Biochar

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The terra preta soil can result in increases in crop yields of two, three, or in one case, nearly nine times greater than the native soil; the technique for creating terra preta soil can extract significant amounts of carbon from the atmosphere, and store it in the soil for millenia; as long as an eight-inch layer of terra preta is left on the surface, it can apparently regenerate itself to a depth of 24 inches over a period of two decades1; and at least one plot of terra preta soil has been continuously cropped for over 40 consecutive years.

Activated carbon has a such complex, spongelike molecular structure that a single gram can have a surface area of 500 to 1,500 square meters (or about the equivalent of one to three basketball courts)4. This char material in the soil has several beneficial effects, including about a 20% increase in water retention, increased mineral retention, increased mineral availability to plant roots, and increased microbial activity. It has been shown to be particularly beneficial to arbuscular mycorrhizal fungi, which form a symbiotic relationship with plant root fibers, allowing for greater nutrient uptake by plants. There is speculation that the mycorrhizal fungi may play a part in terra preta’s ability to seemingly regenerate itself.

More char material in the soil may mean less carbon dioxide in the atmosphere. The carbon sequestration potential of biochar is enormous. By one estimate, biochar-amended soil can contain at least two-and-a-half times the carbon of typical soil. In the Amazon’s poor soil, terra preta soil has eighteen times more carbon.5 Unlike most soil-based carbon (organic matter), the charred matter is essentially permanently sequestered.

How much carbon can be sequestered in this manner? The limits have not yet been determined, but one estimate amounts to 150 metric tons per hectare, or, put another way, over 42,000 tons of carbon per square mile. Bruno Glaser, a researcher with the University of Bayreuth, Germany, believes that by the end of this century, terra preta schemes in combination with biofuels could store up over one billion tons of carbon - more than the total of all carbon emitted by fossil fuels today.