fertilisers and eutrophication

what do fertilisers do?

• they replace nutrietnts lost from soil during harvesting and removing livestock to help maximise yields in agriculture

• increasing nutrient levels by fertilisers allows farming to continue without negative impacts on the crop or livestock quality

agricultural impacts on soil?

• agriculture leads to depleted levels of nutrients in the soil

• 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 nutrients levels because they are not replaced by decomposition

what are the 2 types of fertilisers?

• artificial

• natural

artificial fertilisers?

• they are inorganic

• they are produced specifically for replacing nutrients

• example: ammonium nitrate

natural fertilisers?

• they are organic

• they are taken from organic matter and used to replace nutrients

• examples: composted food waste, manure

process of eutrophication?

• fertilisers that are sprayed onto fields can leach through the soil or flow into ponds, rivers and lakes

• this causes a build-up of nutrients in that water

• 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

• the plants underneath the algae eventually die because their is insufficient light for them to photosynthesise

• 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

what is leaching?

• when water-soluble compounds in the soil are washed away

• they are often washed into nearby ponds and river

  • leaching leads to eutrophication

when is leaching more likely to occur?

• if the fertiliser is applied just before heavy rainfall

why is leaching more likely to occur in artificial fertilisers?

• because inorganic ions in chemical fertilisers are relatively soluble

• this means that excess minerals that are not used immediately are more likely to leach into waterways

why are organic fertilisers (natural) less likely to be leached than inorganic (artificial)?

• the nitrogen and phosphorus are still contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed by plants

• this means that their released into the soil for uptake by plants is more controlled

what is less likely to be leached: nitrates or phosphates

• phosphates because they are less soluble in water

what else do fertilisers change?

• the balance of nutrients in the soil

  • too much of a particular nutrient can cause crops and other plants to die