Terra preta

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 potsherds; 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). Fertile soils such as terra preta show high levels of microorganic activities and other specific characteristics within particular ecosystems.

...
Wikipedia