Comparative Assessment of Soil Carbon Sequestration Under Contrasting Agroforestry Systems in the Humid Forest Zone of Imo State, South East Nigeria

This study conducts a comparative assessment of soil carbon sequestration under contrasting agroforestry system designs in the humid forest zone of Imo State, located in Nigeria's South East geopolitical zone. Agroforestry is both a food security strategy and a climate change mitigation tool, but the comparative carbon sequestration efficacy of different agroforestry architectures in South East Nigeria's humid forest zone has not been empirically quantified. Using a cross-sectional field comparison design, soil organic carbon stocks were measured at three Soil Scienceh intervals (0 to 10, 10 to 20, and 20 to 40 cm) in four agroforestry systems: Gmelina arborea-food crop, Parkia biglobosa-food crop, multipurpose tree-vegetable, and homegarden-type multistrata systems, compared with sole food crop cultivation and secondary forest reference sites. Three replicate sites per system were established across Orlu, Ikeduru, and Njaba local government areas. Aboveground tree biomass was measured and converted to biomass carbon using species-specific allometric equations. Total ecosystem carbon (soil plus biomass) was compared. Findings revealed that the multistrata homegarden system accumulated the highest soil organic carbon stocks (mean 54 tC/ha in the top 40 cm), followed by the Parkia-food crop system (42 tC/ha). Sole crop plots stored only 19 tC/ha. Total ecosystem carbon sequestration rates, including above-ground biomass, were greatest in the Gmelina-food crop system due to rapid biomass accumulation. The study provides empirically derived carbon sequestration coefficients for Imo State agroforestry systems applicable to emissions reduction accounting and carbon payment scheme design. Keywords: carbon sequestration, agroforestry, humid forest, Imo State, ecosystem carbon.