Identification of Plant Genetic Resources with High Potential Contribution to Soil Fertility Enhancement in the Sahel, with Special Interest in Fallow Vegetation

The sandy soil in the Sahel is characterized as low inherent fertility, that is, having nutrient deficiency (total N and available P), low organic matter and high risk of erosion. Under the concept of integrated soil fertility management (ISFM), possible contribution of natural inhabitant plants to the improvement of soil fertility in the Sahel was evaluated. A broad variation in δ 15N values was observed among the plant species commonly found in cropland and fallow land of the Sahelian zone. Annual leguminous herbs, Cassia mimosoides (Caesalpiniaceae) and Alysicarpus ovalifolius (Papilionaceae), had low δ 15N values, showing their higher dependency on biological nitrogen fixation. They will be efficiently utilized as an extensive means of soil fertility management, for example, through more encouraged incorporation into the fallow vegetation. Ctenium elegans, Eragrostis tremula and Schizachyrium exile, greatly dominating annual grass species in the fallow land, though their δ 15N values were high, would contribute to the soil fertility by supplying a significant amount of organic matter.