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).   

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.

 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.
 

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