From the reading and experimenting I've done, here is my take. Some soils are simply better at cycling nutrients than others. It is that microbiome in the soil that plays a significant role in this process. Some soils can support these microorganisms better than others. Biochar, if made properly, essentially forms a home for these microorganisms. The surface area is immense as it has tiny chambers in structures. It can improve the soils ability to hold nutrients. Good loam soils (often glaciated) have plenty of nutrient holding and cycling capacity and can take a lot of abuse with tillage. I'm not sure folks will really see much improvement applying biochar to these soils. Sand and clay often have poor nutrient cycling ability and are low in OM. Nutrients move through sand very fast. Clay too, has little capacity to support this microbiome. While I believe both of these could be improved with biochar, I have seen no practical, cost effective way to apply sufficient quantities in most field applications. That is why my first experimentation was with trees. You get very little true biocar from a kiln.
From what I saw on the old thread what Baker produced was truly biochar. In many cases, what I see is ash an partially burned wood. Not that these are bad, they will decompose and increase OM which is a good thing. Biochar is basically the remaining empty structure when all the organic matter is consumed. I did not see significant benefit with it from containerized trees. Since I can't find a way to make it economical and practical in a food plotting application, I've abandon it. It was a fun experiment.
Building OM from the top down on sand or clay soils by minimizing tillage and being smart about crop selection balancing C & N is a practical way to improve nutrient cycling that actually reduces cost by reducing lime and fertilizer requirements over time.
Thanks,
Jack