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Further theories are mentioned by Smith (1980), which all did not hold against later investigations.It is now widely accepted that these soils were not only used by the local population but are a product of indigenous soil management as proposed by Gourou (1949).

Amazonian Dark Earths have high carbon contents of up to 150 g C/kg soil in comparison to the surrounding soils with 20-30 g C/kg soil (Sombroek, 1966; Smith, 1980; Kern and Kämpf, 1989; Sombroek et al., 1993; Woods and Mc Cann, 1999; Glaser et al., 2000).These soils are therefore highly fertile (Lehmann et al., 2003).Fallows on the Amazonian Dark Earths can be as short as 6 months, whereas fallow periods on Oxisols are usually 8 to 10 years long (German and Cravo, 1999).Continuous cropping for longer periods of time appears to be possible from a soil fertility point of view.How long a field can be continuously cropped and what can be done to prolong this period is not yet clear. (2001) reported that Amazonian Dark Earths in Açutuba were under continuous cultivation without fertilization for over 40 years.

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