Market Farming

[Sojourner <sojournr AT missouri.org>]

SCook21809 AT aol.com wrote:
> 
> Only aerobic soil bacteria have been shown to bind
> atmospheric nitrogen symbiotically in the presence
> certain legume root exudates.  Aerobic bacteria are
> incapable of using the complex carbohydrates and lignins
> found in saw dust and wood chips as a food source.
> They require simpler sugars and carbohydrates from sources
> like straw, crop residues, compost and root exudates.

OK, I had to go look this up, but there are in fact several microbes
involved in decomposition that can and do break down the lignins in wood
and sawdust.  Two such are Azobacter and azospirillium. I'm pretty sure
there are others but don't remember what they are off the top of my
head.  Azobacter, at least, I should've remembered.  Once upon a time I
had more details at my fingertips, but that was then and this is now.

At any rate, azobacter is a free-floating nitrogen fixer (e.g., its not
a typical nitrogen fixer like you would find in root nodules) that most
likely works with various fungi and other microbes to break down the
lignins and cellulose in something like sawdust or wood chips.  Straw,
btw, is also high in lignins but has a higher proportion of cellulose to
lignin than does sawdust.  Or so I've read and that does seem to match
up with hazy memories about this.

So there are in fact microbes other than the aerobic bacteria you are
talking about above that perform this function, AND that can (and do)
breakdown sawdust.  Again, I ask people to consider an undisturbed
forest floor.  What do we see?  Leaves, twigs, branches, bark, wood,
mostly, all of which breaks down quite nicely and the trees and
understory grow just fine.  All plants require some nitrogen, so where,
in the absence of cover crops and nitrogen fixing legumes, is it coming
from?  Mycorrhiza (a class of fungi that fix nitrogen) and microbes like
azobacter.

This from the Microrrhiza web pages at:

http://mycorrhiza.ag.utk.edu/mycor.htm

"Ericoid and EM have a special role in the mineralization of nitrogen.
Most plant litter entering the soil has a high C:N ratio and is rich in
lignin and tannins. Only a few mycorrhizal fungi can mobilize nutrients
from these primary sources. However, a wide range of ericoid and EM
fungi can obtain nitrogen and other nutrients from secondary sources of
organic matter such as dead microbial biomass. A wide range of
hydrolytic and oxidative enzymes capable of depolymerizing organic
nitrogen have been demonstrated."

In a healthy soil system, there is in fact an awful lot of nitrogen
fixing going on that is NOT purely dependent on legumes and their root
nodules, and is not "robbing" the soil of nitrogen.  It's PUTTING it
there.  Slowly, to be sure.

Why then, you may ask, and well you may, does conventional knowledge
insist otherwise?  Well, think about it - in the last 30 to 50 years,
what soils have been being studied?  Well, agricultural soils.  And how
have agricultural soils been treated in that time period? With heavy
applications of chemical fertilizers, anti-fungals, and pesticides.  So
just how accurate a picture of soil life does this give us?

The answer is, not very.  It's like studying the land directly around
Chernobyl to get an idea of biological diversity in Russia.  Nitrites
and other agricultural products and byproducts are known (now) to have
severe deletorious effects on the natural flora and fauna in the soil. 
When you kill off the "bad" fungi you are killing off the "good" fungi
as well, as well as entire classes of microbes and protozoa that
interact with and/or feed on them.  I've seen estimates of soil life in
soil from a conventional farm at something like 1,000 to 10,000 per
teaspoon; it's 10 million for healthy soil that has not been subjected
to a constant barrage of pesticides, fungicides, and chemical
fertilizers.

It's only been in about the last 10 years that any serious work (or that
work being done has been taken seriously) on soil life.  THIS is the
reason that NPK doesn't work the way agricultural scientists insist it
ought; chemical fertilizers (of which 60 to 80% of the nitrogen is
actually wasted because it can't be utilized - there isn't enough soil
life to take it up and store it!) kill microbial soil life.  This has
been known for over 40 years; in fact, one of the early pioneers in the
development of chemical fertilizers recanted later in life - his further
research was showing that microbial and fungal agents were much, much
more active in overall soil health than had previously been suspected. 
But by that time the petroleum industry was making a looooot of money
off of chemical fertilizers, and a lot of people had a vested interest
in supporting the new status quo; so he and others like him were ignored
and often even quietly ridiculed for their "crackpot ideas".

