Fertiliser – IGCSE Chemistry Definition
IGCSE Chemistry definition of fertiliser: a substance providing essential elements for plant growth. Covers NPK, manufacture, and exam tips for Cambridge 0620.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Fertilisers connect several IGCSE topics: neutralisation reactions for their manufacture, environmental chemistry for the problems of overuse (eutrophication), and industrial chemistry for the Haber process. Examiners often combine these angles in a single extended question.
The 0620 definition
A fertiliser is a substance added to soil to provide essential elements (particularly nitrogen, phosphorus, and potassium) that plants need for healthy growth.
Why plants need NPK
| Element | Symbol | Role in plant | Deficiency symptom |
|---|---|---|---|
| Nitrogen | N | Proteins, chlorophyll, leaf growth | Yellow leaves, stunted growth |
| Phosphorus | P | Root development, energy transfer | Poor roots, purple leaves |
| Potassium | K | Flower/fruit production, disease resistance | Brown leaf edges |
Making fertilisers by neutralisation
Fertilisers are salts, made by reacting an acid with a base or alkali:
| Fertiliser | Reaction | Equation |
|---|---|---|
| Ammonium nitrate (NH₄NO₃) | Ammonia + nitric acid | NH₃ + HNO₃ → NH₄NO₃ |
| Ammonium sulfate ((NH₄)₂SO₄) | Ammonia + sulfuric acid | 2NH₃ + H₂SO₄ → (NH₄)₂SO₄ |
| Potassium nitrate (KNO₃) | Potassium hydroxide + nitric acid | KOH + HNO₃ → KNO₃ + H₂O |
Ammonium nitrate is a particularly effective nitrogen fertiliser because both the NH₄⁺ and NO₃⁻ ions contain nitrogen — it delivers nitrogen from both its cation and anion.
Environmental problems of overuse
When excess fertiliser washes into rivers and lakes (runoff), it causes eutrophication — a sequence of events that depletes oxygen and kills aquatic life.
Worked exam question
A farmer uses ammonium sulfate as a fertiliser. (a) State one element in ammonium sulfate that plants need. [1] (b) Write the equation for the manufacture of ammonium sulfate. [1] (c) State one environmental problem caused by excess fertiliser. [1]
Mark scheme
(a) Nitrogen [1] (accept sulfur, but nitrogen is the expected answer)
(b) 2NH₃ + H₂SO₄ → (NH₄)₂SO₄ [1]
(c) Eutrophication / algal bloom / death of aquatic organisms / depleted oxygen in water [1]
Common exam mistakes
- Forgetting to balance the equation for ammonium sulfate — you need 2NH₃ because sulfuric acid provides two H⁺ ions.
- Writing “pollution” as the environmental problem without being specific — the examiner wants “eutrophication” or a description of the eutrophication process.
- Confusing NPK: nitrogen is for leaves/protein, phosphorus for roots, potassium for flowers/fruit.
Studying this yourself? Tutoring arrangements are normally made by a parent or guardian. Message us for the details to share with them, or send them this page.