Complex pedogenesis of ferrallitic savanna soils in South Sudan

Abstract

Complex pedogenesis in ferrallitic savanna soils is demonstrated by means of three typical profiles. The information provided includes relative age relationship of soils on the polycyclic pediment slopes, macro- and micromorphological characteristics, some chemical and complete mineralogical data. The authors compare the operation of basic processes of saprolitization (kaolinization, primary mottling) and pedogenesis (homogenization, local, vertical and lateral redistribution of iron) in forest soils formed on deep saprolite, and savanna soils on generally much shallower saprolite. Complex pedogenesis in the latter results from intermittent erosional impact, changes of climate and the stepwise downward weathering and deepening of the solum. All of these factors cause (homo- or heterogenetic) changes of internal hydrological conditions in the whole or parts of the solum. By means of detailed differentiation of ferruginous precipitates in regard to their crystal form (hematite and goethite) and their successive formation and alteration, the authors attempt to elucidate the history of soil formation.