SOP is better than MOP when the crops are

SOP is Sulphate of Potash and MOP is Muirate of Potash means potassium chloride.
Some of the crops are sensitive to chlorides then in that case SOP is better to be used. SOP is not a naturally occurring mineral and usually must be produced through chemical methods. And because of the resource-intensive process used to create it, SOP is priced higher than MOP.