Role of NPK Fertilisers in Plant Growth

  • Compounds containing nitrogen, potassium and phosphorus are used as fertilisers to increase crop yields.
  • NPK fertilisers are formulations containing appropriate ratios of all three elements.
  • Nitrogen promotes healthy leaves, potassium promotes growth and healthy fruit and flowers and phosphorus promotes healthy roots.
  • A distinct advantage of manufactured fertilisers is that they can be designed for specific needs whereas natural fertilizers, such seaweed or manure, cannot.
  • Fertiliser compounds contain the following water soluble ions:
  • Ammonium ions, NH4+ and nitrate ions, NO3, are sources of soluble nitrogen.
  • Phosphate ions, PO43- are a source of soluble phosphorus.
  • Most common potassium compounds dissolve in water to produce potassium ions, K+.
  • The table below shows the name of some common fertilisers, their formulae and the elements they provide.

Role of NPK Fertilisers in Plant Growth Table, IGCSE & GCSE Chemistry revision notes

Use of Ammonia in Manufacturing Fertilisers

  • Ammonia is an alkaline substance and neutralises acids producing a salt and water.
  • The salt it produces contains the ammonium ion, NH4+ which is a component in a lot of fertilisers.
  • Ammonia also undergoes oxidation to produce nitric acid (HNO3).
  • Nitric acid is used as the source of the nitrate ion, NO3, which is another important ion used in fertilisers.
  • Ammonium nitrate, a fertiliser and one of the most important ammonium salts is made by reacting ammonia with nitric acid:

NH3 + HNO3 → NH4NO3

  • It is prepared on large scale industrial proportions but can also be prepared in the laboratory using a different method.
  • In the laboratory it is prepared by titrating ammonia with sulfuric acid:

2NH3 + H2SO4 → (NH4)2SO4

  • The table below summarises the main aspects of both methods.

Use of Ammonia in Manufacturing Fertilisers Table, IGCSE & GCSE Chemistry revision notes

Use of Phosphate Rock

  • The Earth’s crust also contains useful minerals which are useful raw materials for making fertilisers.
  • Phosphate rocks contain potassium chloride and potassium sulfate as they provide potassium.
  • The rock itself is insoluble in water to it is usually reacted with acid to produce useful compounds with water soluble compounds.
  • The table below summarizes some of these reactions.

Use of Phosphate Rock Table, IGCSE & GCSE Chemistry revision notes

Need help?

AQA GCSE Chemistry Notes

Want to aim for a Level 9?

See if you’ve got what it takes. Test yourself with our topic questions.

Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.