Modelling CO₂ and N₂O emissions from soils in silvopastoral systems of the West-African Sahelian band

Abstract. Silvopastoral systems (SPSs) have been shown to improve ecosystem resilience and provide sustainable land management solutions in the Sahel. However, accurately estimating the contribution of Sahelian ecosystems to the overall greenhouse gas (GHG) balance is a challenge, in particular the magnitude of carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions from soils. In this work, we spatialized and applied the process-based model STEP-GENDEC-N₂O to investigate the magnitude, spatial, and temporal patterns of herbaceous mass, as well as CO₂ and N₂O emissions from soil in Sahelian SPSs. Our results show that over the last decade (2012–2022), there was a heterogeneous spatial distribution of herbaceous mass production, as well as of soil CO₂ and N₂O emissions in Sahelian SPSs. Spatial variations in soil CO₂ emissions are primarily controlled by soil carbon content, temperature, herbaceous mass, and animal load, while soil nitrogen content, soil water content, and animal load are the main factors driving the spatial variations in N₂O emissions from soil. The estimated CO₂ and N₂O emissions from soil in Sahelian SPSs over the 2012–2022 period were equal to 58.79 ± 4.83 Tg CO₂-C yr^-1 (1 Tg = 10¹² g) and 21.59 ± 3.91 Gg N₂O-N yr^-1 (1 Gg = 10⁹ g), respectively. These values are generally lower than estimates reported in the literature for tropical areas and croplands. Furthermore, our simulations indicated a significant annual rising trend of soil CO₂ and N₂O emissions between 2012–2020 as herbaceous mass increases, making more C and N available for nitrification, denitrification and decomposition processes. By mapping soil CO₂ and N₂O emissions, we provide crucial insights into the localization of emission hotspots in Sahelian SPSs, thereby offering valuable information that can be used to devise and implement effective strategies aimed at fostering carbon sequestration in the Sahel.