13.5: Environmental issues concerning nitrogen containing fertilisers

Question 1

Why is nitrogen an essential component for plants

Answer 1

It is needed for growth and increases the surface area of leaves, increasing the rate of photosynthesis and this improves crop productivity

Question 2

Pros of nitrogen-containing fertilisers

Answer 2

Rapidly improve food productivity for cheap

Question 3

Cons of nitrogen-containing fertilisers

Answer 3

1. Reduced species diversity
2. Leaching
3. Eutrophication

Question 4

Why do nitrogen-containing fertilisers cause reduced species diversity

Answer 4

Nitrogen rich soils favour the growth of rapidly growing species, these out-compete many other species, which die as a result

Question 5

What is leaching

Answer 5

The process by which nutrients are removed from the soil

Rainwater will dissolve any soluble nutrients, like nitrate ions, and carry them deep into the soil, eventually beyond plant roots

Question 6

Where do the leached nitrate ions go during leaching

Answer 6

Into watercourses, such as rivers

Question 7

What is the effect of nitrate ions in watercourses

Answer 7

They have a harmful effect on humans if the river is drinking

1. Prevents efficient oxygen transport
2. Causes stomach cancer

Question 8

What is the process of Eutrophication

Answer 8

1. In most lakes nitrate ions are a limiting factor for algae/plants
2. As the nitrate concentration increases, nitrate ions cease to be a limiting factor for plant growth
3. Algal bloom occurs
4. Algal bloom prevents light entering
5. Light becomes a limiting factor and plants die
6. Plant death means more plants to decompose for saprobionts, saprobiont population increases
7. Saprobiotic bacteria reduces oxygen, creating an increased oxygen demand
8. Oxygen concentration decreases and nitrates are released
9. Oxygen becomes limited for aerobic organisms and these die
10. Without oxygen, anaerobic organisms increase in population
11. Anaerobic organisms decompose dead material releasing more nitrates and hydrogen sulphide - this makes the water putrid

Question 9

Causes of Eutrophication

Answer 9

1. Organic manures
2. Animals slurry
3. Human sewage
4. Ploughing old grassland
5. Natural leaching
6. Artificial fertilisers - MAIN CAUSE