Long-Term Integrated Farming System Alters Soil Carbon Dynamics across Soil Depths in the Northwestern Himalayan Region of Jammu and Kashmir

Abstract

A decade-long field investigation was carried out at the one-hectare Integrated Farming System (IFS) research model of the AICRP-IFS, Farming System Research Centre, SKUAST-Jammu, Chatha, and at an adjoining farmer’s field representing the existing farming system (EFFS), to characterise the depth-wise (0–15, 15–30, 30–45 and 45–60 cm) distribution of soil organic carbon (SOC), microbial biomass carbon (MBC), total organic carbon (TOC), oxidizable organic carbon fractions, active and passive carbon pools, and carbon management indices under twelve land use systems of the IFS model vis-à-vis EFFS. SOC, MBC and TOC were all significantly higher under boundary plantation intercropped with turmeric (up to 10.15 g kg⁻¹, 175.34 µg g⁻¹ and 28.00 g kg⁻¹, respectively, at the surface) than under the other land uses, and consistently lowest under EFFS (5.33 g kg⁻¹, 84.78 µg g⁻¹ and 16.80 g kg⁻¹). Among the oxidizable carbon fractions, non-labile carbon (Cₙₗ) formed the largest share of total organic carbon in all land uses, followed by very labile (Cᵥₗ), labile (Cₗ) and less labile carbon (Cₗₗ), with boundary plantation recording the highest values of every fraction at every depth. The active carbon pool (Cₐₚ = Cᵥₗ + Cₗ) and passive carbon pool (Cₚₚ = Cₗₗ + Cₙₗ) followed the same land-use ranking, with Cₚₚ exceeding Cₐₚ at every depth in every land use. The sensitivity index at the surface depth was highest for microbial biomass carbon under boundary plantation (106.82%) and lowest for the non-labile carbon fraction across land uses, while the lability index, carbon pool index and carbon management index (CMI) were all highest under boundary plantation at every depth (CMI = 142.56 at 0–15 cm, declining to 51.95 at 45–60 cm) and lowest under EFFS (CMI = 74.82 at 0–15 cm, the reference value). Most carbon fractions and pools decreased with increasing soil depth, while CMI declined consistently across all land uses. These results indicate that a decade-long integration of tree-based (boundary plantation) and fodder components under IFS, supported by vermicompost recycling, builds up both the quantity and the lability-weighted quality of soil organic carbon more effectively than continuous mono-cropping, with clear implications for soil carbon sequestration planning in the North-Western Himalayas.