"Charcoal formation by biological processes has not been dealt with by any engineer, that I know of. Not in any scientific publication, because when it comes to understanding what biology can do, engineers are really, really poor at ever having attempted to figure it out. Those darn microbes are just a pain to get them to behave in a consistent fashion.
Compost that goes anaerobic does not make big chunks of charcoal, which is another reason why engineers ignore the biological process. It is not an efficient way of making a commercially successful charcoal production facility.
But when you go back to the middle ages, the way charcoal was made from wood was not with extremely high temperatures. Not efficient production methods, but it got the job done.
Look at a compost pile that is black, has pieces of what are analyzed as charcoal in it (no charcoal put into the pile to begin, no wood ash or burned material in the starting materials). Where did the charcoal come from?
Once carbon in a compost pile starts begins to "char" (maybe biological charcoal production should be defined as charring, since big chunks aren't produced, as in commercial charcoal operations), you aren't going to be growing the plants that once could have been grown in that material.
Along with the anaerobic conditions required to produce charcoal, anaerobic biological processes volatilize nitrogen as ammonia, sulfur as hydrogen sulfide, phosphorus as phosphine gas, produces low pH volatile organic acids, and a group of toxic materials that will kill plants if that material is placed near the roots before being aerated properly.
If the pile goes anaerobic, and then you let the biology deal with the problem (it can take years), carbon is blown off, mineral nutrients concentrate again. We then have what I suspect is the Terre Preta that has people so excited (as they should be excited).
If scientists had paid attention to all the conditions that can occur in composting processes, and differentiated aerobic composting from the effects of anaerobic processes during composting, understood what goes on with different starting materials, temperatures, moisture, oxygen concentrations, etc, then we wouldn't be so thrilled with Terra Preta.
But because commercial fertilizer concerns wanted to convince the general public that the compost the general public was making was BAD, and that they should buy inorganic fertilizers, because inorganic fertilizer was "better" and easier to use, scientists who examined compost paid no attention to the fact that what they chose to measure as "compost" was not in fact compost by any definition.
I have been appalled by the composts being produced at most academic institutions. Typically, their "compost" stinks to high heaven, and are health hazards. It is usually black in color (charcoal), the ammonia coming from it is at toxic levels for the machine operator, and the pH is usually lower than anything I would ever pot a plant in. And the human pathogens in it! Egads! You can't kill E.coli when the conditions are ones that favor its growth.
Not that any most commercial composting operations are any better, that I know of. There are no biological standards for most of the organisms that are in compost, but it is all those organisms, from bacteria to fungi to protozoa to nematodes that make compost.
The US Composting Council rejected the idea of any biological assessment of compost EXCEPT E. coli or other pathogens. My opinion of why they did that is because none of the commercial compost makers would have been able to sell their materials as compost, if even minimal biological standards were imposed.
What you can buy at most "compost" yards is not compost, it is mulch, or it is putrefying organic matter. A biological assessment will show you that in an instant. I've been training people to look at compost for a couple years now, and it takes possibly as long as 5 minutes to be able to determine whether you are dealing with real compost, mulch, or anaerobic putrid material.
If the organic matter is pitch black, stinky and slimy, it is not compost, it is putrefying organic matter. Many of the nutrients were blown off as gas, and of course cannot compete with inorganic fertilizers. If you are trying to prove that "compost is bad", then this works perfectly.
But it is not compost.
How then does Terra Preta get to be so wonderful? It went anaerobic, it lost nutrients, and yet, it is a great growing medium.
Time. Time to let the aerobic biology work on the "char", on the anaerobic waste materials and turn all of that into humus.
Well, I've ranted long enough, late for work........"
Elaine Ingham
[Terrapreta] Soil Food Web 2006
http://bioenergylists.org/newsgroup-archive/terrapreta_bioenergylists.org/2008-May/005043.html
Ingham is the only one that I know of who is able to evaluate the "charcoal issue" from a microbiological and composting knowledge and experience.
The justification of her arguments would not differ much from that what the Francés would have said.
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