[SustainableTompkins] Subject for debate

[Marty Hiller]

Hi Karl,
I don't have any personal experience with terra preta soil amendments, 
but I read up on them a couple years ago and they looked pretty 
exciting. I'd love to try them out at some point. My understanding is 
that charcoal differs from manure or compost mulches in two ways: (a) 
the carbon in the charcoal remains sequestered for decades to 
centuries, while most of the mulch decomposes within a few years, and 
(b) the charcoal acts as a nutrient buffer -- it stores excess 
nutrients that are released by decomposition of other organic material 
and prevents them from washing out in the rain, then releases them when 
they're needed by growing plants. (If I remember right, the explanation 
for how this works had to do with charcoal's cation exchange capacity. 
This is how it's different from other relatively inert soil material, 
such as sand or clay.)

The second property -- nutrient buffering -- is what makes charcoal 
interesting from a soil building perspective. We want the nutrients to 
stay in the field, not wash downstream to become water pollution, and 
terra preta may be one way to accomplish that.

Permaculture, by comparison, relies on the living biomass of perennial 
plants to suck up rainwater and soluble nutrients and prevent them from 
washing downstream. Nutrients are retained because they're rapidly 
incorporated into the plants themselves (and perennials with 
established root systems can absorb them more quickly than the younger 
& smaller plants used in field agriculture.) Efficient conventional 
field agriculture minimizes nutrient loss by carefully timing 
fertilizer applications to add nutrients to the soil just as the plants 
are approaching a maximum growth rate.

Environmentalists recommend riparian buffers (bands of perennials 
around streams) and wetlands (which host anaerobic bacteria that 
metabolize nitrogen compounds) to reduce water pollution from nutrients 
washing out of farm fields. Charcoal in the fields is also a potential 
alternative for reducing water pollution in places where environmental 
buffers are inadequate or unavailable.

That's the theory, anyway. Whether it works that way in practice I 
don't know (though terra preta is reputed to dramatically increase soil 
productivity.) Mulches have a cycle of their own where nutrients are 
absorbed or released at different stages of decomposition, but I don't 
know the details. If you have a fixed amount of biomass available, and 
you're using some of it as mulch and converting some to charcoal, my 
guess is you'd want to add just enough charcoal to efficiently do its 
nutrient buffering thing, and you'd want to apply the rest as mulch. 
How much charcoal that comes to, and how much of a dent it would make 
in our carbon debt, I have no idea.

I *might* be able to locate the publication I got this from if you want 
to take a look. If I remember right the details were in eprida's patent 
application (supplemented by an online tutorial on the nitrogen cycle.)
- Marty


  At 01:21 PM 9/10/06 -0400, Karl North wrote:
> Hi All,
>
> One debate that is heating up is around the whole soil organic
> matter/carbon sequestration/biofuels question. I have followed this
> debate for a while because of my long interest in soil organic matter
> accumulation on my farm. My take so far is that most of the debate 
> lacks
> holistic perspective - it fails to consider all the angles. Of the many
> parts of this debate I would like to select one for discussion here: Is
> char/pyrolisation (a la terra preta) and effective solution? For 
> farming?
> For climate stabilization? For energy production?
>
> My question is: Don't the farm-integrated biogas systems developed by
> people like Thomas Preston
> http://www.ias.unu.edu/proceedings/icibs/rodriguez/paper.htm and the
> Institute for Science in Society http://www.i-sis.org.uk/DreamFarm2.php
> produce the same results (fuel, fertility and carbon sequestration)
> without the extra energy cost of pyrolizatiion? In other words, why 
> char
> organic matter before sequestration? And isn't it better for both soil
> biology and aggregation to let soil organic matter additions decompose
> through the various soil carbon pools? Pyrolisation seems like it
> fast-tracks the process toward inert carbon. Its promoters claim that
> carbon in this form is sequestered more permanently. But so is some of
> the carbon added to soils from compost or biogasification residues. And
> the char product of firms like Eprida
> http://www.eprida.com/data/Energy_article.pdf that are piloting
> production of the stuff contains only half the carbon of the original
> organic waste input. Where did the rest go? Don't all carbon
> decomposition processes release CO2?
>
> Lastly, Preston and others have demonstrated that poor peasants can
> afford biogas production systems. Can they afford pyrolization, or is
> this just another capitalist trick whose goal is mainly sequestration 
> of
> profit to international capital? Or is it just another band-aid on our
> main problem: a civilisation addicted to excessive energy consumption?
>
> Maybe Julie Grossman, who has worked with Lehman on terra preta, can 
> shed
> some light on these questions.
>
> Cheers, Karl
>
> Karl North
> Northland Sheep Dairy, Freetown, New York USA
>      www.geocities.com/northsheep/
> "Mother Nature never farms without animals" - Albert Howard
> "Pueblo que canta no morira" - Cuban saying
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