5B - Fertilisers and eutrophication Flashcards
When are nutrients lost from the soil?
When crops are harvested.
Where do crops get their minerals from?
The soil
Why do crops need minerals from the soil as they grow?
To build their own tissues.
Why does harvesting crops decrease mineral concentrations in the soil?
Because 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 cycles.
Apart from through harvesting how are phosphates and nitrates also lost from the system?
When animals or animal products are removed from the land.
Why does removing animals or animal products from the land, decrease mineral concentrations?
Because animals eat grass and other plants, taking in their nutrients and so when they are taken elsewhere for slaughter or transferred to a different field, the nutrients aren’t replaced through their remains or waste products.
Why are fertilisers required in agricultural ecosystems?
Because soil is depleted by minerals unlike in natural ecosystems where minerals removed by plants are returned when the plant is decomposed by microorganisms.
What does adding fertilisers to soils do?
Replaces lost nutrients.
Why is adding fertilisers to soils to replace lost minerals good?
Because more energy from the ecosystem can then be used for growth, increasing the efficiency of energy transfer.
What are the 2 types of fertilisers?
Artificial and natural.
What are artificial fertilisers?
Pure chemicals as powders or pellets, e.g. NPK.
What are artificial fertilisers made from?
Rocks
Give examples of artificial fertilisers
NPK (nitrogen, phosphate, potassium).
Ammonium nitrate.
Are artificial fertilisers organic or inorganic?
Inorganic
Are natural fertilisers organic or inorganic?
Organic
What are natural fertilisers/what are they made from?
Dead and decaying remains of plants and animals and animal wastes, e.g. slurry and manure.
Give examples of natural fertilisers
Manure, composted vegetables, crop residues (the parts left over after the harvest) and sewage sludge/slurry.
Explain how using fertilisers raises environmental issues
1) Sometimes more fertiliser is applied than the plants need or are able to use at a particular time.
2) This can lead to the fertilisers leaching into waterways.
3) Leaching is when water-soluble compounds in the soil are washed away, e.g. by rain or irrigation systems. They’re often washed into nearby ponds and rivers.
4) This can lead to eutrophication.
5) Leaching is more likely to occur if the fertiliser is applied just before heavy rainfall.
6) Inorganic ions in chemical fertilisers are relatively soluble meaning that excess minerals that are not used immediately are more likely to leach into waterways. In natural fertilisers, 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 release into the soil for uptake by plants is more controlled, and leaching is less likely.
7) The leaching of phosphates is less likely than the leaching of nitrates because phosphates are less soluble in water.
8) Using fertilisers also changes the balance of nutrients in the soil - too much of a particular nutrient can cause crops and other plants to die.
What can more fertiliser being applied than the plants need or are able to use at a particular time lead to?
Leaching of fertilisers into waterways.
What is leaching?
Leaching is when water-soluble compounds in the soil are washed away, e.g. by rain or irrigation systems. They’re often washed into nearby ponds and rivers.
What can leaching lead to?
Eutrophication.
When is leaching more likely to occur?
Leaching is more likely to occur if the fertiliser is applied just before heavy rainfall.
How soluble are inorganic ions in chemical fertilisers?
Relatively soluble.
What does it mean for minerals that inorganic ions in chemical fertilisers are relatively soluble?
Means that excess minerals that are not used immediately are more likely to leach into waterways.
When is the release of nitrates and phosphorus more controlled?
In natural fertilisers, 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 release into the soil for uptake by plants is more controlled, and leaching is less likely.
Why is leaching less likely when using natural fertilisers?
In natural fertilisers, 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 release into the soil for uptake by plants is more controlled, and leaching is less likely.
Is the leaching of phosphates or nitrates more likely?
Nitrates.
Why is the leaching of phosphates less likely than the leaching of nitrates?
Because phosphates are less soluble in water.
What do fertilisers change?
The balance of nutrients in the soil - too much of a particular nutrient can cause crops and other plants to die.
What might the fact that fertilisers change the balance of nutrients in the soil mean for a plant/crop?
Too much of a particular nutrient can cause crops and other plants to die.
What is eutrophication caused by?
Excess nutrients (and leaching).
What is the process of eutrophication?
1) Mineral ions leached from fertilised fields stimulate the rapid growth of algae in ponds and rivers.
2) Large amounts of algae (algal bloom) block light from reaching the plants below.
3) Eventually plants die because they’re unable to photosynthesise enough.
4) (Saprobiontic) Bacteria feed on the dead plant matter. The increased numbers of bacteria reduce the oxygen concentration in the water by carrying out aerobic respiration - there is an increased biological oxygen demand.
5) Fish and other aquatic organisms die because there isn’t enough dissolved oxygen (interspecific competition).
