Genesis of a soil sequence in the Middle Plateau Region (Planalto Médio) of the State of Rio Grande do Sul

Abstract

A toposequense of important soils of the middle plateau region of Rio Grande do Sul were studied with reference to their morphological, geomorphological, chemical and mineralogical properties in order to obtain information concerning their genesis, classification, and agricultural capability. The soils of the plateau are derived from basic igneous rocks as well as from deposits of sandy material, whereas the soils of the back slope and footslopes are derived from the underlying basalt, having also received material eroded from the deeply weathered soils of the undulating uplands. In spite of their steep gradients and stoniness, the soils of the slopes are preferred by farmers because they have clay minerals which have undergone fewer transformations and hence have greater fertility. Although the soils of the older surfaces present undulating relief, they are highly weathered and quite acid, with low reserves of plant nutrients.