5 July 2023

According to Brazilian research, the valuable black soil found in parts of the Amazon retains unique characteristics that promote the rapid recovery of deforested land

by Matteo Cavallito


The black soil of the Amazon, or that particular type of soil found in some areas of the forest and famous for its fertility, could prove particularly useful in restoration operations of deforested areas. This is suggested by research carried out by the University of São Paulo in cooperation with two government research organizations: the Brazilian Ministry of Agriculture’s Empresa Brasileira de Pesquisa Agropecuária (Embrapa) and the Instituto Nacional de Pesquisas da Amazônia Research of the Ministry of Science, Technology and Innovation.

“Deforestation of areas for agriculture and cattle breeding is the leading cause of ecological degradation and loss of biodiversity,” says the study published in the journal Frontiers in Soil Science. “The solution to mitigate these damages relies on techniques that improve soil health and the microbial quality of these degraded areas. Here, we demonstrate that the high nutrient and microbiological contents of Amazonian Dark Earths (ADE) can promote the development of trees used in ecological restoration projects.”

The black soil of the Amazon

Known as terra preta (“black soil” in English), this particular type of soil is present, albeit in small quantities, in some places in the Amazon characterized by a previous human presence. This soil is part of a macro-category of terrain known for their legendary fertility and found in various parts of the world from Ukraine, where this type of soil covers more than 65 percent of the country’s arable land, to the Chinese provinces of Heilongjiang, Jilin and Liaoning, which alone contribute to the production of 50 percent of the country’s rice, 41 percent of its soybeans and 34 percent of its corn.

According to the report “The Global Status of Black Soils,” published late last year by the FAO, terra preta sediments, according to the most reliable hypothesis based on archaeological pedological evidence, “were formed unintentionally by pre-Columbian Amerindian societies in the Amazon basin.” Their contents are rich in organic matter, the result of the decomposition of ashes, ceramics, animal bones and other wastes.

The experiment

Researchers filled 36 pots with 3 kilograms of soil and placed them in a greenhouse at an average temperature of 34 degrees Celsius simulating conditions in deforested areas of the Amazon under the climate change scenario, according to the U.S. NGO Mongabay. One-third of the pots hosted normal soil, another third hosted a mixture with a 20 percent black soil content (20%ADE). The remaining 12 pots contained only black soil (100%ADE).

“We simulated conversion from pasture to forest restoration area by planting U. brizantha in all pots,” the authors explain in the research. “After 60 days, we removed it and planted Cecropia pachystachya, Peltophorum dubium, and Cedrela fissilis.”

After 90 total days of growth, the scientists measured the evolution of the seedlings’ roots in addition to analyzing the chemical properties and microbial diversity of the soil. The presence of black soil had increased growth by as much as eight times in some cases. “Both 20%ADE and 100%ADE showed similar numbers of taxa, being significantly higher than in the control soil,” the research says.

A resource for the Amazon

According to the authors, black soil would prove to be “an enhancer of plant development and beneficial microbiota enrichment in the rhizosphere.” As a result, the researchers believe that the data collected “could contribute to speeding up forest restoration programs by adopting new biotechnological approaches for forest restoration ecology.” The availability of black soil in Brazil does not seem sufficient for wide-ranging use in the restoration process.

But the study of its properties could enable scientists to create other organic products capable of replicating its characteristics in the future. And, as a result, accelerate the recovery of deforested areas.

The discovery, meanwhile, takes on significant importance for the Amazon, which, Mongabay recalls, lost 12 percent of its land area between 1985 and 2022 with the disappearance of some 44 million hectares of native vegetation. According to data from the Brazilian nonprofit organization Imazon, quoted by Mongabay, in 2019 the regeneration process-considering only those that have been active for at least six years-was affecting 7.2 million hectares.