VARIABILITE DES CARACTERISTIQUES PHYSICO-CHIMIQUES DES SOLS DU SYSTEME OASIEN DU MANGA AU SUD-EST NIGER

The soils of the Manga oasis system cover the red-brown soils of the dunes, the brown soils of the lowlands and the alluvial soils of the basins. Silting and a decline in chemical fertility are the main forms of soil degradation. Fixing the living dunes (mechanically and biologically) promises to improve the physico-chemical qualities of the soil. To assess the characteristics of soils in the oasis system, carbon, nitrogen, assimilable and total phosphorus and granulometric fractions are measured. The results show that at a depth of 60 cm in the soil of the basins, clays combined with silts account for more than 60%. At a depth of 100 cm, clays and silts make up less than 7% of the granulometric composition in the dunes and lowland rangeland soils. The pH is neutral in the basin soils and slightly acidic in the dune and lowland soils. In the first 60 cm, the carbon, nitrogen, total phosphorus and assimilable phosphorus contents are significantly higher in the basin soils than in the dune and bottomland rangeland soils. Overall, the physico-chemical characteristics of the soils show vertical variability, with the first horizons showing high levels and the underlying horizons showing low levels. Dune fixation has significantly improved the physico-chemical qualities of the first soil horizons. This study could serve as a basis for decision-makers and partners involved in land restoration in the oasis system. It also provides a basis for farmers using oasis basins to boost agroforestry production.