K2O

Production
Potassium oxide is produced from the reaction of oxygen and potassium; this reaction affords potassium peroxide, K2O2. Treatment of the peroxide with potassium produces the oxide : K2O2 + 2 K → 2 K2O

Alternatively and more conveniently, K2O is synthesized by heating potassium nitrate with metallic potassium : 2 KNO3 + 10 K → 6 K2O + N2

Potassium hydroxide cannot be further dehydrated to the oxide.

Potassium Oxide In Fertilizers
The chemical formula K2O is used in the N-P-K (nitrogen-phosphorus-potassium) numbers on the labels of fertilizers. Although K2O is the correct formula for potassium oxide, potassium oxide is not used as a fertilizer in these products. Normally, potassium chloride, potassium sulfate, or potassium carbonate is used as a fertilizer source for potassium. The percentage of K2O given on the label only represents the amount of potassium in the fertilizer if it was in the form of potassium oxide. Potassium oxide is about 83% potassium by weight, but potassium chloride, for instance, is only 52% potassium by weight. Potassium chloride provides less potassium than an equal amount of potassium oxide. Thus, if a fertilizer is 30% potassium chloride by weight, its standard potassium rating, based on potassium oxide, would be only 19%.