Re: [compost_tea] Re: C:N

From: <soilfoodweb_at_aol.com>
Date: Tue, 21 Dec 2004 00:19:56 -0500
Hi Kirk -

I just don't ever percieve myself as being a scary or intimidating person, so its hard for me to see why anyone would have any trepidation working with me.  I suppose as people get older they just don't see that they move into the "silverback" category. 

I don't think of myself in that category.  I'm just not that old!

Oh, wait.  Ah......

just remember that in everyone's mind, you never age past twenty-something.  When I hit 100 years old, I might finally consider thinking of myself as over 30. 

Anyway, I try to be approachable.  I certainly can do stupid things, as does everyone else I know.  There is always something we can chuckle about with everyone......

Anyway, back to compost ----
-------------------------
Elaine from yesterday:
If you alter starting materials, what do you suppose the effect will be on C:N?

Kirk:
Precisely why I approached this with trepidation - I knew I wouldn't have all the answers to questions you'd ask :-) 

Elaine today:
The reason I put my first reply in question form is that I don't have all the answers either, but there is a principle here that you want to think about and start building into your gestalt about compost. 

Think of compost as being built on the basis of three general classes of materials.

Hi N, green and woody.  Yes, high N is genernally green, but if it is high N, then it goes in that category, regardless fo greeness.  You alter the mix of these three categories of materials in order to achieve temperature, physical aeration and microorganism growth.  More woody materials, more fungal food, more fungi.  The more high N, the higher the temp will go (ok, assuming no toxic matrerials come with).

The more woody, the wider the C:N.  If you let if go anaerobic, and really blow off ammonia, the wider the C:N.

Elaine from yesterday:
> If you compost with fungi predominant, where so much less C will be blown off as carbon dioxide, what do you suppose the effect will be on C:N?

Kirk:
Higher C:N.  This might be Composting 101 but how do you compost with fungi predominant and achieve temp?

Elaine from today:
Enough hi N to get high temperatures.  Once fungi get growing, they too generate temperature.

Elaine from yesterday:
> What would lead you to expect that all compost, regardless of starting materials, or way the composting process has been handled, has to finish up at the same composition, and at the same C:N ratio?

Kirk:
Convention.  Everyone who seemed to know has said 10-15:1.  But I'm getting some understanding of why only one of the books I have suggested a "finished" C:N...

Elaine from today:
Bingo!!!!!  I am so glad when people start catching on!  I am NOT being sarcastic here.  I can be told something, in ten different ways, sometimes, and I still don't get it, until, suddenly, bingo!  A light bulb finally completes a circuit. 

Then I feel dumb, for not having caught on, flipped the switch, whatever, for so long.  Take home message here is, don't feel dumb.  You managed to make the connection, something that even the most touted Ph.D.'s haven't managed, after working their whole career with bacteria. 

Elaine yesterday:
> If you allow the compost pile to become anaerobic, and most of your available N is volatilized, what will be the effect on C:N?

Kirk:
Higher C:N.

Elaine today:
Yep.

Elaine yesterday:
> What is in compost that could greatly alter C:N ratio of the final product?  What is the C:N of bacteria, versus fungi?  What kind of metabolites are produced?  What is the difference in the way bacteria versus fungi use C?

Kirk:
I know bacteria are low C:N (~5:1) and fungi higher (20:1+), so I'm getting how a higher fungal content could get to a higher C:N.  Protozoa, etc, are even higher, so I can see how a good compost could have a high C:N.  I have no solid ideas on last two questions.

Elaine today:
Bacteria blow off, on average, 60% of the carbon they use as CO2.  Fungi blow off only 20% as CO2.  So, you see the difference? 

Elaine yesterday:
> What is the difference in anaerobic versus aerobic use of N, and C?

Kirk:
I have absolutely no idea, but I know in anaerobic digestion a lot of C is volatized off as methane, CH4..

Elaine today:
In anaerobic conditions, much less C is lost than in aerobic decomposition.  The ratio of bacteria to fungi have to be looked at as well, something we haven't really gotten around to yet. 

Kirk:
Couple questions...

Does this mean that a C:N of 10-12 indicates a bacterial-dominated compost and that a C:N of 30 in compost that's "finished" - i.e., it doesn't heat more than a few degrees on turning and respiration is low - is
fungal-dominated?  That may be obvious but I want to be clear(er:).

Elaine today:
Haven't seen that.  Part of what you have thought through is correct - bacterial-dominated compost is probably always in the C:N 10 - 12 range, as long as it didn't go anaoerbic.  Then we see the C:N 20 to 30, which is what I thought I was talking about the other day in my e-mail.  Or more correctly, that what I think I was talking about.  Grin, my memory.....

In fungal composts, when properly finished, C:N can range from 10 to 20.  I think it has more to do with the kinds of fungi, which means we have more work to do.....

Kirk:
There's been an interesting sub-thread here of using "young" compost for tea.  Not sure what the theory is.  It would likely be more "active" but tea-making or soil application normally activates critters that aren't dead. 
Maybe someone could expound?

Elaine today:
When compost isn't quite finished, but has gone through the WHOLE heating process and temps are falling below 100 F, the organisms are still active, and thus will get into rapid reproductive mode much more rapidly.  This is discussed in the Compost Tea Brewing Manual. 

Kirk:
Question I want to get to bringing that up is this:  Is C:N changed in the compost "maturation" process.  "Finished" compost can be distinguished from "mature" compost - young compost being finished but not mature, presumably.
Does the C:N of compost change much during the aging process?

Elaine:
Depends on the organisms predominant in the composting process.  The greater the bacterial component, the more CO2 is lost, and the more N is concentrated in bacterial biomass and waste products.  The greater the fungal component, the more carbon remains, and the more other micronutrients remain as well. 

Kirk:
What's the difference between "young" compost and "mature" compost?

Elaine:
I think of young versus mature compost as relative activity of the bacterial and fungal populations.  When young, the organisms are still rapidly growing, generating temperature, and thus activity is high - above 10%. 

Mature compost means the organisms are not growing rapidly, not generating lots of temeprature, and not all that active - less than 10% activity. 

Kirk:
As I noodle through the murk of my books and memory here, I'm getting the impression that C:N is only important on the front end of composting, not the result, except as a potential indicator of B:F ratios?  Is this
something that should have been obvious all along?  Eeek!

Elaine:
You need to design the starting materials right, but I use the Cornell Composting Handbook to give me a general idea of the likely C:N of the mixes I put together.  I use the actual temperature generated as the way to tell me if my guesses about how much chicken manure was actually in the chicken litter I bought, for example.  I adjust the pile within the first 2 to 3 days if my guess proves wrong.  The final C:N ratio - which takes weeks to get back many times - tells me B:F ratio - which takes a couple minutes if I do the qualitative method, or a few days if I send to the SFI lab.

So, what is really most useful as a measure?  Start using the little microscopes.....

Have fun!  See you Wednesday!

--
Elaine Ingham
President, Soil Foodweb Inc.
SFI Corvallis, OR
SFI Port Jefferson, NY
SFI Lismore, NSW, Australia
SFI Cambridge, New Zealand
SFI Culiacan, Mexico
SFI Jerome, Idaho
SFI South Africa
http://www.soilfoodweb.com


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Received on Tue Dec 21 2004 - 00:54:23 EST

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