Benefits & Problems of Fertilisers (WJEC GCSE Chemistry)

• Fertilisers are added to fields that require the nitrogen content to be replenished for optimum plant growth
  • Plants require nitrogen for the production of proteins and chlorophyll
  • Ammonia contains nitrogen which is why fertilisers contain ammonium salts
• Most fertilisers contain phosphorus and potassium which plants also require
  • Potassium promotes growth and healthy fruit and flowers
  • Phosphorus promotes healthy roots
• They are easy and quick to apply but are linked to environmental issues
• One issue is eutrophication which is caused by fertilisers washing into rivers, lakes and streams.
• Rainfall also leaches water soluble minerals from the soil into waterways

What is eutrophication?

• Eutrophication occurs in several steps
• The water soluble minerals from the fertiliser washed into the waterway stimulate rapid growth of single-celled and microscopic plants
• This causes a continuous layer on the surface of the water known as an 'alga bloom'

Photo showing an algal bloom

An algal bloom is a continuous layer of microscopic plants preventing sunlight from reaching the bottom of the waterbody

Photo by Commons/CSIRO 

• Light can not therefore reach the bottom of the water body preventing plants from photosynthesising and causing the level of oxygen to drop
• The reduction of oxygen can cause animals living in the water to die
• The algae bloom is short lived and therefore they will also die
• Aerobic bacteria will break down bodies of dead organisms and use up oxygen in the water further
• This can cause fish to die in large numbers as they require a high level of oxygen in the water to survive

Diagram to show the biological consequences of eutrophication