Subject: Re: [SANET-MG] soil amendments from composting v fermentation

From: Elaine Ingham <[email-masked]>
Date: Sat, 15 May 2004 12:27:06 -0400

Anaerobic metabolism includes several metabolic pathways, and the different end products from the different pathways need to be differentiated, because some pathways end up with plant toxic materials being produced, while others do not.

However, all anaerobic processes result in significantly acidic organic acids being produced, which may or may not be a problem for your plants.  Depends on the plants being grown, right?  What pH do they need?

Those organisms that produce mainly lactic and proprionic acid as the main metabolic end products and do not produce hydrogen sulfide or ammonia.  They can make phosphine gas, however, which means your PO4 may be out-gassing.  So, a little sour smell to the process, some loss pf PO4, somewhat low pH metabolites produced.  This may not lower pH in hte pile much, since the acids mix with the organic matter that have a higher pH.

Most people use the term "fermentative metabolism" for these metabolic processes.  Wine and beer production use particular species that perform this type of anaerobic metabolism.  Can we call this kind of anaerobic metabolism fermentation, please.

As opposed to putrefaction.  Putrefactive processes make the really bad smells, because hydrogen sulfide production is a putrefactive process.  Ammonia is also produced, along with phosphine gas, and a host of really bad smelling organic acids, from vinegar (acetic acid) to vomit (valeric acid) to putrescine.  Alcohol is produced by the bacteria in significant quantities, high enough concentration to kill plant roots.  This can be a real problem if you use mulch that has suffered this kind of anaerobic metabolism.

Note that I do not call this compost, becasue it is not compost.

Putrefactive anaerobic conditions are what you want to avoid.  If the compost pile becomes anaerobic, you need to turn it or dilute the food resources to slow the bacteria and fungi down.  Bacteria and fungi can grow so fast that they use up most of the oxygen in the pile.  They use up the oxygen because they are growing on the foods in the pile so fast.  As they grow, they generate heat.

Thus, if you are careful to never let the pile go anaerobic, heat will tell you when to turn.  But if the pile goes anaerobic, then heat is not related to anything positive anymore.

Composting is by definition an AEROBIC process.  Worm compost has to be aerobic, because the worms require aerobic levels of oxygen.  But the lower layers in a worm compost can go anaerobic.  If that happens, the worms will no longer go down deep into the pile.

And it is the SUM of the pile that needs to be considered.  Pockets of the organic matter can have low oxygen, where the anaerobic metabolites will move into the aerobic areas, but as long as most of the pile is aerobic, the anaerobic metabolites get consumed by the aerobic organisms, and just help increase diversity in the pile.

What's the right balance to achieve a pile that is enough aerobic?  That's what the microbiology of compost course is about that I teach.  A couple students are involved right now in replicating the process so we have the solid, scientifically sound results to present.

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

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