Terra preta (Portuguese pronunciation: [ˈtɛʁɐ ˈpɾetɐ], locally [ˈtɛhɐ ˈpɾetɐ], literally "black soil" in Portuguese) is a type of very dark, fertile manmade (anthropogenic) soil found in the Amazon Basin. 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 ("black soil of the Indian", "Indians' black earth"). Terra mulata ("mulatto earth") is lighter or brownish in colour.
Terra preta owes its characteristic black color to its weathered charcoal content, and was made by adding a mixture of charcoal, bone, and manure to the otherwise relatively infertile Amazonian soil. A product of indigenous soil management and slash-and-char agriculture, the charcoal is very stable and remains in the soil for thousands of years, binding and retaining minerals and nutrients.
Terra preta is characterized by the presence of low-temperature charcoal residues in high concentrations; of high quantities of pottery sherds; of organic matter such as plant residues, animal feces, fish and animal bones and other material; and of nutrients such as nitrogen (N), phosphorus (P), calcium (Ca), zinc (Zn), manganese (Mn). As in fertile soils in general, it also shows high levels of microorganic activities and other specific characteristics within its particular ecosystem.
Terra preta zones are generally surrounded by terra comum ([ˈtɛhɐ koˈmũ] or [ˈtɛhɐ kuˈmũ]), or "common soil"; these are infertile soils, mainly acrisols, but also ferralsols and arenosols. While deforested arable soils in the Amazon are productive for just a short period of time, and farmers are constantly moving to new areas and clearing more land, the terra preta soil is less prone to nutrient leaching caused by heavy rains and floods, because of its high concentration in charcoal, microbial life, and organic matter, accumulating nutrients, minerals, and microorganisms.
Terra preta soils are of pre-Columbian nature and were created by humans between 450 BCE and 950 CE. The soil's depth can reach 2 meters (6.6 ft). Thousands of years after its creation it has been reported to regenerate itself at the rate of 1 centimeter (0.39 in) per year by the local farmers and caboclos in Brazil's Amazonian basin, who seek it for use and for sale as valuable potting soil.
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