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Field measurements across West African savanna and cropland sites in Côte d'Ivoire and Senegal show that soil moisture, vegetation cover, and geographic location primarily govern carbon dioxide, nitric oxide, and methane fluxes. Different ratios of nitrate and ammonium fertilisers did not significantly influence these emissions. Carbon dioxide releases decreased under higher soil moisture because restricted oxygen diffusion lowered soil respiration. Nitric oxide releases peaked in fertilised croplands due to enhanced nitrification activity. Conversely, methane dynamics varied by cover type, with grassy savannas acting as net sources and croplands functioning as methane sinks through soil oxidation. Nitrous oxide fluxes remained low or negative across all studied settings, demonstrating that nitrogen-deficient savanna soils can act as net sinks for atmospheric nitrous oxide under aerated conditions.
Understanding how savanna ecosystems regulate greenhouse gases is essential for accurately modelling tropical land-use impacts on global climate. By demonstrating that agricultural conversion alters whether soils absorb or emit methane and nitric oxide, these findings help environmental scientists, climate modellers, and regional land managers evaluate carbon and nitrogen budgets across sub-Saharan Africa.
This work represents early-stage environmental research with no immediate commercial product described. However, the flux data could be used by carbon accounting platforms, environmental consultancies, and agricultural policymakers seeking to refine regional greenhouse gas inventories and soil emission factors. Any operational application remains distant, requiring translation into verified carbon crediting methodologies and standardized regional land-use models.
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Abstract. This study investigated greenhouse gas (CO₂, CH₄, N₂O) and reactive nitrogen (NO) fluxes at three West African savanna sites: the international research reserve of Lamto (Taabo district, Côte d’Ivoire), the Observatoire de Recherche en Environnement de Nambekaha (OREN) (Korhogo, Côte d’Ivoire), and the Centre de Recherches Zootechniques (Dahra, Senegal). Measurements were carried out during intensive field campaigns conducted in 2024 and 2025, during the wet seasons at the three sites, across tree areas and grassy areas in savannas, and cropland ecosystems subjected to different treatments from March 2023 to September 2025. Overall, soil moisture, vegetation type (grassy areas, trees areas, crops) and site location (Lamto, Dahra, Nambekaha) were the main factors controlling gas fluxes (CO2, NO and CH4), whereas treatments containing different ratio of nitrates and ammonium had no significant effect according to the statistical analysis (ANCOVA). CO₂ fluxes ranged from 8.21 ± 2.5 to 91.35 ± 73.2 µg C m⁻² s⁻¹ and were controlled by soil moisture, with a decrease in soil respiration as water content increased (β = −1.105 ± 0.236 µg C m⁻² s⁻¹; p <0.001), due to a limitation of oxygen diffusion in the soil, highlighting the key role of soil moisture in regulating both heterotrophic microbial respiration and autotrophic plant respiration, in relation to soil aeration conditions. NO emissions, ranging from 0.01 ± 0.0 to 497.39 ± 146.3 ng N m⁻² s⁻¹, showed a significant correlation with vegetation type. The highest values were observed in the cropland plots of Nambekaha (β = +76.779 ± 15.82 ng N m⁻² s⁻¹; p < 0.001) compared with natural savannas, reflecting intensified nitrification processes linked to background fertilization inputs (150 kg NPK ha⁻¹ yr⁻¹). CH₄ fluxes were primarily determined by vegetation type: grassy areas within savannas behaved as net sources (β = +3.836 ± 0.62; p < 0.0001), whereas croplands acted as sinks, suggesting methanotrophic activity capable of oxidizing atmospheric methane in the soil. In contrast, N₂O fluxes were mostly low or even negative across all ecosystems and treatments, with no significant relationship to soil moisture, vegetation type, or treatments. The results indicate that soils could occasionally function as net N₂O sinks: indeed, N2O uptake may occur in nitrogen-poor soils under oxic conditionswhere the limited availability of mineral nitrogen restricts N₂O production and where atmospheric N2O diffuses easily into the soil. These findings highlight the microbial and environmental coupling of carbon and nitrogen dynamics in tropical savanna soils and provide critical insight for predicting greenhouse gas and reactive gas emissions under changing land-use conditions.
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DOI: 10.5194/egusphere-2026-3592-rc1
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