Re: micronutrients and EDTA

> From: Paul Bucciaglia <paul-b at biosci_cbs.umn.edu>
> 1) I currently use Tap water conditioner, which claims to dechlorinate 
> and 'remove heavy metals'.  How long is this active after addition to tap 
> water? 

	What is in it?  Long-chain amines?

> Will this result in a serious reduction of micronutrients (Zn, Mo, 
> Mn) added after dechlorinaiton?  

	Cu, Mn, Fe, Zn:  quite possibly - they are all there as positive
ions, which could well be complexed by the active ingredients of a
conditioner.  EDTA complexation of these ions may slow or prevent
the process.

	Mo, B:  probably not - they are there as oxo anions, not likely 
to be complexed by the same things.

> Any dechlorinators which will not interfere 
> with micronutrient fertilizers?   I remember hearing that Na thiosulfate 
> was  an effective 
> dechlorinator--does it work on choramines, and at what concentration?
	I have not been able to find out about this, but I think it
probably will work, under much the same conditions as for Cl2.  The
products would be chloride ion and ammonia.  I would like to hear
from anyone who has a reference to this process, if it goes (or even
if it doesn't :)  perhaps especially if it doesn't!)

> 2) Do other micronutrients (besides Fe) need chelation (ie Mg, Zn,Mo, Mn) ?  
> For those of you that mix your own fertilizer, how does addition of 
> non-chelated metals to a solution of Fe-EDTA affect their solubility and 
> availability to plants?
	Mo and B will not be chelated (see above).  The chelation of iron
is usually done to stop its precipitation as the oxohydroxide, but the
chelation reaction is an equilibrium, so the complex will come apart, (slowly)
and other ions in solution can then grab the EDTA.  Even calcium will
do this, so the Fe chelate is not likely to reform before the iron
precipitates out.  As far as I know, all the positive ions we use form soluble
chelates.  I have made them in solution without problems.
	Chelation is not a _permanent_ answer to iron precipitation. 

Paul Sears     Ottawa, Canada