Effects of Land Use and Soil Depth on Organic Carbon Fractionation in Tropical Savanna Soils of Gashaka Local Government Area, Taraba State, Nigeria

Abstract

Understanding how land use and soil depth regulate organic carbon fractionation is critical for improving carbon stabilization strategies in tropical savanna ecosystems. This study evaluated the effects of forestland, grassland, and farmland and two soil depths (0–20 and 20–50 cm) on total organic carbon (TOC), particulate organic carbon (POC), and mineral-associated organic carbon (MOC) in sandy loam soils of northeastern Nigeria. Land use significantly influenced TOC (p = 0.0004) and MOC (p = 0.006), with grassland recording the highest TOC (1.46%) and MOC (1.04%). In contrast, POC did not differ significantly among land uses (p = 0.895). Soil depth exerted stronger control on carbon distribution, with TOC declining from 1.62% at 0–20 cm to 1.21% at 20–50 cm (p < 0.0001). POC exhibited pronounced surface stratification (0.46% vs 0.38%), while MOC remained the dominant fraction at both depths, accounting for approximately 69–72% of total SOC. The findings indicate that depth exerts a greater influence on SOC variability than land use, while land use primarily regulates stabilized carbon pools. Mineral-associated fractions govern carbon persistence in these sandy loam savanna soils, highlighting the importance of management strategies that promote organo-mineral interactions for long-term carbon sequestration.