Biochar is pyrolized woody biomass that has a long life span as a soil amendment. It has similarities to the hardwood charcoal that you can buy in a store, but it is made at higher temperatures than charcoal and it is not compressed. The key word in the manufacture of both charcoal and biochar is pyrolysis: the process of burning in the absence of oxygen. The charcoal-making process is known in nearly every country and goes back millennia. The simplest method involves burying a pile of wood under a mound of soil with a small opening to the wood at each end of the pile, and then igniting the wood. At first the smoke from this air-limited fire will be white. After hours or days, ...