Terra Preta. Who Knew?

Ideas to consider.

Many ideas to consider.

“All the world’s problems can be solved in the garden.” –Geoff Lawton, permaculture pioneer.

I just read “The Biochar Solution”, by Albert Bates. I’m not sure I can fully recommend it, as his argument strikes me as a bit scattered and slightly less than incisive. BUT, that being said, there’s an awful lot to consider here, and an amazing number of things that I’d never heard of before. Terra preta? Salt-water greenhouses that distill fresh water from the air? The UN’s Billion Tree program? Step-harvesting? Pre-Columbian Amazonian cultures that rivaled the Inca and Aztec? So while I don’t feel inclined to uncritically endorse all of his ideas, the topics in the book are fascinating, and they have added some nuance to both my vision of ideal agriculture and to potential solutions to the world’s CO2 problem.

Here’s his idea in a nutshell (it’s kind of hard to summarize, the flip side of good storytelling could be called “rambling”). First, Spanish explorers in the mid-16th century, forced by privation to descend the entire length of the Amazon from the Peru side, encountered tremendous Amazonian civilizations that were built in harmony with nature, and whose farming was based on the intentional improvement of the soil by making a form of charcoal and plowing it into the earth to transform thin Amazonian soils into rich “terra preta” soils, with depths in some places of many feet.

Terra_Preta wikimedia by Rsukiennik

Terra preta, or “dark earth”, soil on the right. Such soils were created through human activity over millennia.

These “garden cities” and the surrounding countryside in Amazonia may have supported a population of 30 million or more, according to Bates. Then came the plague of diseases from the Old World, brought by the Europeans, which decimated American native populations with such rapidity that they lost virtually their entire culture, in addition to 99% or more of their populations. All of that incredibly rich soil, now abandoned, was very rapidly overgrown with jungle trees and vegetation, to such an amazing degree that it sucked so much carbon out of the air that it cause the Little Ice Age of the 17th and 18th century. Bates holds that the Amazonian methods were an exception to the story of agriculture as it has been practiced in virtually every other civilization and time (including our own), whereby the agricultural methods are ultimately so destructive to the soil that the environmental underpinnings of the civilizations fail, causing collapse. (Related post– “An Important Piece of the Puzzle“). He extrapolates further from this, and writes that not only can the methods be revived and used again, but that the intentional “farming” of carbon can actually stabilize or even reverse climate change, if fossil fuel use can be brought under control.

Quite fascinating. All of this is plausible, if not completely proven. Recent scientific inquiry, much of it in just the last few years, seems to concur with his position on pre-Columbian Amazonian civilizations, though there isn’t full consensus on the issue. (A few articles– Scientific American, “Lost Garden Cities: Pre-Columbian Life in the Amazon“, and The Washington Post, “Scientists Find Evidence Discrediting Idea that Amazon was Virtually Unlivable“.) Terra preta soils certainly exist, and apparently, even under the lowest estimates, cover thousands of square miles of Amazonia. Analysis has concluded that these soils were definitely created by human activity. Whether that activity was intentional or not is apparently also debated, some (like Bates) holding that it was clearly intentional, others that it was more an inadvertent result of normal kitchen fires and wastes and varied forms of slash-and-burn agriculture. As to whether reforestation in the Americas helped trigger the Little Ice Age, some researchers do seem to feel that it was a contributing factor, and perhaps a major one. (Stanford article here.) If this was indeed true, then it would lend credence to Bates’ ideas that a concerted effort to sequester carbon—to remove it from the natural carbon cycle—would have a similar effect, and could reverse or stabilize global warming. Again, there are experts in all of these fields who would agree, but there are certainly others who would argue about the particulars.

