Fertilizer mixes (N-P-K amounts)

[Graham]

Sorry Ray, you seem to have been appalled by my search for knowledge and to develop from a beginner's understanding... I did mention I was coming at it from a beginner's point of view...

Originally Posted by Ray

You over-interpreted.
[*]Nowhere did I say that nitrogen was "the main" nutritional element. All three are critical to the plant, as are the minor and trace elements.

Going back to the 30-10-10... You said that the 30 is 30% of Nitrogen... But, the P & K values were not 10% each, but 4.4% (P) and 8.3% (K)...so, while 30 (N) appears to be 30%, both the 10 (P) and 10 (K) are not 10%.

Granted, all three are critical to the plant, but as the values are not consistent with the N-P-K value, from a beginner's view point, it looks like the P & K elements are less of a quantity than N.

Originally Posted by Ray

[*]I also did not say the P & K are oxides, I said they are reported as the equivalent of oxides. That is a throwback to the days when the only way you could test for certain elements was to burn them, then weigh the oxide, but now, even though there are better methods, it is the "standard" anyway.

That was my misunderstanding of your interpretation.

Originally Posted by Ray

[*]You're kidding, right? An oxide is an oxide - a chemical that consists of oxygen and another element, often a metal.

No, I'm not kidding Ray... I asked that question to you, as you said that OrchidUSA gave misinformation about the calculation of Fertilizer.

I had intended to take it for granted what oxide meant, following references from the Dictionary.com... However, I thought your authoritative position on the subject of orchids might be worth asking you the basic question.

Your response, "You're kidding, right?" is the sort of stumbling block that holds beginners back from asking questions... they don't want to be seen as the dunce who didn't know what an expert such as yourself would consider an elementary piece of knowledge.

Originally Posted by Ray

[*]"Macro" does not refer to importance, it merely refers the the amount present in the formula.

I see... I mistook 'larger' to mean 'of greater importance' as it's required in larger/greater amounts.

Originally Posted by Ray

[*]The way I came up with the 4.4%P and 8.3%K was by calculating how much of the element is in the oxide.

And that's why I asked 'how'... Maybe I used the wrong terminology, again. Ray, what is the calculation method/formula that turns 10 (P) into 4.4% (P) and 10 (K) into 8.3% (K)?

[AHAB]

Graham,
Perhaps you should have posted your question in the beginners section... where it is understood all of the basics have not been learned yet. The replys, I imagine would be presented in easier to understand language.

Posting your question in the advance section suggests you already understand the fundamentals.
AHAB

[Ray]

Graham, I apologize if I responded a bit over zealously, but it seemed that you were intentionally incorrectly restating stuff. I apparently misinterpreted, too! (I'm also a ceramic engineer [from Ga Tech], so that probably explains the "you've got to be kidding" oxide comment - it's just a "natural" for me.)

To answer that last question, as - by convention - the P is expressed as %P2O5, you simply take the atomic weight of two phosphorus atoms (61.94), and divide it by the sum of two atoms of P and 5 oxygens (141.94), and you come up with the P being 44% of the weight. Multiply that by the label percentage, and you get the true percentage of phosphorus in the formulation. (Likewise for potassium.)

All of the other "minor" elements (as in amount, they are all important) are stated as weight percentage of their elemental forms.

You seem to be hung up a bit on the "importance" of the individual materials, so try thinking of it as you do about food for yourself: the body needs all sorts of stuff, some in large volumes, others in very small amounts, but they are all important to your overall well-being. You also have to consider the fact that large amounts of some of them can actually be toxic, so while they are essential, you don't need a lot. Stuff like selenium is a good example of that.

So now translate that back to the plants. Yeah, the nitrogen, phosphorus and potassium are the "big three" by volume, but the plants still need other stuff. The so-called Michigan State University (MSU) fertilizer is an example of a pretty complete formula for orchids, especially the RO version, as it is intended to be used with pure, mineral-free water, so has to supply all of the necessary nutrients. Here's the info from the label: Fertilizer for Pure Water

Now then, after accepting that everything is needed, and the fact that folks have tested to the point of coming up with the relative ratios of those various elements, you still have to think in terms of the concentration and frequency - literally, the mass of available nutrients - and their availability in solution.

