Factors governing crusting formation in soils in Southern Mali, West Africa: Evaluation of susceptibility indices

In Southern Mali and neighboring semi-arid Sahel regions, soil crusting and sealing are common and significant phenomena for people who depend on agriculture for their livelihoods. These processes form hard, impermeable layers on the soil surface, reducing water infiltration, increasing runoff and erosion, and hindering germination, seedling emergence, and productivity. Factors such as rainfall intensity, topography, soil attributes, and poor management practices contribute to these phenomena. Here, we aimed to analyze soil attributes affecting crust formation and evaluate them using indicators like the structural stability index (StI), particle separability index (PSI), and crusting susceptibility index (CSI). Soils samples from agricultural and native areas in Southern Mali were analyzed for physical, chemical, mineralogical, and micromorphological attributes. Results revealed that the soils in these regions have high silt and fine sand content and low organic carbon content. Poor soil management, leading to prolonged periods of bare soils, significantly contributes to crusting. Kaolinitic clays, Ca²⁺ and Mg²⁺ contents did not appear to affect crusting. The PSI revealed a high risk of aggregate disruption in both agricultural and native lands, demonstrating soil vulnerability to degradation. The StI showed limited risk of structural degradation in native lands, while agricultural soils were more susceptible to crusting. The CSI indicated moderate crusting susceptibility across the regions. By examining the three indices related to texture attributes and organic carbon, this study provides insights into estimating susceptibility to crusting through the evaluation of the risk of soil structural degradation, particle separation, and overall soil susceptibility to surface crusting, all of which underscore the need for improved soil attributes. It emphasizes the importance of implementing effective soil management strategies, particularly the adoption of cover crops, to enhance organic carbon content and increase vegetation cover. These measures are essential for improving soil health and minimizing the risk of crusting.