5B - Fertilisers and eutrophication

Question 1

When are nutrients lost from the soil?

Answer 1

When crops are harvested.

Question 2

Where do crops get their minerals from?

Answer 2

The soil

Question 3

Why do crops need minerals from the soil as they grow?

Answer 3

To build their own tissues.

Question 4

Why does harvesting crops decrease mineral concentrations in the soil?

Answer 4

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.

Question 5

Apart from through harvesting how are phosphates and nitrates also lost from the system?

Answer 5

When animals or animal products are removed from the land.

Question 6

Why does removing animals or animal products from the land, decrease mineral concentrations?

Answer 6

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.

Question 7

Why are fertilisers required in agricultural ecosystems?

Answer 7

Because soil is depleted by minerals unlike in natural ecosystems where minerals removed by plants are returned when the plant is decomposed by microorganisms.

Question 8

What does adding fertilisers to soils do?

Answer 8

Replaces lost nutrients.

Question 9

Why is adding fertilisers to soils to replace lost minerals good?

Answer 9

Because more energy from the ecosystem can then be used for growth, increasing the efficiency of energy transfer.

Question 10

What are the 2 types of fertilisers?

Answer 10

Artificial and natural.

Question 11

What are artificial fertilisers?

Answer 11

Pure chemicals as powders or pellets, e.g. NPK.

Question 12

What are artificial fertilisers made from?

Answer 12

Rocks

Question 13

Give examples of artificial fertilisers

Answer 13

NPK (nitrogen, phosphate, potassium).

Ammonium nitrate.

Question 14

Are artificial fertilisers organic or inorganic?

Answer 14

Inorganic

Question 15

Are natural fertilisers organic or inorganic?

Answer 15

Organic

Question 16

What are natural fertilisers/what are they made from?

Answer 16

Dead and decaying remains of plants and animals and animal wastes, e.g. slurry and manure.

Question 17

Give examples of natural fertilisers

Answer 17

Manure, composted vegetables, crop residues (the parts left over after the harvest) and sewage sludge/slurry.

Question 18

Explain how using fertilisers raises environmental issues

Answer 18

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.

Question 19

What can more fertiliser being applied than the plants need or are able to use at a particular time lead to?

Answer 19

Leaching of fertilisers into waterways.

Question 20

What is leaching?

Answer 20

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.

Question 21

What can leaching lead to?

Answer 21

Eutrophication.

Question 22

When is leaching more likely to occur?

Answer 22

Leaching is more likely to occur if the fertiliser is applied just before heavy rainfall.

Question 23

How soluble are inorganic ions in chemical fertilisers?

Answer 23

Relatively soluble.

Question 24

What does it mean for minerals that inorganic ions in chemical fertilisers are relatively soluble?

Answer 24

Means that excess minerals that are not used immediately are more likely to leach into waterways.

Question 25

When is the release of nitrates and phosphorus more controlled?

Answer 25

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.

Question 26

Why is leaching less likely when using natural fertilisers?

Answer 26

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.

Question 27

Is the leaching of phosphates or nitrates more likely?

Answer 27

Nitrates.

Question 28

Why is the leaching of phosphates less likely than the leaching of nitrates?

Answer 28

Because phosphates are less soluble in water.

Question 29

What do fertilisers change?

Answer 29

The balance of nutrients in the soil - too much of a particular nutrient can cause crops and other plants to die.

Question 30

What might the fact that fertilisers change the balance of nutrients in the soil mean for a plant/crop?

Answer 30

Too much of a particular nutrient can cause crops and other plants to die.

Question 31

What is eutrophication caused by?

Answer 31

Excess nutrients (and leaching).

Question 32

What is the process of eutrophication?

Answer 32

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).