[Terrapreta] CEC

[Sean K. Barry]

Hi Tom,

I think it is fair to infer that CEC is a measure of the health of the microbial community, but somewhat indirectly.  The primary factor for determining CEC in soil is the clay and/or organic matter content of the soil.  In general, higher quantities of clay and organic matter means higher CEC.  But, different types of clays have different exchange capacities.  The issues of soil pH and the concentration of base cations, like Potassium (K+), Calcium (Ca++), Magnesium (Mg++), and Sodium (Na++), so called base saturation, play a role too, along with CEC, in the actual fertility of soil.

But, organic matter alone has a CEC like ~150 mEq/100g, so a healthy population of soil microorganisms; bacteria and fungus, etc., plus things like glomalin - all organic matter, do increase the CEC of the soil.  If the pH is in an acceptable range for these microbes to persist and live and the base saturation of things like plant useless Sodium (Na++) ions and Aluminum ions are low enough, too, then the organic matter CEC can provide a significant nutrient holding and nutrient delivering capacity to the roots of plants growing in the soil.

I'm not a soil scientist, Tom (but I could play one on TV? hehe...), so I might not have this all entirely correct.  I've just learned about CEC in this past year from reading and I only think I understand mostly about how it works.  But I've never been tested?  So, consider the source and get some other opinions, maybe?

Regards,

SKB


  ----- Original Message ----- 
  From: Tom Miles<mailto:tmiles at trmiles.com> 
  To: 'Sean K. Barry'<mailto:sean.barry at juno.com> ; 'Richard Haard'<mailto:richrd at nas.com> ; 'Kevin Chisholm'<mailto:kchisholm at ca.inter.net> 
  Cc: 'Jim Joyner'<mailto:jimstoy at dtccom.net> ; 'Nikolaus Foidl'<mailto:nfoidl at desa.com.bo> ; 'Terrapreta'<mailto:terrapreta at bioenergylists.org> ; 'Todd Jones'<mailto:tjones at nas.com> 
  Sent: Monday, December 10, 2007 10:20 PM
  Subject: RE: [Terrapreta] Charcoal costs


  Can it be inferred from previous posts that the CEC increases with charcoal as microorganisms inhabiting the charcoal provide more binding sites compared with soil? Is CEC a measure of the "health" of the microbial community?

   

  Tom 

   

  From: Sean K. Barry [mailto:sean.barry at juno.com] 
  Sent: Monday, December 10, 2007 6:57 PM
  To: Richard Haard; Kevin Chisholm
  Cc: Tom Miles; Jim Joyner; Nikolaus Foidl; Terrapreta; Todd Jones
  Subject: Re: [Terrapreta] Charcoal costs

   

  Hi Kevin, et. al.,

   

  Described qualitatively, the Cation Exchange Capacity (CEC) of soil, is the ability of soil to attract positively charged ions (cations) to negatively charged sites on molecules or atoms of the substances in the soil.  Quantitatively, CEC is a measure (or an estimate) of the number of negative charges per unit weight of the soil.  The dimensions of this measurement are conventionally in milli-Equivalents per 100 grams (mEq/100g).  This means one thousandth (milli = 0.001 = 10E-3) of an "Equivalent" per 100 grams of the sample.

   

  An "Equivalent" is the term usually given as a measure of positively charged ions, because it means how many grams of a substance that will react with one mole (6.02 E 23) of electrons.  This also applies for negatively charged atomic ions, considering the number of negative charges of magnitude -1 (or again, e-) contained in the ions.  It brings together the concepts of both the atomic weight of the ion and its charge or valence.

   

  However, when speaking of CEC in soil, the # of negative charges does not pay regard to the atomic weight of the molecules or atoms which hold those negative charges.  So, 1 mEq is equivalent to 1 mole of negative charges (e-), period.

   

  So, a CEC measurement of  ...

   

  "1 mEq/100g" is the same as "10 mmole/kg" (10 milli-mole per kilogram) or "1 cmole/100g" (1 centi-mole per 100 grams of sample)

   

  The "mEq/100g" value represents the number of cation binding "sites" in a 100 gram sample of the soil, to which that same number value of monovalent cations (ions with a valence charge of +1, e.g. H+) could attach.  For divalent and trivalent cations (+2 and +3), the number of "sites" is reduced to 1/2 and 1/3 of the "mEq/100g" value, respectively.

   

  I hope this helps everyone understand the units of measurement used for CEC measurements?

   

  Regards,

   

  SKB

   

   

    ----- Original Message ----- 

    From: Kevin Chisholm<mailto:kchisholm at ca.inter.net> 

    To: Richard Haard<mailto:richrd at nas.com> 

    Cc: Tom Miles<mailto:tmiles at trmiles.com> ; Sean K. Barry<mailto:sean.barry at juno.com> ; Jim Joyner<mailto:jimstoy at dtccom.net> ; Nikolaus Foidl<mailto:nfoidl at desa.com.bo> ; Terrapreta<mailto:terrapreta at bioenergylists.org> ; Todd Jones<mailto:tjones at nas.com> 

    Sent: Sunday, December 09, 2007 10:34 PM

    Subject: Re: [Terrapreta] Charcoal costs

     

