Nutrient Transport Associated with Wind Erosion of Sahelian Cultivated Soils: The Case of a Bangou Koiré Millet Field (Southwestern Niger)

Wind erosion is a major environmental problem in the Sahel and other dry regions of the world. It leads to nutrient loss and reduced soil productivity. However, wind transport of nutrients has been poorly studied in the Sahel. The aim of this study is to characterize the seasonal variability of wind transport and determine the associated nutrient losses over an annual cycle. The methodological approach consisted of measuring wind fluxes and determining the levels of physico-chemical parameters in cultivated soils and the fluxes resulting from wind erosion of these same soils. During the monsoon season, between April and September, the fluxes recorded on the millet field represented 97.61% of the annual fluxes, i.e., an average of 7.96 kg∙m−1∙d−1. Only 2.39% of annual fluxes were recorded during the Harmattan, i.e., an average flux of 0.15 kg∙m−1∙d−1. The fluxes contained, respectively, 2 and 1.5 times more fine clay-loam fraction and very fine to fine sands than the contents available in the soil. This is in stark contrast to the skeletal sand fraction, whose soil content tends to increase as a result of wind erosion. As far as nutrients are concerned, wind erosion has resulted in the transport of nitrogen, organic carbon, and phosphorus, on average, 10 times more than is available in the soil. Nutrient transport takes place mainly during the monsoon season, particularly at the beginning, which concerns 49%, 82%, and 60%, respectively, of the annual transport of phosphorus, nitrogen, and organic carbon. In order to protect cultivated soils from degradation, it is therefore imperative to minimize wind erosion of soils at the start of the monsoon season.