[Terrapreta] FW: Charcoal in soil

[Robert Klein]

I posted this commentary on my blog today regarding Nikolaus' post:

arclein

http://globalwarming-arclein.blogspot.com/




Nikolaus Foidl has given us an
excellent report on the experience gained attempting to exploit the products of
an open burn of waste wood.  It also
brings home my ongoing disquiet surrounding the drawing of conclusions from
this and many other similar tests.  In
this case particularly, a huge amount of ash was produced that was not fully
incorporated into the surrounding soils. 
This made the soil initially very rich in soluble salts which had to be
leached away before any benefits could emerge. 
The soil is actually ‘burned’ by an overload of nutrients.


 


I suspect that this is a problem
with traditional slash and burn protocols also, however it may be obviated.


 


When we set out to produce a
uniform end product of either charcoal or bio char or Terra Preta, it is
necessary to manage the variables of temperature, airflow and end product
production.


 


This can be done in an industrial
kiln to great satisfaction.  Tight packed
wood with restricted air flow also seems to work okay.  The earthen kiln that I have proposed for
corn culture fits in between in terms of its ability to manage the process.


 


First and most important, the air
flow must pass through an earthen wall several inches in thickness in order to
reach the hot zone.  This strictly limits
the amount of oxygen and its velocity.


 


Second, the combustion is
primarily fed by the heat generated from light gases such as methane which
ignites first closest to unburnt material producing the most heat directly were
it is needed, continuing the reduction process. 
Heavier unburnt volatiles enter the chimney were they may or may not be
consumed if there is any remaining oxygen. 
These hot gases are then forced back into the stack at the top of the
chimney traveling into the corn and back through the soil cap.  Two things happen.  A lot of the produced heat is absorbed by the
unburnt corn stover preparing it for combustion.  The gases then enter the soil giving up much
of the unburnt volatiles including most pyrolysis fluids.  They are also well distributed in the process
and depending on the thickness of the soil cap, most are captured.


 


Once the fuel is totally processed,
the capping soil is mixed with the reduced bio char and ash to properly
distribute the combustion products throughout the soil.  This virgin terra preta soil blend can then
be taken in baskets or shovel loads to produce seed hills.  Biological agents will quickly destroy any
complex organics not already reduced by the heat leaving a carbon enriched soil
that can hold nutrients for years as demonstrated in the Amazon.  Rather importantly, they must also succeed in
quickly reducing the high acid content of the pyrolysis fluid.  That will need to be studied in field tests.


 


What I find particularly
beguiling about this earthen kiln protocol is that it allows for quite a bit of
variation in the air flow through changing the thickness of the earthen shell
itself.  This allows for a maximization
of output over time.  More importantly,
this method is completely within the skill set and capital resources of every subsistence
farmer in the world.  He and his family merely
need to be shown once.


 




From: Nikolaus Foidl <nfoidl at desa.com.bo>


Date: Wed, 09 Jan 2008 16:28:52
-0400


To: "terrapreta-request at bioenergylists.org"<terrapreta-request at bioenergylists.org>


Conversation: Charcoal in soil


Subject: Charcoal in soil




Dear All!




Looking on the trials done so far with Charcoal in soil and terra preta, the
most common plant used was corn so far. 
I do trials with charcoal since one year and I have as well soils at
hand where huge amounts of forests after clearing where piled up in long rows
and burned down, leaving behind ashes, charcoal and torrefied wood and all the
condensates from the burning.( as well a good amount of soil burned together
with the wood because the soil was on the roots and part of the logs and
branches where covered by soil when they pushed the chained down trees to a row
with caterpillars.



In the first 2 years only certain grasses ( brachiaria) would grow on those
stripes. After some 3 years the planted corn and soy and sunflower show
pronounced growth in the beginning but after about 60 to 70 days all plants in
the field reach the same height and have the same state of development.



Looking at the harvest data there is no significant difference between charcoal
and non charcoal in fertile well fertilized land not suffering drought.  If there is drought during the development of
the plants then the charcoal plot is more sensible and shows earlier drought
damage in the plants.



If you make a mass balance over the amount of forest cut down and dragged with
a caterpillar from a stripe of 50 meter each side to a small long heap of about
15meter width then you accumulate some 5 times the volume of the intact forest
in the stripe of 15 meter or you concentrate the amount of 5 ha forest in one
ha area and burn it . If we suppose a average dry mass yield of total biomass
per ha (including roots) of some 200 to 250 tons this would be some 1000 to
1250 tons of dry biomass burning in this ha.




From sampling I can estimate that there are some 150 to 180 tons of partially
or fully charred material per ha in the burning zone. So this leaves us with a
huge amount of ashes in the same area. As most of the material are trees with
an average diameter of 15 to 20 cm ( some are more then 60 cm, but most are
smaller brush like trees) we have a good amount of barks with quite a high ash
content. Wood without bark is in the range of 0.3 to 0.8 % ash and barks are in
average around 7 to 8 % ash, some more.


 


Do you have any idea what this naturally reduces to in terms of
elemental charcoal?  Otherwise the
amounts appear excellent and suggest that modern land clearing could be
judiciously used to sequester a lot of carbon.




We urgently need to make mineral mass balances about the ashes and we need to
know as well in which chemical form those ashes are in the soil and to what
chemical form they convert. From the first look it seems to me that potassium
and calcium and then magnesium and phosphor would be the mayor constituents.(
someone has figured out the plant availability of those ashes?)




Now imagine that the indios additional used these burn and char areas as waste disposal
and most of there waste where ashes from cooking fire and rests from there
meals like fish heads and spines or bones or non edible parts of the animals
beefing there diet ( as well needed a mass balance over at least a period of
several tens of years to get a grip on quantities and content of minerals) then
you easy can imagine that the terra preta sites are an enormous accumulation of
minerals in different chemical forms. The adding of biologic material enhances
whatever biology is working there and for sure will enhance growth of whatever
plant you grow there.


 


We all believe that this is likely, but I also think that the land needed
by a family was at least four or five acres. 
That means a pretty broad distribution of human and fish waste into the field.  Has anyone mapped distribution over several
acres to find out if it was consistent. 
If I were personally handling high grade wastes in such a setting, I
would focus on the household garden to get the biggest bang for my effort.  Of course a communal village could well have
shifted this every several years.




Now the charcoal does not play an important active role in the beginning but degradation
over the centuries transforms the charcoal into more stable chemics like humic
acid and fulvic acid etc. which have high interchange capacity and high
chelating capacity.


 


Is this a derivative of pure carbon or remnant organics?  Does terra preta show such an acid
profile?  If not why not?


 


Maize reacts very strongly to high amounts of potassium ( the mayor ingredient
of ashes)as well does soy and sunflower. Brachiaria as well is addict to high
potassium. Other grasses do have problems with high potassium and do not grow
in the first years in those burned areas.( dont think that this is a
coincidence)


 


Conclusion is that we may be get
distracted by fast visible effects on corn and other potassium and only relate
those effects with charcoal but not with ashes and other micro minerals
accumulated in waste disposal sites.




I believe in several enhancing effects of charcoal like vigor enhancing from the
liquids produced during charring but I think there is very low direct short
time effect from charcoal itself on growth of plants ( first 10 to 50 years).
There is without doubt a indirect sink and source effect by its capacity to adsorb
micro and macro nutrients.


 


Ancient terra preta soils are been continuously cropped over decades
without significant fertilization.  This
implies that the carbon essentially fixed nutrients in the growing zone.  Otherwise fertility would have collapsed.


 




Best regards Nikolaus





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