Charcoal – fuel or fertiliser?

I received an e-mail comment from a reader in Tasmania on my article, “Peak Oil – expensive food” (Express, July 30), pointing to the research on “agrichar” or “biochar”. The reader was responding to my view that in T&T we have to seek an agricultural system that is less dependent on fossil fuels.

“Agrichar” or “biochar” is indeed an extremely interesting process that fixes carbon in the soil for a very long time. It does so with what I call a catalyst-fertiliser. Furthermore it provides an energy source that is an alternative to fossil fuels. These researchers tell us that we can have an alternative fuel source that, instead of increasing the carbon dioxide in the atmosphere, traps carbon in the earth for an exceedingly long time and also acts as a fertiliser – a negative carbon fuel!


It is well known that planting trees provides a system that removes carbon dioxide from the atmosphere. This is the basis of the Kyoto carbon trading global warming initiative (on the Chicago Climate Exchange for Carbon Dioxide) where a company, say, in the developed world, is allowed to surpass its dumping quota for carbon dioxide into the atmosphere if it were to invest in, e.g. forestry credits in the developing world or wherever. The problem with this system of carbon entrapment is that the forests after many decades mature and start to release as much carbon dioxide as they take up. Also plant biomass, the residue after trees die or are cut, decomposes in a very short time and the carbon stored in the biomass returns to the atmosphere. In other words the long-time entrapment of carbon by a tree is zero.

Some 7,000 years ago the people of the Amazon developed a land management system to help feed large groups of people based on the “dark earth” called “terra preta”. These agricultural patches are enriched with charred-trash or biomass, like today’s charcoal. These thousand-year-old terra preta patches contain even today some nine per cent of carbon compared with 0.5 per cent for the plain soils nearby.

This amazing discovery is that charcoal mixed with earth, agrichar or biochar, can sequester – trap – carbon and retain it in the soil for more that 7,000 years, ages compared with that entrapped by forests, which eventually give up their carbon. But these ancient people were not interested in entrapping carbon since they were not troubled by global warming. The terra preta was built for another purpose. It was used to enhance the fertility of the very poor soils of the Amazon.

Trinidad Express