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Fertilizers & Eutrophication

Chemistry: Cambridge International A Level, topic 2.5.4

Fertilisers

Fertilisers replace nutrients lost from the soil during harvesting and removing livestock to help maximise yields in agriculture.

Agricultural impacts on soil

Agricultural impacts on soil

  • Agriculture leads to depleted levels of nutrients in the soil (e.g. nitrogen and phosphates).
  • This is because when crops are removed for harvest, they are not decomposed and the nutrients are not returned to the soil for reuse.
  • Removing livestock for slaughter also decreases nutrient levels because they are not replaced by decomposition.
Using fertilisers

Using fertilisers

  • Fertilisers can be used to replace the nutrients (e.g nitrogen and phosphate) lost through agriculture.
  • Increasing nutrient levels by fertilisers allows farming to continue without negative impacts on the crop or livestock quality.

Eutrophication

Using fertilisers can have negative impacts on the environment. For example, eutrophication can happen when too much fertiliser is used. The process of eutrophication is:

1) Leaching and overflow

1) Leaching and overflow

  • Fertilisers that are sprayed onto fields can leach through the soil or flow into ponds, rivers and lakes.
  • Leaching is when water-soluble plant nutrients are lost from the soil.
  • This causes a build up of nutrients in the water.
2) Algal overgrowth

2) Algal overgrowth

  • The excess of nutrients cause algae to rapidly grow on the surface of the water.
  • As algae accumulate, light is prevented from reaching the plants in the water beneath.
3) Plant death

3) Plant death

  • The plants underneath the algae eventually die because there is insufficient light for them to photosynthesise.
4) Increase in numbers of bacteria

4) Increase in numbers of bacteria

  • Bacteria decompose the dead plants.
  • As numbers of bacteria increase, the oxygen concentration in the water decreases.
  • Fish and other organisms will now die because there is not enough oxygen.

Test yourself on Fertilizers & Eutrophication

  • Which of the following statements about fertilisers are true?

  • Which of these is NOT a use of fertilisers?

  • Stages of Eutrophication

  • What is the impact of excess nutrients in ponds, rivers and lakes on algae?

  • Which of the following statements about eutrophication is true?

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