Re: Iron - Chelated - Ferrous - Ferric - lost and found

["S. Hieber" <shieber at yahoo_com>]

Roger Miller said:

> Some of the mechanisms that
> plants can use to 
> get different forms of iron are not triggered until
> *after* the plant is 
> already stressed for iron -- not till after the plant is
> already deficient in 
> iron.  Some of the mechanisms plants can use are also
> very expensive to the 
> plant in terms of the amount of chemical energy and fixed
> carbon they 
> require.  It seems like that expense must result in a
> reduction in growth.
> 
> Further, different plants vary considerably in their
> ability to get iron when 
> it is in low supply, so some plants can be failing with
> iron deficiency while 
> other plants in the same aquarium show no deficiency
> problems.
> 
> Plants need something like 1x10-9 molar of biologically
> available iron.  
> That's about 0.06 parts per *billion*.  I don't think
> even good test kits 
> will measure concentrations that low.  Concentrations of
> chelated iron are 
> generally not significant.  That's because the chelated
> iron isn't 
> biologically available until after the chelate complex
> breaks down.  Test kit 
> results that include chelated iron are only useful as a
> general indicator of 
> the size of the dissolved iron "pool" that might be
> available to plants.  The 
> amount of iron you need to register on the test kit
> varies a lot depending on 
> the exact nature of the kit, the kind of chelating ligand
> used and other 
> variables that I don't know or don't understand. 
> 
> For iron, I think the best approach is to throw away the
> test kits and just 
> make sure that the plants have access to multiple iron
> sources -- in soil 
> humus, substrate solids and low levels dissolved in the
> water.

Thanks, Roger, that's some of the best I've read about iron
in I can't remember how long.

I think the rule of thumb is dose it often, but not much,
and you'll probably have enough.

I've wondered for a long time which of two schools was
right about UV sterilizer lamps -- the one saying that they
photoreduce your iron chelators and iron and thereby "rob"
your plants of iron and the other (including UV lamp
manufacturers) that says that they don't hurt iron uptake.

I still don't know the answer but I can see reasons why (in
principle so to speak) each camp could be correct under
different but rather ordinary conditions.

Anyone: what does iron excess look like, I mean in the
tank, not in the wallet ;-)

Scott H.

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