1. The Nitrogen Cycle Science 10 “Old Outcomes”

2. The Importance of Nitrogen Nitrogen is a main ingredient in fertilizer. Why does fertilizer produce better crops; what about nitrogen helps plants?

3. The Importance of Nitrogen (Cont’d) Nitrogen is an essential part of proteins, DNA, and other compounds. Like carbon, nitrogen passes along food chains and circulates between abiotic and biotic parts of the environment. This is called the nitrogen cycle.

4. The Nitrogen Cycle

5. The Nitrogen Cycle Part One-Nitrogen Fixation Although nitrogen makes up 80% of the atmosphere, this is unusable by plants. Atmospheric nitrogen must first be “fixed” by nitrogen fixing bacteria. Nitrogen fixation is simply the forming of nitrogen containing compounds such as ammonium (NH 4 ) and nitrate (NO 3 - ). These can be absorbed by the roots of plants.

6. Nitrogen Fixation (Cont’d) There are two types of nitrogen fixing bacteria: Free living – those that live in soil or water. Symbiotic – those that live in the root nodules of legume plants such as clover, peas, beans, and alfalfa. Once used by plants, nitrogen is passed along food chains.

7. Nitrogen and Decomposers The process of returning nitrogen contained in dead organisms and wastes is more complex than that for carbon. Decomposers (through consumption) convert the nitrogen compounds to ammonia (NH 3 ).

8. The Nitrogen Cycle

9. The Nitrogen Cycle Part Two - Nitrification The ammonia is then converted back to nitrates by nitrifying bacteria in a process called nitrification. It can now be re-used by plants. Nitrates may also be “denitrified” by denitrifying bacteria. They are anaerobic (they don’t thrive in oxygen). Denitrification converts nitrate back to nitrogen gas. Why is this process harmful to farmers?

10. The Nitrogen Cycle

11. Human Impacts on the Nitrogen Cycle

12. Impacts from Farming At the end of the 20 th century, the amount of nitrogen being fixed each year to make fertilizers was estimated as over half the amount being fixed in nature. At the same time, expanded areas of farmland were being used to grow legume crops as a way of adding more nitrates to the soil.

13. Global Volumes of Fixed Nitrogen Source Estimated amount of nitrogen fixed per year (millions of tonnes) Natural Micro-organisms Lightning 90-140 5-10 Human Legume crops Artificial fertilizers 32-53 80

14. Impacts from Fossil Fuels When fossil fuels are burned, the nitrogen they contain is released into the air as nitrogen compounds. These compounds dissolve in moisture in the air and fall back to Earth. The result of these impacts is nitrogen overload.

15. Effects of Nitrogen Overload Effects on soil – makes soil acidic dissolving toxic metals such as aluminium. Effects on the atmosphere – acid precipitation killing many organisms Effects on fresh-water ecosystems – eutrophication and algal bloom.