How to test solubility of potash

Sulphate of Potash

Potash is very important fertilizer 

Solubility of potash....

Potash solubility

SOP

Sop is widely used potash fertilizer in Pakistan. Its chemical formula is K2SO4 and it contains 54% K2O and 18% S, if pure. But for commercial use it is available with 50% K2O and 18% S, as it contains some impurities like

Magnesium

, ammonium, sodium and chlorides.
Its solubility is 115 g/litre of water at room temperature. If SOP then solubility of all brands is same. If some fertilizer company claims more soluble SOP then it is not pure SOP. It may be powdered MOP or blend of MOP and

ammonium sulphate

 (both have higher solubility).
There is no SOP of higher solubility, so don't waste your money on buying costly SOP which is assumed more soluble, because that is not SOP.
Other information please contact me
Thanks
Muhammad Majid Saleem