Fertilisers containing potassium must be applied wherever soil potassium reserves are inadequate for targeted crop or pasture production. Potassium can be applied as a straight fertiliser, or as part of a blended or compound fertiliser with nitrogen and phosphorous. Each of the major potash sources are soluble in water and will readily dissolve when there is adequate rainfall or irrigation is applied. Under high rainfall or excessive irrigation, potassium can be lost in surface runoff or from the root zone by leaching – especially in permeable soils with a low cation exchange capacity.
Potassium is not lost to the atmosphere, as can occur with some nitrogen fertilisers under certain soil and environmental conditions. Potassium can become unavailable if it is fixed by expanding clay minerals, but will be slowly re-released if soil exchangeable potassium levels fall.