Biochar is such an expanding area of investigation, it would be difficult to write a comprehensive book at this point. Of course the root idea of partial-combustion to make soil amendment is well-enough known, but there is much being learned about how to alter the properties of the char by how the pyrolysis is performed. There is much to be learned about how much char to add and how to pretreat the char. Beside burning to make char, there are other ways it can be heated and those affect the type of pyrolysis products that form - molten salt, steam, and subcritical hot water are all gaining prominence. The management and use of the pyrolysis products aside from the char is also a complex topic.