[Terrapreta] Char Addition Parameters

[Kevin Chisholm]

Dear List

Various amounts of charcoal could be added to the soil. Most accurate 
would be knowing the weight of charcoal added to a weight of dry soil. 
However, it is not very practical to dry the soil in the field, and 
often the weight of charcoal is not known either.

A simple way to make char additions is to apply a uniform layer of char 
to the soil area and then till it in. It is very easy to measure the 
area being covered with char, and it is very easy to measure the depth 
of char.

Several questions now arise:

1: Depth of Soil to be treated: What is a good depth of soil to be 
treated with char? I believe the "standard" tillage depth" is considered 
to be 6", or 150 centimeters.
WHAT IS YOUR SUGGESTED PREFERENCE FOR SOIL TILLAGE DEPTH?____________

2: Weight of char to be added: One can add varying amounts of charcoal 
to the soil. Lehman et al suggest that the benefit is a maximum at about 
7% charcoal addition, above which growth performance seems to fall off. 
(Regrettably, I can't find the reference to their work at the present; 
perhaps someone can post it?)
WHAT IS YOUR SUGGESTED PREFERENCE OF CHAR ADDITION RATE, AS A % OF SOIL 
WEIGHT?_________

3: Soil Density: Soil densities can vary significantly...
WHAT IS YOUR SUGGESTION FOR THE RANGE OF TYPICAL SOIL 
DENSITIES?_______________

4: Charcoal Density: Charcoal densities can vary significantly, 
depending on their source material, temperature of charring, size, and 
shape factors.
WHAT IS YOUR SUGGESTION FOR A RANGE OF CHARCOAL DENSITIES?_____________

5: Charcoal Application: I would suggest that the best way to apply the 
charcoal is to spread it uniformly over the area to be treated, and then 
till it in, to give the desired depth of treated soil.
CAN YOU SUGGEST A BETTER WAY TO INTRODUCE CHARCOAL INTO THE 
SOIL?_______________

I would propose to put together a simple spread sheet that would allow 
the grower to calculate how much he could afford to pay for charcoal 
additions to the soil.

Best wishes,

Kevin