This activity is used as part of an upper-level Fundamentals of Ecology Laboratory course, which is an undergraduate required course in the Life Sciences major. It is the only opportunity students in this course have to gain experience with soils and biogeochemistry.

Students must know the basics of ecosystem ecology that allow them to identify places of interest to sample soil. For example, we sample from under legumes vs. other plants (thus, they must know what a legume is and why it differs from other plants). Students are also expected to know the basics of the major biogeochemical cycles that were covered in lecture, but they could come in with no knowledge if more time is spent covering it in lab.

This is a standalone exercise that is in sequence with the nutrient cycles content in lecture, towards the end of the semester.

Understand heterogeneity of soils, understand how humans influence soils, understand the role of soil biology in soil fertility

Formulation of hypothesis about how soil samples will differ, critical thinking to discuss results

writing skills to communicate conclusions succinctly and effectively

Materials needed:
Stereomicroscopes (1 per group)
Trowels
Plastic bags for soil samples
Soil test kit (even a cheap one from the garden center will work) that can measure N, P, and pH
Squirt bottles of water
Rulers with cm markings
Pre-extracted microarthropod samples from the chosen locations
Ethanol
Soil moisture meter (optional)

Student Handout for Soil Ecology Lab (Acrobat (PDF) 205kB Apr13 13)
Answer key to the assignment (Acrobat (PDF) 24kB Apr13 13)

I start the lab with a brief lecture about soil formation, composition, and a reminder of nutrient cycling. We then discuss the sites we'd like to collect soil from, then collect the soil. Upon returning to the lab, I brief them on the importance of the topic of each section before completing that section's methods. Methods are put on the board for students to follow. After each section, I compile on the board the data for each sample and briefly discuss with the students the interpretation.

The assignment is designed for use in our desert ecosystem. We select soils from under a leguminous plant, under a non-leguminous plant, soil interspace not covered by a plant, from a manicured flower bed on campus, from the mowed/irrigated grass area, etc. To be useful in a different ecosystem, you need to select soil locations that you expect to be different in these basic properties. The main challenge students face during the activities is making the soil ribbons for texture. Encourage them to try many times and use the measurement from the longest ribbon and go table-to-table to demonstrate (otherwise they tend to not try hard enough and have ribbons that are too short). Identifying microarthropods would also be challenging, but I include a "cheat-sheet" with pictures of all the taxa present. They then only have to match what they see in the 'scope with what it looks like on the cheat sheet. I also have them tell me their results before putting it on the board, so that I can correct their identifications if they're way off.

Students have to submit a written assignment in which they answer the questions in the handout. Their answers demonstrate whether they understood the material covered.