1966: Biochar en de ontdekker van de terra preta, Wim Sombroek
In the Amazon soils occur that were formed during pre-historical human occupations. These soils are highly fertile and stable and are most commonly referred to as terra preta, Amazonian Dark Earths (ADE) (Woods and McCann 1999), or Archaeological Black Earth or Indigenous Black Earth (Kern 1988, 1996; Kern and Kämpf 1989). It appears that ADE form proper micro-ecosystems where the soils do not exhaust themselves easily, even in the tropical conditions where are exposed for long periods of time. Several process-oriented designations have been suggested for the ADE formation processes, such as: “vegetable soils”, “plaggen epipedon” or “anthropic soils”. The latter one, the most accepted, proposes that the ADE were intentionally formed by the pre-historical inhabitants. Archaeological evidence indicates that ancient human activities in the Amazonian habitats transformed, significantly, the landscapes of the vicinity of their settlements (e.g. Kämpf and Kern 2005). In many areas, indigenous societies formed extensive deposits that altered the soil properties (Lehmann et al. 2003; Woods and McCann 1999). These archaeological sites’ dark soils were created by deposits of vegetal origin (charcoal, ash, leaves and diverse palm fronds, manioc residue, seeds, etc.) and residues of animal origin (bones, blood, fat, feces, chelonian carapaces, shells, etc.). These materials resulted in highly fertile soils with elevated levels of P (more than 1,000 mg/kg of soil), Ca, Mg, Zn, Mn, and C (Kern 1996). The organic matter in ADE is on the order of six times more stable than in the soils of forest (Pabst 1992), owing to the stability of fertility in ADE. In locations where Black Earth is present a strip of soil with dark brown coloration is often also found, without ceramics artifacts, but with elevated levels of OM. These soils were called terra mulata (TM) by Sombroek (1966). According to Sombroek et al. 2002, the areas of TM are the resultant of the intentional application of charred plant materials sometimes associated with human or animal residues (fishing and hunting products, calcium from shells and mollusks from consumption) and from other residues of plant origin. The development of the terra mulata expanses associated with the habitation areas allowed for expansion of horticultural food production and most reliability of sustainable harvests.