Potassium sulfate.

Potassium sulfate (US) or potassium sulphate (UK), also called sulphate of potash (SOP), arcanite, or archaically potash of sulfur, is the inorganic compound with formula K₂SO₄, a white water-soluble solid. It is commonly used in fertilizers, providing both potassium and sulfur.

Potassium sulfate is an excellent source of K nutrition for plants. The K portion of the K₂SO₄ is no different from other common potash fertilizers. However, it also supplies a valuable source of S, which protein synthesis and enzyme function require.