Amazonian dark earths: The first century of reports

Abstract

Amazonian dark earths are anthropogenic soils called terra preta de índio in Brazil, created by indigenous people hundreds, even thousands, of years ago (Smith 1980; Woods and McCann 1999). Terra preta proper is a black soil, associated with long-enduring Indian settlement sites and is filled with ceramics and other cultural debris. Brownish colored terra mulata, on the other hand, is much more extensive, generally surrounds the black midden soils, contains few artifacts, and apparently is the result of semi-intensive cultivation over long periods. Both forms are much more fertile than the surrounding highly weathered soils, mostly Ferralsols and Acrisols, and have generally sustained this fertility to the present despite the tropical climate and despite frequent or periodic cultivation. This fertility probably is because of high carbon content, which retains nutrients and moisture, and an associated high and persistent microbial activity. The high concentrations of pyrogenic carbon in terra preta come mainly from charcoal from cooking and processing fires and settlement refuse burning, and in terra mulata the carbon probably comes from in-field burning of organic debris. Low intensity cool burning, what has been called slash-and-char, resulting in incomplete combustion, can produce carbon in high quantity which can persist in soil for thousands of years. Dated carbon in dark earths is as old as 450 BC (Hilbert 1968; Petersen et al. 2001:100). In contrast, slash and burn shifting cultivation fires today tend to be hot fires, set at the end of the dry season, which produce large releases of carbon dioxide to the atmosphere and more ash of brief persistence than charcoal. © Springer Science + Business Media B.V. 2009.