Terra Preta Soils - Agricultural Miracle from the Past?

Sometimes we literally can't see the forest for the trees. In recent years there has been a great deal of scientific interest in a soil phenomenon in South America's Amazon River basin, a phenomenon called Terra Preta.

Scientists now understand, though they did not until recently, that Terra Preta soils are anthropogenic, created by man. They were, in fact, created hundreds, even thousands of years ago through the efforts of indigenous peoples living and thriving in the Amazon River basin. It was only recently, through efforts to re investigate myths from Spanish explorers about the fabulous golden cities of El Dorado that the forest behind the trees finally started to come into view.[3] It was through those efforts that the full extent of anthropogenic Terra Preta soils in this area were finally realized. It is estimated that as much as 10%, maybe more, of the soils in the Amazon basin are Terra Preta soils. Only after understanding these magnitudes did archaeologists finally understand how there had been a sufficient agricultural base to support the vast ancient civilizations (now estimated to possibly number into the millions of people) in the Amazon basin, civilizations that, until recently, had largely been written off as myth.

What is Terra Preta soil? Essentially, and it is a mistake to believe this gives a complete understanding of what makes Terra Preta work, Terra Preta is soil that has been enhanced by black carbon, derived from charcoal, and other organic matter. But there is more. A report entitled Isolating Unique Bacteria from Terra Preta Systems: Using Culturing and Molecular Tools for Characterizing Microbial Life in Terra Preta, states, "The greater fertility of Terra Preta (TP) soils is thought to be due to their high black carbon (BC) content, which contributes to increased nutrient and moisture retention, and increased pH. It is likely that the unique chemistry of BC results in distinct microbial communities involved in nutrient cycling and organic matter turnover.[my italics]"[1] With a number of extensive scientific investigations underway on Terra Preta soil, in fact, scientists are coming to realize that the similarities of the bacterial colonies in Terra Preta soils at different locations, even hundreds of miles apart, are far greater than similarities to the bacterial colonies in non Terra Preta soil in areas immediately adjacent to Terra Preta sites.[1, 2]

Here is where I launch into my own speculation. Throughout the history of man nomadic peoples have carried with them from site to site materials and items that are of critical value to them. The Polynesians as they hopped from Pacific island to Pacific island took with them the seeds, roots and seedlings of particular plants that were important to their culture. Early men, as yet not knowing how to create fire, took great pains to carry embers from one fire to start a fire at a new site.

It is not unreasonable to speculate, in fact, that the original pockets of Terra Preta soil were not made by man but rather discovered by man. Over time they may have realized that adding charcoal from their fires to the soil resulted in dramatic increases in fertility. They may have taken this knowledge to a new site and found, in fact, that it didn't net them the results they expected. It may have been, at that stage, that they returned to the site with the fertile Terra Preta soil, gathered up some of that soil and carried it with them to the new site where they mixed it, and more charcoal, into the soil at the new site. It is very unlikely that they would understand what made the original Terra Preta soil so fertile. It would probably have been a form of magic to them, and that Terra Preta soil that they carried from site to site would have been seen as magical in its own rite.

This hypothesis of mine (I'm not claiming it is original or unique but I have not seen similar speculation in other quarters) would clearly explain why the bacterial population in one Terra Preta site is so like that at other Terra Preta sites but unlike the bacterial population in non Terra Preta sites adjacent to Terra Preta sites. The bacteria in the Terra Preta soil did not originate in the soil that was transformed into Terra Preta soil but originated in a Terra Preta site elsewhere and was transported there by the indigenous people who established the new Terra Preta site. This would suggest that the development of the Terra Preta soils throughout the Amazon basin was spread over hundreds, even thousands of years as indigenous peoples criss-crossed the basin moving from one site to another, taking their magical Terra Preta soil with them to seed the soil at the next site.

Regardless of whether my speculation is correct concerning how the different pockets of Terra Preta soil were created, the important point is this. What makes Terra Preta soil work is not the black carbon from charcoal that has been added to the soil. It is the unique population of soil bacteria in that soil that utilizes and thrives on that high concentration of organic carbon. Terra Preta soil, like all soils, derives its fertility not from the mineral content of the soil but from the tens of millions of micro-organisms that live in that soil and make those minerals and other soil nutrients available to the plants growing in that soil.

My caution is this..... do not go out and add a bunch of charcoal or black carbon to your garden thinking it will give you Terra Preta soil with its wondrous fertility. You can, however, buy bags of Terra Preta soil at some better garden centres that can be added to your garden, along with charcoal or black carbon, that will give the desired results.

One more caution..... To my knowledge no scientific testing has yet been done to determine if the bacteria unique to Terra Preta soils can survive in non-tropical soils, most specifically in soils prone to a winter freeze. Until such testing has been completed I would be cautious about trying to duplicate Terra Preta soil in your garden in growing zones subject to winter freeze.


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1. Isolating Unique Bacteria from Terra Preta Systems: Using Culturing and Molecular Tools for Characterizing Microbial Life in Terra Preta - 16-Aug-2006
Authors: O'Neill, Brendan; Grossman, Julie; Tsai, S.M.; Gomes, Jose Elias; Garcia, Carlos Eduardo; Solomon, Dawit; Liang, Biqing; Lehmann, Johannes; Thies, Janice
2. Terra Preta
3. BBC - Horizon - The Secret of El Dorado (see particularly minutes 45-48)