Best P/N ratio?

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Stone

Stone

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I have been giving P/N ratio of approx. 1.5 to 1.8. I have increased it lately to about 2.5 to 3. ( to work out the P/N ratio of an NPK fert just divide the %P X the % N)
Most flowering plants are said to get by quite well with 1.5 to 1.8 and Phals, for example, closer to 2 (based on leaf concentrations)
However it has not gone unnoticed that some growers seem to have spectacular results with very high P (for example 10 52 10) P/N 5.2!!!!!!!!!)
Xavier did mention good results on some parvies and brachys with this kind of ratio but never gave a suggestion as to why this might be. (Xavier....?)
Most of what I read on the subject says high P can be disastrous. What is going on? Anyone with a theory?
 
IMHO, leaf concentrations may give a limited indication about the types or ratios of nutrients preferred by the plant. Regulation of nutrient uptake from the growing medium by the plant roots is likely more important but little studied for paphs or even orchids in general. Plants do not take in all nutrients at once, so an occasional high dose of P is not likely to be toxic, especially since a large proportion of the phosphate will be in a non-available form due to adsorption to CEC surfaces of the medium and organic matter. My 2 cents. :)
 
Mike, be aware that N-P-K is not necessarily N P and K. Many Places its N- P2O5-K2O (but they write N-P-K) 43.6% of P2O5 is P so you might have to correct Your numbers accordingly. I read that in Australia the Convention can be N-P-K-S in which case its given as elemental Components, so Yours might be right while others might have to be adjusted. Confused? so am I:rollhappy:
Based on elemental P and N, I fertilise with approximately 10N to 1P (is that a P/N around 10?) Do not see much problems, Things arer healthy and grow, not so much decease etc....
 
Mike, be aware that N-P-K is not necessarily N P and K. Many places its N- P2O5-K2O (but they write N-P-K) 43.6% of P2O5 is P so you might have to correct your numbers accordingly. I read that in Australia the convention can be N-P-K-S in which case its given as elemental components, so yours might be right while others might have to be adjusted. Confused? so am I:rollhappy:
Based on elemental P and N, I fertilise with approximately 10N to 1P (is that a P/N around 10?) Do not see much problems, things arer healthy and grow, not so much decease etc....
 
Mike, be aware that N-P-K is not necessarily N P and K. Many places its N- P2O5-K2O (but they write N-P-K) 43.6% of P2O5 is P so you might have to correct your numbers accordingly. I read that in Australia the convention can be N-P-K-S in which case its given as elemental components, so yours might be right while others might have to be adjusted. Confused? so am I:rollhappy:
I currently use a P/N (elemental) of 1/10. i.e. lots of N as compared to P.
 
Adding to paphioboy's comments, plants have a phosphorus "pump", so take it up whenever it's available, and store in cell vacuoles, whether it is needed by the plant or not.
 
Bjorn said:
Mike, be aware that N-P-K is not necessarily N P and K. Many Places its N- P2O5-K2O (but they write N-P-K) 43.6% of P2O5 is P so you might have to correct Your numbers accordingly. I read that in Australia the Convention can be N-P-K-S in which case its given as elemental Components, so Yours might be right while others might have to be adjusted. Confused? so am I:rollhappy:
Based on elemental P and N, I fertilise with approximately 10N to 1P (is that a P/N around 10?) Do not see much problems, Things arer healthy and grow, not so much decease etc....
Click to expand...

It should show on the label how P is supplied. I believe it is always P2O5 on the label. But if not, 43.6% is substantial enough.
 
P2O5 is not how it is supplied in the fertilizer. More often than not it is in the forms of phosphates or nitrates.

Phosphorus is reported as oxide only because, historically, the only reliable analytical method was to dead burn it to the oxide.
 
Oh, I see. P2O5 is just a conventional name for the NPK system but it's not necessarily supplied as one.

I wonder how we would know when not to add the 43% factor? Every time I see that label, I always factor out.

Thanks
 
gego said:
Oh, I see. P2O5 is just a conventional name for the NPK system but it's not necessarily supplied as one.

