Here is some information from one of the articles linked by the OP The main technique to create biochar, called pyrolysis, involves charring waste vegetation a

Here is some information from one of the articles linked by the OP The main technique to create biochar, called pyrolysis, involves charring waste vegetation at low temperatures in an environment with little to no oxygen. “If you starve it of oxygen, then you cannot oxidize a piece of wood to CO2 and water—and you leave a lot of carbon behind,” said Lehmann. The same piece of wood left to rot or burned in normal (oxygen-rich) conditions would release its carbon into the atmosphere within minutes to months. When vegetation is charred, the carbon remains trapped for decades or even centuries. ... Recent research has found that biochar improves the soil in some contexts and has the most climate mitigation potential of any land-based effort, including agroforestry and afforestation—though Lehmann pointed out that nothing is more effective than keeping forests standing in the first place. https://eos.org/features/the-nutrient-rich-legacy-in-the-amazons-dark-earths https://eos.org/features/the-nutrient-rich-legacy-in-the-ama...