1. Bationo, A., S.H. Chien, J. Henao, B.C. Christianson, and A.U. Mokwunye. 1990. Agronomic evaluation of two unacidulated and partially acidulated phosphate rocks indigenous to Niger. Soil Science Society America Journal 54: 1772–1777.
2. Chen, Y., J. Tarchitzky, J. Brouwer, J. Morin, and A. Banin. 1980. Scanning electron microscope observations on soil crusts and their formation. Soil Science 130: 45–55.
3. FAO. 1988. Soil map of the world. FAO-UNESCO, Paris, France.
4. Greigert, J. 1966. Description des formations cretacées et tertiaires du Bassin des Jullemmeden (Afrique occidentale). Editions du Bureau de Recherches Géologiques et Minières, Paris, France.
5. Hammer, R. 1994. Bodensequenzen und Standortseigenschaften im Südwest-Niger/Westafrika. Hohenheimer Bodenkundliche Hefte 22, Stuttgart, Germany.