Triple superphosphate (TSP) was one of the first high-analysis phosphorus (P) fertilizers that became widely used in the 20th century. Technically, it is known as calcium dihydrogen phosphate and as monocalcium phosphate, [Ca(H₂PO₄)₂ .H₂O]. Despite its excellent history as a P source, its use has declined as other P fertilizers have become more popular.