Terra preta (“dark earth” in Portuguese) refers to expanses of very dark, fertile anthropogenic soils found in the Amazon Basin. It owes its name to its very high charcoal content. It is also known as “Amazonian dark earth” or “Indian black earth”.
Terra preta is characterized by the presence of low-temperature charcoal in high concentrations; of high quantities of pottery sherds; of organic matter such as plant residues, animal faeces, fish and animal bones and other material; and of nutrients such as nitrogen.
Terra preta is VERY productive soil. Biochar, or "Agrichar" is that low temperature charcoal used to enhance the soil.