One of the primary uses of ammonia produced by the Haber Process is in the manufacture of fertilisers. Fertilisers are chemical mixtures that enhance crop growth and improve agricultural productivity. The most effective fertilisers are NPK fertilisers, which contain nitrogen (N), phosphorus (P), and potassium (K)—elements essential for plant growth.

Phosphate rock cannot be used directly in fertilisers and must be treated with nitric acid to produce a soluble salt, which is then incorporated into fertilisers. NPK fertilisers provide essential nutrients that significantly boost crop yields, making them a crucial component of modern agriculture.