Illustration - Micrograph of a piece of charcoal (biochar) showing its extreme porosity, small holes are about 1 / 100 of a millimeter in diameter. It is an ideal environment to retain water, nutrients and microorganisms, increasing soil fertility. (Source: Best Energies)
Over the past ten years, agronomists and environmentalists are increasingly interested in Amazon Terra preta, an extremely fertile black soil resulting from amazing agricultural practices of ancient natives.
Their secret was charcoal buried deep in the soil, hence the name Terra preta, in Portuguese. The appearance of porous charcoal, also called biochar, helps retain nutrients, water and microorganisms. These features facilitate the growth of plants and reduce the need for fertilizer while reducing more than 50% the emission of nitrous oxide, a gas 300 times more potent for global warming than CO2.
To produce biochar, one uses a process of thermal decomposition of biomass called pyrolysis, which involves heating wood or crop residues in an enclosure with scarce oxygen environment. Combustible gases are then released containing, among other things, hydrogen and methane, which are partly used to produce the heat required by the process. A bio-oil is also formed after processing and cooling, that can used in heating furnaces. You can also turn this bio-oil into biofuels more suitable for transport, such as diesel and synthetic gasoline or ethanol with proper thermo-catalytic processes. One obtains then second-generation biofuels.
Now, when we bury biochar, in addition to fertilize the land we also sequester in the ground some CO2 from the atmosphere which had been absorbed by plants. It helps to remove greenhouse gases, a bonus specifically sought these days! The combination of buried biochar and biofuel production, therefore makes these biofuels carbon negative, which is still better than carbon neutral biofuels. Professor Lehmann of Cornell University estimates that implementing these practices on a large scale, could both produce biofuels and withdraw annually 9.5 billion tonnes of carbon from the atmosphere by 2100. That is more than what we send in the atmosphere today in the world by burning fossil fuels!
For more information, please visit Terra preta site and the site of The International Biochar Initiative (IBI), where we find the illustration of the pyrolysis process shown above. In addition, the following video is an excellent documentary on the subject.
Terre preta - biochar
