Organisation of Soils along the Sides of Interfluves in the Western Highlands of Cameroon: Case Study of an Andosolic Toposequence on Trachyte in the Upper Part of the Southern Limb of Bambouto Mountains

Abstract

The acquisition of knowledge on soils tells how to use them sustainably. So, the organization of soils along the sides of interfluves in the western highlands of Cameroon was put into relief in order to understand their genesis, organization, and evolution. Field work and lab analysis helped to reach the focuses. These soils are thin, highly differentiated, with many local specificities. Their organization and their thickness vary from up to downhill. Vertically, they include: An isalteritic horizon; a yellow vague polyhedral horizon; a red distinct polyhedral horizon; a discontinuous breastplate with two facies; a porous vague crumby dark reddish brown horizon; and a strongly dark grey, porous, thixotropic and crumby superficial horizon. The pedon/alterite ratio is about 2/1, and the hardened level/alterite ratio is 1/4. The alteritic level represents about 1/3 of the whole soil profile. Microscopically, these soils lack plasmic separations. Plasmas are respectively isotic in the dark reddish brown and strongly dark grey horizons, clayey asepic in the yellow and red polyhedral horizons, cristic in the isalteritic horizon, cristic and locally isotic in the discontinuous breastplate. Gibbsite, halloysite, kaolinite and allophane are the main minerals; goethite, quartz, hematite and rutile are also present. Geochemically, aluminum is the main chemical component in the deepest horizons, while in those at the top of the soil profile, silicon and aluminum has quite similar concentrations. Others specificities include their low bulk density (0.6 to 0.9 gcm-3), the abundance of clayey particles at the bottom of the soil profile, sand and silt at its summit. Ferrallitic and andosolic characteristics coexist in the studied soils. This ambivalence makes them to be simply «andic ferallitic, desaturated, humic and strongly rejuvenated soils».