SOP is an inorganic compound with formula K2SO4. It is a white water-soluble solid. It is commonly used in fertilizers, providing both potassium and sulfur.
SOP is doubly essential not just because of the potassium, but also because it provides plants with sulphur the first micro-nutrient. Every plant needs sulphur. If you add SOP to soils, the plant gets both sulphur and potassium. With MOP, you still face the additional cost of adding sulphur.
