Are there ‘Amazonian Dark Earths’ in Africa?

Through the theme of Global Transformations researchers are rethinking social adaptation in the context of changing environments and the global economy.

By revealing the existence of anthropogenic dark earths in tropical West Africa, Sussex researchers hope to build on indigenous farming knowledge and practices in efforts to intensify farming, and in ways that mitigate climate change.

Uncovering the ecological and agricultural importance of anthropogenic dark earths in West Africa

Research into Amazonian soils in the last two decades has led to a fundamental reappraisal of the region’s social and natural history. Highly fertile dark soils, commonly known as anthropogenic dark earths (ADEs) and locally as terra preta (black earth), had been thought to be naturally occurring but are now known to be human made. These ADEs are estimated to cover 1.2-1.8 million hectares and were produced by the continent’s pre-Hispanic Amerindian peoples on otherwise extremely poor soils. They are now believed to have supported the tens of millions of people who suffered catastrophic mortality following contact with Europeans.

Previously, research on ADE soils has been confined to Amazonia. However, new research by an international team of anthropologists and soil scientists is revealing the existence of anthropogenic soils in tropical West Africa and, like Amazonian ADEs, they are a phenomenon that appears to have been overlooked by Western research.

Section through soil ADE soil in Liberia, extending almost 2 metres deep in the original soil, visible below

ADEs are not only of historical interest but are potentially very relevant to modern society and agriculture. These soils are highly prized by farmers who are able to use them to farm intensively, unlike the natural soils in which they are formed. Understanding their creation and complex biology holds great scientific interest: if they could be mimicked, it may offer a way to intensify farming in developing regions with poor, highly weathered soil. Additionally, as a key component of the fertility of ADEs is the high proportion of charred carbon, or ‘biochar’, that they contain, farming technologies based on ADEs could be used to sequester enormous amounts of carbon in the soil. A great deal of work remains to be done on the feasibility of reducing atmospheric carbon by such methods. Nevertheless, ADEs suggest a potential research opportunity for improving agricultural practices while mitigating climate change.

It had been argued that ADEs are a feature unique to the Amazonian region, and that mimicking them may offer a useful technology to import into Africa. However, a multidisciplinary team that includes researchers from Sussex, headed by Professor of Social Anthropology James Fairhead, in collaboration with international research groups from the University of Ghana and Cornell University in the USA, is finding that anthropogenic dark earth soils already exist in the West African tropics and subtropics and are an important resource to farmers.

As in Amazonia, however, these soils have been overlooked by soil scientists and anthropologists. With fieldwork funded by the UK’s Economic and Social Research Council (ESRC) in Ghana, Guinea, and Liberia, and in collaboration with researchers in Sierra Leone and Nigeria, the research is examining how ADE soils are created and used, asking: what processes of carbon enrichment and agroecological transformation are significant?; what mix of social, ecological and technical factors is involved?; how do African farmers distinguish, value and use these soils; what is the significance to livelihoods?; and to what extent and in what ways do these soils share characteristics with Amazonian ADEs?

The intention of the research is to advance understanding of previously underappreciated local soil knowledge in Africa. Evidence for ADEs will also help establish a more productive dialogue and collaboration between researchers, building on ADE technologies in South American and African contexts. Whether or not the African dark earths are similar to those in the Amazon, it is hoped that this research will ultimately lead to technological advances to improve modern agronomic practice while addressing climate change.

James’s perspective

James Fraser‘The forests in Liberia are often depicted as primeval, so I was surprised to find that soils and vegetation in the northwest are revealing a long-domesticated landscape. Fertile Anthropogenic Dark Earths are widespread and reveal historic settlement patterns like an archive. I know similar soils from my doctoral research on terra preta in Brazil where farmers profit from soils enriched in pre-Hispanic times. But in Liberia these soils are still forming around villages from the everyday deposition of fresh and charred organic waste.

‘Farmers have also been showing me dozens of anciently abandoned towns which also feature deep ADE, and which they prize for tree crops like cocoa and kola nuts or conserve as forest. The excitement is in finding that biochar practices and dark earths, which are now being explored by the scientific world as a new way to promote sustainable farming in tropical agro-ecosystems while sequestering huge quantities of carbon, are already part of the West African farming repertoire. There is a lot of experience and knowledge here that could be built on and incorporated into strategies to support agriculture on otherwise poor soils.’

James Fraser
Research Fellow, Department of Anthropology