Ammonium Sulfate is

Ammonium Sulphate is an inorganic salt and a single-type fertilizer with several commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen and 24% Sulphur.
The primary use of ammonium is as a fertilizer for alkaline soils. In the soil the ammonium ion is released and forms a small amount of acid, lowering the pH balance of the soil, while contributing essential nitrogen for plant growth.