Nitrous Oxide Emissions from Nigerian Agricultural Soils: Quantification, Process-Level Controls, and Mitigation Pathway Framework

This dissertation provides an original empirical and theoretical analysis of nitrous oxide (N2O) emissions from Nigerian agricultural soils, quantifying emissions across management systems and agroecological zones, identifying the soil process-level controls on emission magnitude, and developing a mitigation pathway framework applicable to Nigeria's agricultural greenhouse gas inventory. Nitrous oxide is a potent greenhouse gas with global warming potential 265 times that of CO2, and agricultural soils are the dominant emission source, yet Nigeria lacks direct measurements of N2O emissions from its agricultural systems, relying entirely on IPCC default emission factors that may substantially misrepresent actual emissions under tropical soil conditions. This study deploys automated closed chamber N2O monitoring systems at 12 field sites spanning the Sahel, Sudan savanna, Guinea savanna, and Humid forest zones, covering seven crop-soil-management combinations over two full seasonal cycles. 15N-labelled fertiliser tracer experiments at three sites partition N2O production between nitrification and denitrification pathways. Soil physicochemical and biological drivers of N2O emission are quantified by multivariate time-series analysis. The process data are used to parameterise and calibrate the DNDC biogeochemical model for Nigerian soil conditions. The dissertation proposes a Nigerian Agricultural N2O Emissions Framework (NANEF) integrating revised emission factors by agroecological zone, management, and soil type into an IPCC Tier 2 compliant inventory methodology. Original contributions include the first Nigerian direct N2O measurement dataset, the DNDC calibration for Nigerian soils, and the NANEF framework for national inventory submission. Keywords: nitrous oxide emissions, Nigerian agricultural soils, greenhouse gas, DNDC model, agroecological zones.