Excess of Potassium

Gutokoro

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Apr 13, 2009
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Hello Fellows,

I was talking with a friend about the excess of potassium, he told me that a expert in fertilizers (but for terrestrial plants) told him that excess of potassium would increase the uptake of nitrate and phosphate, leaving a poor substrate in these nutrients and causing nutritional problems in the plant.

He asked me if this is the same case for a planted aquarium.

Since then, I'm thinking about it.

I think that the same thing occurs in the substrate, and in the water.

If the proportion of potassium is high in substrate, the plants will consume the substrate nutrients faster, and the substrate will exhaust faster. This is a not good point in a substrate, right?

But in the water, if there is a good amount of potassium the plants will consume the nutrients faster, giving no chance for algae.

So, is there any problem if a dose an slightly excess of potassium in the water?

Regards

PS: Sorry by the poor english.
 

barbarossa4122

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Interesting topic. I am sure some experienced/experts will answer. I dose about 50ppm/week of K, mostly via K2SO4.
 

Biollante

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K You Say

Hi,

I would recommend as a starting point reading http://www.barrreport.com/showthread.php/927-Barr-Report-Newsletter-Potassium, the prologue as well as the newsletter.

Potassium is a bit of an odd duck in the plant nutrient world, having no direct component but I believe Tom Barr cites 60 plus essential functions.

As for as I can tell the terrestrial plant issue is one of very high potassium in the soil to the point the salts cause a pressure imbalance that causes reverse osmosis in the root system.

I doubt we ever get to that 800-ppm, Potassium in the substrate. :rolleyes:

Tom Barr has run 100-ppm Potassium in the water column with sensitive plants, without observable problems. I have on occasionally (intentionally) exceeded 50-ppm Potassium, though that turned out to be far more than required, it did no harm I could tell. :cool:

Biollante
 

Tug

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Any plant can be marginally low in a number of nutrients, but only one nutrient at a time will limit overall growth. If the supply of that limiting nutrient (lets say it's potassium) is increased even slightly, the resulting increase in growth will increase the demand for all the other nutrients. I'm no expert, but I think of what your friend said in this way. Without potassium plants struggle to take up NO3 and PO4. Plants can not use phosphate or nitrate when they don't have potassium available. Somewhere there is a post by Tom showing the maximum amount of NO3 and PO4 plants consume in one day. Not that much really, 4ppm NO3 and 0.6ppm PO4. With planted aquarium, nutrient deficiencies tend to happen more often with high light and high CO2 as the plants use up available nutrients that much faster. Light drives nutrient demand, not PO4. I'm not sure if this answers your question, but I hope it helps.
 
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Tom Barr

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K+ is taken up primarily through the leaves in aquatic plants and in horticultural ornamental plants(since they are fertigated, not soil based due to pathogens and shipping issues-sediment is mostly just sand and bark).

This uptake location is very well known and demonstrated in aquatics, see Barko et al for references

The only known excess ranges for K+ would be well in excess of 200ppm (modified hoagland's solutions are in this range, 210-235ppm for N(not NO3 but N-NH4 and N-NO3) and 50ppm as P-PO4, and perhaps much higher than this, maybe 1000-3000ppm more like salt stress, eg, % salinty.

This is only an issue sediment or the water column for any nutrient, if that nutrient is not added and the soil/water column is not refreshed with new K+, NO3, PO4 etc....

Aquatic plants and most oranmental horticulture added nutrients routinely to both locations: sediment and the water column/leaves.

So nothing runs out.

Regards,
Tom Barr

Gutokoro;47899 said:
Hello Fellows,

I was talking with a friend about the excess of potassium, he told me that a expert in fertilizers (but for terrestrial plants) told him that excess of potassium would increase the uptake of nitrate and phosphate, leaving a poor substrate in these nutrients and causing nutritional problems in the plant.

He asked me if this is the same case for a planted aquarium.

Since then, I'm thinking about it.

I think that the same thing occurs in the substrate, and in the water.

If the proportion of potassium is high in substrate, the plants will consume the substrate nutrients faster, and the substrate will exhaust faster. This is a not good point in a substrate, right?

But in the water, if there is a good amount of potassium the plants will consume the nutrients faster, giving no chance for algae.

So, is there any problem if a dose an slightly excess of potassium in the water?

Regards

PS: Sorry by the poor english.
 

Philosophos

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Just to throw in my own experience, I've dosed about 30-40ppm long term on tanks without any harm. This is far and above what most people dose at 14-18ppm (most use KH2PO4 and KNO3, by the time you've dosed both to 2ppm and 20ppm you get about 14ppm). I've done this and never had a phosphorous issue. At the same time though, this depends on dosing that isn't found in something like the ADA lines where N and P are kept lean, with K being acceptable at very best.

As Tom says, non-limiting nutrients are the key to all of this.

Dosing too lean will leave you chasing one deficiency after the next until you find yourself dosing tons of everything. Of course if you don't have your CO2 done right, this means a massive algae outbreak. So it all comes back to light-limited growth with high CO2 and an excess of all nutrients to find a balanced system.
 

Tom Barr

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Seems to be more human nature to want to focus on just one thing at a time, they lose interest and off the next key to solving "everything".
A more holistic approach is wiser in most things, not just with aquatic plants, but agriculture, food, politics, investment, public relations, etc......

But people can get side tracked very easily..........

Regards,
Tom Barr
 

Tug

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You have to wounder...

Was 'crazed' television anchorman Howard Beale shot dead only because of his falling TV ratings?
 

Tom Barr

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That's someone else's issue, I can only stop quackery here in the aquatic plant hobby.

Regards,
Tom Barr
 

Gutokoro

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Apr 13, 2009
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Brazil
Thanks for the responses.

I've been used to dose 30ppm in long-therm without any harm in all my tanks.

As I thought, there is no problems if we have a slight excess of potassium.

And then, if the substrate have a good amount of potassium it won't exhaust faster than other substrates poor in potassium, 'cause the uptake of potassium is done primarily through the leaves, right? Of course that in long therm the substrate will need re-fertilization.

Regards
 

Philosophos

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If your substrate has a decent CEC (turface, kitty litter, ADA AS, akadama, most other clay substrates) then you won't even have to worry about replenishing your substrate when you fertilize well. The substrate will pick up nutrients from what you've dosed in the column.

A great example of this is the results of Tom's ADA aquasoil analysis.