In the manufacturing process, the phosphate rock is treated with sulfuric acid to produce SSP or phosphoric acid to produce TSP. SSP has less P content, but contains also sulfur and calcium, making it an excellent source of three plant nutrients. The presence of both sulfur (S) and calcium in SSP can offer an agronomic advantage where both nutrients are deficient. TSP has the highest P content of P fertilizers that don’t contain nitrogen (N), and also contains 15% calcium (Ca), providing an additional plant nutrient.