A 45-minute-long BBC production entitled “The Secret of El Dorado”, that touches on most of the topics in this post. It’s more even-handed than Bates’ book, and fairly convincing—

At the root of this entire story is charcoal, or, in the parlance of enthusiasts, “biochar”. (Biochar being charcoal that is contaminant-free and therefore useful as a soil amendment). To make charcoal, woody materials or other biomass is exposed to heat in the absence of oxygen, where they off-gas volatile compounds (“wood gas”) in a process known as pyrolization. The gasses can be burned, and if this off-gassing process is allowed to continue the original fuel remains behind as nearly-pure carbon, or charcoal. Cultures around the world have made charcoal for millennia, and many still do so today for use as fuel, and particularly for use as cooking fuel. But, if that charcoal is added to soil as an amendment, it effectively sequesters the carbon it contains, because the carbon in biochar is chemically “recalcitrant”, or resistant to change (as opposed to “labile” carbon, which is what most of the carbon in soils typically is, in humus and other plant matter). As such, it can remain unchanged in the soil for hundreds or thousands of years (and the existence today of these black soils, 500 years after Columbus, certainly seems to give evidence of this). Combining this form of carbon sequestration with afforestation (planting trees), and the raising of carbon levels in soils as a function of organic farming and/or permaculture could measurably reduce atmospheric carbon. According to Bates and others, the idea of actively sequestering carbon in this way could save humanity from rising global temperatures.

Charcoal vendor, Zambia, 2009. Environmental groups around the world report charcoal production as a major pressure on forests.

Charcoal vendor, Zambia, 2009. Environmental groups around the world report charcoal production as a major pressure on forests.

Bates isn’t alone, apparently there are whole groups that exist to promote biochar and related forms of carbon sequestration, such as the “International Biochar Initiative“. One huge proponent is Nathaniel Mulcahy, founder of WorldStove, (oddly pictorial website here). His organization makes simple pyrolizing cookstoves for poor people around the world (their tagline is “A Million Stoves”). The stoves burn cleanly and help avoid the soot inhalation that kills up to four million people every year, they are efficient, and, they produce biochar. (Apparently their high efficiency makes up for the fact that some of the potential energy in the fuel remains as charcoal). When the charcoal is used as a soil amendment (or better yet, first used in composting toilets and then as a soil amendment) then the use of the stove actually becomes carbon negative, as long as the fuel was sustainably harvested.

Rural outdoor kitchen, of an inefficient design.

Rural outdoor stove, of an inefficient design. Smoke inhalation from such stoves that are used indoors contributes to the death of over 4 million people a year.

If millions used these efficient stoves, they could potentially improve the health, sanitation, and food production of poor people around the world, and sequester carbon at the same time. It’s a pretty bold vision, and Mulcahy and his company are active in poor regions around the world, including Haiti after the earthquake of 2010. Below is a video demonstration of a stove like the ones the company makes. This one is “homemade”; the precision parts of the factory-built stoves burn even cleaner, with a nearly invisible blue flame. Once the stove gets to operating temperature, it is wood-gas that is burning, as the woody fuel pyrolizes—

Not all environmental groups agree with the vision of the biochar proponents. One such group is Biofuelwatch, a UK-based group that opposes most large-scale uses of biofuel, fearing for the safety of both forests and natural areas, and of the rural peoples who live there. Charcoal production already puts pressure on forests around the world, and I can understand their fear of what might happen if biochar as a soil amendment was given international sanction as a measurable carbon offset. Biochar proponents, however, point to the tremendous amounts of agricultural wastes that exist worldwide, such as rice straw, that could be utilized without any negative effect on forests.

In the end, as with everything else, the truth is often nuanced and far from the extremes. IF the source fuel for biochar was gathered sustainably, the use of biochar in agriculture seems to fit in very well with sustainable paths forward. As the world (hopefully) switches to regenerative, sustainable permaculture of the type espoused by Mark Shepard and others, huge amounts of carbon will be captured and stored in the trees and soils of these systems. According to Mark Shepard, these systems also produce more woody biomass, in the form of nut shells, pruned and coppiced wood, etc., than can generally be used. Such waste biomass would be perfectly suited for biochar production, and the resulting amendments could be added to the soil during keyline plowing or during planting operations.

One last video, if you’re interested—small-scale production of biochar. Pretty amazing, note the near absence of smoke once the kiln reaches gasification temperature—

So, I’m not sure that you need to read the book. But, you do need to add the word “biochar” to your vocabulary, and we all need to keep it in mind as perhaps an important part of new permaculture systems, and perhaps even, if Bates is correct, as a carbon sequestration option that might help “save humanity”.

 Terra preta image: Rsukiennik, Wikimedia Commons.
Charcoal vendor image: CIFOR; Creative Commons at http://www.flickr.com/photos/45423546.
Rural kitchen image: CIFOR; Creative Commons at http://www.flickr.com/photos/cifor/8620660813.