[Terrapreta] 80 degrees Fahrenheit

[Juergen Botz]

William Carr wrote:
> On Jan 26, 2008, at 7:08 PM, Gerald Van Koeverden wrote:
>> I wonder if this is key to understanding why the effect of charcoal
>> amendments might turn out to be so much more dramatic in tropical
>> than in temperate zones?
> 
> That's been suggested.   Like the sand in my garden, poor soils in a  
> tropical environment might gulp down digestible organic matter and  
> blow it off as CO2.
> 
> Bio-char, however, is indigestible and provides a substitute for the  
> missing OM.
> 
> It may store nutrients by absorbing and "adsorbing" them, improving  
> the soil fertility.

Hi... I live in Brazil and am in the early stages of practicing
organic/sustainable farming here.  We're on the coast, in Southern
Bahia, but from what I understand the environment here (Atlantic
rainforest, poor clay soils) is quite similar to that of the
Amazon basin.

Here's my list of the primary reasons the soil here is difficult
for any kind of agriculture...

- Poor water retention.  Despite the fact that atmospheric 
  humidity here averages more than 80%, without the modulated
  climate of a dense forest canopy the soil dries out rapidly 
  under the hot tropical sun.  Clear some trees for agriculture 
  and the soil dries and dies in no time.

- Soil compaction.  The cycle of heavy rain followed by thorough
  drying forms crusts and hardpans that most roots simply can't
  penetrate.  (It also leads to rapid erosion on even gentle 
  slopes.)

- Low organic matter content.  Everything here happens fast...
  especially decomposition.  Organic matter is reduced rapidly
  and what's left is often washed out by the next heavy rain,
  and the rest locked up in the highly compacted clay.

These three factors are highly interdependent, and even have a
positive feedback: poor moisture retention feeds the soaking-
drying cycle that leads to compaction, which prevents both
water and organic matter from entering, which leads to poor 
moisture retention, etc.

So the proscribed treatment should be: losen the soil, help it
retain moisture, secure and keep available the nutrients resulting
from decomposition of organic matter.

Biochar helps with all of these.  I have not yet begun controlled
experiments (I will, this year, and report results here), but in
my preliminary dabbling I have already found that those garden
beds to which I added more char have produced better and suffered
less compaction.

I thus find it entirely reasonable that biochar is particularly
helpful in this type of environment and may be of of little value
in the thick, humus-rich soils of Northern temperate regions, for 
example.

:j