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# What is NPK all about?

#### SmokzAlot

##### New Member
N-P-K
Most of us have grown accustomed to seeing the numbers, what ever combination they may come in.

10-15-10
12-9-10
15-0-0
18-54-20

Most think it is the content of each, well sort of...
Ok then, what am I looking at?

N-P-K is used to label fertilizer based on the relative content of the chemicals nitrogen(N), phosphorus(P), and potassium(K) that are commonly used in fertilizers. The numbers are more relative to the component makeup, but we can do a little math and get valid numbers. Number that tells us what we have at hand. The result will be the actual elemental amount of each based on weight.

P consists of 56.4% oxygen and 43.6% elemental phosphorus. The percentage of elemental phosphorus is 43.6%
Formula - P = 0.436 x P

K consists of 17% oxygen and 83% elemental potassium. The percentage (mass fraction) of elemental potassium is 83%
Formula - K = 0.83 x K

Nitrogen values represent actual nitrogen content, no conversion needed.

So lets take an example from above..
---
10-15-10

P = 0.436 x 15
P = 6.54%

K = 0.83 x 10
K = 8.3%

Result:
10% N
6.5% P
8.3% K

---
18-54-20

P = .0.436 x 54
P = 23.544%

K = 0.83 x 20
K = 16.6%

Result:
18% N
23.5% P
16.6% K
---

The rest is filler...

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