hide
Free keywords:
-
Abstract:
There is general agreement that the alluvial soils of the várzea, which are derived from the settled suspended load of the Amazon River, are rich in nutrients sustaining a high natural productivity (Sioli 1954a, 1969, 1975; Irion 1978; Cochrane and Sanchez 1982; Nascimento and Homma 1984; Sombroek 1984; Fearnside 1985; Meggers 1985; Lima 1986; Furch and Klinge 1989; Junk et al. 1989; Martinelli et al. 1989). Sediments originate in the Andes and the pre-Andean zone, they contain clay minerals, i.e., montmorillonite, illite and chlorite, with relatively high cation exchange capacities (Gibbs 1967; Irion 1976b, 1984a; Sect. 2.4). In contrast, the soils of the black-water floodplains, the igapó, are considered to be poor in nutrients and of low production potential (Sioli 1954a, 1969, 1975; Irion 1978; Fearnside 1985; Singer and Aguiar 1986; Furch and Klinge 1989). These soils partly originate from erosional processes of strongly weathered and lixiviated tertiary sediments containing mainly kaolinite which has a low cation exchange capacity (Irion 1976b, 1984a; Irion and Adis 1979).
