In article om,
" wrote:
Some comments in line
...snip... quite good stuff on the role of microbes and plants
Soil life creates soil structure
A good point.
...
of snakes, birds, moles, and other animals. Simply put, the soil is one
big fast-food restaurant. In the course of all_ this eating, members of
a soil food web move about in search of prey or protection, and while
they do, they have an impact on the soil.
Nicely put.
.....
The soil food web, then, in addition to providing nutrients to roots in
the rhizosphere, also helps create soil_ structu the activities of
its members bind soil particles together even as they_ provide for the
passage of air and water through the soil.
Soil life produces soil nutrients
When any member of a soil food web dies, it becomes fodder for other
members of the community. The nutrients in these bodies are passed on to
other_ members of the community. A larger predator may eat them alive,
or they may _be decayed after they die. One way or the other, fungi and
bacteria get involved,_ be it decaying the organism directly or working
on the dung of the successful_ eater. It makes no difference. Nutrients
are preserved and eventually are retained in the bodies of even the
smallest fungi and bacteria. When these are in_the rhizosphere, they
release nutrients in plant-available form when they, in_ turn, are
consumed or die.
Without this system, most important nutrients would drain from soil.
Instead, they are retained in the bodies of soil life.
Not necessarily. Many nutrients are bound fairly tightly to colloidal
surfaces in clay and humous. OK the microbes have a big role in
making humous but they don't make clay.
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I think the nutrients would have a hard-time penetrating the clay. Until
it is turned and amended, clay soils cause puddling. My understanding of
clay is that it is not colloidal. The charge separation in the molecules
that comprise the clay will attach to the hydrophilic (or polar end) of
colloidal material. This is how it is used to clear wine and honey of
colloidal hazes. This clay (bentonite) is made into a slurry ond then
added to the wine. (I'm a bit hazy on how it is done with honey but I'm
sure it is essentially the same thing.) It is turned into a slurry to
increase its' surface area. The retention area of clay soil would be
it's surface and any cracks it develops during the dry season. Clay also
hangs on to its' water making the intake of ions more difficult.So it
seems that the problem with clay soil is its' resistance to flows of
nutrients through them. Eve if there are nutrients in the clay, they
must still find their way to the rhizosphere for them to be of use to
the plant.
-------
Here is the
gardener's truth: when you apply a chemical fertilizer, a tiny bit hits
the rhizosphere, where it is absorbed, but most of it continues to drain
through soil until it hits the water table._
Once again not necesarily. If you have sand-based soil you spend you
life building it up with organic material to stop this happening but
with clay-based soil you don't, they hold most nutrients well.
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Here I think the question is hold or block? If the chemical nutrients
are blocked at the surface then that is were some other plant will have
to use them. If you have amended your soil so that the chem ferts can
reach the rhizosphere then, as contended by the authors, it will kill
the bacteria and fungi in the soil and consequently the nematodes and
protoplasms as well. From there on out, the natural fertility of the
soil is dead and you are obliged to renew it by adding more
petrochemical fertilizers to feed you plants.
---------
..snip....
All nitrogen is not the same
Ultimately, from the plant's perspective anyhow, the role of the soil
food web_ is to cycle down nutrients until they become temporarily
immobilized in the bodies of bacteria and fungi and then mineralized.
What does 'mineralized' mean here? It's not clear to me.
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I'm with your there. All I know, I found at
http://en.wikipedia.org/wiki/Mineralized . I presume it has to do with
converting NH4 (organic) to HNO3 (inorganic).
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...snip..
Ingham and some of her graduate students at OSU also noticed a
correlation between plants and their preference for soils that were
fungally dominated_ versus those that were bacterially dominated or
neutral. Since the path from_ bacterial to fungal domination in soils
follows the general course of plant succession, it became easy to
predict what type of soil particular plants preferred_ by noting where
they came from. In general, perennials, trees, and shrubs prefer
fungally dominated soils, while annuals, grasses, and vegetables prefer
soils_ dominated by bacteria.
One implication of these findings, for the gardener, has to do with the
nitrogen in bacteria and fungi. Remember, this is what the soil food web
means _to a plant: when these organisms are eaten, some of the nitrogen
is retained by_ the eater, but much of it is released as waste in the
form of plant-available ammonium (NH3).
I presume they mean NH4+ the soluble ammonium cation (positively
charged particle), NH3 is ammonia gas.
--------
Sounds right to me. So we are talking NH3 + H2O --- NH4 + OH. The
equilibrium will still be far to the left.
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Depending on the soil
environment, this can either remain as_ ammonium or be converted into
nitrate (NO3,) by special bacteria.
Here they mean NO3- the soluble nitrate anion (negtively charged
particle).
Why am I being picky about these being ions (that is charged)?
