Terra Preta and biochar: are they the same thing?
‘Biochar’ is the name of a technology that consists of carbonizing biomass with low oxygen and applying it to the soil. But what does it have to do with Terra Preta? When scientists started investigating the physical and chemical properties of these anthropogenic soils, they found out that they contain large amounts of charcoal (or ‘pyrogenic organic matter’), which gives these soils their dark colour. This charcoal, originating from the slow burning of different kinds of household waste in pre-Columbian times, is responsible for several important properties of Terra Preta, including its high cation exchange capacity (i.e., its ability to ‘hold’ nutrients) and its microbial activity, besides that charcoal itself is a very stable form of carbon in the soil.
Soon these properties of Terra Preta called the attention of agronomists and soil scientists, who envisioned that recreating some of the properties of these soils would be an opportunity to improve soil fertility while sequestering carbon. Although the use of charcoal as a soil amendment had long been known, the discovery that this material played a key role in Terra Preta inspired a ‘rebirth’ of this technology (and now under a new name: ‘biochar’), which rapidly called the attention of a large and diverse group of scientists and companies.
Adding to the initial ‘win-win’ of biochar (i.e., improving soil fertility and sequestering carbon), other potential benefits (or ‘wins’) of biochar started to be identified, such as disposal of organic waste, production of biofuels and bioremediation. While in the early days of biochar this technology was very connected to the Amazonian anthropogenic soils, it later followed an independent trajectory and gained much more attention than Terra Preta itself. Today, biochar is being studied and promoted worldwide by scientists, policy-makers and businessmen, and given its placement in the carbon economy, some critics argue that it has become a sort of ‘green commodity’ strongly embedded in an ‘ecological modernization’ discourse.
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