An Original Analysis of Soil Carbon Feedback Sensitivity to Land Use Policy in the Context of Nigeria’s NDC Commitments: Modelling Evidence from All Six Geopolitical Zones

This dissertation provides an original integrated analysis of soil carbon feedback sensitivity to alternative land use policy scenarios in the context of Nigeria's Nationally Determined Contributions (NDC) under the Paris Agreement, using calibrated biogeochemical modelling across all six Nigerian geopolitical zones to provide the first zone-specific soil carbon policy evidence base. Nigeria's NDC commits to a 20 percent unconditional and 45 percent conditional reduction in greenhouse gas emissions by 2030, and land use and agriculture are the largest sectoral contributors, yet the soil carbon consequences of alternative land use policies are not modelled with Nigerian-specific parameters. This study develops a modelling dataset from 360 soil profiles across all zones and uses the RothC and CENTURY models calibrated against 15-year experimental data from the International Institute of Tropical Agriculture and regional universities to project soil carbon dynamics under six policy scenarios: business as usual, agroforestry expansion, organic farming promotion, forest protection, reforestation of degraded land, and full NDC implementation. Uncertainty in projections is quantified through Monte Carlo parameter sampling. The dissertation proposes the Nigerian Soil Carbon Policy Simulator (NSCPS) as an original applied modelling contribution, delivering scenario-specific soil carbon sequestration projections at geopolitical zone level with 95 percent confidence intervals. Full NDC implementation is projected to generate an additional 48 to 76 million tonnes CO2-equivalent soil carbon storage nationally over 10 years. The NSCPS is provided to the Federal Ministry of Environment as a policy decision support tool. Keywords: soil carbon, land use policy, NDC commitments, RothC model, Nigeria.