As you mentioned, Jan found that targeting 125 ppm N was appropriate for the MSU orchid collection. I find that to be a good level for mine as well, but If I still lived in Atlanta, where temperatures, light levels, and humidity (i.e., the good stuff for growing) are greater, I might increase that a bit. For example, Dr. Yin-Tung Wang of Texas A&M found that 250 ppm N was best for phals down in his College Station, Texas greenhouse.

Now then, you also have to consider the frequency of feeding.

In semi-hydro culture, I feed at every watering, usually 2 or 3 times a week. If I fed half as frequently, I'd have to use twice the fertilizer concentration to provide the same mass of nutrients. Unfortunately, when increasing the amount of dissolved solids in the nutrient solution, you run the risk of literally poisoning the plants, so you have to strike a balance. Then there is pH to consider.

Fertilizers are made up of blends of mineral salts (check the MSU label again). When they go into solution in water some can disassociate into different ions depending upon the pH, some usable by the plant, some not (and some won't dissolve at all if the pH is wrong), so having the solution at the correct pH is part of the nutrient design.

Fortunately, most reputable fertilizer companies think about that, so if you use the right fertilizer for your water supply, you usually don't have to worry about it. For example, Dyna-Gro "Grow" formula is pretty well-respected in the orchid world, and when added to most folks' tap water, it's fine. Put it in pure water (RO, DI, distilled) and the pH will be entirely too acidic. The MSU "RO" formula, on the other hand, will give you the correct pH in pure water.

To wrap all of this up, it's good to have a basic understanding of the role of nutrients and the ramifications of their use, but you need not obsess on it. Know enough to acquire a formula appropriate for your plants (I recommend against the 30-10-10 example we'd used in this thread), then trust that the fertilizer formula has the correct ratios of the individual nutrients. Then control your feeding by the ppm N, knowing that the other minerals will "follow along" in the correct ratios, and by adjusting the solution concentration and frequency of feeding, observe how your plants do, and you will eventually come up with a feeding regimen that's right for you and your plants.

One thing to keep in mind on all of this though - feeding is probably one of the least significant aspects of orchid growing. Finding the right air- and moisture management strategy for the potting medium is far more critical, and a lot more difficult, as there are so many possibilities!

[Graham]

I guess the Ga Tech phrase is something that hasn't travelled too well.

No harm done, I'm more interested in getting a good understanding of practical, usable 'stuff', so we'll consign what's been said to distant history.

You seem to be hung up a bit on the "importance" of the Individual materials

Probably could be argued, but I'm unable to leave alone the tiniest bit of information I don't understand... If there's a practical element to something, I'm interested in the mechanics of how it works, the more accurate, as practically possible, the better...and I make no apologies for thinking this way; if there's an inconsistency, then I want to know the reason rather than going on in ignorance, even if it seems a small matter to others...

So, when the 10 of both Phosphorous and Potassium didn't calculate in the same way as the Nitrogen, I for sure wanted to know why.

Besides, if academia and the likes of Dyna Grow are funding research to find specific formulas, then it must be because they place a value on what they want to know.

..
..

For this next bit, feel free if you don't think it's necessary to answer...

It's to do with the P and K calculations and I have two queries...

To answer that last question, as - by convention - the P is expressed as %P2O5, you simply take the atomic
weight of two phosphorus atoms (61.94), and divide it by the sum of two atoms of P and 5 oxygens (141.94), and you come up with the P being 44% of the weight.

Multiply that by the label percentage, and you get the true percentage of phosphorus in the formulation. (Likewise for potassium.)

Now, my Chemistry high-school education went a bit awry, so I had to rely on the Period Table at Chemistry: WebElements Periodic Table to clarify the atomic weights

First query

The weight of the Phosphorous atoms came out correct.

