Effects of Soil Organic Matter Fractions on Some Selected Physical and Chemical Properties of Forest Soils in Gashaka Local Government Area, Taraba State, Nigeria

Abstract

Soil organic matter fractions provide important insights into the mechanisms regulating soil carbon stabilization and nutrient dynamics in tropical ecosystems. This study investigated the distribution of soil organic carbon fractions and their relationships with selected soil physical and chemical properties in forest soils of Gashaka Local Government Area, Taraba State, Nigeria. Soil samples were collected from twenty-five auger sampling points at two depths (0–20 cm and 20–50 cm) using a systematic sampling approach within a 100-hectare forestland. A total of fifty soil samples were analyzed for total organic carbon (TOC), particulate organic carbon (POC), mineral-associated organic carbon (MOC), and selected soil physical & chemical properties using standard laboratory procedures. The results revealed clear vertical stratification of soil organic carbon fractions, with higher concentrations observed in the surface soil depth. Total organic carbon declined from 1.62% in the 0–20 cm depth to 1.21% in the 20–50 cm depth, while particulate organic carbon decreased from 0.46% to 0.38% with increasing soil depth. Mineral-associated organic carbon constituted the dominant carbon pool, accounting for approximately 71–73% of total organic carbon. The reduction in soil organic carbon fractions with depth corresponded with increases in bulk density and reductions in soil porosity, water holding capacity, and nutrient status. Surface soils with higher organic carbon concentrations also recorded greater total nitrogen and cation exchange capacity.  The findings highlight the importance of vegetation-derived organic inputs and organo-mineral interactions in regulating carbon stabilization and sustaining soil productivity in tropical savanna ecosystems.