Acid soil profiles of the semiarid and subhumid tropics in Central and West Africa

Abstract

Soils of the semiarid and subhumid tropics of Central and West Africa are frequently strongly acid. In an investigation using soils from Cameroon in Central Africa and Mali and Niger in West Africa, selected pedons were described and classified using the U.S. soil classification system. Selected chemical and physical methods were used to analyse samples from the various profiles. Greenhouse and pot experiments were conducted to evaluate crop response to fertilizer P. The Mbomi 2 pedon from Cameroon was described and classified as clayey, kaolinitic, isohyperthermic Aeric Kandiaquult while the Cinzana Pedon from Mali and Dayobu Pedon from Niger were classified as mixed, isohyperthermic Grossarenic Paleustalf and coated, isohyperthermic Ustoxic Quartzipsamment, respectively. The pH of the profiles was strongly acid for Mbomi 2 to acid for Cinzana and Dayobu sites. All three sites have low effective cation exchange capacity. The Mbomi 2 and Dayobu sites are predominantly Al saturated and the Cinzana site is predominantly Ca saturated.

Pot and greenhouse experiments indicate that plant available P is one of the most limiting plant nutrients. Application of fertilizer P doubled rice dry matter yield for the Mbomi 2 soil, increased sorghum dry matter yield by 243 percent over the local check for the Cinzana soil, and increased millet dry matter yield by 100 percent for the Dayobu soil. Application of N, P, K and lime increased sorghum dry matter yield by 338 percent for the Cinzana site and millet dry matter yield by over 800 percent over the local check at the Dayobu site.