This study is based on the analysis of field-measured nitrous oxide (N₂ O) emissions from a Sahelian semi-arid grassland site in Senegal (Dahra), tropical humid agricultural plots in Kenya (Mbita region) and simulations using a 1D model designed for semi arid ecosystems in Dahra. This study aims at improving present knowledge and inventories of N₂ O emissions from the African continent. N₂ O emissions were larger at the agricultural sites in the Mbita region (range: 0.0 ± 0.0 to 42.1 ± 10.7 ngN m⁻² s⁻¹) than at the Dahra site (range: 0.3 ± 0 to 7.4 ± 6.5 ngN m⁻² s⁻¹). Soil water and nitrate (NO₃⁻) contents appeared to be the most important drivers of N₂ O emissions in Dahra at the seasonal scale in both regions. The seasonal pattern of modelled N₂ O emissions is well represented, though the model performed better during the rainy season than between the rainy and dry seasons. This study highlighted that the water-filled pore space threshold recognised as a trigger for N₂ O emissions should be reconsidered for semi-arid ecosystems. Based on both measurements and simulated results, an annual N₂ O budget was estimated for African savanna/grassland and agricultural land ranging between 0.17–0.26 and 1.15–1.20 TgN per year, respectively.