Agricultural suitability of sandy ferruginous soils in the Senegalese Groundnut Basin: a FAO – fuzzy AHP assessment in the Niakhar Observatory

Sahelian agriculture in the Senegalese Groundnut Basin is constrained by chronic degradation of sandy ferruginous soils, declining rainfall and land pressure. Crop diversification having become a national priority, an updated quantitative assessment of soil agricultural suitability is required. This study assessed the agricultural suitability of soils in Diarère and Ngayokhème municipalities (Niakhar Observatory, central Senegal) by combining the FAO limiting-factor framework with a fuzzy Analytic Hierarchy Process (AHP). Sampling was stratified using digital soil mapping from Sentinel-2 (2024) spectral indices (NDVI, NDWI, SAVI) combined with topographic and geological covariates from the 30-m SRTM digital elevation model. A conditioned Latin hypercube design produced 100 sub-samples aggregated into ten composite samples, analysed at the National Institute of Pedology for texture, pH, electrical conductivity (EC), organic matter (OM), total nitrogen, available phosphorus, exchangeable bases, cation exchange capacity (CEC) and exchangeable sodium percentage (ESP); statistical analyses were performed in R 4.5.1. The Agricultural Suitability Index (ASI) ranged from 0.464 (E-C7) to 0.601 (E-C2). All profiles were classified as unsuitable (CA5) under the strict FAO approach due to severe deficiencies in available phosphorus, potassium and CEC. The fuzzy AHP refined the diagnosis into two classes (moderately suitable (CA3: E-C1, E-C2, E-C5, E-C6, E-C8) and marginally suitable (CA4: E-C3, E-C4, E-C7, E-C9, E-C10), and identified organic and phosphate amendments, liming of the most acidic profile (E-C6) and salinity management of the lowland profile (E-C4) as priority interventions. This framework supports targeted, soil-specific management for sustainable diversification of the Senegalese Groundnut Basin.