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[Clansgian AT wmconnect.com]

> >In the Amazon basin, when they dig some of the Terra Preta up, as long as 
> they only take a little at a time and leave enough in the patch, it seems 
> to 
> "grow back"...  

Terra Preta was a hot topic on another forum a while back and we all did a 
bit of reading about it.  I found that literature from the US was very 
heavily 
tainted by agribusiness thinking, forever coming back the notion that we 
could 
somehow mine the Dark Earth or at least put something in a bag  that could be 
sold and scattered on our gardens.

But the Brazilian literature was different, more analytical, more examining 
what the phenomenon is rather than how we can sell it.  

In the Brazilian literature it is called "Terra Preta do Indio"  (Indian Dark 
Earth). This is one of the most informative articles on the subject (says I):

http://www.museu-goeldi.br/destaqueamazonia/tpa.htm

Under the section "hipoteses" the first sentence begins:

"Pesquisadores estimam que um centímetro de terra preta leve pelo menos 10 
anos para se formar"

(Analysists estimate that a centimeter of dark earth takes at least 10 years 
to form.)

Yowser, guys!  A millimeter a year!?  Sorry, but I'm already doing much 
better than that by my own humble composting.

As to the charcoal being the key, there are also areas of "terra mulata" 
(brown earth) which have the same characteristics of fertility longevity as 
the 
terra preta but lacking the charcoal of the latter.   Like the terra preta 
the 
terra mulata sites are identified as areas of long habitation and cultivation.

The places where these phenomena occur are laterite soils.  The game plan of 
these soils is very different from temperate soils.  Here organic matter lies 
in the ground decaying and harboring the bulk of the fertility.  There, 
because the bacteria can work around the calendar, organic material does not 
abide 
long in the soil.  The scheme is for plants to take up all the nutrients and 
hold them with the soil being more or less sterile.   That's why when rain 
forests are cleared for agribusiness agriculture, it permanently harms if not 
ruins 
the ground.  All the nutrients of thousands of years are removed in a day 
when the overlying vegetation is removed.

So compared to the laterite soils, the terra preta and terra mulata are very 
persistently fertile indeed.  Why?  Dunno.  And apparently neither does 
anyone 
else.  But the notion that what's going on down there in that type of soil 
can be successfully duplicated here in a very different climate and very 
different soils has yet to be demonstrated ..... except to demonstrate the 
general 
concept that accumulated organic material makes the soil more fertile seems 
to 
be a universal principle.

This same thing comes into play, I think,  in John Jeavon's double digging.  
He showed dramatic improvement in yield by double digging compared to shallow 
tilling .... in Palo Alto, California.  What's the soil and climate like?  
Not 
the same as here, and that's the main thing.  Double digging just doesn't 
give the same results for the labor everywhere.

James