ED-STEEP: Education Solutions to Environmental
and Economic Problems
Soil Organic Matter and Biodiversity
Subjects
Biological Sciences, Environmental Sciences, Agricultural Sciences
Introduction
In this lesson, students will conduct a research project to explore the soil ecosystem. Most
students know very little about soil systems and quickly become fascinated with the complexity
and diversity of soil invertebrates. The lesson is designed as a comprehensive experiment,
including the development of hypotheses and methods, field research, lab activities, data
analysis, and lab reports. However, it can be modified easily to fit into any classroom format.
Extracting and examining soil invertebrates is an excellent activity by itself. Related lesson
plans include the following:
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Biodiversity of Ground-dwelling Arthropods
Biodiversity of Soil Invertebrates
Soil Organic Matter
Soil Chemistry and Physics
Relevant STEEP Research Projects
Several STEEP research projects focus on soil organic matter and soil biodiversity, because both
are essential for healthy soils and productive ecosystems. Scientists at Washington State
University, University of Idaho, Oregon State University, and with the U.S. Department of
Agriculture are conducting studies to define the role of soil organic matter and soil biodiversity
in agroecosystems, trying to figure out ways to preserve and enhance soil organic matter so it can
be used to improve plant growth, and are studying ways organic matter can be used as a carbon
sink to minimize the effects of global warming. Here are some highlights of their research:
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Tilling soil can greatly decrease soil organic matter, soil carbon, soil nitrogen, the activity
of microorganisms, earthworms, and populations of beneficial insects.
One way for farmers to improve soil quality (i.e., increase organic matter, enhance
biodiversity) is to use no-till methods where seeds are planted directly into the ground
without tilling the soil. This also reduces soil erosion from wind and water, reduces air
pollution, improves water quality, can reduce global warming by keeping carbon in the
ground, and enhances biodiversity.
Additional research highlights and links to research reports can be found at:
o STEEP Research Summaries
Objectives
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Students will define soil organic matter and its function in terrestrial ecosystems
Students will measure the soil organic matter content of different soils
Students will define biodiversity and its function in terrestrial ecosystems
Students will estimate and compare the diversity of soil organisms in different soils
Students will conduct an experiment to determine relationships between soil organic
matter, habitat type, and biodiversity of organisms in soil
Major Concepts
Biodiversity, Classification, Invertebrates, Nutrient Cycling, Scientific Method, Soil Ecosystems,
Terrestrial Ecosystems
Standards
AAAS Benchmarks
Idaho State Science Standards
Oregon State Science Standards
Washington State Science Standards
Materials
Print Resources
 Choosing a Sample Site and Preparing Soil Samples
 Diversity Data Analysis
 Soil Organic Matter Fact Sheet
 Soil Invertebrates Fact Sheet
 Soil Organism Picture Guide (MS Word file)
 Soil Organism Picture Guide (PowerPoint file)
 Constructing a Berlese Funnel for Collecting Soil Invertebrates
 Constructing a Baermann Funnel for Collecting Soil Nematodes
 Simple Soil Analyses (optional)
 Scientific Experiments and Lab Report Format
 Constructing Bar and Line Graphs
 Student Handout
Collecting Soil Samples
 soil and litter samples from 2 or more habitats (1 sample per student group)
 shovels, trowels, and/or soil corers
 ruler
 2 plastic bags per sample (1 for litter and 1 for soil)
 markers
Analysis of Organic Matter
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small containers for air drying ca. 20 g of soil (1 per sample)
mortar and pestle (or any other means of grinding soil samples)
1-mm mesh sieve or screen for sifting soil
balance with 0.01 g accuracy
crucible or ceramic boat to hold ca. 5 g of soil
kiln or combustion oven
Soil Invertebrates
 Trays or large sheets of paper for hand-sorting soil samples
 Berlese funnel (1 per group) and collection vessel with alcohol
 Baermann funnel (1 per group)
 Test tubes (1 per Baermann funnel sample) and Pasteur pipettes
 Water-agar plates for counting and examining soil nematodes
 Plastic petri dishes for examining invertebrates in alcohol
 Forceps, slides, etc., and microscopes for examining invertebrates
 Invertebrate picture key
Web Resources
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Ecological and Ecosystem Diversity, National Biological Information Infrastructure
Biodiversity Fact Sheet, Ecological Society of America
USDA National Resource Conservation Service - Soil Biology Primer. An introduction
to the living component of soil, intended as a resource for farmers and ranchers,
agricultural professionals, scientists, students, and educators.
