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Part 4b. Methods of increasing food production and improving sustainability

GCSE level biology exam revision notes on food production

4b. Ways of improving the quality of soil, increasing fertility and crop yields - but there are issues!

[Author © Dr Phil Brown PhD: Doc Brown's biology exam revision notes suitable for students of UK IGCSE & GCSE level biology courses & ~ US grades 9-10 biology [food page updated Mar 14th 2026 *]

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4(b) Poor soil is improved by application of fertilisers - overuse causes environmental problems

(but there are both advantages and disadvantages using artificial fertilisers)

Ways of improving soil fertility.

Ideally, fertilisers contain important nutrients for plants to grow e.g. nitrates for nitrogen, phosphates for phosphorus, ions of magnesium and sulfate (for sulfur) and compounds of trace elements like copper, zinc and boron.

The idea of using fertilisers is twofold:

(i) bring into use poor quality soil deficient n nutrients,

(ii) replace nutrients used up by the previous crops,

(iii) grow crops with increased yield,

(iv) although (i) to (iii) apply to any fertiliser, naturally produced organic fertilisers produce a much better quality of soil.

Organic farming with compost and cattle muck produces much better quality of soil, whose structure and nutrient and water retaining properties are important.

BUT overuse of synthetic inorganic fertilisers has created eutrophication problems in lakes and rivers and they are not cheap, particularly in the context of a poorer country.

Eutrophication is when an excess of nutrients like nitrates and phosphates causes algal blooms, so water is covered in a thick mass of green slimy algae that reduces oxygen levels in water and kills most aquatic life beneath it.

Manure and compost

Organic fertilisers based on plant and animal waste are more beneficial for soil quality and probably produce food of a higher nutritious quality.

See The manufacture & use of fertilisers

and NPK fertilisers-environmental problems

Infertile soils too acidic for growing crops or raising cattle (pH <7), can be treated with lime to increase the pH to a more optimum value for crop growth.

4(b) contd. Ways in which farmers can increase the nitrate content of soil

As plants grow they will use up the available nitrates in soil, which can become deficient in essential nutrients. 

When the crops are harvested, the nitrate content of the soil is now reduced - its ended up as protein in the grain. 

Unless the nitrate is replaced, the nitrate content in the soil will decrease with each crop grown.

To avoid the soil becoming infertile leading to poor plant growth and deficiency disease, the nitrate must be replaced.

 

There are several ways of doing this.

(i) Spreading an organic fertilisers like animal manure or some composted plant material which is decomposed by bacteria/fungi to release nitrogen compounds into the soil. This is a good method because it is essentially recycling organic substances from animal waste or plant material, both returning nitrogen compounds to the soil on decomposition.

 

(ii) Spreading synthetic fertilisers (e.g. NPK products) made from ammonium and nitrate ion compounds. Can you name them?

NPK means the synthetic inorganic fertiliser supplies nitrogen, phosphorus and potassium to the plants.

However, the use of artificial fertilisers can create pollution problems like eutrophication if overused. See the notes on ...

Biodiversity, land management, waste management, maintaining ecosystems - conservation and already mentioned in Part 4b.

 

(iii) Crop rotation avoids growing the same crop in the same field over and over again. Several different crops are grown each year in a seasonal cycle. The cycle should include a leguminous plant (nitrogen-fixing crop) like beans or peas that will naturally return nitrates to the soil for another crop the following year - the plant itself can also be ploughed into the field.

Key biology points Source of information are based on the syllabus-specifications for students taking the AQA GCSE, Edexcel GCSE and OCR GCSE level biology examinations (~US grades 9-10).

Further thoughts on using fertilisers

Biology Revision Notes – Synthetic vs. Organic Fertilisers for Soil Quality and Crop Yields

1. Introduction

Fertilisers are substances added to the soil to increase fertility, improve crop yields, and enhance plant growth.

They provide essential nutrients, such as nitrogen (N), phosphorus (P), and potassium (K), which plants need for development.

Fertilisers can be divided into two main types:

  • Synthetic Fertilisers – Chemically manufactured substances designed to provide specific nutrients.

