»Terra Preta« is Portuguese and means »black soil«. The term refers to an anthropogenic, that is, man-made form of soil, which was discovered by archaeologists in the Amazon Basin at the end of the 1980s. About 10 % of the Amazonian area is covered by Terra Preta, partly in meter-thick layers.
In the 16th century, the conquistador Francisco de Orellana was the first European to venture an expedition to the Amazon. He gave an account of high cultures with prosperous agriculture and colonies with several hundred thousands of inhabitants.
When Europeans settled in the Amazon a few decades later, they found no sign of the civilization described by Orellana. For centuries, his reports were considered exaggerated, therefore, – not least because of the infertility of the Amazon soil. In combination with the former agro-technical facilities, this soil would not have been able to steadily sustain a large civilization.
Archaeological finds at the end of the 20th century rehabilitated Orellana. Archaeologists discovered numerous clay fragments indicating a high culture, which had been imbedded in very eutrophic black earth soil – soil which naturally does not occur in the Amazon area. This soil posed another scientific riddle: Why does black earth occur in the yellow, infertile alteration soil (called »oxisole«) of the Amazon?
Since the 1990s, agrologists worldwide have been exploring the consistence of this Terra Preta do Indio and the secret of its origin. A team of the University Bayreuth led by the agrologist Dr. Bruno Glaser succeeded in proving that the Terra Preta was created by man.

• age: 500 – 3000 years
• square dimension: ca. 10 % of the Amazon area
• high cultures with several million people in the 16th century (despite infertile soil)
• today only roughly 350,000 people
• Terra Preta areas between 0,1 and 350 ha in size
• ground height up to 20 m (partly mounds)
• soil is exceedingly fertile without mineral fertilizing (multiple harvest)
• high concentration of durable humus and nutrients
• exceedingly high buffer capacity and cation exchange ability
• high persistence
• high water storage capacity
• phenomenon: highly reduced dissimilation of biomass, alteration to solid durable humus instead!