Because of the fact that by and large it has been already-unhealthy soil
systems that have been getting studied, microbes like azobacter, which
is seldom found in chemically abused soils, have been assigned a much
smaller role in the nitrogen fixing cycle than is their due.  The fact
is that much of the activity and effects of the variously intertwined
microbes and fungi in a healthy (read: not found in conventional
agricultural) soil systems is STILL not fully understood.  This is a
case of the whole being greater than the sum of the parts; when the
argument is made that azobacter doesn't fix "enough" nitrogen to make
the soil "fertile enough", the effects of other bacteria and fungi and
their interactions in a healthy system are being ignored.

We have observable results - back to that forest floor again - that show
that in fact the actions of all these myriad tiny creatures in the soil
DO affect soil fertility, tilth, and soil composition in a positive
way.  Cover cropping, intercropping, and crop rotation, are all methods
of both maintaining soil health AND providing the extra fertility needed
for an unnaturally heavy feeder crop such as corn.

There's more to the whole situation - there are a lot of theories
floating about concerning crops that benefit from microbial nitrogen
fixers versus fungal nitrogen fixers - but it has been shown that if you
avoid planting INTO a sawdust based mulch (e.g., if you are planting in
soil underneath a mulch cover as opposed to planting into the mulch
itself as a medium, which is often done in no-till systems) you are not
going to observe any deletorious effects on a crop, while still gaining
the soil building and moisture conserving benefits of the mulch itself. 
This response is already ridiculously long so I won't go into all that
in any more detail now.  The important point is that sawdust as mulch is
ok; sawdust as a planting medium may be problematic for some crops.

It's true that not all sawdust is equally benign; you mention red cedar
and locust (I assume you mean black locust).  The red cedar may have
some tannins or other components that might cause some problems if you
are applying fresh sawdust;  I can't say about black locust.  Black
WALNUT, on the other hand, should be avoided, be he alive or be he dead,
because it contains significant growth inhibitors.  I'm told these
growth inhibitors don't affect soybeans, hence the practice lately of
intercropping black walnut groves with soybeans.  But I know these
growth inhibitors affect a lot of other plants, grass being one type in
particular (hence, no black walnuts will be going into my pasture - I'll
have to use something else, like honey locust or willow oak, to get some
light shade out there).

Just about anything else should be OK.  If you're unsure, use only aged
materials.  Sounds like, at 3 to 5 years reported for the original horse
stable sweepings, this would not be a problem for the original poster.

It occurs to me that when I mention that I'm getting sawdust from small,
local sawmills here in the Ozarks that those of you unfamiliar with
places like these might be misunderstanding just what it is I have to
deal with.  What we have here are small sawmills that have been in
operation in the same place for 50 years and more, upwards of 100 years
in some cases, I'm told.  So what we have are big, huge, whopping, YEARS
and YEARS old piles of sawdust.  Mountains of sawdust.

Some of this stuff hasn't been "fresh" in 10 years.  Towards the middle
of some of these piles I imagine it's even older than that.  These piles
are so big that it occurs to me to wonder if I might not be at risk of
burying myself if I were to dig into one incautiously.  (Not really, but
the thought did cross my mind.  Briefly.  Once or twice.)

Some of the mills take a bulldozer and shove it all into a nearby ravine
every few years, but others don't bother (or more likely don't have a
nearby ravine to shove it into).  This is the case at both of the mills
I have visited asking for sawdust.  "Sure, just load it up.", they tell
me.  "How much for a truck load?"  "You mean, how much does it weigh? 
Depends on your truck and how wet it is."  "No, I mean how much do I
have to PAY."  "PAY?  For SAWDUST?  Nothing."  "Well, how much can I
take?"  Moment of shocked silence.  "C'mon over here."  (Stepping to a
window behind the desk).  "See out there?  You can take ALL of it if you
can load it up."  Piles and piles and piles and piles . . .

I imagine the stuff in the center is pretty thoroughly composted, but
the stuff on the outsides is at least aged if not partially composted. 
None of it (except from the newest piles, which I won't be taking) is
fresh by any stretch of the imagination.  It's all oak and pine sawdust
as these mills only deal in oak and pine.  There are other mills that
deal in cedar but I'm not going to any of those.  The oils in pine are
very volatile; they're long gone by the time I'm going to get to it.

Another thing to watch out for, if you are getting your sawdust from a
woodworking shop or industrial setting, is sawdust that has been
contaminated by the chemicals and substances used in finishing wood, and
also sawdust from pressure treated woods.  You do NOT want that in your
garden, a little ground up arsenic-containing wood can really spoil your
day.

-- 
Holly ;-D
Contrary Peasant
sojournr AT missouri.org