Left - a nutrient-poor oxisol; right - an oxisol transformed into fertile terra preta

From Wikipedia, the free encyclopedia

Terra preta (literally “black earth” in Portuguese) is a type of very dark, fertile anthropogenic soil found in the Amazon Basin. Terra preta owes its name to its very high charcoal content, and was indeed made by adding a mixture of charcoal, bone, and manure to the otherwise relatively infertile Amazonian soil over many years.^[1] It is also known as “Amazonian dark earth” or “Indian black earth”. In Portuguese its full name is “Terra preta do índio” or “Terra preta de índio”. Terra mulata is lighter or brownish in color.^[2]

Terra preta is characterized by the presence of low-temperature charcoal in high concentrations; of high quantities of potterysherds; of organic matter such as plant residues, animal feces, fish and animal bones and other material; and of nutrients such asnitrogen (N), phosphorus (P), calcium (Ca), zinc (Zn), manganese (Mn).^[3] It also shows high levels of microorganic activities and other specific characteristics within its particular ecosystem. It is less prone to nutrient leaching, which is a major problem in most rainforest soils. Terra preta zones are generally surrounded by terra comum, or “common soil”; these are infertile soils, mainlyacrisols,^[3] but also ferralsols and arenosols.^[4]

Terra preta soils are of pre-Columbian nature and were created by humans between 450 BC and AD 950.^[5][6] The soil’s depth can reach 2 metres (6 feet). Thousands of years after its creation it has been reported to regenerate itself at the rate of 1 centimetre per year^[7] by the local farmers and caboclos in Brazil‘s Amazonian basin, and they seek it out for use and for sale as valuable compost.