Soil property variations related to homegarden agroforestry and wheat monocropping across slope positions in central Ethiopia

Agroforestry is widely promoted as a strategy for restoring soil fertility in smallholder systems; however, its capacity to modify topography-driven soil variability remains insufficiently understood. In strongly sloping landscapes, soil properties are largely shaped by erosion–deposition processes, yet it is unclear whether agroforestry systems actively mitigate these gradients or simply benefit from nutrient accumulation in lower slope positions. This study addresses this gap by examining the interactive effects of land use and slope position on soil physicochemical properties in the central Ethiopian highlands. Soil samples (0–30 cm) were collected under homegarden agroforestry (HG) and wheat monocropping (WC) across upper, middle, and lower slope positions using a stratified design. Results showed that both land use and slope position significantly influenced soil properties (p < 0.05), but the magnitude and consistency of slope-related gradients differed markedly between systems. WC exhibited strong spatial differentiation, with pronounced nutrient depletion and increased bulk density on upper slopes and accumulation in lower positions, indicating a system dominated by erosion-driven redistribution. In contrast, HG maintained significantly higher soil organic carbon, cation exchange capacity, and nutrient availability, while exhibiting reduced variability along the slope continuum. These findings demonstrate that agroforestry systems do not merely enhance soil fertility but buffer slope-induced soil heterogeneity through continuous organic inputs, improved soil structure, and biologically mediated nutrient cycling. By partially decoupling soil quality from topographic constraints, HG systems sustain more balanced soil conditions across heterogeneous landscapes. This study advances current understanding by showing that agroforestry functions as a landscape-level regulator of soil processes, rather than solely a plot-level soil improvement practice. Targeted expansion of agroforestry on erosion-prone upper and middle slopes therefore offers a strategic pathway for reducing soil degradation and improving long-term agricultural sustainability in the Ethiopian highlands.