Soil nitrous oxide and methane emissions in contrasting land use of the West African Sudanian savanna

Abstract

Changes in land use and land management can have significant effects on the global emissions budget, influencing the climate through biogeochemical processes. However, their impacts on major soil greenhouse gas (GHG) emissions in West Africa remain poorly documented and understood. This study provides the assessment of soil GHG emissions in the Sudanian savanna region of West Africa using a chamber-based experimental setup. The measurements are taken at four sites with contrasting land use and land management practices: pristine savanna forest, cropland, degraded grassland, and a rainfed rice field. Over two consecutive years (2023-2024) of weekly chamber measurements during the rainy season (corresponding to the rice-growing period), our results reveal significant variation in methane (CH₄) fluxes across the sites. However, nitrous oxide (N₂O) fluxes did not vary significantly, likely due to uniformly low nitrogen input across all systems. The highest seasonal CH₄ emissions were recorded in the rainfed rice field (0.69 ± 0.17 and 0.82 ± 0.22 kg C ha^{- 1} season^{- 1}, on average), while the forest reserve acted as a net CH₄ sink (- 0.019 ± 0.20 and - 0.42 ± 0.13 kg C ha^{- 1} season^{- 1}). In contrast, soils across all sites, both managed and natural, were sources of N₂O, with fluxes ranging from 0.01 kg N ha^{- 1} season^{- 1} in the forest reserve to 0.16 kg N ha^{- 1} season^{- 1} in the rice field. This study also analyzed the environmental drivers of GHG fluxes and found that CH₄ variability was significantly influenced by soil water content and soil temperature (partial R² between 0.21 and 0.42). No significant relationship was observed between these variables and N₂O emissions. These results highlight that land cover degradation in the Sudanian savanna can substantially increase CH₄ emissions, while its impact on N₂O fluxes is marginal but leads to higher CO₂-equivalent.