Ammonium sulfate ((NH4)2SO4) is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer since the chemical contains 21% (w/w) nitrogen and 24% (w/w) sulfur.

Ammonium sulphate is widely used as a sulphur (S) fertilizer, constituting about 50% of global S use. Within nitrogen (N) management, it is well known that ammonium-based fertilizers are subject to ammonia (NH3) volatilization in soils with pH > 7, but this has been overlooked in decision making on S fertilization.