Who this is for: Cambridge IGCSE Chemistry (0620) students who want fertilisers — NPK components, ammonia production and environmental effects — to become linked explain answers instead of isolated facts about “plant food”.
What query it owns: how to understand and revise fertilisers in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the fertilisers revision-guide angle, while Tutopiya’s Fertilisers subtopic page owns the learning resource and the free Fertilisers quiz owns the practice.

Fertilisers are a key application topic in the Chemistry Of The Environment unit of Cambridge IGCSE Chemistry (0620). Examiners expect you to state what NPK means, describe how ammonia is made and converted to nitrate fertilisers, and explain eutrophication from fertiliser runoff. This guide connects industrial chemistry to environmental consequences.

Key takeaways

• Fertilisers supply essential elements — mainly nitrogen (N), phosphorus (P) and potassium (K) — for plant growth.
• Ammonia (NH₃) is made in the Haber process from nitrogen and hydrogen, then converted to nitric acid and ammonium nitrate.
• Nitrate fertilisers (e.g. ammonium nitrate, potassium nitrate) are soluble and quickly absorbed by plants.
• Overuse of fertilisers causes eutrophication — algal blooms, oxygen depletion and fish death in rivers/lakes.
• Fertiliser bags show NPK numbers — the percentage of each element present.

What are fertilisers in Cambridge IGCSE Chemistry?

Fertilisers are chemical compounds added to soil to replace essential elements lost through harvesting. At IGCSE you describe the manufacture of ammonia, the production of nitrate fertilisers, the meaning of NPK labels, and the environmental problems caused when excess fertiliser washes into water courses.

Read the full notes on Tutopiya’s Fertilisers subtopic page before attempting questions.

The core ideas you must master

Idea	What it means	How the exam uses it
NPK	Nitrogen, phosphorus, potassium for growth	”State what NPK stands for.”
Ammonia production	Haber process: N₂ + 3H₂ ⇌ 2NH₃	”Name the process used to make ammonia.”
Nitrate fertilisers	NH₃ → HNO₃ → NH₄NO₃ or KNO₃	”Describe how ammonium nitrate is made.”
Eutrophication	Excess nitrates → algal bloom → O₂ depletion	”Explain the effect of fertiliser runoff on rivers.”
NPK label	Numbers show % of N, P and K	”Interpret the NPK values on a fertiliser bag.”

How to explain eutrophication — step by step

1. Excess fertiliser (nitrates/phosphates) washes into rivers or lakes (leaching).
2. Rapid algal growth (algal bloom) on the water surface.
3. Algae block sunlight — underwater plants die.
4. Dead matter decomposed by bacteria using dissolved oxygen.
5. Oxygen depletion — fish and aquatic animals die.

Test yourself with the free Fertilisers quiz.

Manufacture vs environmental impact: which does the question want?

Situation	What to write	Typical signal words
Making ammonia	Haber process, N₂ + H₂, catalyst, high pressure	”how ammonia is manufactured”
Making fertiliser	NH₃ oxidised to HNO₃; neutralisation	”how ammonium nitrate is produced”
NPK meaning	N, P, K elements for plant growth	”what NPK stands for”
Pollution	Eutrophication sequence	”effect of fertiliser on a lake”

Fertilisers in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical fertilisers stem
State	Named process or element	”State what the K in NPK represents.”
Describe	Manufacture steps	”Describe how ammonia is used to make a fertiliser.”
Explain	Environmental consequence	”Explain why fertiliser runoff harms fish.”
Name	Process or compound	”Name a common nitrate fertiliser.”
Give the advantages	Increased crop yield	”Give one advantage of using fertilisers.”

Worked exam-style stems (how to answer the wording)

1. “State what the letters N, P and K stand for on a fertiliser bag.” Nitrogen, phosphorus and potassium. Reward: all three elements named.
2. “Describe how ammonia is used to make ammonium nitrate fertiliser.” Ammonia is converted to nitric acid (catalytic oxidation). Nitric acid is neutralised with ammonia to form ammonium nitrate. Reward: HNO₃ formation + neutralisation.
3. “Explain how excess fertiliser in a river can lead to the death of fish.” Nitrates cause eutrophication — algal bloom, bacteria decompose dead algae using dissolved oxygen, oxygen levels fall and fish suffocate. Reward: algal bloom + oxygen depletion + fish death.

When you can recognise the wording instantly, work through the Fertilisers quiz and Water for pollution links.

How fertilisers connect to the rest of the syllabus

Fertilisers link to Air (nitrogen from fractional distillation), Water (eutrophication in rivers) and industrial chemistry (Haber process). The Cambridge IGCSE Chemistry resource hub links every environment subtopic.

Common mistakes students make

• Describing eutrophication without the oxygen depletion step — fish death needs low dissolved oxygen.
• Confusing ammonia with ammonium nitrate — ammonia is the intermediate, not the fertiliser applied directly.
• Forgetting phosphorus and potassium when only nitrogen is discussed.
• Saying fertilisers “pollute” without naming eutrophication or leaching.
• Missing the link between Haber process and fertiliser manufacture.

When you need more support

If fertiliser manufacture or eutrophication questions keep losing marks, work through the Fertilisers quiz, then get focused help from a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

What does NPK mean on fertiliser bags? Nitrogen, phosphorus and potassium — the three essential elements for healthy plant growth.

How is ammonium nitrate fertiliser made? Ammonia is oxidised to nitric acid, which is neutralised with ammonia to form ammonium nitrate.

What is eutrophication? Excess nitrates in water cause rapid algal growth, followed by oxygen depletion when bacteria decompose dead algae, killing fish.

How do I revise fertilisers effectively? Learn NPK, practise one manufacture route and one eutrophication explain answer, then take the Fertilisers quiz.

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