Abstract
Abstract The paper briefly outlines work being done on the movement of cations under a Palmetum-type rain forest near Manaus, Amazonas. It is suggested that the low cation content of river waters Is concerned with the nature and dynamics of water movement in relation to soil moisture and tension as much as lack of availability of cations in the soil. Preliminary results support the idea of a 'by-pass' mechanism whereby the smaller pore spaces, saturated with water, only drain and provide cation-rich water late in the dry season.
Highlights
A commonly presented paradox of the Amazonian tropical rainforest is that soils are excessively deficient in available nutrients whilst they support some of the most dense, luxuriant forest in the world
Stark sup ports the hypothesis and suggests that this state of affairs is of long standing because the deposits on which the present forest is de veloped were originally nutrient deficient al luvium exposed during the Miocene
A s the solute concentrations of many Amazonian streams and rivers have been found to be so low (e.g. Edwards and Thornes, 1970), it has been generally concluded that the soils had low sources of leachable materials
Summary
A commonly presented paradox of the Amazonian tropical rainforest is that soils are excessively deficient in available nutrients whilst they support some of the most dense, luxuriant forest in the world. Richards (1966) states that "It can be seen that in mature soil the capital of plant nutrients is mainly locked up in the living vegetation and the humus layer, between which a very nearly closed cycle is set u p " This theme has been elaborated upon by Sioli (1966) and Stark (1971). A s the solute concentrations of many Amazonian streams and rivers have been found to be so low (e.g. Edwards and Thornes, 1970), it has been generally concluded that the soils had low sources of leachable materials The arguments underlying these conclusions together with those for a 'nearly closed cycle' are presented by Jordan & Kline (1972). In addition detailed studies have been made of the soil over the whole slope length, though as yet no analytical results are available for this part of the investi gation
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