Pearl millet yield reduction by soil erosion and its recovery potential through fertilizer application on an Arenosol in the Sahel

Despite the heightened contribution of soil erosion to soil degradation in the Sahel, its impact, particularly topsoil loss, on crop productivity remains unclear. To address this issue, we investigated the effects of simulated erosion by removing topsoil on the grain yield of pearl millet in the Sahel. Three-year field experiments conducted on an Arenosol in Niger examined different levels of topsoil removal (0, 1.0, 2.5, 5.0, and 10 cm) and fertilization (unfertilized and fertilized) on the grain yield of pearl millet. Results showed that topsoil removal of 2.5 cm or more significantly reduced grain yield, with effects projected to become apparent in 5–6 years based on erosion rates previously reported. Under normal rainfall conditions in the first and third years, 2.5-cm topsoil removal under unfertilized conditions resulted in a yield reduction of 37 % cm⁻¹, surpassing the values reported in other humid to semi-arid regions of sub-Saharan Africa. Conversely, the grain yield remained unaffected following a 1-cm topsoil removal. Fertilizer application compensated for the grain yield loss in the plots of 2.5- and 5.0-cm topsoil removal but not effectively in the 10-cm removal plot. In conclusion, the loss of the thin Ap horizon markedly reduced plant-available water and nutrients in soils, leading to a decreased grain yield of pearl millet in the Sahel. Given the Ap horizon thinness and soil erosion prevalence in the Sahel, recognizing the topsoil loss in the early stages of soil erosion and implementing countermeasures are imperative to avoid a sharp decline in grain yield.