[Terrapreta] The Science of Terra Preta Formation

[Jim Joyner]

Greg, Sean,

There's another peculiar characteristic of clay that can only be 
addressed with calcium.

Clay will hold lots of water. Unfortunately that water is not available 
to plants unless . . . What makes clay friable and the water in it 
available is calcium/magnesium. Without sufficient calcium  (60 to 70% 
of the base saturation is considered ideal) clay will not grow much of 
anything even if nutrients are in the clay. I can't speak about char but 
the same applies to humus in the soils. There are places in Ohio and 
Indiana where they have muck soils (extreme high levels of OM/humus) 
that require huge amounts of calcium to unlock nutrients and moisture.

I don't know, but I doubt that char changes these rules (ideal soil has 
60-70% of base saturation is calcium; 12% magnesium; 2% potassium). If I 
remember right, the Amazonian clays are acid which would indicate low in 
potassium (Unlike bentonite that is very alkaline with lots of 
potassium). Potassium is important but to much -- relative to calcium -- 
makes soil into brick, seals pond bottoms.

Jim