    Dear Richard

    Richard Haard wrote:
    > S,K,J,N and Tom
    >
    > Jim and I have been discussing CEC and soil nutrition and charcoal for 
    > a few rounds offline and the apparent anomaly of my data not showing a 
    > boost in CEC with charcoal addition.
    Could it be that with low temperature char, still containing volatiles 
    and/or products of incomplete charring, the future CEC sites are 
    presently blocked, but that with some combination of microbial action 
    and weathering over several years, the tars and volatiles still on the 
    char will be decomposed or removed to yield an "active" char?
    > Rereading Steiner etal tonight I have concluded my  first year data is 
    > consistent with first year results obtained by Steiner in Brazil. 
    >
    > It seems that charcoal addition to soil does not make terra preta and 
    > that terra preta itself is the product of a long term biological, 
    > chemical and physical process. The process we used to make our 
    > charcoal 2 was identical to the local production method where Steiner 
    > obtained his charcoal. 
    >
    > Jim or anyone do you have a citation that supports your statement in 
    > an earlier posting
    >
    > Jim Joyner wrote:
    >> The CEC increases with compost and charcoal (in Brazil)  . . . well, 
    >> of course it does.
    I don't have any specific references to support this on its own, but 
    washed char tests by Cheng Lehmann and Thies
    http://www.georgiaitp.org/carbon/PDF%20Files/Posters/ChengPoster.pdf<http://www.georgiaitp.org/carbon/PDF%20Files/Posters/ChengPoster.pdf> 
    shows that char will increase the CEC.
    They used char which was much smaller than the lump and stick charcoal 
    you used. Two differences between your protocol and theirs were washing 
    and finer size.

    This is a big reach, but is it possible that there was sampling bias? 
    Specifically, is it possible that when taking samples, the large lumps 
    of char were removed inadvertently in the field, or perhaps by screening 
    at the Lab?

    Note also that your units for CEC seem to be cmole/kg while Cheng et al 
    use mmole/kg. How does one convert between teh different units.?

    How did you measure crop yields? Did you see much difference between the 
    various plots?

    Best wishes,

    Kevin


    >
    >
    > Here are some quotes from Steiner et al (2007) and my comments that 
    > might be interesting for this topic of CEC and charcoal in soil.
    >
    > Paper cited: Long term effects of manure, charcoal and mineral 
    > fertilization on crop production and fertility on a highly weathered 
    > central Amazon upland soil 
    >
    > abstract here<  
    >
    > ------------------------------------------------------------------------
    >
    > >
    >
    > from Steiner et al et al p 2
    >
    > Terra Preta research has shown that oxidation on the edges of the 
    > aromatic backbone and adsorbtion of other OM to charcoal is 
    > responsible for the increased CEC, although the proportion of these 
    > two processed is unclear (Liang et al 2006) 
    >
    > cited  Liang B et al Black Carbon increases cation exchange capacity 
    > in soils Soil Sci Soc Am J 70:1719-1730
    >
    > and from page 12 - ' the period of this study might have not been 
    > sufficient for oxidation'
    >
    > 'and SOM was only effective at increasing CEC levels above pH 5.5 
    > which is consistent with the blockage of exchange sites by either Al 
    > or Fe at lower values ---- In our study only plots fertilized with CM 
    > had pH values higher than 5.5 and increased CEC. '
    >
    > His charcoal was derived from a secondary producer and manually 
    > crushed ( not special charcoal and made with a technique identical to 
    > our charcoal 2 = heap burn)
    >
    > Definitions of his treatment blocks
    >
    > C  control
    > L  leaf litter
    > LB   simulated slash and burn (burned litter)
    > F    inorganic fertilizer
    > CM  chicken manure
    > 2CO  compost
    > 2CC   charcoal
    > 2CO+F  compost +F 
    > 2CC+F   charcoal + F
    > CC+CO  Charcoal + Compost
    > 2CC+CO   Charcoal + Compost
    > 2CC+CO+F Charcoal + Compost + Fertilizer
    > 2CCp charcoal pieces
    >
    > From Table 2 page 11 of Steiner et al soil Chemical Properties after 
    > first harvest (CEC only)
    >
    > (cmole+kg-1)
    >
    > Steiner et al  after first harvest values first -  then my own after 
    > first harvest (charcoal 1 then charcoal 2)
    > C 1.61          9.85
    > L 1.52
    > LB 1.73
    > F 2.16 12.05
    > CM 12.55
    > 2CO 1.94 11.9
    > 2CC 1.80 10.4,11.9
    > 2CO+F 2.45 12.3
    > 2CC+F 1.94 10.1, 11.25
    > 2CC+CO  1.8 10.95, 12.3
    > 2CC+CO+F 2.11 12.7, 12
    > 2CCp 1.65
    >
    > Interesting pattern here. Charcoal 1 showed the best indication of 
    > enhanced growth above ground and roots. I might speculate the lower 
    > CEC values represent greater nutrient utilization. Additionally, CEC 
    > may be incidental to the role of charcoal in soil. We should include 
    > also biological factors in our considerations. 
    >
    > In terms of biological contribution to beneficial effects of charcoal 
    > additions Steiner et al concluded
    >
    > The conditions of ADE (Amazon Dark Earth) are ideal for maximum 
    > biological N2 fixtation. About 77% of the ADE sampled showed positive 
    > incidence of /Aspospirillum sp./ compared to only 10 % of the 
    > Ferralsols. Charcoal provides a good habitat for the propagation of 
    > useful microorganisms such as free living nitrogen fixing bacteria and 
    > mycorrhizal fungi. Ogawa holds the charcoals weak alkalinity, porosity 
    > and ability to retain water and air responsible for stimulation of 
    > microbes (citations excluded).
    >
    > Steiner et al did conclude that 
    >
    > 'Charcoal proved to sustain fertility if an additional nutrient source 
    > was given. Even though significantly more nutrients were exported from 
    > the charcoal plots (with higher yields) the available nutrient 
    > contents of the soil did not decrease in comparison to just mineral 
    > fertilized plots'
    >
    > In addition he demonstrated highest mineral losses in plots treated 
    > with Chicken Manure, followed by compost, then litter and control. 
    >
    > Rich H
    >



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