Wednesday, June 27, 2007

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.

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)


Anonymous said...

Dear Richard,

Your ideas seem sound that native folks inoculated new TP with old TP.
I'm sure that temperate charcoal soils are quite different in both variety and density of wee-beastie populations, however the work by Danny Day in Georgia and the work done in Japan & Germany seem to show increases in the local soil microbes and fungi.
My feeling is that if you build it, they will come.
Maybe not with the intensity of the tropics, given the moisture and solar inputs, but good soil infrastructure will be just as appealing to our bugs.

Closed-Loop Pyrolysis; Burning our way back to a stable climate.

I think I will make this the title of my next TP article

Erich J. Knight

kjmclark said...

It seems to be working well in my garden in Michigan. Granted, we've worked hard for over a decade to build organic, humus rich, biotic soil in our garden, but the plots with charcoal seem more productive than the ones without. We had our best pepper harvest in the fifteen years we've had a garden last year in the first plot we put charcoal in.

I think the charcoal provides a home for microorganisms, so that you get better biotic soil with the charcoal than without. It may well be that the terra preta soils in the Amazon were cross-inoculated, but it may also be that certain microorganisms prefer to live in terra preta soils. I can't see any reason not to add charcoal - if nothing else, you're sequestering carbon in your backyard!

Lizzie Connor said...

A friend has just referred me to your blog and I find it very interesting - if bleak.
When I first heard about terra preta I was struck by it because it was just another example of how we underestimate the achievements of ancient peoples outside "the cradle of civilization" area.
By the way I think that migrating people might have carried fire with them because it was much easier to get a fire going that way, not necessarily because they didn't know how to start one. How long is it since any of us tried making fire without matches - or even with matches?
I intend to keep up with your blog - even if I don't read every single word.

eboy said...

It is the most attractive of propositions. Can we have our cake and eat it too.

Sequestering carbon and improving the soil and yields at the same time.

I am thinking about how instead of composting my o.m maybe it should be pyrolized and the resultant heat be used to heat water and the exhaust. If you didn't already know this will run a gasoline engine which could drive a generator.

So in short make a charcoal kiln placd a boiler in the center above the kiln to capture the heat. Run the exhaust to a generator and the by-product goes to the fields.

I have yet to put charcoal in my garden, but I have heard it takes a while to see the results.

Per out email conversation Richard
I think there is a fit with Engineer Poet's sustainable proposition from his blog

With respect to your seeding proposition of terra pretta soil for innoculent. I think this would be hard to test. Though I imagine if cultures were compared after several years of adding charcoal to the soil with t.p. soil maybe there would be similar types of bacteria.

Elaine Ingham from Soil food web and Acres u.s.a. would be a person to ask about this. Her company does bacterial analysis of composted materials and identifies various bacteria.

Good post.