August 18, 2006

Organic Carbon Sinks - Terra Preta

Carbon dioxide, coal, ash, soot, methane, charcoal, smog, carbohydrates, greenhouse gases, trash, recyclables, carbon monoxide, wood, petroleum, hydrocarbons, ethanol, manure - what do all these have in common? Carbon.

Any discussion about changes we make in agriculture, forestry, waste management, energy, and the health of the atmosphere necessarily must come to grips with the environmental impact of redistributed carbon. Are we creating more or less, are we releasing to the atmosphere, can we recycle it to where it came from, can we sequester it, what are the long and shortterm consequences of each solution?

What we are looking for are "carbon sinks" - safe places to store carbon so they don't contribute to global warming. Most solutions being proposed that involve utilization of brute technology - like plans to pump CO2 into the earth's crust to extract more petroleum. They seem to be the equivalent of burying uranium wastes - solutions for today that will wreak consequences for future generations.

No matter how practical using carbon to refortify soil is, it sounds like a safe, nurturing alternative to other industrial solutions. Here's the gist of the concept thanks to the Biopact Blog and the Nature article some of the original content was published in.

Terra preta: how biofuels can become carbon-negative and save the planet

Commonly proposed carbon sequestration strategies face some major hurdles. Technical 'geosequestration' methods consist of pumping large amounts of CO2 deep underground. But these techniques are still under development, and recent evidence suggests that CO2 leakage forms a major problem and could in fact worsen matters.

On the other hand, natural methods that store carbon in living ecosystems may be possible in the short term but require huge swathes of land and are only as stable the ecosystems themselves. These strategies would come down to planting biomass and leaving it untouched.

An ideal solution, in particular for tropical countries, would consist of combining the quick fix of biological methods with the absolute potential of technical ones, while deriving energy from doing so. Terra preta may offer exactly the basis for such a strategy, as a recent article in Nature reveals.

Amazonian Dark Earth', or terra preta do indio, has mystified science for the last hundred years. Three times richer in nitrogen and phosphorous, and twenty times the carbon of normal soils, terra preta is the legacy of ancient West African societies and Amazonians who pre-date Western civilization.

The difference between terra preta and ordinary soils is immense. A hectare of meter-deep terra preta can contain 250 tonnes of carbon, as opposed to 100 tonnes in unimproved soils from similar parent material, according to Bruno Glaser, of the University of Bayreuth, Germany (Terra Preta website).

To understand what this means, the difference in the carbon between these soils matches all of the vegetation on top of them. Furthermore, there is no clear limit to just how much 'biochar' can be added to the soil. Claims for biochar's capacity to capture carbon sound almost audacious. Johannes Lehmann, soil scientist and author of Amazonian Dark Earths: Origin, Properties, Management, believes that a strategy combining biochar with biofuels could ultimately offset an incredible 9.5 billion tons of carbon per year -- an amount equal to the world's total current fossil fuel emissions!

Terra preta's full beauty appears in this closed loop. Unlike traditional sequestration rates that follow diminishing marginal returns-aquifers fill up, forests mature-practices based on terra preta see increasing returns. Terra preta doubles or even triples crop yields. More growth means more terra preta, begetting a virtuous cycle. While a global rollout of terra preta is still a ways away, it heralds yet another transformation of waste into resources.

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Anonymous said...

I've been doing some calculations with Ron Larson, chair of the American Solar Energy Society, to find out how much of our carbon emissions we may actually be able to sequester using charcoal to create modern terra preta. The (very preliminary) numbers look excellent... this has the potential to sequester most of the world's carbon emissions on an ongoing basis. Look for Ron's article in the next issue of Solar Today.

C. Scott Miller said...

Soil sustainability is a very hot topic of ACORE's BioEnergy Coordinating Council (BCC) headed by Bill Holmberg (see They are concerned about the stress on topsoil from the cultivation of energy crops. I am sure Bill and the BCC would be interested as well in your findings.