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[APD] Potassium problems
----- Original Message -----
From: <aquatic-plants-request at actwin_com>
To: <aquatic-plants at actwin_com>
Sent: Saturday, January 17, 2004 6:02 PM
Subject: Aquatic-Plants Digest, Vol 5, Issue 65
> From: Roger Miller <roger at spinn_net>
> Subject: [APD] Potassium problems
> To: aquatic-plants at actwin_com
> I've followed reported problems with potassium for quite a while and I've
> built up some background on it. I may have even had some of those
> or similar problems myself. The information I have seen comes exclusively
> from agricultural, hydroponic and horticultural sources. Many of our
> "aquatic" plants are closely related to plants in common agricutural and
> (more often) horticultural use so I have reason to believe that
> from those sources should apply to aquatic plants. The exception is that
> mechanisms involving potassium uptake from soil through the roots should
> not apply to foliar uptake.
> On the basis of my reading I think a few things are indicated.
> 1) Potassium at reasonable concentrations (into the hundreds of ppm) is
> toxic to plants.
> 2) There is an antagonistic relationship between the four common alkali
> alkaline earth elements such that a large excess of one element can cause
> deficiencies in another. The published sequence is (as I recall)
> K > Na > Mg > Ca
> I'm working from memory so the order of Ca and Mg in the sequence could be
> Where elements on to the left in the sequence are more likely to
> elements on the right. This sequence was originally published in (as I
> recall) Science in or about 1934. It is well founded and widely
> The mechanism for the antagonism is not simple. In the specific case of K
> and Ca, there appear to be problems both at the root-soil interface and
> transport within the plant. Information on the mechanism has proven very
> difficult to come by. I have no reason to believe that the mechanisms
> the same in every case or that the mechanisms are simple in any case.
> 3) Common recommendations are that in order to avoid antagonistic effects
> should not exceed Ca , but some sources recommend that K can easily be 2x
> calcium concentrations without problems.
> 4) The sensitivity of different plants to antagonistic effects is highly
> variable. Furthermore, there are a number of other contributing factors
> may make the occurance of problems difficult to predict under normal
> conditions. I can think of:
> a) Actual (not estimated) potassium concentrations. There are very few
> measurements of potassium concentrations available.
> b) Ca:Mg ratios in measured hardness and the actual concentrations of
> and Mg.
> c) The nature and composition of the substrate
> d) The concentration of sodium in the aquarium water.
> I'm sure there are other factors.
> Given what I have read, I would not expect potassium:calcium antagonism to
> set in unless water was soft. For instance, if the aquarium water has 5
> of calcium hardness (about 35 ppm calcium) then there should be *no*
> antagonism unless the potassium concentration was well in excess of 70
> In the case where someone has hard water (say 20 dGH with normal Ca:Mg
> ratios) potassium:calcium antagonism should not occur in fresh water. In
> particular, with the experimental conditions that Tom is using to test for
> potassium effects on Ammania, I would expect that there should be no
> I am not saying that the problems report to be cured by stopping or
> potassium doses were not caused by potassium:calcium antagonism but in
> cases people need to look for different cause:effect relationships and
> they need to question their own observations.
> We went through this on the Aquabotanic list months ago and from that I
> finally concluded that in most cases either; potassium concentrations
> originally *much* higher than people estimated they were; the symptoms
> reported as cured were *not* calcium deficiency symptoms or; the
> were too non-specific to be useful, regardless of how convinced the
> I also think that there have been a few good observations of real problems
> that probably are potassium:calcium antagonism. Because of those cases
> because plants don't need particularly high potassium concentrations for
> healthy growth I think it is advisable to be pretty conservative when
> Intenet forums (all of them, as near as I can tell) are pretty strange
> it comes to things like this. When a new mechanism comes up that might
> problems some people over react. They assign problems to that mechanism
> when there is no indication for it. Some people even invent problems so
> can jump on the bandwagon. It's all a little weird.
> Roger Miller
Very intesting point. Roger. I believe is something between ionic ratios,
and untill we have test on hobbyst level to measure K, Ca, Mg, and Na we
will not solve a lot of questios about this "real" effect. As well I
believe, Tom is not eable to see it because the frecuency and the amount of
his water changes impedes the acuarium water to became unbalanced.
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