Further, the potential for enhancing sequestration by active management of black C could be established with important linkages to energy production and land use (see biochar soil management).
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).
The structural similarity of organic matter in Terra preta to biochar led scientist to assume that accumulation or purposeful application of organic carbon from incomplete combustion may have been the primary reason for the high carbon contents and fertility of these soils (Glaser et al., 2001), a theory that had been proposed by Smith (1980).
If all or some of these soils were actually created by char applications to improve soils for agriculture has still to be demonstrated.
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).Other images and text belong to their respective owners. "Terra Preta de Indio" (Amazonian Dark Earths; earlier also called "Terra Preta do Indio" or Indian Black Earth) is the local name for certain dark earths in the Brazilian Amazon region.These dark earths occur, however, in several countries in South America and probably beyond.Only short fallows are presumed to be necessary for restoring fertility on the dark earths.However, precise information is not available, since farmers frequently fallow the land due to an overwhelming weed infestation and not due to declining soil fertility.Continuous cropping for longer periods of time appears to be possible from a soil fertility point of view.