|MARQUES, JOSE - Sao Paulo State University (UNESP)|
|LA SCALA, NEWTON - Sao Paulo State University (UNESP)|
|NATER, ED - University Of Minnesota|
|SIQUEIRA, DIEGO - Sao Paulo State University (UNESP)|
Submitted to: Encyclopedia of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2015
Publication Date: 1/12/2017
Citation: Spokas, K.A., Marques, J., La Scala, N., Nater, E. 2017. Black Earths (Terra Preta): Observations of wider occurrence from natural fire. Encyclopedia of Soil Science. 3:2312–2315. Available: https://doi.org/10.1081/E-ESS3-120052897.
Interpretive Summary: Biochar additions to soil are gathering widespread attention as a means to combat global warming by increasing soil C sequestration, while also transferring atmospheric CO2 into a slower cycling carbon pool. A significant portion of the argument towards the use of biochar has been linked to the anthropogenic additions creating the fertile black soils (“terra preta”) in the Amazon. However, the full formation history of this fertile and productive soil is not fully known. Based on our recent observations in the Southern regions of Brazil (away from the Amazon), we hypothesize that natural fire occurrence plays a more significant role in the development of these “terra preta” soils than previously acknowledged. This notion of the soil resulting for long-term natural fire history would unite the observations of “terra preta” like soils on other continents, as well as establish a more probable model for their creation. Natural fires could be a key factor in this fertile soil development in the Amazon and elsewhere. These results have applicability across multiple disciplines from plant physiology, agronomy, soil science and global climate change.
Technical Abstract: Recently, the occurrence of fertile dark-colored soils in the Amazon (Anthropogenic Dark Earths or terra preta de Indio) has been associated with prehistoric anthropogenic soil modification through long term additions of black carbon and other organic amendments from both agricultural and waste management activities of ancient Amazonian natives. This hypothesis was supported by the presence of artifacts (e.g., ceramic pieces) located within these soils, which typically decrease with depth. The association of these soils with anthropogenic artifacts has led to the assumption that that these deposits are unique to the Amazon region and that their occurrence is only associated with long-term human occupation of these lands. However, the exact pedogenic history of these soils is unknown. Here we show data that support the wider occurrence of terra preta soils outside of the Amazonian region in Brazil. Our fundamental conclusion is that these terra preta soils developed under a natural fire regime. The resulting fire residuals form a new soil horizon, with unique soil chemistries compared to surrounding geologic derived soils. Our observations, coupled with other studies illustrating the importance of fire in the Amazonia region and the wider occurrence of terra preta like soils, support this larger scale formation hypothesis. This new parent material classification for these fire residuals would provide harmony and clearer linkages between other localized occurrences of increased black carbon soils present across all of Brazil as well as on other continents.