Initial Publication Date: January 13, 2021

Elaborate: What do soil Microbes do for You?

Part A. Measuring Soil Microbial Activity

Key point: Soil life depends on and contributes to the carbon cycle.
Time required: Two to seven 50-minute class periods. 

Description: The following lesson set examines how soil microbes, such as bacteria and fungi, are involved in carbon cycling. Students design experiments to explore the relationship between microbial respiration rates and soil variables such as temperature, habitat, soil type, and agricultural management choices. Four methods for measuring CO2 released from soil are provided, one in the field (CO2 probe), and three in the lab (CO2 probe, bromothymol blue (BTB) and acid-base titration).

Click the link below to access the complete teacher's guide, background materials, PowerPoint presentations, and student handouts. Clear simple background reading is available in the student materials Great Lakes Bioenergy Research Center Microbial Life activity. Note: Instructors will need to go to the website and download the full package of materials to access the supplemental materials and handouts. 
Measuring Soil Microbial Activity

Part B. Decomposition as an indication of microbial activity

Students complete the Tea4Science activity they started in Module 1. The investigation involves burying a tea bag and recovering it after three months and measuring its decomposition rate. Note: Instructors will need to start this activity several months ahead of the module or have students bury the tea bags and return later in the term to complete the investigation.

Alternate Activity: Bury your Undies

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Soil your undies video
Educators may choose to bury undies or another cotton fabric, as described here. How active is your soil? Try the underwear test.


Part C. Soil Glue

Key point: Soil life contributes to soil structure. 
Time required: 30-minutes 
Description: A well-structured soil has clumps (aggregates) that are held together by microbial "glue" which consists of microbial gums, glues, and fungal hyphae. In this activity, students test soil samples to see how strong the soil aggregates are using this simple aggregate stability test. This activity includes background, activity instructions, student worksheets, and evaluation questions.
Soil Glue (Acrobat (PDF) 2.8MB Dec17 20) 
Discussion questions are included in teaching materials.

Note: this activity was also included in Module 2 – as a demonstration of physical properties of soils. Now that students have a better understanding how soil microbial life influence soil properties repeat the activity with a new focus.