# Ever wonder?



## Rick (May 6, 2011)

How come there is so much K in plants when K is generally less common in the environment than Ca or Mg?


A lot of fertilizers are based on what is typically found in plants with the logic being that if that is what's in a plant then that must be what it needs, so supply it in the same ratio.

However most plants (certainly in the wild) do not access soil or aquatic systems that have high potassium levels (unless they are robbing it directly from adjacent plants). But they seem to be very efficient at uptaking and sequestering the nutrient. This also applies to materials that have ionic exchange capacity.

generally calcium and magnesium are more abundant in soil/water substrates than K (especially on limestone cliffs). But the orchids we culture from these sites generally get fertilizer mixes that have more K available than Ca or Mg.

I'm proposing a notion that poor growth in our "calcareous" paph species or fast/big growing multis is not due to Ca or Mg deficiency (per se) but by K overdose (which causes Ca and Mg deficiency).

I would also conjecture that calcerious (or calciolus) species do not have a special Ca or Mg need, as opposed to an extra sensitivity to K.

This is similar to the work I'm doing with freshwater mussels. For some reason they can suck K up more efficiently than other fresh water organisms, but they seem to be unable or very inefficient at eliminating from their systems (relative to other freshwater organisms). Subsequently, their internal body burden goes up higher (to toxic levels) than other critters and die.

It could be that many of our favorite orchids coming from K impoverished systems are similarly extra good at sucking up K, and when given fertilizers with all that K (and inadequate Ca and Mg to offset) that they get overloaded with K and die from what look like Ca or Mg deficiencies.


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## ehanes7612 (May 6, 2011)

my guess would be that potassium can be more freely absorbed around the entire root region whereas calcium and magnesium are restricted to apical regions, this is how it works for barley and corn


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## Rick (May 6, 2011)

I'm wondering if a good feeding strategy would be to find a fertilizer with reduced K, but plenty of nitrogen and phosporus and occaisonly supplement K (with potash).


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## SlipperKing (May 6, 2011)

That's a good notion you have there Rick. So have you found any such fertilizer?


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## Rick (May 6, 2011)

SlipperKing said:


> That's a good notion you have there Rick. So have you found any such fertilizer?




I just thought of this idea this afternoon, and haven't had much time to look yet.

Since some of the MSU's are hand formulated (I think Robert's gets his version assembled in small lots), maybe I can request a custom tweak on the next batch. It depends on what the potassium salt is for the mix, (i.e. what anion is hooked to it) that could make it easy to reduce the K without loosing any N or P.

Otherwise you probably start playing with old time things like blood meal / bone meal combos


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## Heather (May 6, 2011)

Pretty interesting ideas Rick. You're such a smartie! Curious to see or hear it tested.


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## paphioboy (May 6, 2011)

Some mycorrhizas living in association with plant roots are able to extract K from the surrounding substrate.. They are also very good at solubilizing P..


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## Justin (May 6, 2011)

while we're at it, anyone know of a low-iron fertilizer that also has N-P-K and other micronutrients?

I've read that iron can be bad for sanderianum...


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## Rick (May 6, 2011)

Justin said:


> while we're at it, anyone know of a low-iron fertilizer that also has N-P-K and other micronutrients?
> 
> I've read that iron can be bad for sanderianum...



Lots of people are growing and blooming sanderianum like crazy now, and probably aren't paying any attention to iron content at all.

I have a half a dozen myself, and since starting my magnesium kick and transferring them to sphag and limestone gravel baskets they are growing at an incredible rate now. In retrospect I think the times when I have put my older ones into tail spins was due to chronic K overdose of both the plant and the potting mix (which was primarily CHC until recently).

My irrigation water is mostly RO which I know has no iron. The house hold well water I supplement 10-20 percent with has obvious iron in it, and the weekly dose of MSU fert has some iron in it too. But at least at the levels I see they are not a deterrent of growth in my sandies.


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## Ernie (May 6, 2011)

Depending on your conditions, excess P may cause deficiencies. 

