Potassium nitrate is a chemical compound with the chemical formula K N O 3. It is an ionic salt of potassium ions K + and nitrate ions NO 3 − .It occurs as a mineral niter and is a natural solid source of nitrogen. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpeter or saltpetre.Major uses of potassium nitrate are in fertilizers, tree stump removal, rocket propellants and fireworks.t occurs as a mineral niter and is a natural solid source of nitrogen. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpeter or saltpetre.