Influence of Acacia senegal (L.) Wild Density on Soil Fertility in the Western Sahel of Mali (Nioro)

Acacia senegal (L.) Wild colonizes the Western Sahel of Mali. This agroforestry species plays an important role in the socio-economic life of local populations. The density of this species has declined sharply recently because of climate change and anthropogenic factors. However, the influence of this density on soil fertility has been documented in very few studies in Mali. This study reports the influence of the density of natural Acacia senegal stands on soil fertility. Three municipalities of the region (Gadiaba, Nioro, and Korokodjo) were selected for the study. At each site, three plots of 2500 m2 each were marked out. The Acacia woody stand within each plot was measured (basal circumference, total height, and circumference total height and circumference at 1.30 m). These measurements were preceded by an exhaustive inventory of the woody plants. Juvenile plants with a circumference of 10 cm were systematically counted and considered as regeneration. In parallel with these measurements, soil samples were taken from the tops and undersides of four-foot trees at the ends and centers of the plots. A 500 g composite sample was taken from these samples. These samples were sent to the Sotuba soil-water-plant laboratory for particle size and chemical analysis. Natural stands are very dense in Gadiaba, with an average of 690 plants/ha, medium density in Nioro, with 430 plants/ha, and very low density in Korokodjo, with 120 plants/ha. The natural stands in the study area are characterized by small, medium-diameter trees. At Gadiaba, the soil is sandy-loamy, while at Nioro and Korokodjo, the proportion of sand dominates at over 90%. The soils were all deficient in organic carbon, nitrogen, and assimilable phosphorus. Comparison of the magnesium content, sand, and silt proportions between the sites studied showed highly significant differences (p ˂ 0.001). The C/N ratios and phosphorus levels were not significantly different between the three sites. The C/N ratio is 4.55% at Gadiaba, 5.95% at Korokodjo and 3.36% at Nioro du Sahel. Phosphorus levels were 3.79% in Gadiaba, 1.73% in Korokodjo, and only 0.21% in Nioro du Sahel. For other mineral elements and pH, however, the differences are significant at the critical threshold of 5%. Therefore, it is important to identify suitable management methods for these resources.