Quantifying trends in soil microbial biomass carbon (SMBC) under contrasting management conditions is important in understanding the dynamics of soil organic matter (SOM) in soils and in ensuring their sustainable use. Against such a background, a 60-day greenhouse simulation experiment was carried out to study the effects of straw placement, mineral N source, and tillage on SMBC dynamics in two contrasting soils, red soil (Ferrasol) and black soil (Acrisol). The treatments included straw addition + buried (T1); straw addition + mineral N (T2); and straw addition + tillage (T3). Straw was either buried in the soil or placed on the surface. Sampling was done every 15 days. Straw placement, addition of external mineral N sources (Urea, 46 % N) and soil type affected SMBC. SMBC levels decreased with exposure durations (15 days, 30 days, 45 days, and 60 days). Rate of SMBC fixation was more in buried straw than in surface placed straw at all sampling dates in both soils. Addition of an external N source significantly increased SMBC level. Soil pH increased in both soil types, with a greater increase in black soil than in red soil. The study could not, however, statistically account for the effect of tillage on SMBC levels because of the limited effect of our tillage method due to the artificial barrier to mechanical interference supplied by the mesh bags, although differences in absolute values were quite evident between treatments Tl and T3. Quantifying trends in soil microbial biomass carbon (SMBC) under contrasting management conditions is important in understanding the dynamics of soil organic matter (SOM) in soils and in ensuring their sustainable use. Against such a background, a 60-day greenhouse simulation experiment was carried out to study the effects of straw placement, mineral N source, and tillage on SMBC dynamics in two contrasting soils, red soil (Ferrasol) and black soil (Acrisol). The treatments included straw addition + buried Straw was either buried in the soil or placed on the surface. Straw placement, addition of external mineral N sources (Urea, 46% N) SMBC levels decreased with exposure durations (15 days, 30 days, 45 days, and 60 days). Rate of SMBC fixation was more in buried straw than surface placed straw at all sampling dates in both soils. Addition of an ext ernal N source greatly increased SMBC level. Soil pH increased in both soil types, with a greater increase in black soil than in red soil. The study could not, however, statistically account for the effect of tillage on SMBC levels because of the limited effect of our tillage method due to the artificial barrier to mechanical interference supplied by the mesh bags, although differences in absolute values ​​were quite evident between treatments Tl and T3.