But, I divided your 5 Oxygens to find out the weight of one (141.94 / 5 = 28.388); cross-referencing with WebElements.com, their atomic weight for one Oxygen atom is 15.9994 (3)... I'm not sure what the (3) represents.

Back to your calculation:

"Divide it by the sum of two atoms of P (61.94) and 5 oxygens (141.94)

61.94 / 141.94 = 0.436381... rounded off to 0.44

"Multiply by the label percentage (10)"

0.44 * 10 = 4.4 = 4.4% of P in the Fertilizer mix.

Using your Oxygen result (141.94) formula for P (in the Fertilizer mix) I did get 4.4%; when I used their 15.9994*5 (79.997), I got 7.7%

WebElements.com 1 Oxygen = 15.9994...5 Oxygens = 15.9994*5 = 79.997

61.94 / 79.997 = 0.7742790... rounded off to 0.77

"Multiply by the label percentage (10)"

0.77*10 = 7.7 = 7.7% of P in the Fertilizer mix.

Second query

When I replicated your formula for calculating Potassium, I got...well, stuck...

Potassium (K) = K2O (2 Potassium atoms, 1 Oxygen Atom?)

(Referring back to WebElements for the Atomic Weight of Potassium) K: 39.0983 (1) ...again, not sure what the number in brackets signifies.

K2 = 39.0983*2 = 78.1966

O = 28.388 (we'll stick with your calculation)

In the your formula, the first element was divided by the second, so:

K2 / O = 78.1966 / 28.388 = 2.754565 ...rounded off to 2.75

"Multiply by the label percentage (10)"

2.75*10 = 27.5 = 27.5% of K in the Fertilizer mix.

27.5% Potassium (K)? Where am I going wrong with the calculation, as I'm stuck as how to get the 8.3% you achieved

The macronutrients - N, P, & K - are expressed as elemental nitrogen, but as oxides of the other two. Therefore, while a 30-10-10 does contain 30% nitrogen, it contains the equivalent of 10% P2O5, and 10% K2O, meaning that in terms of the elemental ingredients, it's 30% N, 4.4% P, and 8.3% K.

[Ray]

You forgot the mass of the phosphorus and potassium in the denominators, that's all. We're looking for the weight percentage of the metal compared to the entire oxide, not just the oxygen.

In the case of P2O5, the numerator is (rounding) 2 x 31, and the denominator is (2 x 31) + (5 x 16), while for the K2O, the numerator is 2 x 39 and the denominator is (2 x 39) + 16.

By the way, are you a member of the AOS? There is a good article in the February Orchids magazine that talks about fertilizer that might be worth reading.

[orchids3]

Ray
The 5 articles by Bill Argo were the second most informative discussion of fertilizer I have ever read. I dont see them on your web site anymore. ? The imformation on pH adjutment is included - one of the best summaries of the subject. Its even better than his book.

[Graham]

Excellent...got both of them... Thanks Ray.

I know there's more to the fertilizer than those 3 elements alone, and I've taken on board the greater significance of the environmental conditions (finding the right air- and moisture management strategy for the potting medium)

One thing that's also becoming apparent is the need to grow the orchid based on its preferred environmental conditions; so, what may work well in Pennsylvania might not work so well in, say, UK, Brazil, or across in Asia.

As for the AOS membership, no I'm not yet affiliated to any society; this OrchidBoard has been answering my questions, it seems almost like an orchid society in itself.

[Ray]

Orchids3, they're there - Plant Nutrition

Graham, I would paraphrase that third paragraph a bit - the keys to successful orchid growing are many, but one of them is to carefully analyze the conditions you can easily provide (i.e., that exist without much intervention), then select plants that do well under those conditions. As you gain experience, then you can "push the envelope".

[nhman]

There is an excellent article in the latest edition of the American Orchid Societies publication that addresses this very topic and, I believe, would be very helpful to you in this regard.

[orchids3]

Is that the Feb publication? Have not received mine yet?