1. The nitrogen cycle describes how nitrogen is converted between its various forms and moves between the atmosphere, soil, plants, and animals. 2. Atmospheric nitrogen is converted to ammonia or nitrates through nitrogen fixation, which allows plants and animals to use it. 3. Nitrification and ammonification convert ammonia into other nitrogen forms that plants can use, and denitrification returns nitrogen to the atmosphere, completing the cycle.

1. THE NITROGEN CYCLE

2. Where is nitrogen found in the environment?

3. The largest single source of nitrogen is in the atmosphere . Nitrogen makes up 78% of our air!

4. What happens to atmospheric nitrogen (N 2 ) in the nitrogen cycle? N N N N N N

5. Atmospheric nitrogen is converted to ammonia or nitrates . Ammonia (NH 3 ) Nitrogen combines with Hydrogen to make Ammonia Nitrates (NO 3 ) Nitrogen combines with Oxygen to make Nitrates Atmospheric Nitrogen (N 2 ) N N N N

6. Why does atmospheric nitrogen need to be converted? N N N N N N

7. It is one of nature’s great ironies… Nitrogen is an essential component of DNA and proteins—the building blocks of life. Although the majority of the air we breathe is nitrogen , most living organisms are unable to use nitrogen as it exists in the atmosphere !

8. How does atmospheric nitrogen get changed into a form that can be used by most living organisms? N N

9. By traveling through one of the four processes in the Nitrogen Cycle ! (1) Nitrogen Fixation (3) Nitrification (2) Ammonification (4) Denitrification Nitrogen Cycle

10. The first process in the nitrogen cycle is… Nitrogen Fixation ! (1) Nitrogen Fixation Nitrogen Cycle

11. What is “nitrogen fixation” and what does it mean to say nitrogen gets “fixed”? N N

12. “ Nitrogen Fixation ” is the process that causes the strong two-atom nitrogen molecules found in the atmosphere to break apart so they can combine with other atoms. Nitrogen gets “ fixed ” when it is combined with oxygen or hydrogen. N N N N N Oxygen Hydrogen Oxygen Hydrogen N

13. There are three ways that nitrogen gets “fixed” ! (a) Atmospheric Fixation (b) Industrial Fixation (c) Biological Fixation Bacteria

14. Atmospheric Fixation (Only 5 to 8% of the Fixation Process) The enormous energy of lightning breaks nitrogen molecules apart and enables the nitrogen atoms to combine with oxygen forming nitrogen oxides (N 2 O) . Nitrogen oxides dissolve in rain, forming nitrates. Nitrates (NO 3 ) are carried to the ground with the rain. Lightning “fixes” Nitrogen! Nitrogen combines with Oxygen Nitrogen oxides forms Nitrogen oxides dissolve in rain and change to nitrates Plants use nitrates to grow! (NO 3 ) N N O (N 2 O)

15. Industrial Fixation Under great pressure, at a temperature of 600 degrees Celcius, and with the use of a catalyst, atmospheric nitrogen (N 2 ) and hydrogen are combined to form ammonia (NH 3 ) . Ammonia can be used as a fertilizer . Industrial Plant combines nitrogen and hydrogen Ammonia is formed Ammonia is used a fertilizer in soil (NH 3 ) N N H N H 3

16. Biological Fixation (where MOST nitrogen fixing is completed) There are two types of “ Nitrogen Fixing Bacteria” Free Living Bacteria (“fixes” 30% of N 2 ) Symbiotic Relationship Bacteria (“fixes” 70% of N 2 )

17. Free Living Bacteria Highly specialized bacteria live in the soil and have the ability to combine atmospheric nitrogen with hydrogen to make ammonia (NH 3 ) . Free-living bacteria live in soil and combine atmospheric nitrogen with hydrogen Nitrogen changes into ammonia N N H N H 3 (NH 3 ) Bacteria

18. Symbiotic Relationship Bacteria Bacteria live in the roots of legume family plants and provide the plants with ammonia (NH 3 ) in exchange for the plant’s carbon and a protected home. Some of the ammonia escapes into the surrounding soil enriching it with usable nitrogen for all plants. Legume plants Roots with nodules where bacteria live Nitrogen changes into ammonia. NH 3 N N

19. Most atmospheric nitrogen (N 2 ) is “fixed” and changed to ammonia (NH 3 ) . Ammonia is highly toxic to many organisms. Can plants use ammonia?

