You will not get the same result if you just light up a bunch of shrubs in a trash can and spread the ashes onto your soil. We promise! There is a difference in how biochar is made. Biochar is made with agriculture in mind. You use biochar for a healthier soil. It is specifically pyrolized (charred) to support the improvement of soil. The method is proven. One key point is the resulting carbon. Carbon storage is different between charring and burning. Burning is combustion — reaction of combustible material in the presence of air (nitrogen and oxygen), but charring is a degradation of material due to heating in absence of oxygen.
The products from burning and charring are also different. In a simple example, burning of plant matter produces carbon dioxide and water; whereas, charring is produces carbon ( a complex form of carbon) and low molecular weight compounds (smoke). Burning returns carbon, as part of carbon dioxide (27%) gas to the atmosphere, however, charring returns carbon to the land as a solid, char. This explains why biochar is said to sequester-capture carbon dioxide in form of char.