Iron salts vs chelators

Simon Cole

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I'm struggling to understand the benefits of different iron chelators, specifically EDTA and DTPA; also the benefits of certain ferric salts, including iron ascorbate, iron citrate, and iron gluconate.

I am using EDTA EI trace fertilizers daily, hard tap water, and EI macros.
I am also using Seachem Iron (Fe ascorbate) immediately after weekly water changes. Mainly because it seems logical before chelator and phosphate levels rise due to EI.

I had a look back across some of the old threads and I feel rather lost. It would be nice to have some sort of idea of what does what because I have a dutch hybrid where I am looking to reduce nitrogen and raise iron levels - probably. I'm not sure this is the best approach - but I just need to understand these fertilizers so that I have the knowledge to deliver iron in the most effective way.

Many thanks -
 

Oldguy

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iron chelators

They are all chelated. The iron ion is covalently bound to the organic ligand(s) and the resulting complex has an ionic change typically balanced by sodium ions. The chelated complex can be directly taken in through cell walls.

The chelates have different stabilities to the central ion (in this case iron) and can be replaced by other metal ions, in our case by GpII metals calcium and magnesium resulting in the iron being present as a simple ferrous salt (as say in ferrous sulphate) [strictly speaking it is still a complex with water molecules as ligands, but these are weakly attached]. The simple iron ion will oxides and fall out of solutions over several hours as a mixture of ferrous and ferric oxides and hydroxides (rust) and will not be readily available for plant uptake.

People on the forum with hard water have favored DTPA over EDTA. I have soft water [moderately soft tapwater mixed 50:50 with rain water, remineralised with magnesium and potassium sulphates to produce moderately soft water but rich in magnesium and potassium and use the EDTA Iron and EDTA Iron with Traces.

The others that you mention appear to be 'health supplements' and would be readily available over the counter. Substances such as EDTA and DTPA have only recently been easily available in smallish amounts being typically sold for horticultural use.

Most assume a 24/48hr period in the water column. Regardless of complex, iron not taken in by plants will become rust. The half life is essentially dependent on GpII competition and photo degradation.
 

Geoffrey Rea

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People on the forum with hard water have favored DTPA over EDTA. I have soft water [moderately soft tapwater mixed 50:50 with rain water, remineralised with magnesium and potassium sulphates to produce moderately soft water but rich in magnesium and potassium and use the EDTA Iron and EDTA Iron with Traces.

Headed towards this as well, using RO very slightly cut with Cambridgeshire tap water though. EDTA iron seems more than adequate now. I’m sure the drastically lowered amount of calcium compared to our tap parameters is of benefit as well from what little I understand of the iron calcium ratio.
 

Simon Cole

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Do we know for certain that each of these chelators are able to lose iron to Fe(III)-chelate reductase in the root cell membrane?
If not then we might safely assume that iron ions are only available to plants in their ionic form, a product dependent upon the breakdown of chelators and subsequent ion availability.

It seems logical to me that I need a complex that has the greatest tendency to lend iron ions to Fe(III)-chelate reductase.
I'm not too worried about environmental degradation rates (efficiency), just in finding the most effective transport mechanism.

Incidentally the health supplement iron citrate is also transporter of iron in the plant xylem. If common chelators were able to diffuse into plant tissue then I can see this affecting the transport of iron citrate in plant tissue. Some sort of stability constant is needed for both chelated complexes and Fe(III)-chelate reductase, and iron transporters.

Thanks for your comments above.
 

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