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Re: mineral needs

On Wed, 22 Sep 1999, Scott McLaughlin wrote:

> I still would like to know though, if anyone has
> determined wether Ca and Mg are more valuable to plants than Na and K. If so
> what ratio of these two sets of ions is the most beneficial?

Ca++, Mg++ and K+ are all essential to plant growth.  Na+ is not.  Of
these three, I think that plant composition indicates they are used in the
order K+ > Ca++ > Mg++, though I don't suppose this necessarily reflects
the order in which they need to be present in the environment.

K is the most likely to be in short supply because it's used in large
amounts relative to the usual supply.  Ca++ is often present in excess
(except in very soft water) and any Na+ is superfluous. If the exchanger
could pull either of these and replace them with K+, then fine.  If Ca++
and Mg++ are instead replaced by Na+ (the usual pattern for cation
exchangers) then don't bother.

Roger Miller