Fertiliser

Fertilisers replace some of them and can improve agricultural productivity. NPK stands for nitrogen, phosphorus and potassium: an NPK fertiliser contains compounds supplying all three elements. Plants take up nutrients through their roots as dissolved ions, so the chemical form of an element matters as well as its presence.

A fertiliser adds nutrients so that plants can continue to grow well. It supplies them as compounds containing the needed elements, rather than as the pure elements themselves.

For example, ammonia reacts with nitric acid to make ammonium nitrate, a fertiliser salt. This connects an industrial chemical process to the nutrients available to crops.

Fertilisers are added to replace these lost nutrients. Three particularly important nutrient elements are nitrogen (N), phosphorus (P) and potassium (K). They are supplied in compounds rather than as pieces of the pure elements.