From Martin Motes, backing the general "MSU" formulation...
"Now is also a good time to apply a soluble trace or micro element fertilizer. Follow the dilution rates on the package as mixtures and strengths differ. You can apply this in conjunction with the Epsom salts/potassium nitrate but never with the 15-5-15, 20-20-20 or any other fertilizer containing phosphorus. In South Florida's highly alkaline water the phosphorus interacts with the other metallic elements, reducing the effectiveness of the trace elements. Potassium nitrate, 13-0-46, is the perfect companion to minor elements because it not only lacks phosphorus which would hinder the absorption of the trace elements but the nitrate nitrogen seems to enhance their uptake."


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## Rick (May 6, 2011)

paphioboy said:


> Some mycorrhizas living in association with plant roots are able to extract K from the surrounding substrate.. They are also very good at solubilizing P..



Yes I did see in an ag paper that the bulk of K in soils is in insoluble crystal form like feldspar. So the bacteria and fungi in the rhyzosphere would be important for making K bio available to plants. 

However most of our favorite orchids are either epiphytic, attached to rock cliffs, or in mosses and broken down leaf litter over weathered tropical soil (notoriously mineral poor). 

I would expect pretty fast turnover and extraction of the nutrients in the decomposition of leaf litter. There is probably a very high rate of competition for it though. Living on rocks and branches I would suspect is a fairly impoverished lifestyle which might be why cooperative systems with mychorrizae may develop.


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## Rick (May 6, 2011)

Ernie said:


> Depending on your conditions, excess P may cause deficiencies.
> 
> From Martin Motes, backing the general "MSU" formulation...
> "Now is also a good time to apply a soluble trace or micro element fertilizer. Follow the dilution rates on the package as mixtures and strengths differ. You can apply this in conjunction with the Epsom salts/potassium nitrate but never with the 15-5-15, 20-20-20 or any other fertilizer containing phosphorus. In South Florida's highly alkaline water the phosphorus interacts with the other metallic elements, reducing the effectiveness of the trace elements. Potassium nitrate, 13-0-46, is the perfect companion to minor elements because it not only lacks phosphorus which would hinder the absorption of the trace elements but the nitrate nitrogen seems to enhance their uptake."



Yes there can be loss of micronutrients (like iron) from excess P, but these are simple chemical precipitations outside of the plant. Within the plant itself, an excess of K can block the cellular uptake of N, Ca, Mg, Fe, Mn, Zn, and Cu (from Bob Wellensteins site on Mineral Nutrition for Paphs).

So given that orchids seem to be able to build up K so effectively to the point of locking out both macro and micro nutrients I would be cautious about the use of potassium nitrate supplementation to boost N. I also noted that Motes advocated the use of epsom salts (MgSO4) with potassium nitrate to balance the Mg with the K. Water in south Florida is not only alkaline but very hard (most is over limestone) so lots of Ca, Mg, (and often P) in the irrigation water to start with.


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## Eric Muehlbauer (May 6, 2011)

Hmmm....what does that say for people who use Pro-Tekt? Its loaded with K. I only use it on the rare occasions when I have a very acidic fertilizer...to raise pH.


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## paphioboy (May 7, 2011)

Rick said:


> Yes I did see in an ag paper that the bulk of K in soils is in insoluble crystal form like feldspar. So the bacteria and fungi in the rhyzosphere would be important for making K bio available to plants.
> 
> However most of our favorite orchids are either epiphytic, attached to rock cliffs, or in mosses and broken down leaf litter over weathered tropical soil (notoriously mineral poor).
> 
> I would expect pretty fast turnover and extraction of the nutrients in the decomposition of leaf litter. There is probably a very high rate of competition for it though. Living on rocks and branches I would suspect is a fairly impoverished lifestyle which might be why cooperative systems with mychorrizae may develop.



True, but for my current study project, I have read lots of papers on the presence of endophytic actinobacterial and fungal species (which live WITHIN plant tissue and not just on the root surface) which do contribute significantly to plant health by deterring pathogens and improving nutrient absorption. Most of the study has been done on crop plants, but I suppose there are bound to be certain species which can coexist symbiotically with epiphytes, xerophytes etc...


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## Rick (May 7, 2011)

Eric Muehlbauer said:


> Hmmm....what does that say for people who use Pro-Tekt? Its loaded with K. I only use it on the rare occasions when I have a very acidic fertilizer...to raise pH.



