Pedogenic processes and fertility constraints across a Basement Complex toposequence in Southwestern Nigeria

Abstract Inadequate soil characterisation and classification remain a major constraint to agricultural development and sustainable land management in Nigeria. This study investigated and taxonomically grouped soils across an area of approximately 12.5 hectares at Olowogbo Village, Akinyele Local Government Area, Ibadan, Oyo State, Nigeria, using the USDA Soil Taxonomy, the WRB framework, and the indigenous classification system of Smyth and Montgomery. Following reconnaissance surveys, five representative profiles (Profile 1 to 5) were identified, excavated, and described. Results showed that soil colour varied from dark yellowish brown (10YR 4/6) at surface horizons to strong brown (7.5YR 5/6) and very pale brown (10YR 7/4) in subsoil horizons. The soils have a high sand fraction, and textural classes ranged from sandy to sandy clay loam. Soil pH ranged from 4.69 to 5.66, organic carbon content from 9.43 to 48.24 g kg⁻¹, while total nitrogen (0.03–0.22 g kg − 1 ), available phosphorus (1.08–6.09 mg kg − 1 ), exchangeable potassium (0.16–0.43 cmol kg − 1 ), and effective cation exchange capacity (3.61–6.29 cmol kg − 1 ) were low. However, percentage base saturation was high (89.98–98.14%) and dominated by calcium and magnessium. The soils were classified as Alfisols, Inceptisols and Entisols in the USDA Soil Taxonomy, equivalent to Lixisols, Fluvisols and Leptosols respectively in the WRB system and to the Ibadan, Jago, Mamu, Iwaji, and Balogun series in the indigenous classification. An integrated soil fertility management strategy is recommended to enhance fertility and correct acidity. This study provides a baseline assessment of soil fertility, land use planning and sustainable agricultural management in study area and similar agroecological zones.