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[APD] RE: K+/Ca++

Okay found a bit more to back up my claims:

Calcium, magnesium, and potassium compete for the same sites of absorption
by the plant; so increasing one may decrease another.
We have said in the past these sites are different due to the valancies of
the cations in question, but I think from what I've read that is stil true,
but the over all salinity/dissolved ion content/hardness influeces the
sites, not just one particular ion.

Using more NO3 vs NH4 also helps decrease any higher K+ effect. 
High temps also were cited for increases in Ca+ blockage.

Ca+ is transported only in the xylem, not much of an issue in aquatic
plants but there is transport of nutrients in the vascular tissue((See Ole
Peterson) and perhaps fluxes in K+ can cause changes if the Mg/Ca/K+ ratios
are off somehow.

>From hydroponic's research: K+ Toxicity ? saline condition, marginal leaf
burn, wilting and drying due to poor water uptake.
These are symtoms of excess K+. But this does not sound like the reported
aquatic growing tips. 

So perhaps low Ca, Mg?
I think the likely hood of low Mg seems a more likely candidate because few
people have EVER tested for Mg.
I have always added Mg at 4:1 ratio with Ca, not just using CaCO3 or CaCl2
alone if I rasied my GH, and also suggested Dolomite which has Ca, Mg and
CO3 in place of CaCO3.

Has anyone even suggested or looked at Mg?
Tested for it?
Ca++ alone for that matter?


In most of the hydroponic literature and horticulture, I found solutions of
150-500ppm of both K+ and Ca++ recommended.
Clearly at these levels, which are over 3x the max levels I used in
aquariums, there should be no inhibition of Ca if you have enough Ca+ say a
1:1 ratio of K+ to Ca.

I've said it for a long time, I don't see the the effect on my plants. 
Folks really wanting to understand why they are having problems when they
dose K+ may want to measure the Ca++ and the Mg++ and get a good handle of
the K+ levels, perhaps do bigger water exchange top re set things then be
careful in your measurements.

Also, what is the soruce of K+ that folks are using here? KCL or K2SO4?

That will also help.
Many have not reported any ill effects with KCL, but I have used
exclusively K2SO4.
GH is another thing that is needed. Ideally Ca++ levels. Salt water Ca++
test should work fine and be available also.
Much of what I've read suggests Mg deficiency and some do not mention
anything about Ca++ inhibition at high levels from high K+.

A potassium excess can cause a potassium-boron imbalance, which may also
result in transverse cracking and "brown checking".
So it might not be anything to do with Ca++, B yields similar deficiencies
as Ca++.
The other thing, high Ca++ levels are suppose to cause K+ deficiency, I've
had extyremely high Ca++ levels 400+ppm, lower K+ levels at 10-20x less
than Ca.
I've never seen any signs of K+ deficiencies. 

While some of the older plant books and even some coming out today suggest
that plants prefer soft water, one things was clear that plants prwefer
moderately hard water. Excessive Potassium can inhibit Nitrogen uptake. 
Excessive calcium can inhibit Magnesium uptake.
Some high/low K+ levels in _SOIL_:

low: < 150 ppm (< 0.4 meq/100 g soil)
high: 250-800 ppm (< 0.6-2.0 meq/100 g soil)
excessive: > 800 ppm (> 2.0 meq/100 g soil)

Magnesium, manganese, and calcium deficiencies become more pronounced with
excess K. 
An adequate soil supply of boron must also be maintained in order to
optimize the utilization of K (to support active root development for K
Most plants simply will not take up excess K+ once they reach their limit.
Excess K+ is very rare in soil, and at the levels mentioned, I think 50ppm
is not much K+ in the water column truthfully.

The problem is more complex than a simple K+/Ca++ issue, there are issues
with Ca/Mg/B/Mn and K+ ratios. 

Tom Barr




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