Identifying the Pre-Columbian Anthropogenic Input on Present Soil Properties of Amazonian Dark Earths (Terra Preta)

Abstract

Soil degradation is one of the most serious problems of land use in the tropics, in particular the Neotropics, because the majority of the soils are very old, deeply weathered, and rather infertile (Zech 1997). Under tropical conditions, hydrolysis of primary minerals, for instance, is enhanced by a factor of 100 in comparison to temperate regions (Whitmore 1993). In combination with the high precipitation, the released nutrients are highly susceptible to leaching. Clearing of forests or woodlands and their conversion into farmland reduces the soil organic matter (SOM) contents due to higher mineralization rates and reduced litter input and increases soil erosion (Sombroek et al. 1993). Tiessen et al. (1994) calculated a mean turnover rate of 4 years for particulate SOM in undisturbed soils of the Venezuelan rain forest. These phenomena explain why most of the tropical soils become infertile within a few years after cultivation. Soil amelioration with mineral fertilizers or organic manure is often limited by high costs, low cation exchange capacity of the soils, and poor knowledge about the nutrient depletion from the composts (Tiessen et al. 1994).