Soil Biota

Katherine McCarville, Upper Iowa University

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In teams of two, students collect samples from one or two different environments -- agricultural fields, sports turf areas, lawns, forest floor, wetland/pond margin, greenhouse, etc. They construct a Berlese funnel apparatus, process their two samples, identify and photograph (under a microscope) the organisms they isolate. The class aggregates their data from all the different environments, calculates a Simpson's diversity index for each environment, and uses this value to compare the diversity of the different environments.

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Upper division soil genesis (USDA Soil Taxonomy) course

Skills and concepts that students must have mastered

No specific prior experience is required. I find that almost everything about this activity is new to most students.

How the activity is situated in the course

I teach this course starting in mid-October through mid-December, so it is the first lab we do, to ensure that we find lots of active organisms.


Content/concepts goals for this activity

--Students achieve a far greater knowledge of soil biota than they start with
--Students learn to document their observations with photographs (using a microscope and including scale)
--Students compare diversity among different soil environments by calculating a diversity index
--Students draw conclusions regarding the relative diversity among the environments that are compared

Higher order thinking skills goals for this activity

--Once we decide what environments we will sample, we develop a hypothesis by ranking the different environments in order of increasing/decreasing diversity
--Analysis of data involves calculating an index (I use Simpson's) to quantify diversity
--Identifying the factors that affect diversity of soil biota is especially interesting in the case of the greenhouse samples -- where there are factors that might promote OR reduce diversity

Other skills goals for this activity

Field notes, sample numbering, use of the microscope and camera, including a scale in microphotographs, working in groups, use of a binomial key and web resources for identifying the organisms, writing the lab report

Description and Teaching Materials

As a group, we begin the activity by establishing an hypothesis that the diversity of soil organisms will be influenced by the environment. We discuss some of the factors that may affect biodiversity of soil organisms. The hypothesis is just a ranking of the different environments from high to low anticipated diversity. In our case, we write the ranked list on the board in the lab and it stays up until we complete the activity.

We review some of the "likely suspects" that we may find in our samples and take a quiz.

Student handout for Soil Biota lab (Microsoft Word 38kB Jun9 13)

Each team of two students (if there needs to be a team of three, assign them more samples) collects two samples and processes them over the course of a few days. Each sample requires about 24 hours in the Berlese funnel. Students record their team results in a table on the board in the lab.

Students take the photographs of the most interesting of their organisms -- each student should have at least one organism that they selected and photographed. We look at these together, and discuss the results -- did our results support or refute the hypothesis? Why? What factors might we have missed that would influence the diversity or abundance of soil biota? Each student writes up the lab individually.

Student handout - lab writeup instructions (Microsoft Word 2007 (.docx) 16kB Jun9 13)

Teaching Notes and Tips

I like to offer a "prize" to the teams reporting the largest total number of organisms, and the largest number of taxa -- usually a small gift certificate to a restaurant or coffee shop.

Wrapping this back to looking at nutrient availability and other factors that might affect abundance and diversity of organisms would be a potential opportunity.


References and Resources