Ammonium Polyphosphate (APP) is a nitrogen–phosphorus fertilizer widely used in liquid fertilizer production, fertigation systems, and specialty fertilizer formulations. Known for its high nutrient concentration, good water solubility, formulation flexibility, and metal-ion complexing properties, APP has become an important raw material in modern fertilizer manufacturing. Compared with conventional phosphate fertilizers such as Monoammonium Phosphate (MAP) and Diammonium Phos