20. Very few plants can use ammonia (NH 3 )… … but, fortunately the second process Ammonification can help! (1) Nitrogen Fixation (2) Ammonification

21. What is ammonification ?

22. Ammonification : Decomposition by bacteria and fungi breaks down amino acids from dead animals and wastes into ammonia . Bacteria decomposers break down amino acids into ammonia

23. Why is ammonification necessary?

24. Because plants cannot use the organic forms of nitrogen that are in the soil as a result of: (1) wastes (manure and sewage) (2) compost and decomposing roots and leaves

25. How does ammonification occur?

26. Microorganisms convert the organic nitrogen to ammonis. The ammonia is either taken up by the plants (only in a few types of plants) or is absorbed into the soil particles. Ammonia (NH 3 ) in the soil is stored up to later be changed into forms of nitrogen that most plants can use. Ammonia (NH 3 ) is stored in soil. Bacteria converts organic nitrogen to ammonia (NH 3 ) Ammonia (NH 3 ) is used by some plants Bacteria

27. What happens to ammonia (NH 3 ) stored in the soil?

28. It travels through the third process of the nitrogen cycle called Nitrification ! (1) Nitrogen Fixation (2) Ammonification (3) Nitrification

29. Let’s “run through” a general overview of the Nitrification Process

30. Nitrifying bacteria in the ground first combine ammonia with oxygen to form nitrites . Then another group of nitrifying bacteria convert nitrites to nitrates which green plants can absorb and use! Nitrifying bacteria in soil combine ammonia with oxygen Ammonia changes to nitrites Nitrifying bacteria in soil convert nitrites to nitrates Plants absorb nitrates and grow! Ammonia Nitrites Nitrates (NH 3 ) (NO 3 ) (NO 2 )

31. How does nitrogen reenter the atmosphere in the nitrogen cycle?

32. Through the fourth process called denitrification ! (1) Nitrogen Fixation (2) Nitrification (3) Ammonification (4) Denitrification

33. What does denitrification do ?

34. Denitrification converts nitrates (NO 3 ) in the soil to atmospheric nitrogen (N 2 ) replenishing the atmosphere. Nitrates (NO 3 ) in Soil Nitrogen in atmosphere (N 2 )

35. How does the denitrification process work? Nitrates in soil

36. Denitrifying bacteria live deep in soil and in swampy sediments where conditions make it difficult for them to get oxygen. The denitrifying bacteria use nitrates as an alternative to oxygen, leaving free nitrogen gas as a byproduct. They close the nitrogen cycle! Denitrifying bacteria live deep in soil and use nitrates as an alternative to oxygen making a byproduct of nitrogen gas. Nitrogen in atmosphere closes the nitrogen cycle! (NO 3 ) (N 2 )

37. Other ways that nitrogen returns to the atmosphere… Emissions from industrial combustion and gasoline engines create nitrous oxides gas (N 2 O). Volcano eruptions emit nitrous oxides gas (N 2 O).

38. (1) Nitrogen Fixation (3) Nitrification (2) Ammonification (4) Denitrification Nitrogen Cycle Nitrates in Soil Ammonia is converted to nitrites and nitrates. Decomposition converts dead material into ammonia (a) (b) (c) N 2 NH 3 NO 3 N 2 O Nitrates are converted back into atmospheric nitrogen Nitrogen in the atmosphere is converted into nitrates or ammonia LEGUMES SOIL BACTERIA

40. THE NITROGEN CYCLE