Properties, some criteria of classification and genesis of upland forest Podzols in Rwanda

Abstract

In southwest Rwanda, upland forest soils developed on quartzites and micaceous sandstones along steep slopes have sometimes the macromorphological look of ‘true’ Podzols. An investigation of the micromorphological, mineralogical and chemical properties, however, reveals only weak indications of illuviation of amorphous organic complexes. This process of cheluviation seems to be secondary relative to biological activity, Fe precipitation and weathering. The concept that cheluviation is the dominant process in the formation of spodic horizons and spodic materials would exclude these soils for the class of Podzols. Definitions of spodic horizon and spodic materials proposed in international soil classification systems, should give preference to macro and micromorphological properties over chemical properties, because the former are directly related to different genetic processes (biological activity, oxido-reduction) which also could be responsible for their formation.