Examining the Research Gap in Soil Carbon Sequestration Potential Under Different Land Use Systems in the Middle Belt

Soil carbon sequestration through improved agricultural land management can simultaneously improve soil fertility and contribute to climate change mitigation, but the sequestration potential under different land use systems in the specific savanna-forest transition ecology of Nigeria's Middle Belt has been inadequately quantified. This study examined the research gap in soil carbon sequestration studies in the Middle Belt and conducted original measurements across five land use systems (continuous arable, agroforestry, rotational fallowing, permanent pasture, and natural forest reference) in Benue and Kogi States. A scoping review of seven databases identified 31 publications from 2018 to 2024 addressing soil carbon in Nigerian agricultural systems, of which only 6 specifically addressed Middle Belt land use systems and none compared all five land use types in the same study. Soil samples from 0-20 cm and 20-40 cm depths were collected at 10 sites per land use system and analysed for organic carbon content, carbon stock (using bulk density), and carbon fraction distribution (particulate organic carbon and mineral-associated organic carbon). Results showed that natural forest stored 42.7 Mg C ha-1 in the 0-40 cm layer, compared to 38.2 Mg C ha-1 under agroforestry, 29.4 Mg C ha-1 under permanent pasture, 24.1 Mg C ha-1 under rotational fallowing, and 17.3 Mg C ha-1 under continuous arable management. The study fills a carbon measurement gap and recommends agroforestry as the highest-impact carbon sequestration land management system for the Middle Belt zone.

Keywords: soil carbon sequestration, land use systems, Middle Belt Nigeria, agroforestry, carbon stock