Human influence on the nitrogen cycle

1. Human influence on the nitrogen cycle Energy in Ecosystems

2. The nitrogen cycle Re-cap The last lesson was about the nitrogen cycle. • What do organisms use nitrogen for? • How do animals get their nitrogen? • How do plants get their nitrogen? • Which types of decomposers are responsible for • releasing nitrogen from dead organisms? • Which type of organisms convert ammonium • compound to nitrates? Energy in Ecosystems

3. Today we are learning about: How humans can influence the nitrogen cycle • Success criteria • Be able to explain how and why humans influence • the levels of nitrogen in the cycle Energy in Ecosystems

4. Human influence on the nitrogen cycle • Humans influence the nitrogen cycle particularly in • relation to their farming activities. • Harvesting crops removes nitrogen locked up in • the crops that could have gone back into the soil. • How do farmers put the nitrogen back into the soil? Energy in Ecosystems

5. Did you get all of these? • Adding fertiliser • Adding manure • Adding compost • Growing crops like clover • Fertilisers are (man made) chemicals used to add a • variety of essential minerals including nitrogen (N), • phosphorus (P) and potassium (K) to the soil. • This why fertiliser bags are labelled N:P:K Energy in Ecosystems

6. The N:P:K balance can be altered to provide to provide the correct mineral balance for the crops being grown. • For root crops a high proportion of P • For leaf crops a high proportion of N • For flower and fruit crops a high proportion of K Energy in Ecosystems

7. Manure or compost which are natural fertilisers can also be added to the soil by farmers which adds nitrates as it decomposes. • Growing crops like clover (legumes) will return • nitrogen because they have root nodules with • bacteria that fix nitrogen into nitrates. • The clover is ploughed back in to the soil before a • new crop is planted. • Increasing the nitrates (and other minerals) will • increase the yield in the crops being grown. Energy in Ecosystems

8. Excessive use of fertilisers • Farmers can apply more fertilisers or manure than • the crops can use. • These excess nitrates can end up in fresh water like • rivers, reservoirs and lochs as run-off when it rains. • This can cause an increase in the growth of algae • in the water (algal blooms) which can block out light. Energy in Ecosystems

9. Excessive use of fertilisers • As the algae die they sink to the bottom and decay. • This decay uses up a lot of oxygen that is in the water. • This lowers the oxygen level and increases the deaths • of other organisms in the water like invertebrates • and fish. • This means the water will support less life so it • reduces the biodiversity. Energy in Ecosystems

10. Human influence on the nitrogen cycle • Before you leave you need to write down on • your exit ticket answers to the following. • 3 ways humans add nitrogen to the cycle • What can happen to the excess nitrogen added? • Why this could be negative for the environment? • Let the teacher see your exit ticket. Energy in Ecosystems