I wonder how we would know when not to add the 43% factor? Every time I see that label, I always factor out.

Thanks
Click to expand...

I believe if the label states the P as P2O5 you should use the % factor regardless of the P source.
 
Bjorn said:
Mike, be aware that N-P-K is not necessarily N P and K. Many Places its N- P2O5-K2O (but they write N-P-K) 43.6% of P2O5 is P so you might have to correct Your numbers accordingly. I read that in Australia the Convention can be N-P-K-S in which case its given as elemental Components, so Yours might be right while others might have to be adjusted. Confused? so am I:rollhappy:
Click to expand...

We don't use the old American system here. It is law here that the exact amount of each element you are buying is stated on the label. For eg: 20 20 20 would be....
N = 20 P is 0.44 x 20 = 8.8 K is 0.83 x 20 = 16.6 so in actual fact you are giving your plant (potentially that is) 20%N 8.8%P and 16.6%K from the fertilizer which is what really matters to the plant.

Based on elemental P and N, I fertilise with approximately 10N to 1P (is that a P/N around 10?)
Click to expand...
No that is P/N 0.1
Click to expand...
 
Ray said:
Adding to paphioboy's comments, plants have a phosphorus "pump", so take it up whenever it's available, and store in cell vacuoles, whether it is needed by the plant or not.
Click to expand...

But the question remains that if through many trials (that I have seen) it was found that increasing P reduced growth on a downward curve until death, how is it that some paphs can not only handle but flourish with something like 10 52 10 which is almost 23% P?
P toxicity is well known. For example, Poinsettia growth reduced with a P/N of 0.45 compared to 0.2 (20 20 20 has a P/N of 0.44)
I think Xavier's mastersianum leaves had a P/N of 0.4 (very high for a plant)
(from memory)
 
Stone said:
But the question remains that if through many trials (that I have seen) it was found that increasing P reduced growth on a downward curve until death, how is it that some paphs can not only handle but flourish with something like 10 52 10 which is almost 23% P?
P toxicity is well known. For example, Poinsettia growth reduced with a P/N of 0.45 compared to 0.2 (20 20 20 has a P/N of 0.44)
I think Xavier's mastersianum leaves had a P/N of 0.4 (very high for a plant)
(from memory)
Click to expand...

One possibility is that P sensitive plants might not be adept at storing excess P as phytic acid in vacuoles or may have poor regulation of P uptake and efflux. It is known that the vacuolar P is the most variable P compartment of the total P in plant leaves for plants grown at different P levels.

Another example of P sensitivity is the Australian shrub Verticordia plumosa, which shows growth inhibition starting at 3 ppm P in the feed. In the study they show that sugar metabolism is affected and that the toxicity can be reversed by foliar feeding of Zn.
http://link.springer.com/article/10.1023/A:1020432512980#page-2

A brief scan of the literature shows a number of papers indicating a link between Zn and phosphate sensitivity in other plants. Clearly other cationic micronutrient deficiencies would be possible at high P due to precipitation, but this is highly pH dependent and the Zn issue seems to be more specific than general precipitation in that high P seems to increase the requirement for Zn in P sensitive plants. I didn't come across a compelling explanation for this Zn effect ?
 
The amount of P in a plant at any given time is really small and application of a high P fert generally wastes 99.999999% of what you throw on the plant.

However, phosphate binds to iron, calcium carbonate, and alumina/clays. These are all proven materials for the removal of phosphate from waste water, and are present in most soils too.

So application of a high P fert may have utility if your potting mix is full of phosphate sponge materials

You could also look at citrate/malic acid addition with your normal low P feed to improve P uptake. Plants exude OA's from their roots to increase access to environmental P.

A lot of the research playing with odd ratios of NPK in crop plants has more to do with the soil/plant interaction with pulsed and sporadic application of the fertilizer. For understanding plant physiology (especially for orchids) I'd look more into the hydroponic research applications, since these are continuous application systems with reduced variables from soil chemistry.
 

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