Fertilisers and Eutrophication

How are nutrients lost by plants

• Crops take in minerals from the soil as they grow and use them to build their own tissues

• When crops are harvested, they are removed from the field where they are grown rather than being allowed to die and decompose there.

  • This means that the mineral ions that they contain (e.g. phosphates and nitrates) are not returned to the soil by decomposers in the nitrogen or phosphorus cycles 

How are nutrients lost by animals

• 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

What is the purpose of fertilisers?

• Fertilisers are added to soils to replace the lost minerals, so more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer

What are the two type of fertilisers?

artifical and natural fertilisers

Describe Natural fertilisers

• Natural fertilisers are organic matter - they include manure, composted vegetables etc.

• Have a variable composition, but will contain trace elements in addition to N,P,K (nitrates, phosphates and potassium)

• Release nutrients slowly over a long period of time, reducing the risk of leaching

• If the manure is produced on the same farm, it is cheap to use and gets rid of waste that might otherwise cause pollution

  • However manure is heavy to transport and can cause soil compaction when heavy machinery is used

Describe artifical fertilisers

• Artificial fertilisers are inorganic and they are chemically made for a specific crop and consist of an appropriate balance of mineral nutrients

• They are applied in forms like powders or pellets

• They have a known composition so can be applied in the correct concentration

• They are concentrated so can be applied in smaller amounts, reducing the damage done by heavy machinery

• Release nutrients more quickly and are more likely to cause leaching

What is the cause and effect of leaching?

• Sometimes more fertiliser is applied than the plants need or are able to use at a particular time

• This can lead to the fertilisers leaching into waterways

• Leaching is when water-soluble compounds in the soil are washed away by rain or irrigation systems and are carried deep into the soil and into water in lakes and rivers

• This can lead to eutrophication

Why is leaching harmful?

• Leaching is harmful for the environment because it can trigger eutrophication

• Leaching is harmful for human health as nitrogen-rich water may enter drinking water

Explain eutrophication

• Excess soluble nitrates and phosphates leach into water sources like ponds from the soil

• This leads to the rapid growth of algae at the surface of the water source. This is called an algal boom

• The algae then block the light so light can’t reach the plants at lower depths

•  The plants die due to insufficient light for photosynthesis

• Levels of aerobic saprobiontic bacteria increase as they decompose the dead plant material

• This depletes oxygen levels in the water, resulting in the death of fish and other aquatic life, disrupting food webs

• Anaerobic organisms increase in number, further decomposing dead material and releasing more nitrates and toxic wastes