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Iron, chelates, and pathways


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

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.


Christopher Coleman
christopher.coleman at worldnet_att.net