Our Npk 13 : 00 : 45 Potassium nitrate (KNO3) is a natural occurring mineral source of nitrogen. This enhances its application as a fertilizer to provide the soil ample amount of nitrogen. As a fertilizer potassium nitrate has an NPK rating of 13-0-45 which indicates 13.9%, 0%, and 45% of nitrogen, phosphorus and potassium by mass, respectively.