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The "Terra Preta" Phenomenon: A model for Sustainable Agriculture in the Humid Tropics


Many soils of the lowland humid tropics are thought to be too infertile
to support sustainable agriculture. However, there is strong evidence
that permanent or semi-permanent agriculture can itself create
sustainably fertile soils known as ‘Terra Preta’ soils. These soils not
only contain higher concentrations of nutrients such as nitrogen,
phosphorus, potassium and calcium, but also greater amounts of stable
soil organic matter. Frequent findings of charcoal and highly aromatic
humic sub- stances suggest that residues of incomplete combustion of
organic material (black carbon) are a key factor in the persistence of
soil organic matter in these soils. Our in-vestigations showed that
‘Terra Preta’ soils contained up to 70 times more black carbon than the
surrounding soils. Due to its polycyclic aromatic structure, black car-
bon is chemically and microbially stable and persists in the environment
over centuries. Oxidation during this time produces carboxylic groups on
the edges of the aro- matic backbone, which increases its
nutrient-holding capacity. We conclude that black carbon can act as a
significant carbon sink and is a key factor for sustainable and fertile
soils, especially in the humid tropics.