Andosolization of ferrallitic soils in the Bambouto Mountains, West Cameroon

Soils along a toposequence (1500–2260 m) on the southern slope of the volcanic Bambouto Mountains in western Cameroon were investigated to elucidate the occurrence and development of andic properties at high altitude (> 1800 m) in the study area. The surface layer that has these properties has in the past been interpreted as a weathered volcanic ash layer, overlying ferrallitic soils that developed from lava flow deposits and derived pediments. Physico-chemical and mineralogical data demonstrate that the andic properties of the high-altitude pedons result from SOM accumulation, favoured by climate and vegetation. The ‘andosolization’ process affecting these profiles involves the formation of organo-metallic complexes, which is mediated by organic ligands and controlled by the dissolution of gibbsite and iron oxides. Increasing andosolization with increasing altitude, due to SOM accumulation, is well reflected by soil classification names, especially by the humic qualifier for the soils below 1800ma.s.l. and the protoandic subqualifier for the soils at higher altitude. All analysed properties show features that are incompatible with derivation of the upper part of the high-altitude pedons from volcanic ash. In studies of soils from similar settings, care should be taken to avoid misinterpretation of surface horizons marked by environmentally conditioned development of organo-metallic complexes as ash-derived layers