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 regarding the magnitude of carbon dioxide (CO2) and nitrous oxide (N2O) emissions from soils. In this work, we spatialized and applied the process-based model Sahelian Transpiration Evaporation and Productivity – GENeral model of litter DEComposition – N2O (STEP–GENDEC-N2O) to investigate the magnitude and spatial and temporal patterns of herbaceous mass, as well as CO2 and N2O emissions from soil (not net emissions) in Sahelian SPSs. Our results show that over the last decade (2012–2022), there was a heterogeneous spatial distribution of herbaceous mass production and 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 and 2020 as herbaceous mass increased, making more C and N available for the 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.