Interactive effects of land use, toposequence, and soil depth on soil quality and soil organic carbon stocks in northwestern Ethiopia

Land-use change, topography, and soil depth are key controls of soil quality and soil organic carbon (SOC) dynamics in semi-arid agroecosystems, yet their combined effects remain insufficiently quantified in the Northwestern Lowlands of Ethiopia. This study integrated soil physicochemical analyses, principal component analysis (PCA), and a Soil Quality Index (SQI) approach to evaluate spatial and vertical variability in soil properties across contrasting land-use systems and slope positions. Soil samples were collected from replicated plots representing different land-use types and topographic positions to ensure representative spatial coverage. Results indicated that land use and topography significantly influenced SOC, soil physical properties, and nutrient status ( p < 0.05). Forest and grassland soils exhibited higher SOC stocks and SQI values than cultivated and bare lands, reflecting lower disturbance intensity and greater organic matter inputs. SOC and SQI consistently decreased along slope gradients, indicating erosion-driven redistribution and reduced organic carbon inputs in downslope and degraded positions. PCA identified soil organic matter, structural properties, and nutrient availability as the main drivers of soil variability, explaining 78.3% of the total variance. The close agreement between PCA-derived indicators and SQI patterns highlights the robustness of multivariate approaches for soil quality assessment. Overall, land-use change emerged as the primary driver of soil quality variation, while topographic position modulated SOC redistribution and nutrient dynamics. These findings indicate that intensified cultivation in dryland systems accelerates SOC depletion and soil functional decline, increasing vulnerability to climatic variability and environmental stresses. The PCA-based SQI framework provides a practical tool for soil quality assessment and supports targeted land management and restoration strategies in semi-arid landscapes.