Soil Organic Carbon Content Under Different Land Use Systems in Kwara State, North Central Nigeria

This study investigates soil organic carbon content under contrasting land use systems in Kwara State, located in Nigeria's North Central geopolitical zone. Soil organic carbon is a central indicator of soil health, influencing nutrient cycling, water retention, and soil biological activity, and its depletion under agricultural use is a widely documented concern across Nigeria's derived savanna landscapes. Using a cross-sectional comparative design, composite soil samples were collected at 0 to 20 cm and 20 to 40 cm Soil Sciencehs from five land use types: natural forest, bush fallow, continuous arable cultivation, agroforestry parkland, and irrigated vegetable plots. Three replicate sampling sites were established for each land use type in Ilorin East and Moro local government areas. Organic carbon was determined by the Walkley-Black wet oxidation method, total nitrogen by the Kjeldahl method, and the carbon-to-nitrogen ratio was calculated for each treatment. Findings revealed that natural forest soils contained the highest organic carbon (3.2%) while continuous arable plots showed the lowest (0.7%), representing a 78 percent depletion relative to forest reference levels. Agroforestry parkland maintained intermediate organic carbon levels of 1.9 percent, suggesting that tree retention within farmland significantly buffers carbon losses. The study recommends the promotion of agroforestry systems and the incorporation of crop residues as priority strategies for organic carbon restoration in Kwara State farmlands. Keywords: soil organic carbon, land use, Kwara State, agroforestry, carbon depletion.