Land Use-Driven Changes in Soil Quality across Eastern Himalayan Hill Ecosystems of Assam, India

Abstract

Soil quality under six major land-use systems in the hill zone of Assam, Eastern Himalayas, was assessed during 2018–2021 using a Principal Component Analysis (PCA)-based Soil Quality Index (SQI) derived from a minimum data set. Profile-weighted mean SQI values were highest under natural forest (0.81), followed by home garden (0.72), rubber plantation (0.70), shifting cultivation (Jhum land) (0.62), bamboo plantation (0.59), and rice/maize cropland (0.49). Accordingly, forest soils were classified as good (SQI > 0.75), cropland soils as poor (SQI < 0.50), and soils under shifting cultivation, rubber, bamboo, and homegarden systems as medium (SQI 0.50–0.75). The PCA-based minimum data set comprised nine indicators: soil organic carbon (SOC), cation exchange capacity (CEC), soil pH, water-stable aggregates (WSA), mean weight diameter (MWD), available phosphorus, microbial biomass carbon (MBC), and exchangeable calcium and magnesium. Indicator contribution analysis revealed that declines in SOC (26.32–39.29%) and soil structural stability (40.48–52.46%) were the dominant factors driving soil quality degradation. Tree-based land-use systems, particularly natural forests and diversified home gardens, were more effective in maintaining soil quality than annual cropping systems, highlighting the potential of agroforestry interventions for sustainable soil management in the Eastern Himalayan region.