Nitrogen Cycle

    Nitrogen Cycle

    PDF of This Lesson


    To diagram the nitrogen cycle and provide examples of human actions that affect this cycle.


    Students will learn about the nitrogen cycle through discussion and the construction of a diagram. They will also measure the nitrate levels in various water samples and discuss how humans affect nitrate content in the water.

    See discussion questions that provide some background information and some leading questions to help guide classroom discussions.

    The lesson is designed in three parts: 

    1. A classroom activity that helps students understand what they will be measuring and why;    
    2. follow up STEM activities, data analysis and presentation of results;
    3. and watershed connections.

    Materials Needed:Nitrogen sampling

    *Click here for information on purchasing equipment and supplies or creating your own equipment.  Contact USU Water Quality Extension ( or 435-797-2580) for information on borrowing equipment. 

    Classroom Activity:

    Part One:

    crimson trail waterfall1.  Discuss the nitrogen cycle with your students  

    • -Ask them to identify where nitrogen is found. Talk about how nitrogen is found in many different forms, both organic and inorganic (see background information).    
    • Ask the students what the most common inorganic form is (nitrogen gas, which makes up 80% of the atmosphere). 
    • Ask students where organic nitrogen might be found (plants and animals and dead material – nitrogen is used in proteins). 
    • Ask the students what type of nitrogen most plants can use (nitrate or ammonia – two common forms of inorganic nitrogen). Point out that only a few very specialized plants and microorganisms can use nitrogen gas directly. All other plants use nitrogen in the form of nitrate or ammonia.

    2.  As the students talk about forms of nitrogen. Draw a nitrogen cycle on the board, adding reservoirs and process lines as the students suggest them.

    nitrogen cycle

     Part Two:

    1.  Explain to the students that they will measure one type of nitrogen found in water - nitrate. Nitrate is a common form of inorganic nitrogen that is easily used by plants. 

    2.  Divide students into groups of no more than six so that everyone can be involved.

    3.  Give each group a water sample. Have the groups follow the directions found on the
    nitrate sampling sheet.

    4.  Have students record their results on the board and discuss why different sources of water have different levels of nitrate. 

    5.  Explain that nitrate is extremely soluble and moves into our groundwater easily. Explain that in surface waters, the nitrate is used up rapidly by aquatic plants.

    Part Three:

    1. Return to the drawing of the nitrogen cycle from your earlier discussion. Ask the feedlotstudents to suggest ways that humans may have affected the nitrogen cycle.

    2. Discuss their answers. Be sure to mention the points below.

    • Inorganic Fertilizers - fertilizers have been produced commercially since the 1950’s and now account for a large portion of fixed nitrogen entering the global environment every year. 
    • Feedlots introduce a lot of ammonia into the air.
    • Fossil fuel combustion (cars and coal burning energy plants) convert nitrogen gas into nitric and nitrous oxides, which are dissolved into rainwater and fall as nitric acid. In addition to being a source of acid rain, it is also a nitrogen fertilizer.

    STEM Activity:


    1.  The following are suggestions to help students gain a better understanding of nitrogen and the role it plays in a system.

    2.  Collect water from different sources (river, lake, tap, tap + fertilizer, etc.) and grow plants, like radishes or lettuce,  with the water.  Test each source of water for nitrates. Water with higher levels of nitrates can act as a fertilizer and can make the plants grow larger.

    3.  Collect  two or more samples of water from a lake or stream.  Leave one of the samples alone as a control.  To the others add varying levels of plant fertilizer.  Place in the classroom and observe the results. Normally the fertilizer will stimulate algae to grow like in this video example. What happens to the clarity of the water? What are the effects of fertilizer getting in our water ways?

    4.  Discuss how temperature, pH, and exposure times influence ammonia toxicity in water. For ideas and graphs click here.

    5. Discuss the nitrate  nitrite process. For more information about this process click here.

    Watershed connections  

    Watersheds are natural outdoor laboratories. Use the map below to find the watershed you teach in. Use the watershed connections in the Stream Side Science lessons to learn how you can use specific stream locations, local data sources, local contact and other information in your area to make the Stream Side Science experience more relevant to your students.   

    What watershed do you live in?

    If you live in Utah, the map below shows all of the watersheds that either drain into or out of Utah.
    OR go to Surf Your Watershed to locate your watershed anywhere in the U.S.


    Curriculum and Teacher Materials 

    Core Alignments by Grade:

    6th Grade:

    7th Grade:

    8th Grade:

    High School:



    Materials and Worksheets: 

    Worksheets and More: