[Terrapreta] FW: Charcoal in soil

[Sean K. Barry]

Hi Nikolaus

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.


Black charcoal chunks left after an open burn could be 90-95% carbon "fixed Carbon", after ash is taken out.  So, a proximate analysis" of a "charcoal" sample, a chunk from the "burn zone" field wind row, will tell the relative amounts of water%, VM%, ash%, and remaining "fixed Carbon%" ... 

... in that single chunk of charcoal.

As for what the 150 to 180 tons ha-1 of "charred material" left in the "burn zone" are, that's another question.  A larger sample could be taken, scooped from several different parts of the "burn zone" perhaps, mixed, and sample tested.  The sample population would have to be larger in number, to assure statistical significance, be random, and be assured to take as much charcoal and ash together as in their present ratio.  This might give a better picture of the average amount of "fixed Carbon" content ha-1 left on the land.  Underlying soil contamination in the sample is another potential problem.

I'd guess a "proximate" analysis of an random sample of "charred material and ash" taken from the "burn zone" you describe might have
~50-70% ash content.  That's a guess, but it meshes with your description of the combustion that occurred in the "burn zone".  So, assuming 1000 to 1200 tons of green wet biomass ha-1, what would the 150 to 180 tons of "charred material" yield from a partial (but mostly) combustion consist of mostly?  Probably, mostly ash content; 7-8% of 1000 - 1200 tons ha-1 is 70 to 96 tons or 38%=70/180 to 64%=96/150, 38-64%.

The woody biomass may have had an intial "ash content" of 7-8% before it was burned.  If the combustion was mostly completed, then liberally, most of the carbon in the biomass may have been released as various gases, chiefly in the complete combustion gas, CO2, then varying amounts of other less completely combusted carbon-bearing pyrolysis byproducts (CO, CH4, C2H6, trace other longer chain hydrocarbons, etc), and "soot".

Only if the oxygen source were limited during the burn, would there be anything other than mostly complete combustion gases; CO2 and H2O exhausting from the fire.  With any limit on
the oxygen, then the fire goes out and larger amounts of the other "fuel bearing" gases may escape "un-burned" in the exhaust.  There may be large amounts of soot created, too.  If this did not land back on the burn zone, then it is "lost carbon" (back to the soil elsewhere?) and cannot contribute to the measurable or estimable 150-180 tons ha-1 left on the field.

Soot is "blown" off bits of carbon coming from explosive pyrolysis, occuring in the biomass; roughly C5H7O3 => CO + H2.  The explosive reactions are caused by great and direct heat coming from oxygen reduction reactions, H2 + CO + O2 => H2O + CO2 + heat.  If more oxygen is added or still present, (as noramlly is in an open burn), then the H2 and CO pyrolysis products just burn up immediately, too, in gaseous hot exhaust.  Carbon is alighting fast and not being left to "fix" out of the atmosphere at all.

With "full combustion", the amount of complete combustion exhaust gases is largest: CO2, H2O, hot N2, trace O2, VM (longer string hydrocarbons), and soot.  Then, the amount of fuel gases H2, CO, CH4, C2H6, etc, is small, and most of all, the original 7-8% ash is left on the ground in the waste from the fire.  But, the ash is the bulk of the density.  The carbon went up into the air.

I have a wood burning boiler that combusts to ash 10 cords of oak yr-1.  There are bits of charcoal in that ash, but it is most definitely mostly ash, by weight, and volume. I've taken to spreading this probably alkaline ash under the drip lines of evergreen trees; pine, balsam, spruce, etc. and onto grasses with field ant mounds.  It doesn't seem to cause any problems for plants or ants.  There is only 6 years or so of ash and that totaling about 2 or 3 cubic meters of the ash piles (a guess at that volume and I don't guess an amount).  I don't know how much land I've spread it over, either, or how many times I've repeated (guess 1 hA, 2 or 3 cubic meters) that.

Your discussion of Terra  Preta charcoal affects over the long term versus short term is very interesting.  You seem to suggest the beneficial effects on cropping with TP soil are not merely the result of there just being charcoal in soil alone, but rather, that it is a chemical and structural capacity built into the soil over time, through the interaction of the soil and soil microorganisms with the charcoal.  Can you think of any way to accelerate the creation of humic and fulvic acid in soils containing charcoal?!  This could be the way to achieve the agricultural benefits of of Terra Preta sooner.


Regards,

SKB
  ----- Original Message ----- 
  From: Robert Klein<mailto:arclein at yahoo.com> 
  To: Nikolaus Foidl<mailto:nfoidl at desa.com.bo> 
  Cc: terra pretta group<mailto:terrapreta at bioenergylists.org> 
  Sent: Thursday, January 10, 2008 4:57 PM
  Subject: Re: [Terrapreta] FW: Charcoal in soil


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

  arclein

  http://globalwarming-arclein.blogspot.com/<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<mailto: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<mailto:terrapreta-request at bioenergylists.org%22%3Cterrapreta-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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