[Stoves] Oxygen depletion

[Crispin Pemberton-Pigott]

Dear Pat

Very interesting assessment. Good comments below too. Both sides seem to
offer arguments laced with emotion and scare-mongering.

Every time I put real numbers to the large scale implementation of biochar,
based on the dozen or so proposals I have seen, the macro figures are not
very attractive. The Oxygen depletion angle is off the wall and does not
present a convincing argument against biochar for the same reasons other
hold so much for it: weak evidence and poor social and monetary economics.

If a stove were to produce 25% yield of dry biomass when cooking, putting
down 12.4 tons per hectare per year would require growing 50 tons (dry mass)
of bio-something to do it. 50 tons of fuel would weigh about 58 tons of air
dried fuel (15% WWB). If a consumer cooked with 2 kg of fuel per day, it
would take 80 families to produce the necessary char in a year. That would
enhance 1 ha and would continue for quite a number of years, like 200 or
300.  I don't think 80 families will give their char to only one of their
number to build up 1 ha for a few centuries.  Spreading it around to all the
families only delays by millennia realisation of the proposed benefits.

As the article implies, leaving 12 tons of coal in the ground would
sequester about the same amount of carbon, if carbon is the 'angle' (it
certainly was in the comments section). So making 6 coal stoves that save 2
tons per year would have the same effect. That sounds cheaper than making 80
stoves plus all that work.

It is clear that a lot of interesting biological things happen with biochar
and I look forward to more convincing evidence that the effects of its
application are understood.

Regards
Crispin in Smoky Johannesburg where coal is not sequestered....



++++++++

This would seem to refute the idea that burying charcoal in the soil is a
good idea:

http://permaculture.org.au/2010/11/18/beware-the-biochar-initiative/


Pat