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Volume 6: Table of Contents TEACHING ISSUES AND EXPERIMENTS IN ECOLOGY
ISSUES: FIGURE SETS

Figure Set 3: Nitrogen Fertilizers Increase Nitrous Oxide Emissions

Purpose: To teach students that nitrous oxide is a very important greenhouse gas produced in soil, and that excess nitrogen fertilizer results in high levels of greenhouse gas emissions.
Teaching Approach: Guided Class Discussion
Cognitive Skills: (see Bloom's Taxonomy) - knowledge, interpretation, synthesis
Student Assessment: Post Lesson Assessment Essay

STUDENT INSTRUCTIONS

Part 1

There are several gases produced by human activities that contribute to climate change. Carbon dioxide (CO2) receives the most attention in the media, but other gases are also very important contributors to climate change by trapping heat in the Earth's atmosphere. Nitrous oxide (N2O) is considered to be one of the other important greenhouse gases, as human activities have increased its concentration in the atmosphere since pre-industrial time periods.

Examine Table 3a, which provides data from the Intergovernmental Panel on Climate Change (IPCC) 2007 report. Think about what the data mean and make sure you understand all of the terms. Ask your instructor if you are unfamiliar with any of the terms. After interpreting Table 3a, consider the following questions.

Part 2

It has been estimated that 50% of human induced nitrous oxide (N2O) emissions are produced in agricultural soils (IPCC 2001). Nitrogen fertilizers applied to soil increase plant growth and food production, but plants are not the only organisms that use the nitrogen. Soil microorganisms also use nitrogen for growth and energy. Specifically, certain bacteria are involved in the process of nitrification and denitrification, and nitrous oxide is a minor product in both of these reactions.

Figure 3a and 3b show data of N2O emissions and corn crop yields in a study conducted in corn fields of southwest Michigan. The researchers measured N2O emissions from soil, but also measured corn crop yields.

Interpret Figure 3a and 3b for a moment on your own. Ask your instructor to describe anything that you do not understand. After examining the figure, consider the following questions.

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