Topic 5—B: Energy Transfer and Nutrient Cycles- 4. Fertilisers and Eutrophication

Question 1

Loss of nutrients

Answer 1

• Crops take in minerals from the soil as they grow and use them to build their own tissues
• When crops are harvested, they’re removed from the field where they’re grown rather than being allowed to die and decompose there
• This means the mineral ions that they contain e.g. phosphates and nitrates) are not returned to the soil by decomposers in the nitrogen or phosphorus cycle.
• Phosphates and nitrates are also lost from the system when animals or animal products are removed from the land
• Animals eat grass and other plants, taking in their nutrients
• When they are taken elsewhere for slaughter or transferred to a different field, the nutrients aren’t replaced through their remains or waste products.

Question 2

What does adding fertilisers do?

Answer 2

• It replaces the lost minerals e.g. ( nitrates and phosphates ) (lost by harvesting plants, removing livestock and leaching from the soil)
• This means more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer

Question 3

What are the two types of fertilisers?

Answer 3

1. Artificial fertilisers (Inorganic)
2. Natural fertilisers (organic)

Question 4

Artificial fertilisers

Answer 4

• They are inorganic
• They contain pure chemicals
  E.g. (ammonium nitrate) as powders or pellets

Question 5

Natural fertilisers

Answer 5

• They are organic
• They include manure, composted vegetables, crop residues (the parts left over after the harvest and sewage sludge)

Question 6

Environmental issues

Answer 6

• More fertiliser can be applied than the plants need
• This can lead to fertilisers leaching into waterways
• Inorganic ions in chemical fertilisers are relatively soluble meaning that excess minerals that are not used immediately are more likely to leach into waterways

Question 7

When is leaching more likely to occur?

Answer 7

• If the fertiliser is applied just before heavy rainfall

Question 8

Definition of leaching

Answer 8

• When water-soluble compounds in the soil are washed away e.g. by rain or irrigation systems
• Often washed into nearby ponds and rivers
• It can lead to Eutrophication

Question 9

What is leaching less likely with?

Answer 9

• Natural fertilisers

Question 10

What is the reason leaching is less likely with natural fertilisers?

Answer 10

• Because the nitrogen and phosphorus are still contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed by plants.
• Meaning that’s their release into the soil for uptake by plants is more controlled

Question 11

Why is the leaching of phosphates less likely than the leaching of nitrates?

Answer 11

• Phosphates are less soluble in water

Question 12

What will using fertilisers change the balance of?

Answer 12

• Nutrients in the soil
• Too much of a particular nutrient can cause crops and other plants to die

Question 13

What is eutrophication caused by?

Answer 13

Excess nutrients

Question 14

Process of eutrophication

Answer 14

• Fertiliser from fields washed into stream/lakes by rain (leaching)
• Fertiliser causes algae to grow quickly, covering the water surface
• Algae blocks out light from penetrating the water, so underwater plants die as they’re unable to photosynthesise
• Bacteria decompose the dead plants which reduces the oxygen concentration in the water by carrying out aerobic respiration
• Fish and other animals die due to anaerobic conditions