Indigenous Knowledge About Terra Preta Formation

Throughout the world intensive agricultural land use often has resulted in soil physical and chemical degradation, due to erosion and higher output than input rates of nutrients and OM. In contrast, the intentional and unintentional deposition of nutrient-rich materials within human habitation sites and field areas has in many cases produced conditions of heightened fertility status (Woods 2003). An anthropogenic enriched dark soil found throughout the lowland portion of the Amazon Basin and termed Amazonian Dark Earths (ADE) or terra preta de índio (TP) is one such example. Its fertility is the secondary result of the transport of natural and produced foods, building materials, and fuel to prehistoric dwelling places (Woods 1995). These materials and their byproducts were then transformed and differentially distributed within the zone of habitation and associated garden areas. The resulting soil contains high concentrations of black carbon (C) as charcoal (Glaser et al. 2001a); significantly more C, nitrogen (N), calcium (Ca), potassium (K), and up to 13.9 g kg⁻¹ P2O (almost 4 g kg⁻¹ available P) (Lima et al. 2002); and significantly higher cation exchange capacity (CEC), base saturation (BS), and pH values than in the surrounding Oxisols (Glaser et al. 2000; Zech et al. 1990). ADE is found at pre-Columbian settlements throughout Amazonia in patches ranging in size from less than a hectare to many square kilometres (Woods and McCann 1999). Today these soils are and presumably in the past were intensively cultivated by the rural population. The enormous total area encompassed by these soils suggests a large sedentary pre-Columbian population (Erickson 2000; Heckenberger et al. 2003). The existence of ADE proves that infertile Ferralsols and Acrisols can be transformed into permanently fertile and refractory TP in spite of rates of weathering 100 times greater than those found in the mid-latitudes. Such a transformation cannot be achieved solely by replenishing the mineral nutrient supply, however; the soil organic matter (SOM) is also of prime importance for insuring the retention of soil nutrients (Zech et al. 1990).