Soils of the Amazon region

Abstract

In the eastern part of the sedimentary basin, the upland soils form in unconsoliolated kaolinitic sediments, sometimes with concretionary ironstone gravels. Permanent cropping is possible on these xanthic Ferralsols. In the western part, the soils are less pre-weathered and are derived from marine sediments. They are ferric Acrisols where the soils have textural differentiation within the profile and Cambisols and Nitosols of varying base status where there is no significant textural differatiation. The north and south edges of the region have predominantly ferric Acrisols overlying crystalline basement rock. Low lying terraces with seasonally fluctuating groundwater table have soils containing plinthite, plinthic Acrisols. If the forest cover is removed, irreversible hardening of the plinthite is likely. Podzolized soils and deep white sands (gleyic podzols and albic Arenosols respectively) cover low lying interfluves and terraces. They have no agricultural value, and if the savannah cover is destroyed, a marshy white sand desert will result. Bottomlands of upland areas have humic or dystric Gleysols with high exchangeable aluminium content and limited agricultural potential. The Amazon floodplains are predominantly covered by Fluvisols in the west and Gleysols in the east. They are mainly acidic, except where the rivers originate in the Andes. Coastal areas have saline or alkaline soils with limited agricultural use.