Carbon has an important role in making soil fertile. It allows fungi to from a web providing nutrients to plants and keeling the soil alive. The black of the earth is pure carbon, as is the darkness of compost. Humans have made Terra Preta for thousands of years. Denise Rojas does not explian it very thouroughly, below video is more informative.
Char, Agrochar, Harbargar
The above video is great, but there is nothing special or scientific about agrochar, it is char, just like there is no difference between methane an liquid natural gas. It can be made in any oven that allows oxygen supply to be managed. It is a method for sequestering carbon that should be promoted everywhere, also because agricultural land is degrading rapidly endangering the global food supply.