  • Organic Fertilisers – Natural materials derived from plant, animal, or mineral sources, which gradually enrich the soil.

Each type has advantages and disadvantages, impacting food production and environmental sustainability.

2. Advantages of Synthetic Fertilisers

Synthetic fertilisers are widely used in commercial farming due to their efficiency and immediate effects.

a) Rapid Nutrient Availability

  • Contain high concentrations of essential nutrients, which are immediately available to plants.

  • Help crops grow faster, leading to higher yields in a shorter time.

b) Precise Composition

  • Manufactured to provide specific ratios of nitrogen, phosphorus, and potassium (e.g., NPK fertilisers).

  • Farmers can tailor applications based on soil requirements.

c) Increased Food Production

  • Essential for feeding the growing global population, ensuring maximum crop output.

  • Supports intensive farming practices, where large quantities of crops are needed.

d) Easy to Transport and Apply

  • Can be stored for long periods without degradation.

  • Easier to handle, transport, and spread compared to organic fertilisers.

3. Disadvantages of Synthetic Fertilisers

Despite their benefits, synthetic fertilisers can have negative effects on soil health and ecosystems.

a) Environmental Pollution

  • Excess fertiliser can run off into rivers and lakes, causing eutrophication (excessive algae growth that depletes oxygen in water bodies).

  • Leads to water contamination, harming aquatic life.

b) Soil Degradation

  • Overuse can reduce soil quality, making it dependent on fertilisers.

  • Prolonged use reduces organic matter, affecting soil structure and water retention.

c) Long-Term Effects

  • Excessive nitrogen application can lead to acidification of the soil.

  • Some synthetic fertilisers release greenhouse gases, contributing to climate change.

d) High Cost and Resource Dependency

  • Expensive compared to organic alternatives.

  • Requires large energy inputs for manufacturing, making production unsustainable in the long term.

4. Advantages of Organic Fertilisers

Organic fertilisers improve soil health naturally and contribute to sustainable farming.

a) Improves Soil Structure and Retains Moisture

  • Adds organic matter to the soil, improving water retention and nutrient absorption.

  • Prevents soil erosion by strengthening soil particles.

b) Sustainable and Eco-Friendly

  • Biodegradable and naturally recycled in ecosystems.

  • Reduces chemical pollution and enhances biodiversity.

c) Slow Nutrient Release

  • Provides gradual nutrient availability, ensuring long-term soil fertility.

  • Reduces risk of nutrient overdose, preventing plant damage.

d) Less Risk of Water Contamination

  • Unlike synthetic fertilisers, organic materials do not cause eutrophication.
  • Helps maintain healthy aquatic ecosystems.

5. Disadvantages of Organic Fertilisers

Although beneficial, organic fertilisers have certain drawbacks.

a) Slow Nutrient Release

  • Takes longer to break down, meaning nutrients are not immediately available.

  • Less effective for rapid crop growth, which is essential for large-scale food production.

b) Lower Nutrient Concentration

  • Contains less concentrated nutrients than synthetic alternatives.

  • Farmers need larger quantities, which can be impractical for intensive agriculture.

c) Difficult to Transport and Apply

  • Can be heavy, bulky, and costly to transport.

  • Requires more effort to apply evenly across large areas.

d) Risk of Disease Transmission

  • Animal manure-based fertilisers may contain pathogens, requiring proper treatment before use.

  • Risk of contamination if not processed correctly.

6. Conclusion

Both synthetic and organic fertilisers play an important role in global food production.

Synthetic fertilisers are effective for rapid yield increases, but they can harm the environment. Organic fertilisers enhance soil health and sustainability, but they have slower effects and lower nutrient concentrations.

The best approach for achieving food security is to balance synthetic and organic methods, using sustainable farming techniques such as:

  • Integrated Nutrient Management – Combining both types of fertilisers to maximise efficiency.

  • Crop Rotation and Green Manures – Maintaining soil fertility without excessive chemical use.

  • Precision Agriculture – Using technology to apply fertilisers more efficiently.

WHERE NEXT?

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INDEX of all my BIOLOGY NOTES

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