On reading the last newslsletter:
The two photos were not like for like. One appears to be a deep tropical soil and the other a temperate uncultivated soil.
My plant roots do not go down as far as 2 metres either. The photos are not like for like, one is a very deeply dug soil (or midden) and the other an uncultivated woodland type setting. It's this sort of trickery along with the drive to make Youtube money (which is a big dirvers with the biochar Youtubers, which make me tend toward the idea that it is just the next fad.
Before I am convinced I would want to see some independent comparative studies. For example is the biochar dug in deeply and how does that compare to digging in muck and/or compost to the same depth?
Secondly: what happens to the carbon on the char? Carbon is chemically stable and does not break down easily if at all. So is it merely a neutral porous substance charged with bacteria, fungi and nutrients? If so are those flora and fauna found in composts? If not does charging compost with them produce similar results?
Lastly on the subject of flora and fauna. If one is adding exotic (e.g. non local) flora and fauna to the soil are they still present a year later? This is important. One reads a lot about people getting hold of one hundred year old sourdough starter cultures. These have supposedly improved steadily over time developing into exotic yeasts and such which make particularly tasty bread. Research over the last ten years has found that if you remove such a culture to your own place of abode then the original yeasts and bacteria are rapidly overtaken by your local wild populations. Is this relevant to biochar?
I believe a lot more independent work needs to be done before this is a 'good way to go', especially given the environmental concerns of burning wood and the large amount of work involved.