Rediscovering Terra Preta

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Seven thousand years ago, the peoples of the Amazon basin developed a kind of 'super-soil' we now call terra preta. Today, companies in Canada and across the world are working hard to duplicate their discovery. Terra preta may just save modern agriculture.

Up to two meters of dark, rich earth can be found throughout the ordinarily-poor soils of the Amazon basin. This is the terra preta—a soil so rich that it is dug up and sold by the locals as compost, despite being, in some cases, thousands of years old. Indeed, the terra preta is more than simply rich loam: the local people believe that it self-regenerates at a rate of up to one centimeter a year. It is certainly extremely long-lived.

Nutrients leach out of tropical soils. Typically, a rainforest's biomass is almost entirely contained in the foliage, with the soil being very poor. The lush greenery of a rainforest is a bit of an optical illusion; you might think that all this fertility rests on an amazingly rich soil, but the opposite is the case. Cut down the forest for farming, and you get extremely poor farmland. This situation is strikingly analogous to what is occurring in North America after generations of intensive monoculture farming using fertilizers, herbicides and pesticides. The natural nutrients of our own soils are leaching away, into the groundwaters, the rivers, and ultimately the sea.

The Amazonian terra preta has not lost its nutrients, so it is highly prized. It contains large concentrations of charcoal, which is what gives it its black colour, so it's been known for a long time that it was artificial. Exactly how the Amazonian people produced it wasn't entirely clear. Simple surface burning isn't sufficient. Lately, though, researchers at at Cornell University, the University of Georgia, and Iowa State University, as well as companies such as Eprida and Best Energies, have isolated the active ingredient in terra preta. It's called agrichar, or sometimes biochar. It's not just a charcoal additive; but it can be produced locally using low-tech equipment available on nearly any farm. Agrichar is, in other words, not so much a substance as a recipe.

Imagine a field that produces its own rich fertilizer; this is the promise of agrichar. Once it's in place, the soil is enriched essentially for all time. It can restore soils whose nutrients have been leached away, and it can greatly reduce the need for conventional fertilizers. It does this while simultaneously sequestering large amounts of carbon.

It gets better. The process of producing agrichar can also produce ethanol fuel as a byproduct. The Eprida website contains a description of this process:

With modern technology low temperature charcoal can instead be made by a hybrid pyrolysis process whereby biomass such as wood chips or agricultural waste is heated in a sealed vessel. Once started, this process actually gives off heat while it drives off steam and hydrogen, which can be captured, purified and used for energy. Hydrogen can be used to make transitional fuels such as GTL biodiesel today, or used directly in a fuel cell to make electricity or power vehicles in the future.

This process sequesters more carbon than it releases so, rather than being carbon-neutral, it is actually carbon-negative. You can even add coal, and sequester much of its byproducts.

We're rapidly learning what is and isn't sustainable. Forests are carbon sinks, but peat bogs are even better. Growing corn to make ethanol may be slightly green; but just converting farmland in general from chemical fertilizers to agrichar is even better. Best of all, agrichar is very far from being theoretical: in Canada alone companies like Advanced Biorefinery Inc., Agritherm, Ensyn, and Dynamotive are all developing agrichar-related technologies.

The black terra preta of the Amazon should remind us that, in a very real sense, our generation does not have to face the challenge of climate change alone. A helping hand has been extended across seven thousand years of time, and we gratefully accept the aid. Global climate change is a crisis for all of humanity; yet all of humanity, even our ancestors, can play a part in resolving it.

Front Page Photo Credit and Inside Middle Photo Credit: Eprida
Top Inside Photo Credit: Photo of Terra Preta: Dr. Bruno Glaser

Also on Worldchanging:

Terra Preta: Black is the New Green
A Carbon-Negative Fuel