incubation periods. Highest value of CO₂ evolution was observed in FYM (28 mg CO₂) at 45 DAI. A marked increase in SMBC was recorded with application of FYM followed by sludge and fresh cow dung. Maximum SMBC occurred (392 µg g^-1 soil) at 45 DAI. Treatment with FYM application found to be efficient in increasing C: N ratio and showed superior over all treatments.