IN SITU STUDY OF SOIL PROCESSES IN AN OXISOL-SPODOSOL SEQUENCE OF AMAZONIA (BRAZIL)

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Abstract
We performed an in situ experiment with the aim of getting evidence for contemporary podzolization in a soil sequence near Manaus, Amazonia, Brazil. Samples of a test-mineral [high cation exchange capacity (CEC) vermiculite], as well as small bags of cation exchange or chelating resins, were inserted in soils (Oxisols, Ulti-sols, and Spodosols). We based the study on the following principles: when placed in an acidic and complexing system (podzolization), the vermiculite undergoes a desaluminization process and its CEC saturates with Mg by relative accumulation. In a simply acidic system, aluminum accumulates in the interlayers, and rapid hydroxylation leads to the formation of an Al intergrade mineral easily detectable by X-ray diffraction. The resins inserted in soils gave information about the chemistry of the soil solutions. We concluded that podzolization is a currently active process in the lower part of the sequence, even in soils where morphological podzolic features have not yet developed. This process would be active during the rainy season only.