I used Pro-Tekt for quite a few years too (primarily for the same reason as you). But the results of my Pro-Tekt years are paling quickly in comparison to what my collection is doing with emphasis on reducing K relative to Ca and Mg.

I think if you want to boost K you should do it only when the plant is in very rapid growth, and co supplement with Mg at the same time. I think this would be consistent with Motes.


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## Ray (May 7, 2011)

I may be remembering this incorrectly, but I understand that plants actually have "pumps" that selectively grab up K, even if they don't need it at the moment, socking it away in the vacuoles for a "rainy day" when they might.

If that's true, then lowering it in the fertilizer _might_ result in a slower accumulation, but won't stop it.


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## Hien (May 7, 2011)

SlipperKing said:


> That's a good notion you have there Rick. So have you found any such fertilizer?



How about using only half of the commercially available fertilizer , mixed it with horticultural hydrated lime in whatever dose you need (which listed calcium & magnesium and very cheap for a gigantic bag), or alternating feeding with the two above items.
I think you can reduce the percentage of K available this way, no?


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## Justin (May 7, 2011)

Rick said:


> Lots of people are growing and blooming sanderianum like crazy now, and probably aren't paying any attention to iron content at all.
> 
> I have a half a dozen myself, and since starting my magnesium kick and transferring them to sphag and limestone gravel baskets they are growing at an incredible rate now. In retrospect I think the times when I have put my older ones into tail spins was due to chronic K overdose of both the plant and the potting mix (which was primarily CHC until recently).
> 
> My irrigation water is mostly RO which I know has no iron. The house hold well water I supplement 10-20 percent with has obvious iron in it, and the weekly dose of MSU fert has some iron in it too. But at least at the levels I see they are not a deterrent of growth in my sandies.



Thanks for the feedback.


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## paphioboy (May 7, 2011)

> How about using only half of the commercially available fertilizer , mixed it with horticultural hydrated lime in whatever dose you need (which listed calcium & magnesium and very cheap for a gigantic bag), or alternating feeding with the two above items.



Be careful. Hydrated lime (calcium hydroxide) is fast acting initially and can cause pH levels to soar... Unless you mean agricultural lime (mainly calcium carbonate)..


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## Rick (May 7, 2011)

Hien said:


> How about using only half of the commercially available fertilizer , mixed it with horticultural hydrated lime in whatever dose you need (which listed calcium & magnesium and very cheap for a gigantic bag), or alternating feeding with the two above items.
> I think you can reduce the percentage of K available this way, no?



That would also cut the N and P in half too, which I don't want to do at present.


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## Rick (May 7, 2011)

Ray said:


> I may be remembering this incorrectly, but I understand that plants actually have "pumps" that selectively grab up K, even if they don't need it at the moment, socking it away in the vacuoles for a "rainy day" when they might.
> 
> If that's true, then lowering it in the fertilizer _might_ result in a slower accumulation, but won't stop it.



I think you are close to my understanding too Ray. Except I'm leaning towards the notion that many orchids don't have control of when to stop those pumps, and/or the storage vacuoles are inadequate to keep up with the high concentration offered in fertilizers leading to K toxicity (which actually causes deficiencies of N, Ca, Mg). If there is plenty of Ca and Mg then I think the situation in the plant is reversible. Also there is potential for the plant to grow out of this stockpile if conditions are right.

This is similar to the freshwater mussel situation I was talking about earlier too.

In the wild freshwater mussels never see more than a few ppm of K in the water. They still need it for metabolic and muscular activity, so they use selective cell pumps to grab up as much as they can (since there's virtually none to get in the first place). But if you put them in a solution high in K, the pumps still work like crazy and overload the mussel tissue (causing paralysis). I think that as more K gets into the mussel tissue it kicks out Ca. The mussels seem to be able to control the system partially if there is more sodium than K so when you put them back into low K water they regain muscle control. If sodium is low, then generally there is no recovery of movement after going back into low K water. Most other aquatic organisms(like fish and crustaceans) seem to have more controllable pumps or means of getting the K back out of their tissues.


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