Modern soil DNA testing reveals the rich microbiology of Amazonian Dark Earth
The story of terra preta — known scientifically as Amazonian Dark Earth (ADE) — lies at the intersection of history, archeology, geology and soil science. The mystery and potential of ADE is alive today as modern agribusiness struggles to maintain soil productivity. Understanding ADE — particularly, as discussed below, the microbiological diversity it helps create — could help regenerative agriculture create profound global impacts on the environment and society.
In Dirt: The Erosion of Civilizations, David Montgomery makes a compelling geology-based argument that the degradation of anthrosols (soils modified by human use) over the course of hundreds and thousands of years led to the downfall of many civilizations. Modern agriculture similarly tends to extract resources from the soil and does not follow the fundamental law of return — the necessity of the farmer to put back into the soil the organic matter that was removed via harvest.
While ADE may seem comparable to the soil created by modern organic cultivation practices, ADE’s unique chemistry and physical composition leads to a more dynamic and robust microbiome, which creates exceptional fertility and longevity.
ADE is not an isolated phenomenon. Ancient, rich anthrosols developed for highly productive agricultural use have been also identified by archaeologists in Africa, Mexico and Germany. These farmers applied composted agricultural waste, charcoal, broken pottery and other organic waste products to the soil — a practice that increased elemental nutrients, improved water holding capacity, and aided in drainage. A study from 2019 analyzed 300 samples of ADE discovered elevated nutrient levels, including of P, Ca, K, Mg, Mn, Ba, Zn, Sr, Cu, Rb, Ni, Li, Cd, Cs, Co, Tl and Be. One of the most striking aspects of ADE — one that is currently being adopted by many organic producers — is that the fraction of biochar, or black carbon, is about 70 percent higher than adjacent jungle ultisols (soils in humid areas that are typically highly weathered).
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