Because the fact that they are charged is important to understanding
how they bind to colloids, which is key to nutrient retention, a point
which is overlooked by the author.
------
Let's get on the same page here. Colloids, in my understanding, (and I
presume that I couldn't stop you from correcting me even if I tried) are
composed of molecules that have one water soluble end and one that
isn't. The colloidal particle has all its' non-water soluble ends
together in the interior of the particle and exposes its' water loving
end at the surface to its' aqueous solvent or (vice-a-versa). Why is
this important to nutrient retention?
------
When does_ this conversion occur?
-------
In the soil by nitrogen fixing bacteria (those that can make the
conversion from ammonia to nitrate, not N2 to nitrate), hopefully in the
rhizosphere where it will be of use to the plant.
--------
When ammonium is released in soils that are dominated by bacteria. This
is because such soils generally have an alkaline pH_(thanks to bacterial
bioslime), which encourages the nitrogen-fixing bacteria to thrive. The
acids produced by fungi, as they begin to dominate, lower the pH_ and
greatly reduce the amount of these bacteria. In fungally dominated
soils, much of the nitrogen remains in ammonium form.
Ah, here is the rub: chemical fertilizers provide plants with nitrogen,
but_ most do so in the form of nitrates (NO3). An understanding of the
soil food_ web makes it clear, however, that plants that prefer fungally
dominated soils ultimately won't flourish on a diet of nitrates. Knowing
this can make a great deal_ of difference in the way you manage your
gardens and yard. If you can cause_ either fungi or bacteria to
dominate, or provide an equal mix (and you can-_just how is explained in
Part 2), then plants can get the kind of nitrogen they prefer, without
chemicals, and thrive.
All well and good but ignores the fact that the alternative to adding
synthetic nitogen compounds (ignoring nitrogen fixing for now) is
adding manures or urine. It's true that these don't contain much in
the way nitrates from the beast but nitrates are formed naturally in
manure heaps. Gunpowder use to be made from potassium nitrate
gathered from manure heaps.
------You were as hammered as I was, weren't you?? Synthetic nitrogen is
a salt, the osmotic pressure it engenders kills the soil flora and
fauna. In manure it comes from the break down (de-aminization) of amino
acids (NH3, not salt), which in turn nurture the soil flora and fauna.
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Negative impacts on the soil food web
Chemical fertilizers negatively impact the soil food web by killing off
entire_ portions of it.
Evidence please. The following isn't good enough.
------Look at
http://www.biodynamic.org.nz/guides/intro_ch1.pdf that was
pointed out to me by a Kiwi, George.com. At the end of the pdf is the
bit about fertilizer salts and some references. That's all I know mate.
Suspect we'd need a microscope to make the evidence more tangible.
---------
What gardener hasn't seen what table salt does
to a slug?
Irrelevant. You don't put salt (sodium chloride) in your soil and the
way it kills slugs has little to do with the topic. Remember that
salts are a class of chemical substances which are NOT just common
salt (sodium chloride) in general, although sodium chloride is in fact
a salt.
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First line below. Fetilizers are salts. They separate into cations and
anions, creating osmotic pressure that kills the microbes.
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Fertilizers are salts; they suck the water out of the
bacteria, fungi, protozoa, and_ nematodes in the soil.
In excess yes. In excess synthetic fertiliser AND natural ones will
both kill your plants in the same way. This does not mean that there
are no dissolved salts (as ions) in healthy soil nor does it mean that
you should never add such ions to your soil. You do it every time you
apply chicken manure or **** on the lemon tree.
--------
Very good point. Chem ferts can be used but we don't know the safe
dilution level. Maybe it's just me but I don't trust recommended dosages
because, I reason that they want you to use them up quickly and come
back for more. Secondly, if you do kill your microbes then you are
relaiant on the chem ferts to feed your plants. Now with ammonia, you
can smell it and a radical increase in the pH of the soil is apt to kill
your plants. So don't apply, if you can smell it. Also it (nitrogen) can
be safely added as protein. Microbes won't break it down if products
become toxic.
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...snip...
If the salt-based chemical fertilizers don't kill portions of the soil
food web, rototilling will.
Agreed. Once your beds are established heavy soil turning either
manually or mechanically is harmful rather than helpful.
-----
Right on, right on.
------
.snip....
Overall this is not a bad chapter but (unless some details are
corrected in later chapters) it is incomplete and in part misleading.
The main point that soil is a living community that must be maintained
is very valuable.
David
It always seems the more we know, the less we know. I was surprised that
most of the books that I turned to to get some background on the
interaction between plants and soils, had very little information. It
was like I was looking for physiology and the books were giving me
anatomy.
Thanks for the questions because I think I have a better grasp of the
subject now.
Scratch yer Crater,
--
Billy
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