Evolution of the hydraulic conductivity of a cultivated sandy soil in West Niger

Description of the subject. The present study aims to present and analyze the evolution of the hydraulic conductivity of soils in cultivated and fallow areas in the loamy-sand superficial soils within the granitic basement region of West Niger. To this end, experimental plots considered representative of the area were chosen in the Sahelian cultivated area. Objectives. Our objective was to evidence the effect of cultural practices and of both wet hoeing and dry hoeing on this evolution and their consequences in terms of soil infiltrability and runoff. Method. A tension disc infiltrometer was used together with a pair of minitensiometers in one-dimensional flow geometry. Results. Measurements were carried out and variations in total rainfall were calculated, allowing us to determine and quantify the effects of the following on the evolution of conductivity: (i) hoeing, (ii) the level of soil moisture prior to this operation and (iii) the lack of cultivation in fallow areas. Hydraulic conductivity was consistently found to be minimal at the surface. Conductivity in the fallow field was stable at 20 mm. h(-1). In the cultivated zones, conductivity was very high (120 mm. h-1) after hoeing in wet conditions, decreasing to the fallow value after 70 mm of rain and even down to half of this value after 230 mm of rain. Hoeing in dry conditions showed poor efficiency, both in terms of conductivity and the duration of the effect. Conclusions. The benefits of hoeing were found to be only short-lived, with the task needing to be repeated after 100 mm of rain.