The primary use of ammonium sulfate 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. The main disadvantage to the use of ammonium sulfate is its low nitrogen content relative to ammonium nitrate, which elevates transportation costs.
It is also used as an agricultural spray adjuvant for water-soluble insecticides, herbicides, and fungicides. There, it functions to bind iron and calcium cations that are present in both well water and plant cells.
Growers apply ammonium sulfate primarily where they need supplemental N and S to meet the nutritional requirement of growing plants. Since ammonium sulfate contains only 21percent N, other fertilizer sources more concentrated and economical to handle and transport often make a better choice for N-deficient fields. However, it provides an excellent source of S, which supports or drives numerous essential plant functions, including protein synthesis.
Because the N fraction is present in the ammonium form of ammonium sulfate, rice farmers frequently apply it to flooded soils, since nitrate-based fertilizers are a poor choice due to denitrification losses.
A solution containing dissolved ammonium sulfate is often added to post-emergence herbicide sprays to improve their effectiveness at weed control. This practice of increasing herbicide efficacy with ammonium sulfate works particularly well when the water supply contains significant concentrations of calcium (Ca), magnesium (Mg) or sodium (Na). A high-purity grade of ammonium sulfate often works best for this purpose to avoid plugging spray nozzles.
It’s also a component in fire extinguisher powder and flame-proofing agents. And it serves many purposes in the chemical, wood pulp, textile and pharmaceutical industries.