Characterization and Classification of Acidic Soils in the Akuma Watershed, Tocha District, Dawuro Zone, Southwestern Ethiopia

Topographic variation strongly influences soil development, fertility, and sustainable land management in the Ethiopian highlands. This study characterized the morphological, physical, and chemical properties of soils along an upper-middle-lower slope toposequence in the Akuma Watershed, southwestern Ethiopia. The results demonstrated clear topographic effects on soil development and fertility. Upper slope soils were clayey, well-drained, and strongly acidic (pH 4.76–4.83), with higher exchangeable acidity and lower concentrations of exchangeable base cations. Middle slope soils exhibited intermediate physical and chemical characteristics, reflecting transitional pedogenic conditions. Lower slope soils showed greater accumulation of organic carbon, exchangeable Ca and Mg, and relatively higher pH values (5.20–5.60), indicating the depositional enrichment of nutrients and finer materials. Bulk density generally increased and total porosity decreased with depth across all profiles. According to WRB, the soils were classified as Dystric Acrisol on the upper slope, Dystric Nitisol on the middle slope, and Dystric Fluvisol on the lower slope, reflecting contrasting pedogenic processes associated with landscape position. The observed acidity gradient from upper to lower slopes confirms that topography governs nutrient redistribution, soil development, and fertility status within the watershed. These findings provide baseline information for site-specific soil management and indicate that liming and erosion control should be prioritized on upper slopes, integrated nutrient management on middle slopes, and conservation of organic matter and balanced fertilization on lower slopes to improve agricultural productivity and sustain soil resources.