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Re: Thanks for your help

At 19.03 23/01/99 -0800, you wrote:
>Thanks Luca for interpreting for me what happened in my tank. 
nothing! you're welcome! :)

> Am I right in thinking that the combined iron chelation
>will continue to be in a useful form to the plants as long as I continue to
>get readings on my test kit?

Who can say??? :))) your answer blows in thw wind... :)))

well... this answer implies less chemistry and more aquatic plants phisiology. 

Let's start from chemistry. As far as I know not all the iron test kits are
the same, depending on a specific kit the reading could measure:

- the ferrous iron only
- the ferric  iron only
- both ferric and ferrous iron ions.
- both ferric and ferrous iron ions and _their_ chelated(*) forms.

(*) Of course the capacity of the iron kit to read a chelated iron presence
is strictly related to the type of ligand is used in the fertilizer. And,
on the other hand, on the type of reagents are used in the kit to make iron
in the sample react. We can say that some test kits can read iron chelated

1) sulfonic acids
2) amino acids
3) (poly)-gluconates

I'm not sure ...some might read also DTPA iron (partially used in PMDD to
chelate iron only) but I don't think there are test kits available that can
read iron chelated with 
These ligands are too strong to be broken easily.

Now I know nothing about HACH tests, we have HACH in Italy as well but I
chosed LA MOTTE instead because the receptionist girl was nicer to me !!
:)))) very scientific method to choose, uhh??:))))
But I think you can simply ask them by e-mail and ... let me know the
answer. :)

Now the phisiology part comes. I have confused ideas here. Let's start from
what I learnt.
Ferrous iron is assumed by plant through leaves and stems, and it's the
iron form preferred by aquatic plants for sure.
Ferric iron, _once_ precipitated deeply into the substrate (and in the
filter canister too!), is reduced to ferrous form and adsorbed by roots.

that's for sure. What I don't know.. is which role has EDTA iron. I mean
from many sources I found that it cannot assimilated directly by plants.
But as EDTA should only bind the ferric iron(or at least most common iron
chelators, including EDTA, used are much stronger with the oxidized Fe),
this leads me to the following considerations:
* it's unlike that plants cannot uptake EDTA-ferric form by leaves too,
because many experiments show clearly that in iron-free tank, when you add
EDTA iron you can see oxygen bubbles in few hours... too short period of
time to hyphotezise the precipitation and the subsequently reduction in
deep substrate.
* So there are two possibilities still left:
     1) plants can assume ferric ions also through leaves and reduce it to
its bivalent form inside leaves.
     2) plants can assume EDTA iron directly and then break it down inside
the plant tissue.

1), 2) or both must be true to expain the evidence.

Of course for all the other forms of iron this is not a problem.
Gluconates, or amino-acids binds the ferrous form of iron and so in this
case they all are immediately (almost!) available to plants leaves.

I hope this can help despite my doubts (too many!).

PS: Romano mean "from Rome" in Italian, do you have italian origin BTW?

PS2: this is for Neil Frank: I must say sorry to you because I promised you
an article on iron matter for AGA and I've nver fulfilled that promise..
I'm kinda lazy.. sorry!