Impacts of unsustainable farming Cambridge IGCSE Environmental Management revision
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In plain words
Push a field too hard and it pushes back. Salt creeps into the soil, pests shrug off the spray, the river turns green. Every impact in this unit starts with a method that worked well, used too much.
9 things to know
- Overproduction of food leads to food wastage. The water, energy and fertiliser used to grow the wasted food are wasted too.
- Food shortages can follow when land is used for cash crops, such as coffee, cotton, soya beans and palm oil, or for biofuel crops, in place of food crops.
- Mismanagement of irrigation. Too much water causes water logging, which fills the pore spaces and starves roots of oxygen, and it washes soil away. Salinisation is the build-up of salts in the topsoil: irrigation water evaporates and leaves its dissolved salts behind.
- Overuse of pesticides. A few pests survive each spraying and breed, so the population becomes resistant. Pest resurgence happens when the pesticide also kills the pest's predators, so the pest returns in larger numbers. Pollinators such as bees are killed.
- Overuse of fertilisers. The excess is leached, washed down through the soil, into rivers and lakes. This nutrient enrichment causes eutrophication.
- In eutrophication, the extra nutrients make algae grow very fast. The algae block the light, so water plants die. Bacteria decompose the dead material and use up the oxygen in the water. Fish and other animals die.
- Exhaustion of nutrients: growing crops year after year without replacing nutrients uses up the organic content and the inorganic ions.
- Removal of natural vegetation by deforestation, overcultivation and overgrazing leaves the soil bare.
- Monoculture and intensification pollute soil and water with chemicals, and reduce biodiversity. Soil erosion removes the topsoil, which holds most of the nutrients.
Worked example
Explain how using too much fertiliser on fields can kill fish in a nearby lake.
- Rain leaches the excess nitrates and phosphates through the soil and into the lake.
- The nutrients make algae grow rapidly, covering the surface and blocking the light.
- Plants below cannot photosynthesise, so they die, and the algae die too.
- Bacteria decompose the dead material and use up the oxygen. Fish die for lack of oxygen.
Tips and tricks
- In eutrophication the fish are not poisoned by the fertiliser. They die because bacteria have used up the oxygen. That one step earns or loses the mark.
- Salinisation is about salt. Water logging is about too much water. Both come from poor irrigation, but they are separate problems.
It lands in your notebook with its questions as flashcards.
Impacts of unsustainable farming: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is salinisation?
Evaporating irrigation water leaves its salts behind.
Which is a cash crop?
A cash crop is grown to sell.
What is leaching?
Leached nutrients end up in rivers and lakes.
In eutrophication, what uses up the oxygen in the water?
The bacteria respire as they decompose.
How do pests become resistant to a pesticide?
Each spraying selects the survivors.
Why does the loss of topsoil reduce crop yield so much?Stretch
The fertile layer is the one that goes first.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 7 marks. Write your answers on paper, then check them.
Impacts of unsustainable farming
Cambridge IGCSE Environmental Management 0680 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Explain how irrigation can cause salinisation.[3]
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Irrigation water contains dissolved salts. The water evaporates from the soil. The salts are left behind and build up in the topsoil.
Explain what is meant by pest resurgence.[2]
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A pesticide kills the natural predators of the pest as well as the pest. With no predators, the pest population returns larger than before.
Explain how growing cash crops can lead to a food shortage.[2]
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Land that grew food is used for crops to sell, such as cotton or coffee. Less food is grown locally, so there may not be enough.
Answers: Impacts of unsustainable farming
- 1. Irrigation water contains dissolved salts. The water evaporates from the soil. The salts are left behind and build up in the topsoil.
- 2. A pesticide kills the natural predators of the pest as well as the pest. With no predators, the pest population returns larger than before.
- 3. Land that grew food is used for crops to sell, such as cotton or coffee. Less food is grown locally, so there may not be enough.