Single Superphosphate (SSP)
The modern fertilizer industry was instigated in the 1840s with discovery that by reacting naturally occurring phosphate, in the form of bones, with sulfuric acid produced an excellent soluble fertilizer, given the name superphosphate.
Single superphosphate (SSP) was the first commercial mineral fertilizer and it laid the foundation for the development of the modern plant nutrient industry.
Now largely replaced by MAP and DAP due to its relatively low P content, SSP was once the most commonly used phosphate fertilizer. It does however remain valued for its cost-effectiveness and suitability for acidic soils and is still widely used in both Brazil and India.
Making SSP is somewhat like what naturally occurs with bones or rock phosphate in acid soils. The basic technique has changed very little in the past century. The process begins with grinding phosphate rock into a fine powder. This increases the surface area of the rock, facilitating the subsequent chemical reactions with sulfuric acid. A semi-solid is then formed, which cools for several hours, followed by several weeks of curing. The hardened material is then milled and screened to the appropriate particle size or granulated. One of the main benefits of SSP is that it can easily be produced on a small scale to meet regional needs.
Where P, sulphur (S) and calcium (Ca) are deficient, SSP can provide an advantage over other phosphorus fertilizers. As a source of P alone, SSP often costs more than other more concentrated fertilizers, therefore it has declined in popularity.