Hearing this, the only remaining question is how could they not form earthen kilns to produce valuable biochar the exact same way? In the Amazon, the extra step could well have been slapping wet clay on top of the outer shell formed by the roots. It would take a little extra effort, yet even better burn control could be achieved. Plenty of pottery like shards would also be produced over the decades as has been discovered.
Obviously the natives fully understood the value of the method if only because this biochar product from corn stover served no purpose other than somewhat convenient disposal and soil enhancement. However, the work load change was trivial as the corn was been pulled in any event and needed to be burnt. This was not a valid value proposition for wood which is very costly to cut and pack and was done only to provide a valuable fuel.
I also learned something very important about dry land agriculture. If you form a seed hill, normal planting usually provides erratic results. If ash is added to the hill, or zeolite for that matter, moisture is drawn in during the night supporting vigorous growth. He was able to plant melons side by side with dramatic results.
This informs us that the additional strength of biochar as a water attractor is been underestimated. I would now like to see the three sisters method applied in places in Africa were common sense suggests otherwise. One could even begin seed hills with wood ash to get it all going and then follow up each year with a dressing of biochar.
I also understand better the importance of squash to the three sisters system. The broad leaves of the squash would shade the intervening soil between the seed hills keeping it cool and speeding up the absorption of moisture from the atmosphere were possible.
As I have posted in the past, activated carbon, zeolite and ash form a class of substances that are called solid crystalline acids. They are all strong absorbers of water and the free ions of nutrients. This is why they create and sustain fertile soils.
I do not yet understand why the three sisters culture has not been adopted worldwide among subsistence farmers. Most of it has to do with the advent of draft animals that enforce a row cultivation system and the three sisters simply do not accommodate that. Most small plots are done with hand seeding anyway, which again begs the question. It seems little to ask to stand over a three foot seed hill and to plant a handful of corn and bean seeds properly spaced with a couple of squash seeds every third hill. In fact it would be fast and economical of effort.