Developing an Original Bioenergy Crop-Soil Interaction Model for Jatropha Production on Degraded Soils of North Central Nigeria

This dissertation develops and validates an original bioenergy crop-soil interaction model for Jatropha curcas cultivation on degraded soils in the North Central geopolitical zone of Nigeria, encompassing Niger, Kogi, and Benue States. Jatropha has been extensively promoted across Nigeria as a biodiesel feedstock that can be grown on marginal and degraded land without competing with food crops, but its actual performance-soil interactions are poorly characterised under Nigerian conditions, and no mechanistic model predicting Jatropha growth and oil yield as a function of soil quality exists for the Nigerian context. This study establishes a six-year longitudinal experiment on three contrasting degraded soil types (compacted savanna Lixisol, eroded Ultisol, and mined-out Leptosol) in Minna, Lokoja, and Makurdi environs. Jatropha growth parameters, root architecture, leaf litter inputs, soil organic carbon dynamics, nitrogen cycling, and soil hydraulic property changes are measured annually. The DNDC model extended with a custom Jatropha phenology sub-model is parameterised from the experimental data. Sensitivity analysis identifies the most critical soil properties governing Jatropha productivity on degraded soils. The dissertation proposes the Nigerian Jatropha-Soil Interaction Model (NJSIM) as an original contribution, capable of predicting seed yield and soil quality trajectories under different soil amendment scenarios. Findings reveal that degraded Lixisols with targeted phosphorus and organic matter amendment achieved the highest long-term oil productivity, while Leptosols remained economically non-viable even with amendment. The NJSIM provides decision-support tools for identifying suitable degraded land for Jatropha investment in North Central Nigeria. Keywords: Jatropha curcas, bioenergy crop, soil interaction model, degraded soils, North Central Nigeria.