Mysteries and musings at the biochar/plant/stress/ growing media interface

Since the late 1990s revival of the pyrolysis/biochar platform by the soil scientist Wim Sombroek, who promoted the development of “Terra Preta Nova”, peoples reactions to Biochar have taken on an almost religious fervor. There is a large set of enthusiasts, scientists and business people that makes up the believers, a similar group comprising the non-believers, and yet a third collection of people who find themselves at the interface - the agnostics'. Indeed, delving into the literature, whether it be black, gray, or otherwise, one learns that biochar can improve almost anything: soil fertility, climate change, farmer's yields, planetary albedo, waste treatment, animal health, soil pollution, bioenergy, building composites, air quality, etc. the list is practically endless. At the same time, we learn that biochar has numerous negative attributes: toxic to fauna and flora, locks up nutrients, releases rather than sequesters soil carbon, hazardous to health, flammable, emits gaseous and particulate air pollutants, causes waterlogging, contains dangerous organic and metallic pollutants, and more. Pity the poor agnostics - usually scientists - who are supposed to make sense of this all. They often find themselves at the intersection between two polarized sects. This is because the impact of the pyrolysis/biochar platform is generally a function of its extent of implementation, for example, in soil, the amount added. In other words, to credit Paracelsus, “The dose makes the poison”. The other difficulty is that the biochar, particularly when used in soil systems, becomes a part of an already complex and multi-faceted network of linked micro and macro compartments, where processes in one will then feed back into others, most commonly in obscure and unknown ways. Often a concentration that benefits one aspect may be detrimental to another. Pulling apart and looking at some of these intricacies through the lens of research from my group is the purpose of this address.