Sulphate of Potash – SOP SULPHATE OF POTASH – SOP SOP is considered a premium-quality potash. It contains two key nutrients for growing crops: potassium and sulfur. Using SOP improves both quality and crop yield and makes plants more resilient to drought, frost, insects and even disease. SOP has been known to improve the look and taste of foods and can boost a plant’s ability to absorb key nutrients like phosphorus and iron. Most often, SOP is used on high-value crops like fruits, vegetables, nuts, tea, coffee and tobacco. It works better on crops that are sensitive to chloride, which can be toxic to some fruit and vegetable plants.