Who can explain NPK please?

[Bigmallly]

As the above says really as it's doing my head in. An NPK ratio of 5:5:5 for example isn't equal ratios of NPK as one would think. I am finding it so misleading.

[ugley_matt]

NPK rating - Wikipedia, the free encyclopedia

might help

[Bigmallly]

Nah, that's a cop out Matt..........I'd like you to explain...........

[ugley_matt]

where did u read that it wasnt an equal ratio for 5-5-5?

[veggiechicken]

Your link also says is is not the same ratio,

[Nicos]

At THIS time in the morning?

Ok....this I know...
N = Nitrogen. = leaf growth
P = Phosphorus. = root growth
K = Potassium = flower/ fruit growth

N:P:K is percentage ratio of the nutrient in the packet .....

...and now a more learned person needs to take over....cos I don't know if that is by weight or volume

[Bigmallly]

N:P:K is percentage ratio of the nutrient in the packet .....

That's what I thought but in fact Nitrogen is the only true figure. Phosphorous is 43% element, the rest being Oxygen & Potassium is 83% element, the rest being Oxygen so in fact if you buy fertiliser with an equal ratio on the bottle, you are really getting less P & K elements. In fact you may even see a ratio of P is higher than N on the bottle but because of the % you are still getting more N element.............Right I'm off to bed to have an NPK nightmare........................now why did I ask someone to explain it to me?............Seriously, it was just to make grapes aware that what is on the bottle is not an elemental figure but an oxide figure for P & K.

[Bren In Pots]

Can't help BM because I don't give NPK a thought.

I use blood fish and bone on my beds before planting out, then nettle tea for my greens and comfrey for my fruiting crops.

Not sure if i do things right but it works for me plus it doesn't give me a headache working things out.

[veggiechicken]

After a sleepless night wondering about NPK I've decided its like making a cup of tea:-
N= a spoonful of tea leaves (pure tea)
P= a spoonful of sugar (sweet stuff diluted in water)
K = a spoonful of milk (a bit of calcium but mostly water).

So 7.7.7. would have equal quantities (spoonfuls) of tea, sugar and milk but only tea would be 100% tea. Only a small part of Sugar and Milk is "good" - the remainder is water to make it usable.
Please bear in mind that this is my nutty way of trying to understand NPK ratios and does not reflect the way I like my tea..................I don't take milk or sugar so I'll have a cup of weak N please with a large slice of CAAAAAAKE

Some of you (your plants) may need lots of sugar or milk to make it enjoyable at different times of the day - its all comes down to the individual.


Right, I'm going back to sleep now

[Snadger]

This is the way I see it.

A soil analysis will theoretically let you how many grammes per square metre or kilogrammes per Hectare of the three main elements you need to apply per annum for the crop you are trying to grow. You could apply this total amount in one go but because of leeching and scorching and the crop growth cycle this would usually be applied little and often or possibly in spring and Autumn.
It would depend on your source, and what was the base of these three main elements as to how the ratio would be calculated.

For instance, sulphate of ammonia per kilo would not give you the same ammount of nitrogen as Urea per kilo.
Sulphate of potash would give you a different amount of Pottassium to say Comfey tea
Superphosphate of lime would give you a different amount of Phosphate to Bonemeal.

When we buy fertiliser with an NPK equivalent ratio, this is based on whatever base material is used as the source and is for guidance purposes only.
If we know what our source material is we can calculate the percentage of raw element within that material and add extra material to bring the total amount of element up to 100%. Once we have done this we can apply the total amount of NPK required for the particular crop per annum.

Phew...........

[Greenleaves]

I thought it was next to South Korea

I didn't have a clue BM, but thanks to the answer above I now have a modicum of understanding.

[Bigmallly]

What I don't get is if there is a formula available for converting the P & K values from oxide to actual element values then why don't they just put those figures on the bottles.

[Bal]

What I don't get is if there is a formula available for converting the P & K values from oxide to actual element values then why don't they just put those figures on the bottles.

Good point!

[Bigmallly]

This is the Formula I am referring to:

Method for converting an N-P-K value to an actual composition.
The factors for converting from P2O5 and K2O values to their respective P and K elemental values are as follows:

P2O5 consists of 56.4% oxygen and 43.6% elemental phosphorus. The percentage (mass fraction) of elemental phosphorus is 43.6% so elemental P = 0.436 x P2O5
K2O consists of 17% oxygen and 83% elemental potassium. The percentage (mass fraction) of elemental potassium is 83% so elemental K = 0.83 x K2O
Nitrogen values represent actual nitrogen content so these numbers do not need to be converted.
Using these conversion factors we can determine that an 18−51−20 fertilizer contains by weight:

18% elemental (N)
22% elemental (P), and
17% elemental (K)
In the U.K., fertilizer labeling regulations allow for reporting the elemental mass fractions of phosphorus and potassium. The regulations stipulate that this should be done in parentheses after the standard N-P-K values.

[Martin H]

Does anyone here know in what proportion plants use N, P and K? I wouldn't know what an ideally balanced fertilizer would contain, but surely plants use more N than they do the other two?