[Terrapreta] Depth of char incorporation and mixing?

[code suidae]

Articles I've read about Amazonian Terra Preta mention that the char
enhanced areas can extend anywhere from a foot to as much as 5 feet below
the surface. I suppose ideal depth for a given crop depends mostly on how
deeply the crop roots, but it also seems that there might be a component of
how deeply the soil microbes keep up their activity. Is there a point of
diminishing returns where lack of microbial and fungal activity reduce the
effectiveness of the char, or where water that would otherwise have been
held where crops would use it ends up draining down through the charcoal too
deeply to be of use to the crops?

When dealing with a garden it is possible to manually pulverize and
incorporate the char as finely and deeply as desired. On a larger scale what
are reasonable limits to the particle size and how well mixed does the soil
have to be to provide immediate benefits? Can you just plow in the char to
get the process started and allow nature to take over at that point?

I've read some of the research covering results of charcoal incorporation,
but I haven't seen much covering the specifics of getting it into the soil.
Does anyone have links to research examining the results of various methods?

DOK
-- 
"Our ignorance is not so vast as our failure to use what we know." - M. King
Hubbert
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