Soil degradation
Big idea: Soil degradation is one of the biggest threats to food security. We lose billions of tonnes of topsoil every year — faster than it can be replaced.
Types of soil degradation
- Erosion — topsoil blown or washed away (wind/water erosion)
- Salinization — salt accumulates, toxic to plants (from irrigation in dry areas)
- Compaction — heavy machinery crushes pore spaces, reduces aeration
- Nutrient depletion — continuous cropping without replenishment
- Contamination — pollution from chemicals, heavy metals, waste
- Desertification — productive land becomes desert
Human causes of degradation
- Deforestation — removes root systems that hold soil, increases erosion
- Overgrazing — animals remove vegetation, compact soil
- Intensive agriculture — monocultures deplete specific nutrients
- Irrigation — can cause salinization and waterlogging
- Urbanization — soil sealed under concrete, lost permanently
ESSAY TOPIC (9 marks): "Discuss human impacts on soil." Structure: (1) types of degradation, (2) human causes, (3) environmental impacts, (4) management strategies, (5) balanced conclusion on whether degradation can be reversed.
IB-style question — explaining soil degradation
A farming region clears its forests to grow a single crop and irrigates the land heavily. Explain how these practices can degrade the soil. [4]
How the marks are earned
- Clearing forest
• bare soil erodes — topsoil, nutrients and organic matter are lost
• result: thinner, less fertile soil - Heavy irrigation
• water evaporates and leaves salts behind (salinisation)
• over-watering leaches nutrients below root depth → lower fertility
Final answer
Name the process (erosion / salinisation) AND explain the mechanism — a label alone scores nothing.
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