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.
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 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.
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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.