[compost_tea] Re: C:N

From: Kirk Leonard <kirkleon_at_open.org>
Date: Mon, 20 Dec 2004 10:20:56 -0800
> Date: Sun, 19 Dec 2004 21:38:54 -0500
> From: soilfoodweb_at_aol.com
> Subject: C:N
>
[snip]

> If you alter starting materials, what do you suppose the effect will be on
C:N?

Precisely why I approached this with trepidation - I knew I wouldn't have
all the answers to questions you'd ask :-)  It seems like the range of
choices in this instance is greatly constrained by combinations of materials
that will actually achieve 55 dC temps (and not go past 70).  Beyond that I
don't know what the final C:N effects might be.  I assume it could be all
over the map.

> 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?

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

> 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?

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...

> 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?

Higher C:N.

> 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?

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.

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

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

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:).

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?

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?

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

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!

Kirk


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Received on Mon Dec 20 2004 - 15:00:35 EST

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