[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: EDTA and Mineral nutrition

Ferric compounds are only sparingly soluble in oxygenated water of 
moderate pH... on the order of, in some cases, 10-25M (thats a decimal place 
with 25 zeros behind it).

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).

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

pKa refers to the point at which the protonated and unprotonated ACID are 
at the same concentration. Again, for EDTA, that is about 2.0, 2.7, 6.2 
and 10.0 for the four carboxylic acid groups. 

The ability of EDTA to chelate iron is relatively stable between pH 6 and 
10. At these pH values the HY-3 form predominates (as is evident from the 
pKa values).

If you want to actually read some research regarding EDTA go to your 
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.

Research has shown for a variety of plants that Ca and Mg and K are 
required in the water column for normal growth. There are several reasons

1. The transport of Ca and Mg is difficult and in aquatic plants the 
'tarnspiration' stream is just too slow to effectively deliver these cations.

2. There is an external requirement for Ca. In aquatic plants this is 
critical since an external medium bathes the apoplasm (the area approx. 
between the outside of the celll membrane and inside the cell wall) of the 
leaf tissue.

3. K is used for balancing the charge inside and outside the plant and 
therefore must be available for transport into and out of the plant 
cells. If K is removed from solution, then Na replaces K on a molar basis 
(in at least one plant) though flowering and biomass production suffers.