Soil organic carbon and its labile pools as modulated by soil microbes under different land use practices in Typic Ustochrepts.

Rainfed lower Himalayas are being faced by soil degradation due to change in land use practices which in turn influence the carbon (C) inputs into the soil and microbial activities. A study was carried out to evaluate the labile organic C pools, soil enzymes and microbial indices in the dominating land use practices of the region. There were six land uses practices viz. forestry, agroforestry, silvipastoral, horticulture, agro-horticulture and agriculture. Soil samples were collected from three depths 0–5, 5–10, 10–15 cm for the labile C pools and the microbial activities were studied for 0–15 cm soil layer. The labile organic C pools viz. permanganate-oxidizable carbon (POXC), microbial biomass C (MBC), cold water extractable organic carbon (CWEOC) and carbohydrate carbon (CHO-C) content were significantly higher in soils under forestry (1.46 g kg⁻¹, 0.227 g kg⁻¹, 80 µg g⁻¹, 389 µg g⁻¹, respectively) and silvipastoral (1.15 g kg⁻¹, 0.193 g kg⁻¹, 70.7 µg g⁻¹, 379 µg g⁻¹, respectively) land uses and was lowest in soils under agriculture (0.88 g kg⁻¹, 0.115 g kg⁻¹, 56 µg g⁻¹, 310 µg g⁻¹, respectively). The labile C pools decreased with the increase in soil depth and the decrease being higher in soils under forestry. The microbial quotient (qmic) decreased on moving from forestry to other land uses and the decrease was highest in soils under agriculture by 38.6%. However, the metabolic quotient was highest in soils under agriculture (0.175 μg CO₂-C day⁻¹ μg biomass C⁻¹) and lowest in soils under forestry (0.128 μg CO₂-C day⁻¹ μg biomass C⁻¹). The metabolic potential was highest in soils under agroforestry (0.046 μg TPF h⁻¹ μg C⁻¹). Principal component analysis identified qmic and MBC as the most dominant and reliable indicators for the assessment of soil quality under different land uses. The results indicate that under rainfed conditions, silvipastoral land use seems to be comparable to forestry in influencing the microbial indices, labile C pools and C stock. [ABSTRACT FROM AUTHOR]