PODZOLS IN AMAZONIA

In the area near Manaus, Amazonia (Brazil), soil sequences including Oxisols, Ultisols and Spodosols (podzols) are widely distributed. Such toposequences occur on slopes leading down into valleys cut in a nearly level plateau. The geochemistry of the organic and mineral components of one of these sequences has been investigated. Spodosols develop on quartzose sands which may be the results of an intense hydrolysis of clays and/or an impoverishment of clays through eluviation or selective erosion. Large analogies with podzolization in the temperate zone were found, especially in the organic matter dynamics: as the clay content decreases more organic compounds with increased aromaticity and more polycondensed structures were allowed to move, forming the Bh horizons or reaching the water streams. An in situ experimentation was also performed to characterize presently active soil forming processes. It was found that podzolization in Amazonia was mainly active during the rainy season. © 1990.