[Terrapreta] Developing a biochar protocol

[Robert Klein]

In reviewing my posts on terra preta and the comments
since generated by the expanded participation around
the terra preta website in particular, I realize that
this is a good time to share with everyone the thought
processes that led to the corn culture hypothesis.
This will also serve to air my response to the many
nagging questions that I see recurring on the site.

I proceeded by developing my understanding of the
constraints under which the farmers operated and
investigating possible solutions. This approach should
also inform other researchers looking at alternative
solutions which may be out there.

It is fairly trivial to determine the time and place
that the original terra preta soils were created.
Archeology has pushed the time line back to 2500 years
ago and to as recently as 500 years ago. It was
clearly linked to an agricultural civilization with
all the archaeological evidence lined up behind it.
Although The apparent beginning coincided with the
late European Bronze Age, I an unaware of any
Archaeological evidence to suggest that we are dealing
with a technology level that was any thing other than
late stone age. That could still imply very limited
access to some copper tools but nothing that would
likely leak into the agricultural economy. Even the
late European Bronze age I suspect had trouble using
their only form of portable wealth to help their
farmers.

So we can be fairly sure that our farmer worked with
what tools could be made out of wood and stone. This
is sufficient to girdle trees and to painfully do some
wood cutting. So slash and burn becomes practical as
does a limited wood processing industry. My best
informant on this is the eighteenth century state of
woodworking on the Pacific Northwest which then
blossomed into the artistic explosion we know with the
advent of steel axes. Cutting and splitting wood was
possible but clearly not easy.

I then investigated traditional open air charcoal
making which deforested much of the Eastern woodlands
in the nineteenth century. Nothing like checking with
the real experts who were relying on a thousand year
old tradition. What is immediately evident, is that
high yield charcoal making in open air is dependent on
limiting air flow through the maximizing of packing
ratio and the uniformity of that ratio. This is
perhaps obvious but the fact that the packing ratio
needs to be better than 75% is not obvious.

Packing ratio is a mathematical concept that measures
the amount of open space to solid as a ratio. For
example, a bucket of balls has a best packing ratio of
51%. This is not obvious.

Cutting hardwood to length and splitting out four inch
blocks, which are then tight packed achieves both a
75% plus packing ratio but also good heat circulation.
This is why the high yields were achieved.

To replicate the same packing ratio and heat transport
with any biomass is a tall order. Most biomass is
often almost unpackable, such as woodland waste or any
branched crop. The simple jumbling together of waste
ensures a lousy packing ratio and heat transport
problems. In fact, it is fair to say that charcoaling
woodland waste was also not very convenient without
steel tools to cut the wood to length to get the
needed packing ratio.

Once one realizes that the jungle is not a viable
source for high volume ongoing biochar production, one
must retreat to their crops. Recall that these fields
are created first by the process of slash and burn
which produces only a little charcoal which likely
burns in the next cycle of slash and burn.

Again the packing ratio has a lot to say. Most of the
burn happens just on the ground or above it. There is
a lot less heat penetration of the soil than you would
suppose. Recent comments on prairie grass misses this
effect, since prairie grass has a packing ratio of
possibly less than 20%, most of the heat is dumped
into the atmosphere. I learned this lesson by
attempting to roast a potato under a mound of better
fuel than prairie grass. (the neighbors all came out
to see the 'barn' burn:)).

If we want to produce biochar at all we have to grow
the feedstock and then tightly pack it in order to get
the necessary conditions in place. This limits us
quickly to stalk plants that have a natural
theoretical packing ratio of 77%.

Most grain crops seem to lend themselves to this
except for their low volume on a per acre basis.
Modern crops such as sugar cane would be possible if
we did not use the cane. some other plants can be
obviously used in this way. However, we very quickly
are forced to consider corn simply because its non
edible part consisting of the stalk represents a ten
ton per acre source of biomass and a potential one to
two ton source of char per acre.

This very high per acre yield is very necessary to the
farmer because he has to see that he is visibly
changing the seed bed and not expending a huge effort
on haulage. Even today, this is the one crop producing
enough bio mass to make terra preta practical.

The antique farmer had a waste product that he had to
pull out of the ground and build into a waste stack to
begin with so that he could raise the next crop. It
was a likely ten ton stack since that was as far as he
wished to haul this material. He then simply burned it
as farmers do to this day. Even without proper packing
some char was produced. It was not a big leap to
optimize the packing and eventually to optimize the
biochar production from this base.

I had reached these conclusions before I queried
google scholar and ran down the pollen profile of the
terra preta soils which immediately confirmed the
predominance of corn pollen. Cassava also showed up
which is also suitable for packing.

I will develop the rest of the story in my next post,
but it can be found piecemeal in my earlier posts.

This is a list of posts dealing with terra preta in
particular and is meant to help you navigate through
the development of my thinking. There are other posts
apropos to the subject, but this should get you
through it.

http://globalwarming-arclein.blogspot.com/2007/06/carbonization.html

http://globalwarming-arclein.blogspot.com/2007/06/corn-cultures-bright-furure.html
http://globalwarming-arclein.blogspot.com/2007/06/total-carbon-sequestration-potential.html
http://globalwarming-arclein.blogspot.com/2007/06/tropical-soils_26.html

http://globalwarming-arclein.blogspot.com/2007/07/discussion-with-ron-larsen-on-terra.html
http://globalwarming-arclein.blogspot.com/2007/07/human-labor.html
http://globalwarming-arclein.blogspot.com/2007/07/those-amazonian-soils.html
http://globalwarming-arclein.blogspot.com/2007/07/pollutants-from-carbonization.html

http://globalwarming-arclein.blogspot.com/2007/07/nutrient-accumulation.html
http://globalwarming-arclein.blogspot.com/2007/07/uniqueness-of-corn-culture.html
http://globalwarming-arclein.blogspot.com/2007/07/amazon.html

http://globalwarming-arclein.blogspot.com/2007/08/heat-distribution-and-terra-preta-soils.html
http://globalwarming-arclein.blogspot.com/2007/08/getting-job-done-biochar-on-modern-farm.html
http://globalwarming-arclein.blogspot.com/2007/08/tom-miles-comments-on-biochar.html

http://globalwarming-arclein.blogspot.com/2007/08/mel-landers-and-jackie-foo-on-field.html
http://globalwarming-arclein.blogspot.com/2007/08/methane-and-pottery.html
http://globalwarming-arclein.blogspot.com/2007/09/glopbal-corn-culture.html





       
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