[Terrapreta] Charcoal costs

[Kevin Chisholm]

Dear Tom

Tom Miles wrote:
>> Capacity of the soil, but that Torrified Wood has the Cation Exchange 
>> sites tied up, and that it would not work a effectively as char.
>>     
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> So what's the marginal value of CEC? I don't think we know this yet.
>   
This paper shows that an increment of charcoal to a soil increased the 
CEC from 24.9 to 47.2.:
http://www.georgiaitp.org/carbon/PDF%20Files/Posters/ChengPoster.pdf

I am not certain of the quantity they used in their test. They state:
"An incubation experiment was performed in which either water-washed 
charcoal or a charcoal-soil
mixture in a ratio of 50:1 was incubated at either 30°C or 70°C."

I find this confusing. This suggests the test mixture was either 100% 
water washed charcoal, or 98% water washed charcoal and 2% soil mixture. 
However, their Table 2 lists the tests they performed with variables as 
follows: Soil, Soil + Char, Soil + Char +Fertilizer, Soil + Char + 
Microbes, Soil + Char + Manure, Soil + Charcoal+ Fertilizer+Manure.... 
This suggests that they measured the changes to the soil with additions 
of various ingredients.

If we ASSUME that the actual tests involved soil as the starting point, 
and that there were 2% additions of each ingredient, we can calculate 
the marginal or incremental value for the CEC of Char. If this was the 
case, then a 2% addition of char increased the CEC of the soil from 24.9 
to 47.2, a change of  22.3 mmole/kg. From this we calculate that the CEC 
for the Char alone would be about 50 times greater, or about 1,115 mmole/kg.

Would you think that these assumptions are reasonable? Is this a 
reasonable interpretation of the data presented?

Best wishes,

Kevin
> Tom
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