Land use induced variations in soil fertility and physicochemical properties across surface and subsurface layers

Land use change and soil depth are key determinants of soil fertility in tropical highland agroecosystems; however, their interactive effects remain insufficiently quantified in the Ethiopian highlands. This study evaluated the influence of three dominant land use types (forest, grazing, and cultivated cropland) across two soil depth intervals (0–20 cm and 20–40 cm) on selected soil physicochemical properties in the central highlands of Ethiopia. A factorial randomized complete block design (RCBD) was employed, and a total of 18 composite soil samples were collected and analyzed for soil organic carbon (SOC), total nitrogen (TN), available phosphorus (Av. P), cation exchange capacity (CEC), base saturation (BS), and soil pH. Forest soils consistently exhibited significantly (p < 0.05) higher SOC, TN, Av. P, CEC, and BS, along with lower soil acidity, compared with grazing and cultivated land use types. Across all land uses, surface soils (0–20 cm) contained significantly (p < 0.05) higher concentrations of SOC, TN, BS, and CEC than subsurface soils (20–40 cm), reflecting greater organic matter inputs, root activity, and microbial processes in the topsoil. The pronounced decline of these fertility indicators with depth suggests limited vertical transfer of organic inputs and progressive nutrient impoverishment of subsoil layers under continuous cultivation. Overall, the results demonstrate that conversion of forest land to grazing and cultivation adversely alters soil fertility profiles, underscoring the need for integrated soil fertility management and strategic land use planning to sustain agricultural productivity and mitigate land degradation in tropical highland environments.