BIOLOGY · Stage 9 · Chapter 9: Plants and Photosynthesis
Biology 9.6 The use of fertilisers — NPK Fertilisers and Eutrophication — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
5 min read 6 parts Lesson 6 of 9
Lesson summary
9.6 The use of fertilisers — NPK Fertilisers and Eutrophication — Alhussan International Academy — Biology (Stages 7–9) notes: Explain why farmers use fertilisers, compare natural and artificial types, and describe how run-off causes eutrophication.Harvesting — in a wild ecosyste…
- Fritz Haber
- Carl Bosch
- Drinking water
- Evaluation
- Algal bloom
- Haber-Bosch process
Section 1 of 6Why fertilisers are used
- Harvesting
- in a wild ecosystem decomposers return nutrients to the soil, but harvested crops take their minerals out of the field and each crop removes more.
- Fertiliser = a substance that replaces minerals such as nitrates in the soil.
- Using fertilisers increases the yield of crops.
- Reliance
- scientists estimate that almost 50% of the world population relies on food grown with artificial fertilisers.
Section 2 of 6Natural and artificial fertilisers
| Feature | Natural (organic) | Artificial (inorganic) |
|---|---|---|
| Examples | Manure and compost | Factory-made NPK fertilisers |
| Speed | Release nutrients slowly | Work fast and act quickly |
| Supply | Limited supply | Always available |
| Soil structure | Improve it | Do not improve it |
| Cost and composition | Cheap but nutrient content varies | Expensive, but composition is known and farmers control the amount |
- Age
- people have used natural fertilisers for thousands of years but artificial fertilisers for only about 100 years.
Section 3 of 6NPK fertilisers
| Element | Taken up as | Used for |
|---|---|---|
| Nitrogen (N) | Nitrate ions | Amino acids, proteins, growth |
| Phosphorus (P) | Phosphate ions | DNA, cell membranes, root growth |
| Potassium (K) | Potassium ions | Enzyme action, flowers and fruit |
- NPK
- N, P and K are the symbols for nitrogen, phosphorus and potassium.
Section 4 of 6Haber and Bosch
- Problem
- air is about 80% nitrogen, but most plants cannot use it and need nitrates from the soil.
- Fritz Haber
- in the early 20th century this German chemist developed a way of making ammonia from nitrogen in the air.
- Ammonia acts as a nitrate-rich fertiliser.
- His laboratory method made only small amounts.
- Carl Bosch
- this chemist and engineer developed a way to use Haber's reaction on an industrial scale.
- The Haber-Bosch process still makes around 120 million tonnes of nitrate fertiliser a year.
- Impact
- it is an example of science applied to industry that has saved billions of lives by growing food for the increasing world population.
- Crop yields, for example canola (used for cooking oil) and wheat (a staple food), rise strongly as the nitrate fertiliser applied increases.
Section 5 of 6Eutrophication step by step
- Too much fertiliser, or fertiliser applied before heavy rain, is carried by run-off into rivers, ponds and lakes.
- Extra nitrates and phosphates make algae and water plants grow rapidly, producing an algal bloom that covers the surface.
- The bloom blocks sunlight, so plants below cannot photosynthesise and die.
- Bacteria break down the dead plants and algae, multiply and use up oxygen in the water in respiration.
- Fish and other animals die from low oxygen and the biodiversity of the water falls.
Section 6 of 6Reducing the problem
- Apply the correct amount of fertiliser at the right time, avoiding wet weather.
- Leave buffer strips of vegetation by waterways to absorb run-off.
- Use crop rotation, legumes and manure to lessen the need for artificial fertilisers.
- Treat sewage and limit phosphates in detergents.
- Drinking water
- water contaminated with nitrates can harm babies, so water companies monitor levels.
- Evaluation
- fertiliser use should weigh increased food production against environmental damage.
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