permaculture

[Mark <mpludwig@facstaff.wisc.edu>]

Excellent reply Georg, I appreciate you taking the time.
Mark
At 03:59 PM 11/29/02 +0100, you wrote:
> let me try to run that one by once again - admittedly i had to look through
> my notes to get it all clear. but i am working on this so i will eventually
> reach the point where it is all simple and easy to explain for me. ok, here
> we go:
>
> since this is a glance into the quite complex interactive web of life,
> linear language fails me a bit. so please patiently follow my fragmented
> narrations, and put them together within your systemic mind.
>
> since us gardeners main interest is the health and production of the
> plants, i will look at it from the point of the plant. how the degradation
> of pesticides and other things tie in can then easily be concluded when
> looking onto the various aspects of the action.
>
> plants generate energy in their leaves. apparently they deposit up to 25% of
> this energy in the soil through their roots - part as extrudates, part as
> shedding of dead matter. this apparent loss of energy in the form of carbon
> is actually a well spent investment. microorganisms living in the
> rhizosphere gobble it all up, and due to the energy boost they multiply so
> fast, that they use up all the available oxygen. this way anaerob
> microniches are created. in order to understand why this is important we
> will have to appraoch from a different angle as well.
>
> soil is full of iron - 2 to 12% of it's weight are made up by it. in well
> aerated soils this iron exists in the trivalent form of tiny ironoxide
> crystalls. now if the microclimate turns anaerobic this fairly inert
> trivalent iron crystalls fall apart and change to the mobile bivalent form,
> also called reduced form. and this is important for 2 reasons: one is, that
> this reduced form of iron is needed in order to produce ethylene - when
> ethylene is generated in the soil, it stops the life processes of the
> microorganisms that fed on the energy bonus given to them by the plants. but
> fortunately ethylene doesn't kill them, but makes them inert. when the
> microorganisms in the rhizospehere become inactive, they stop using oxygen,
> thus oxygen can diffude back into these temporary anaerob microniches,
> making them aerobic again. the inert microorganisms wake up and become
> active, starting the cycle all over again.
>
> the second good thing that happens when the iron oxyde crystalls
> desintegrate, is this: these crystalls have a big surface and a strong
> electric charge. thus they bind phosphate, sulphate and various trace
> minerals closly to them, making those unavailable for the plant. when the
> iron oxyde crystalls fall apart, they free those nutrients into the soil
> solution, where they can be used by the roots of the plant. other nutrients
> (namely calcium, potash, magnesium und ammonia) are tied to the surface of
> clay particles and organic matter. these high concentrations of reduced,
> mobile iron help break those nutrients free, thus making them available for
> the plant as well.
>
> just to round the picture off (and to expose some of the folly of till
> agriculture) it might be good to take a look onto ethylene again. we need to
> understand, that the bivalent form of iron can only make ethylene, if a
> precursing substance of ethylene is already present in the soil. this
> precursing substance is also supplied by the plant - but incidentially we
> find it only in mature leaves. so without decaying mature plant matter the
> ethylene cycle doesn't happen - the multiplying microbes are not stopped in
> time, thus they keep going until they get killed by the lack of oxygen, when
> they decompose in the anaerob situation substances are formed that are
> burdening the health of the plant. i guess we could say, that ethylene is
> needed in order to form a safe anaerob surrounding in the rhizoshere -
> without it anaerob situations can still happen, but then they are a sign
> that something went wrong.
>
> it is also interesting, that in natural soils close to a hundred percent of
> nitrogen in the soil is there in the form of ammonia, only traces of
> nitrates can be found. plowing furthers a kind of bacteria that transforms
> ammonia to nitrates. plants and microbes don't mind a whole lot, they can
> use both forms. but nitrates interfere with the development of completely
> anaerob microniches - thus the nutrients stay in their unavailable form,
> because the iron oxyde crystalls never break up. also the ethylene cycle is
> never triggered, even if everything is available, but the reduced form of
> iron never becomes available.
>
> while all this may sound quite complicated, it isn't, it is only complex.
> the very beautiful thing about this cycle is imho that the nutrients become
> available where they are needed - in the close vicinity of the plant root.
> also it is a safe method, to make the nutrients available in their solutible
> form in the anaerob situation  - because if they are not used up or washed
> away from the root, as soon as they leave the anaerob situation, the
> bivalent iron reverts back to ironoxyde crystalls, which again tie up the
> nutrients in their immobile form.
>
> georg
>
> ----- Original Message -----
> From: "Mark Ludwig" <mpludwig@facstaff.wisc.edu>
>
> > >between aerobic and anaerobic constantly happens - this ia what makes a
> reed
> > >bed working so effectively, and the everpresent ethylene-cycle works the
> > >same way.
> > >
> > >georg
> > interesting!
> > Would this take place better in a saturated soil like a reed bed has or is
> > a fairly dry soil similar.
>
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Mark P. Ludwig
Poultry Research Lab
University of Wisconsin -Madison
608-262-1730 WK
608-846-7125 HM