Re: EDTA and Mineral nutrition

[Greg Morin <greg at seachem_com>]

> Iron in aquatic soils exists as Fe+2. If you dont believe me go check a
> pe-pH diagram in Stumm and Morgan or Schlesinger (Biogeochemistry).

Hmmm... that's curious, I wonder why ferrous iron would be predominant in 
aquatic soils but that ferric is predominant in terrestrial soils...?


> Aquatic plant leaves most definitely are able to absorb chelated iron.

So you're saying definitive research has shown that _all_ aquatic plants 
can absorb chelated iron through a foliar route?   ;-)


> Again, for EDTA, that is about 2.0, 2.7, 6.2 and 10.0 for the four 
> carboxylic acid groups.

Ok, looking at this again I see that these are probably in fact the pKas 
for the acids, but I'm still at a loss as to why my reference gave values 
of 0.2 and 0.9 as well... maybe so weirdo gas phase kinetic values... in 
any case, I think we're still in agreement that as the pH goes up the EDTA 
complex becomes more stabile (increased acid ionization and decreased amine 
ionization... looking at the pKas of amines of similar compounds 
(ethylenediamine diacetic for example) show values in the 6 and 10 range as 
well).


> nearest research library, put in the 'Biological or Life Sciences' disc
> and type in EDTA and Nutrition. That should keep you in reading for months.


I'll put that on my Christmas list :-)


-Greg Morin
Gregory Morin, Ph.D.  ~Research Director~~~~~~~~~~~~~~~~~~~~
Seachem Laboratories, Inc.      www.seachem.com     888-SEACHEM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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