[Terrapreta] Scientific American Story on Charcoal Decomposition

[Lloyd Helferty]

How much extra carbon has been added to the soil by the addition of the C
(char)?  IF it is more than 2 tonnes per ha per year then it is net
positive, if not then we have produced a negative effect on soil carbon.  We
can't forget the contribution of the char itself!

	Lloyd Helferty


-----Original Message-----
From: terrapreta-bounces at bioenergylists.org
[mailto:terrapreta-bounces at bioenergylists.org] On Behalf Of andrew
Sent: May 11, 2008 10:08 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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