In earlier posts, I have described the corn stover protocol that I suggest was used as the only practical means available to the populations. What I have not discussed are some of the likely derivative benefits of the approach.
The most important characteristic of corn stover is that it will produce a fine grained product. There will be almost no lumps to breakdown, although there will be remnant roasted plant fiber that will be slowly degraded by bacteria in the soil.
The covering of dirt maintained while the stack is burning is still porus to air. This permits a steady supply of oxygen to the burn but at a low level. We anticipate that the average temperature will be around 380 to 400 degrees. This is hot enough to drive off the volitiles and char most of the carbon. It is not hot enough to do more to the stover than properly carbonize most of it.
However for the stack to reach a general average of 400 degrees, the volitiles must burn at much higher temperatures. That means that we will have a distribution of high temperature carbon products within the stack that will include high temperature activated charcoal. This is one of the benefits of the stack method that is hard to replicate in a carbonizing device were one gets a little too efficient.
I know that the agricultural carbonizer design that I posted on earlier posts separates the volatiles and burns them at 2000 dgrees before throwing the heat back into the fuel to produce more volatiles. More direct combustion within the fuel may well be called for.
I think that we need to sample the production of dirt covered burn stacks and measure not just the carbon output but the distribution of types by size and if possble, activity. then we can use better production methods and blending to match the terra preta profile.