Accessibility
  • Change text size

    • Normal Text
    • Medium Text
    • Large Text
  • Contrast

    • Black&white
    • High
    • Normal
  • Display

    • Cursor White
    • Cursor Black
  •  

Pioneering the Future

You are here

Haifa Blog

06Dec2018
How to calculate NPK formulae

This blog is part of an ongoing knowledge sharing activity of the Haifa Group Modern Greenhouses  special task force.

A frequent question I get from growers is how come potassium nitrate 13-0-46 = 59% and not 100%

Nutrients content
I’d like to start with a basic explanation about the NPK nutrients and their percentages (%) in fertilizer formulae.
Fertilizer's formula usually refers to the content of nutrient in their oxide forms (N-P2O5-K2O). In Scandinavia, Australia and South Africa it is more common to refer to elemental forms (N-P-K).   

For example:
The nutritional composition of Multi-K™ Classic is 13-0-46.
This means that the fertilizer contains
13% nitrogen (N)
0 % phosphorus oxide (P2O5) = 0% phosphorus (P)
46% potassium oxide (K2O) = 38.3% potassium (K)


So how we sum to 100% ?

Here we have to consider the actual form of the nutrients in the fertilizer:
In mineral fertilizers, nitrogen may be present as ammonium, nitrate or amide (urea), phosphorus is present mainly as phosphate, and potassium is present as K+ ion.  The following table shows the ratios between elements, oxides, and the forms mentioned above.

Ammonium

NH4 =

N x 1.28

 

Nitrate

NO3 =

N x 4.43

 

Amide

(NH2)2CO=

N x 2.14

 

Phosphate

H2PO4=

P x 2.68

P2O5 x1.15

Potassium

K =

K x1

K2O x 1.2

 

Now, 13% N as NO3 means that 13x4.43= 57.6% of the product is NO3  
and 46% K2O are 46/1.2= 38.3% K.
Together these sum to 57.6+38.3=95.9%

 Not 100% yet….
The difference is attributed to
-    The fact that the actual analysis is somewhat higher than 13-0-46
-    Presence of trace impurities in the product
-    Moisture 

 

Premium Multi-K™ products such as Multi-K™ GG and Multi-K™ Reci contain higher analysis, and less impurities. For actual analyses see product data sheets.
 

 

Pure Element

Multiply by

Oxide form

Multiply by

Pure Element

N

4.426

NO3

0.226

N

N

1.288

NH4

0.776

N

P

2.292

P2O5

0.436

P

K

1.205

K2O

0.83

K

Ca

1.399

CaO

0.715

Ca

Mg

1.658

MgO

0.603

Mg

S

2.996

SO4

0.334

S

S

2.497

SO3

0.4

S

 

This blog is part of an ongoing knowledge sharing activity of the Haifa Group Modern Greenhouses task force.

You may also be interested in this