permaculture

[Kevin Topek <ktopek@bellsouth.net>]

    In regard to your question on composting David, a whole buncha stuff
happens to organic matter when it degrades. Bacteria utilize the
available nutrients in vegetative matter, such as nitrogen compounds,
and digest the available carbon compounds to derive energy. When the
material is piled dense enough and moisture and temperature will allow,
the thermophillic bacteria are active. Before and after that point the
mesophillic bacteria do the digesting. In addition to bacteria, there
are fungi, actinomycetes, single celled critters, worms, insects and
other detritivores eating away at the material. All these creatures
digest the material for its nutritional properties and leave behind
their waste products, which are then eaten by another creature. The
final product is a waste that has been digested innumerable times and
has been augmented with byproducts from the digetion process of each
species. In the end, compost is nothing like the material it started as,
either structurally or chemically.

    Two key components of vegetative waste that are digested in the
composting process are cellulose and lignin which comprise plant cell
walls and extracellular structural material. When cell wall structure is
broken most of  the cell nutrients become available for digestion.
Lignin is one of the hardest materials to digest, but it is done by a
combination of fungi, slime molds and bacteria. This is the process that
helps make the end product look different from the plant material from
which it came. The entire process of composting is not really well
understood, and it may take many more centuries to comprehend the
billions of chemical reactions that occur during the process. I hope
this helps a bit.

Kevin Topek

Addendum:

The process of organic matter degradation in a compost pile is
essentially that of oxidation. The carbon cycle basically begins with
CO2 (carbon dioxide) in the atmosphere. Plants "fix" CO2 by turning it
into sugar, using energy from the sun (photosynthesis). CO2 is "reduced"
by this process, meaing that the carbon is given more electrons by
taking them from H2O. Remeber CO2 +H2O +light-->C6H12O6 +O2   from High
School biology?

To complete the cycle, organisms (like bacteria and humans) turn the
sugar into CO2 by digesting them with enzymes (protein catalysts). By
digesting the sugar, we get energy and the carbon becomes oxidized or
"mineralized" to CO2. The problem is that plants don't want to be eaten,
so they synthesize carbon compounds resistant to most digestion
processes. These compounds include hemicellulose, lignin, tanins, cutins
etc.

When these complex molecules enter the environment, they can be
partially oxidized by special fungi (white rot fungi, brown rot fungi)
with powerful oxidizing enzymes and by certain bacteria. Instead of
turning to CO2, the compounds are parially broken down by adding -COH or
-COOH groups onto the carbon backbone of the molecule. The compounds
become somewhat smaller and more polar and also more reactive. They  can
recombine with each other in strange new ways. In this way,
microorganisms oxidize compounds, using whatever energy they can from
the bonds, leaving molecules to spontaneously reform and start the whole
process over again in unlimited crazy ways. Now, add to this the fact
that microorganisms have their own biomolecules that are resistant to
degradation which enter this cycle, and you begin to see how complicated
this is. Carbon is oxidized and reduced and oxidized and reduced and
either ends up as CO2 or moves down into the deep soil and stays for a
long time.

Of course, in the absence of oxygen or in an 'anaerobic' environment,
the chemistry is different and even less understood. Anaerobic
environments include the deep soil and anything underwater, like swamps
and marine sediments.

Soil organic matter represents the most complex and poorly understood
set of chemical reactions in the universe. Many people have spent their
lives trying to figure out what is going on exactly, but this has
resulted in very little satisfying factual information.

Mindy Vanderford