B4. Fertilisers and Eutrophication

Question 1

Loss of nutrients
Crops take in __________ from the ____as they grow and use them to build their own tissues. When crops are harvested, they’re removed from the field where they’re grown rather than being allowed to ____and _____________there. This means the _________ ____ that they contain (e.g. ___________and _________) are not returned to the soil by ______________in the nitrogen or phosphorus cycles.
Phosphates and nitrates are also ____from the system when animals or animal products are ___________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 _________through their ________or ________ __________.

Answer 1

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

Question 2

Using fertilisers
Adding fertiliser replaces the _____ _________, so more ________from the ecosystem can be used for ________, increasing the __________of ________transfer. Fertilisers can be artificial or natural. (artificial vs natural)

Answer 2

Adding fertiliser replaces the lost minerals, so more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer. Fertilisers can be artificial or natural.

• Artificial fertilisers are inorganic-they contain pure chemicals (e.g. ammonium nitrate) as powders or pellets.
• Natural fertilisers are organic matter - they include manure, composted vegetables, crop residues (the parts left over after the harvest) and sewage sludge.

Question 3

Environmental issues
Sometimes more fertiliser is applied than the plants need or are able to use at a particular time. This can lead to the fertilisers ________into waterways. Leaching is when water-soluble compounds in the soil are _________ _____, e.g. by rain or irrigation systems. They’re often washed into nearby _____and _____. This can lead to _________________
_____________ions in chemical fertilisers are relatively ___________. This means that excess minerals that are not used immediately are more likely to leach into waterways. Leaching is also more likely to occur if the fertiliser is applied just before ______ _________.
Leaching is less likely with _______ __________-that’s because the nitrogen and phosphorus are still contained in ________molecules that need to be _______________by ________________before they can be __________by _______. This means that their release into the soil for uptake by plants is more ____________. The leaching of phosphates is less likely than the leaching of nitrates because phosphates are ____soluble in water.
Using fertilisers may also change the balance of nutrients in the soil -too much of a particular __________can cause crops and other plants to die.

Answer 3

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, e.g. by rain or irrigation systems. They’re often washed into nearby ponds and rivers. This can lead to eutrophication.
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. Leaching is also more likely to occur if the fertiliser is applied just before heavy rainfall.
Leaching is less likely with natural fertilisers-that’s because 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. The leaching of phosphates is less likely than the leaching of nitrates because phosphates are less soluble in water.
Using fertilisers may also change the balance of nutrients in the soil -too much of a particular nutrient can cause crops and other plants to die.

Question 4

Eutrophication is caused by excess nutrients.

Answer 4

1. Mineral ions leached from fertilised fields stimulate the rapid growth of algae in ponds and rivers.
2. Large amounts of algae block light from reaching the plants below.
3. Eventually the plants die because they’re unable to photosynthesise enough.
4. Bacteria feed on the dead plant matter. The increased numbers of bacteria reduce the oxygen concentration in the water by carrying out aerobic respiration.
5. Fish and other aquatic organisms die because there isn’t enough dissolved oxygen.

Question 5

Tip: Eutrophication is where too many ________ ____in the ______cause a sequence of “mega-growth, mega-death and mega-decay” involving most of the plant and animal life in the water.

Answer 5

Tip: Eutrophication is where too many mineral ions in the water cause a sequence of “mega-growth, mega-death and mega-decay” involving most of the plant and animal life in the water.