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Re: Iron, chelates, and pathways



> Steve Pushak wrote:

>> Chris Coleman wrote [in part]:
>> It seems to me that if the iron is taken up during stage 2,
>> that this must be done quickly as Fe++ in an oxygenated
>> environment becomes reduced to Fe+++ very quickly.

> I think you mean "oxidized" rather than "reduced" to
> Fe+++. It will also precipitate as ferric oxide.
Yes,  you can see chemistry is not my forte.

> Iron is also reduced to ferrous iron (Fe++) in the anoxic
> conditions in the substrate and can be recombined with various
> organic complexes to become available to plant roots
do you know what types of complexes may be typical?

> and move into the water to be available to plant shoots and
> leaves. It's not necessary for the iron to be complexed only
> by the stable (EDTA, EDDHA or DTPA) chelating chemicals
> to be used by plants. There are plenty of natural humins which
> can do the job, particularly if there is plenty of aged organic
> material (peat or detritus).
> Steve

Interesting.  Upon returning to the water column,  are these complexes
stable?

I think what I am hearing is that a soil substrate can have a tendency to
turn the iron pathway I described into a cycle.   And I am reminded from
George S. that in the substrate ( soil or gravel ) that bacteria in the
substrate
can reduce fe+++  to fe++.  Thus an updated pathway would be:

   1) starts out as a chelate ( FeEDTA, FeDTPA,
        FeEDDHA, etc. )
   2)  becomes unbounded as Fe++
   3)  forms a colloid / eventually precipitates as a result of
        combining with orthophosphate or being oxidised to Fe+++
   4)  In the substrate, becomes reduced to Fe++ by
        bacteria and is available to roots
   5)  In a soil substrate, combines with humins to
        form organic complexes which may return
        to the water column, forming a cycle

I suspect that this too is still an over-simplification.  What
started my thinking about this was some recognition that the
iron we supplement for the benefit of our plants faces quite
a bit of competion from other aspects of our systems before
it actually gets to them.

Christopher

------------------- original post

Hi,

I have read that iron will combine with orthophosphate and
precipitate and also that ferrous iron in oxygenated environments
will form ferric and similarly precipitate .... This got me thinking
about the various pathways for iron in our tank and ultimately, the
factors determining how much ferrous is available for plants.

I see the pathways of iron in our systems being as follows:

   1) starts out as a chelate ( FeEDTA, FeDTPA,
        FeEDDHA, etc. )
   2)  becomes unbounded as Fe++
   3)  precipitates as a result of combining with
        orthophosphate or being reduced to Fe+++

It would  seem to me that progression to stage 2 only happens in
response to one of the events in stage 3 and as a result stage 2 is short
lived.

Since plants prefer Fe++,  it seems to me that it would be available
to them during stage 1 ( as a result of uptaking the chelate and processing
it further ) or during stage 2.

It seems to me that if the iron is taken up during stage 2, that this
must be done quickly as Fe++ in an oxygenated environment becomes
reduced to Fe+++ very quickly.

Regardless of the method of uptake ( stage 1 or 2 ),  it seems to me that
a competition for Fe++  exists between plants and stage 3 events which will
vary from system to system depending on the particular levels of phosphate
and reductivenes.

Comments?

Christopher Coleman
christopher.coleman at worldnet_att.net