If MOP contains 60% K2O, what is the other 40%?

Canpotex Granular MOP

We are frequently asked this question.   The chemical name for Muriate of Potash (MOP) is Potassium Chloride (KCl).  However, the Chloride content is never listed on fertilizer bags. 

If the chemical purity were 100%, the Potassium (K) would be 52.4% (63.1% K2O) and the Chloride (Cl) would be 47.6%.   

However, the simple answer is approximately: 

• 50% Potassium (as K) [ 50% K is equivalent to 60.2% K2O ] 

• 48% Chloride (as Cl)

• 2% Magnesium (Mg), Calcium (Ca), Sodium (Na), Sulfates (SO4) and insolubles such as clay.   

The logical next questions: Are Chlorides helpful or harmful to plants and soils and why isn’t the Chloride content listed on the bag?

Stayed tuned.