The provinces of Guéra, Batha, and Hadjer Lamis are under severe environmental pressure due to overgrazing, deforestation for fuelwood, and soil degradation, compromising essential ecosystem services. Despite the populations’ dependence on these services, no up-to-date environmental monitoring system exists, limiting understanding of the dynamics of degradation. In this context, the study aims to assess soil chemical characteristics and quantify soil organic carbon (SOC) in three provinces of Chad (Guéra, Batha, and Hadjer Lamis) in order to evaluate their fertility and carbon sequestration potential. A hierarchical sampling system, based on 10 km2 sentinel sites stratified into 16 clusters, was used to capture the spatial variability of the soils. The analyses show high grain size heterogeneity, with very clayey soils in Amdjamena and Bokoro (78%) and predominantly sandy soils in Temki (73%). pH values ranging from 4.94 to 10.74 indicate conditions ranging from slightly acidic to alkaline. The soils have high aluminum content, contrasting with very low levels of boron and zinc, indicating potential micronutrient deficiencies. Phosphorus, magnesium, and potassium levels are generally low, suggesting limited chemical fertility. Average nitrogen (0.04%) and COS (5.23 g kg⁻1) concentrations confirm a marked lack of organic matter. SOC varies greatly between sites, from 0.68 to 30 g/kg, with high values in Melfi and very low values in Amdjamena and Bokoro. These results highlight limited fertility and contrasting carbon sequestration potential, requiring appropriate management approaches to restore soil health and enhance agroecological resilience.