Very low PK fertilizers. (K-lite)

[DavidCampen]

Originally Posted by Ray

Actually K-Lite is 12:1:1,

Yes, I meant to write "K-lite is 100-10-10" to compare it against the MiracleGrow 30-10-10. And actually it is 120-10-10 compared to MiracleGrow's 30-10-10. Or you could say that K-lite is 12-1-1 compared to 3-1-1 for MiracleGrow. So K-lite could also be called N-Extreme.

And, so as to not confuse anyone, while NPK is actually an expression of absolute percentages it can also be thought of as a ratio. For example, 1 gram of a 30-10-10 fertilizer diluted in a liter of water gives the exact same amounts and concentration of nitrogen, phosphorous and potassium as 2 grams of a 15-5-5 fertilizer dilluted in a liter of water.

but I have puzzled over that one myself, David, and feel that it's not necessarily just the ratio that's the issue.

I think there are several things going on: One is the mass applied. I remember when I volunteered feeding the orchids at what is now the Atlanta Botanical Gardens back in the mid-70's, the concentrations applied were easily 10x-20x what is considered normal now.

The second part is closely tied to that - the rate of nitrogen uptake by a plant is greater than that of the other ions, so just because you apply a solution of a certain ratio, it does not mean that the plant takes them up in that same ratio. A high concentration of applied nitrogen means a large uptake - likely at a larger percentage than it would be at lower concentrations. Conversely, if I have a 12-1-1, 30-10-10, or a 1-1-1, and mix the solution to 50 ppm N, then I would expect the plant to take up the same amount of nitrogen from each of the solutions; at the dilution rates those are, I doubt there are any ion-interaction interferences going on.

The same argument could be applied be applied to potassium. But a little farther on you argue that "Plants have nutrient pumps that take up as much phosphorus (among other ions) as they can, storing it in cell vacuoles, so there is no need for high levels "
So that you have just argued that neither concentration or ratio is extremely important and I agree.

I will add that - and this is part of the basis for the "K-Lite" concept in the first place - plant metabolic rates are slow. Many of the minerals we apply are absorbed and stored, even though the levels far exceed what the plant needs physiologically. Some of those are mobile within the plant, so new tissues can be supplied by the internal stores if they are not provided from outside, while others are not, so must be constantly replenished. The gist of all of this being that some nutrient minerals - N, Ca, and Mg - appear to require a steady supply in appreciable quantities as they are used by the plant in relatively large quantities and/or are not mobile and transferable to newly-formed tissues. Pretty much everything else is used in very small amounts and/or is relocatable, so the demand is low.

Yep, that is one of the points that I was making - calcium and magnesium availability are as important as that of nitrogen, phosphorous and potassium.

Plants have nutrient pumps that take up as much phosphorus (among other ions) as they can, storing it in cell vacuoles, so there is no need for high levels - that's the basis of the MSU formulas.

Yes, and given sufficient concentration in the nutrient media the plants can adjust those pumps to take up each nutrient in the amount needed. So again, over a reasonable range, ratio is not critically important.

It is also known that potassium is stored by plants far in excess of its needs,

So I wonder why the plant wastes energy doing this? Actually, I thought that the more correct statement is that scientists have not been able to explain why plants store so much potassium, not that it has been determined that the amounts are in great excess of need.

and it also can interfere with the uptake of other ions.

Yes, in huge, osmotically significant excess but as you said, "plants have nutrient pumps" and aren't these pumps selective.

It also is preferentially trapped by potting media, potentially leading to more overdosing.

Preferential to what? The humic acids and other chelating agents in potting media should much prefer the divalent alkali metals calcium and magnesium and other multivalent cations such as iron and copper. Besides, if something is strongly bound to the substrate then it is not readily availabe to the plants.

(Which brings up another topic that I will start another thread about - the extremely strong chelating agents that are being used to prepare plant trace element nutrients)

The K-Lite fertilizer was designed to compensate for that, reducing the potassium level, thereby slowing the rate of buildup in both the plant and the medium.

Again, as you have noted, plants have pumps that selectively absorb what is need if it is available in sufficient concentrations. But unlike a canine they will not gorge themselves on everything that is put in front of them.

I guess the bottom line is that we need to think of plant food as both an immediate "fix", and as a "long-term integration" process, and understand that the label formula is not representative of what is taken up - sort-of like a kid who has a meal on his plant, and eats his meatloaf, gobbles up a second helping of mashed potatoes, but picks at his Lima beans.

Yes, that is my point and that is why I don't understand this belief that very low K ratios are important.

If anything, I think having phosphate and sulfate levels that are not to high is likely much more important than the potassium level. Sulfate and especially phosphate can form insoluble salts with calcium, magnesium, iron, and copper unless a suitably low pH is maintained.

So I think it likely that any beneficial efects of K-lite are due to the phosphorous ratio that was lowered as dramatically as that of potassium and that K-lite perhaps would be more properly named P-lite or N-extreme.