Soil Carbon Stock Assessment in the Derived Savanna Soils of Benue State Under Different Land Use Systems

Soil organic carbon stocks in the derived savanna soils of Benue State, North Central Nigeria, are sensitive to land use change and represent an important component of Nigeria's greenhouse gas inventory, yet quantitative assessments distinguishing the impacts of different land management systems on soil carbon remain limited for this region. This study assesses soil organic carbon stocks across five land use systems, including continuous cropping, fallowed land, agroforestry, degraded pasture, and riparian forest, in Benue State derived savanna soils. A systematic sampling design stratified by land use type and soil mapping unit yielded two hundred and seventy soil samples from three depth increments to one metre. Total organic carbon was determined by the Walkley-Black wet oxidation method calibrated against high-temperature combustion analysis. Bulk density was measured on undisturbed cores to compute organic carbon stocks per unit area at each depth increment. The study applies analysis of variance and post-hoc Tukey tests to determine statistically significant differences in carbon stocks between land use systems. Depth-weighted organic carbon stock estimates are compared against literature values for comparable West African savanna soils. Multiple regression analysis identifies the soil texture, clay mineralogy, and mean annual rainfall as the strongest predictors of organic carbon variability after controlling for land use effects. Results are communicated to the Benue State Agricultural Development Programme and the National Agricultural Land Development Agency. Keywords: soil organic carbon, land use, derived savanna, Benue State, carbon stocks.