Did Ancient Amazonian Civilizations Sequester Carbon with Biochar?

Amazonian Soils & Biochar

In the Amazon Basin, primarily located in modern Brazil, we find very dark man-made soils that are rich with minerals. These soils are referred to as the “terra preta” (black soil in Portuguese) due to the black or near-black color, which is in contrast to the lighter brown natural soils of the Amazon. This fertile soil is black due to its charcoal and manure biomass content, tilled through a process known as slash-and-char. Unlike the more commonly known slash-and-burn, this method is the charring of biomass that results from the slash. The end-result of the charring is called biochar, which you can see me holding below.


Biochar made from mixed hard and softwood

The amendment of biochar, which has a porous chemical composition, increases the microbial activity and water retention. In poor soils, such as in the Amazon basin, this can lead to significantly improved soil fertility. Biochar can be thought of as a sponge for water and microorganisms that the soil can draw from as-needed for growth. While not always the case, depending on feedstock and other variables, many scientific experiments and industry claim that biochar increases not only plant strength but also the actual crop yield. It is important to emphasize that there is quite a bit of variation in getting positive yield increases that requires testing and tweaking at first, but for many farmers and gardeners, biochar has had tangible benefits. There is little doubt that the Amazonian Basin soils saw an increase in fertility from biochar with such a staggering change in soil.

Biochar & Sequestration

Biochar is often referred to as a carbon-negative technology because it takes existing CO2 out of the atmosphere. It is considered a technology because it is man-made but it’s a very old technology undergoing a new wave of popularity in the face of degrading soils and those concerned with carbon capture. Biochar itself is nearly pure carbon that is amended to a fertilizer, which is then tilled into the soil, for the most positive results. The pure carbon is what climate and soil scientists are interested in for sequestration.

Biomass is better-known in the climate change policy circles as a way to make use of ecological waste in a long-term sustainable way. The waste is burned, the energy from the burning is used for energy, and bio-oil such as ethanol is produced for fuel purposes. Biochar goes through a process called pyrolysis in which the waste feedstock is not actually burned. In advanced systems, the heat is still captured and used for energy, but the result is biochar rather than oil. The key difference in pyrolysis is that the biochar maintains the carbon it contains from the atmosphere rather than releasing it again as would happen in a burning. The biochar is then planted into the soil and the carbon is able to remain captured for hundreds to thousands of years. This is why biochar is considered carbon-negative.

Less advanced backyard systems, as shown in the video above, do not capture all of their carbon cleanly but still have a net-negative carbon effect. Even the more basic systems are much better than simply burning the waste and produce potential value in the biochar that is made. These smaller systems do not capture waste heat but make it simple for almost anyone to produce their own biochar without much by the way of capital costs nor risk. This is also the way in which the Amazonian cultures would have been producing biochar, thus sequestering carbon. It’s not necessarily a surprise that humans found ways to improve their land. From inter-cropping to fertilizers to pesticides, ingenuity in agriculture has prevailed and this goes all the way back to the ancient Amazonian civilizations with biochar in the terra preta.

Deep Green Permaculture shared a nice Tedx Talk here that is a good watch for anyone interested in learning more about biochar and how it relates to climate change.


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