[Terrapreta] torrefied wood or charcoal?

[Gerald Van Koeverden]

To Tom, Jim, Sean, Greg, et al,

As a farmer, I know that generally ashes enrich the soil.  Every  
example of brush burn piles I have seen, has resulted in more healthy  
plants.  The effect lasts 3 or 4 years.  Of course, I'm sure that too  
much of any good thing turns out bad.  But in general, wood ashes in  
moderation are good for the soil.

The first place I've read of ashes being toxic to growth is when I  
did an Internet search of compost-making recipes.  In them, I was  
shocked to read how many of them discouraged using charcoal in  
general, even though the only 'bad' material ever specifically  
mentioned was briquette charcoal ashes.  For some reason, compost  
makers have allowed their bad experiences with briquette ash to  
colour their experiences with charcoal in general.

If we could understand the chemical basis for these bad experiences  
with this briquette ash,  we would then be able to explain it and  
help educate others in better appreciating the merits of using  
charcoal as a soil amendment.  The answer might be as simple as  
determining that boron (from the borax added to charcoal briquettes)  
is toxic to plant growth especially at the higher concentration after  
briquettes are reduced to ash.  Boron is an essential plant  
micronutrient, but, for example, becomes poisonous to lemon trees at  
concentrations of only 1 part per million!   (If anybody finds out  
how much borax is in a bag of briquettes, we could do some  
calculations for it in the ash content.  I don't think it vaporizes,  
otherwise they wouldn't allow us to us it for cooking, right...?)

Unfortunately, none of us have the facts to explain this briquette  
ash quandry, at present.

Gerald






On 2-Mar-08, at 2:56 PM, Jim Joyner wrote:

> Sean,
>
> While agree with your conclusion, "torrefied is likely not as  
> useful or
> effective in making an improvement to the soil as is low ash  
> charcoal",
> I'm afraid your reasoning is based on faulty information.
>
> Sean K. Barry wrote:
>> High ash content means higher pH.
> This may be true but not necessarily. If there is a proper amount of
> calcium and magnesium in the soil, the increased pH, mostly due to
> adding potassium in ash, will not persist long. It will wash out.
>> This is not good for any soils unless they are very acidic to  
>> begin with.
> Raising the pH of soil with ash (potassium), without regard to calcium
> and magnesium, will create brick. So, this would not be good,
> necessarily, for a acid  or any other soil.
>> Raising the soil pH lowers the cation exchange capacity (CEC),
> This is simply not true. You've got it backwards. CEC is not  
> affected by
> pH. Ph may be affected by the things used to increase the CEC like  
> clay
> particles (mostly silicates) or carbon (not charcoal). One typically
> adjusts soil calcium, magnesium and potassium according the CEC. Once
> that is done, pH will be slightly acid to neutral.
>
> If charcoal in the soil raises CEC, it doesn't do it directly by
> addition. It may indeed create a habitat more conducive to the  
> creation
> and holding of stable humus, which does increase CEC.
>>  Higher pH is not a habitable environment for many soil
>> micro-organisms, either.
> Just about everything that grows likes a pH of 6.8. But the  
> addition of
> charcoal or torrified wood are unlikely to affect pH at all.
>
> More importantly, pH is a boogey man. It's just a concept for  
> measuring
> something that is rarely useful. A good, balanced soil will have a
> slightly acid ph. However, a soil that has a slightly acid soil  
> will not
> necessarily grow anything. There are only nutrients and cations in
> active soil (I do not include charcoal as active -- it's virtue  
> seems to
> be in its inactivity and crystalline structure). There are no pHs.
>
> Having said all that, since many of the compounds in torrified wood  
> can
> be acted upon by organic processes, my concern for adding torrified  
> wood
> to soil would be that it would be much adding sawdust. It won't affect
> pH but it will tie up nitrogen, taking it from crops . . . for a  
> long time.
>
> Jim
>
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