Fertilizers branded under this label provide a supply of nitrogen (N), phosphorus (P) and potassium (K). Some advanced formulations further incorporate sulfur, a vital element for the synthesis of amino acids in plants.NPK fertilizer is a type of fertilizer that contains three primary nutrients essential for plant growth: nitrogen (N), phosphorus (P), and potassium (K). These three nutrients are often referred to by their chemical symbols N-P-K.