[Terrapreta] Scientific American Story on Charcoal Decomposition

[Mark Ludlow]

I gather that the association of char and loss of organic matter is related
to the activity of fungi resident in carbon granules. Char has a very large
surface area, per unit of mass, but I would expect that the highest level of
OM metabolism would occur on or near the surface of the charcoal granules.
(Someone please correct me if my ignorance is showing!)

IF this is so, then the overall balance of benefits should be able to be
shifted by varying the size of the charcoal granules; i.e. in OM rich soils
with labile OM (humus) a larger carbon granule may be more appropriate, but
when establishing soil fertility more rapidly (say, converting more intact
carboniferous material to a form that is better suitable for plant
metabolism) a smaller granule may be required.

Over time, tilling and natural weathering probably makes the mean size of
all applied char smaller. At this point, perhaps it should be displaced to a
deeper soil horizon where it will be less affective to OM.

Mark

-----Original Message-----
From: terrapreta-bounces at bioenergylists.org
[mailto:terrapreta-bounces at bioenergylists.org] On Behalf Of andrew
Sent: Sunday, May 11, 2008 7:08 AM
To: terrapreta at bioenergylists.org
Subject: Re: [Terrapreta] Scientific American Story on Charcoal
Decomposition

On Sunday 11 May 2008 13:35, Lloyd Helferty wrote:
> I note that the author only indicated that using Charcoal (black
> C) for enhancing ecosystem C sequestration ... can be "partially
> offset by its capacity to stimulate loss of native soil C".  The
> important point is that the carbon sequestration capacity of Char
> is only Partially Offset by losses elsewhere (from humus) ~ which
> would mean the net carbon sequestration potential is still
> positive. 

It may be that organic matter rich soils should be avoided for neo 
tera preta schemes. We do know that soil organic matter (som) is 
respiring to CO2 and Water more rapidly as soils become warmer in 
any case, so there's already a positive feedback mechanism working 
against accumulation carbon in the soil.

Can we have a stab at some figures for a typical mineral arable soil, 
neglecting any benefits to growth that char additions may bring?

Perhaps someone can add better figures for this assumption:

How about a hypothetical soil with 4% som to plough depth of 23cms, 
That's 2300m^3 of soil per hectare, on an oven dry basis can we 
allow that to be 3500 tonnes of soil? Which yields a som of about 
140 tonnes and carbon of about 82 tonnes. If soil carbon is recycled 
over a 40 year period then it's half life is 20 years ( matmeticions 
please correct me where I'm wrong), say adding an amount of char 
doubles the rate of respiration and reduces the half life to 10 
years. Then by adding the char we're increasing the respiration of 
soc (soil organic carbon) by 2 tonnes per ha per year, what benefits 
offset this?

AJH

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