Soil Biogeochemical Cycles

Colin Robins, W.M. Keck Science Dept., Claremont McKenna, Pitzer, and Scripps Colleges

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This group activity charges students with teaching their colleagues about the biogeochemical cycle of one key soil element (e.g., either C, N, S, P, Ca, or Fe). Students are given a single class period to summarize their knowledge and to develop a lesson that includes (1) an organized, 5-8 minute oral presentation, (2) a graphical, conceptual model of their assigned element's soil-biogeochemical cycle, and (3) a list of discussion questions with which to engage their colleagues on the other teams. A second class session is used to refine and to expand upon the submitted models as necessary.

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This activity is most appropriate for upper-level undergraduate courses in Earth and/or Environmental Sciences; however, it can be tailored to introductory courses very easily.

Skills and concepts that students must have mastered

This type of assignment can be adjusted for any topic, but as written is meant to follow half-a semester's worth of modules explaining the basics of soil science, including soil genesis, mineralogy, hydrology, biology, soil organic matter, and microbial decay.

How the activity is situated in the course

This is a stand-alone activity that I introduce half-way through my one semester Principles of Soil Science course. It is meant as a chance to gauge student learning, and to encourage students to work together to develop deeper subject knowledge.


Content/concepts goals for this activity

The goals of this project are to explain (model) the mechanics and controls of biogeochemical cycles in soil environments; and to broadly illustrate linkages between soil nutrient cycles and environmental conditions.

Higher order thinking skills goals for this activity

Higher order thinking skills are needed to link factual knowledge into a dynamic concept model, and to link specific biogeocemical components and cycles to changes in environmental conditions. Furthermore, students must evaluate each other's work, and look for ways to improve or add detail to the presented models.

Other skills goals for this activity

This activity involves delegated group fact-gathering, in-class oral presentations, and peer review.

Description and Teaching Materials

Students summarize their existing knowledge and use textual resources to construct and explain a conceptual model of a particular element's soil biogeochemical cycle. Resources include the course textbook, notes, and web resources in public domain.

Student handout for Soil Biogeochemical Cycle activity (Microsoft Word 2007 (.docx) 22kB Apr29 13)

Teaching Notes and Tips

Given that the outcome of this activity depends largely on student participation and preparation, the instructor must carefully build towards this activity over several weeks, and ensure that reading assignments are adequately completed. During the activity the instructor must circulate between groups to ensure adequate student understanding and participation. Groups should be established to balance more advanced students with the less-experienced.

A second class session will be necessary if presentations run long, and is anyways needed to carefully critique the biogeochemical models for accuracy and expected level of detail. Anonymous peer review and detailed discussion of changing chemical conditions are optional components of this activity.


Groups are evaluated by the instructor based on their presentation, their model, and their questions to the class. If peer review is a desired component of this activity, critiques and ratings from the other groups can also be weighed in evaluating group performance.

References and Resources

Resources can be chosen based on instructor preference. This activity was designed with Brady and Weil, 2007 "The Nature and Properties of Soils" in mind as a required course textbook.