USDA National Resource Conservation Service – Soil Organic Matter
USDA National Resource Conservation Service - Soil Quality Information Sheets. A
series of introductory fact sheets.
o Soil Quality Introduction
o Compaction
o Soil Biodiversity
o Available Water Capacity
o Indicators for Soil Quality Evaluation
o Organic Matter
o Aggregate Stability
o Infiltration
o Soil pH
General Procedure
The general producers involve collection litter/soil samples, extracting out invertebrates using
Berlese and Baermann funnels, sorting and identifying the invertebrates, recording data and
calculating diversity, determining soil organic matter content, and writing a report. Ideally,
students should be allowed to collect soil and litter samples in two or more different habitats.
However, this depends on the availability of suitable and readily available habitats, and the time
of year. Many different kinds of habitats can be used, including old fields, grasslands, alfalfa
fields, no-till crop fields, and forests. The more diverse the habitat and the more soil organic
matter, the more abundant and diverse the soil invertebrates. The time of year is also critical and
is best done before November and after April. Other times will also work depending on the local
climate. If habitats are not readily available and students can’t collect their own insects, then the
teacher can easily collect enough litter/soil samples for students. It takes less than a minute to
collect a single sample. Students enjoy making the Berlese and Baermann funnels for extracting
the invertebrates, which should take only 10-15 minutes. It takes about 3 days to extract
nematodes from the soil samples, and it takes about 1 week to extract other invertebrates with the
Berlese funnels.
Procedures
Preliminary
1. Plan on about 2 weeks to complete the activity (actual class time is 2-5 periods).
2. Follow the instructions in Choosing a Sample Site and Preparing Soil Samples for collecting
litter and soil samples.
3. Present students with information on soil invertebrates (Soil Invertebrates Fact Sheet),
biodiversity (Biodiversity Fact Sheet), and soil organic matter (Soil Organic Matter Fact
Sheet). Alternately, allow them to explore the topics on their own (see Web Resources).
4. Working in groups, have students write down a testable hypothesis relating habitat/soil
characteristics to soil biodiversity. For example:
a. biodiversity of soil invertebrates is greater in more diverse and complex habitats
because there are more food resources available
b. biodiversity of invertebrates is greater in forest soils than crop soils because there are
more plant species in forests to support more soil invertebrates.
5. Have students construct the Berlese funnels and Baermann funnels.
Collecting Soil Samples
6. Choose 2 or more sites to collect soil samples (see: Simple Soil Analyses). Either collect the
soil samples (1 per group) a day or two ahead of time, or allow students to collect samples, if
nearby sites are available.
7. Using a shovel or trowel, remove the litter and top 1 inch of soil from an area of ca. 1 ft2 and
place in a plastic bag, label, and store in a refrigerator or cool place for 1-2 days. Do not
leave the samples in the sun or the invertebrates in the samples may die.
8. Also remove a cupful of soil from a depth of 1-5 cm from each sample site. This will be
used for Organic Matter analysis.
9. Remove another cupful of soil from a depth of 1-5 cm from each sample site. This will be
used to extract soil nematodes from the soil.
Collecting Soil Invertebrates
10. Have the students place their own samples in the Berlese Funnel. Follow the direction in
Constructing a Berlese Funnel for Collecting Soil Invertebrates.
11. Have the students place their own samples in the Baermann Funnel. Follow the directions in
Constructing a Baermann Funnel for Collecting Soil Nematodes.
12. Remove the invertebrates, examine them with a microscope, classify them into morphospecies, and count them; See the Soil Organism Picture Guide and Student Data Sheet.
Organic Matter
13. Air dry the soil sample collected for the Organic Matter analysis. This will take about 2
days.
14. Using a mortar and pestle, break up the soil and pass it through a 1 mm mesh sieve
15. Place about 5 grams of air-dried soil in a crucible (or ceramic boat) and weigh; this is the preweight. Weigh to the nearest 0.01 g and record the weight in the data table.
16. Place the crucible with soil in a furnace or kiln and heat to about 360oC (680oF) for 3 hours
to burn off all the organic matter, leaving just the mineral soil.
17. After cooling, reweigh the sample again; this is the post-weight. Record the value in the data
table.
18. Calculate the % organic matter:
% Organic Matter = (pre-weight – post-weight)/pre-weight x 100.
Data Analysis
19. Have the students record the number of individuals within each group in the data table (the
data table in the Student Data Sheet will need to be adjusted according to the exact
experiment).
20. Have the students calculate species diversity (See: Diversity Data Analysis)
21. Have the students prepare a Bar Graph showing their results (Constructing Bar and Line
Graphs)
22. Have students discuss results and conclusions, or prepare a formal lab report (see: Scientific
Experiments and Publication Formats for Lab Reports)
Assessment
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Student Worksheet
Student Lab Report
Questions:
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What is a “morpho-species” and why is it used instead of real species?
Which habitat had the most and least individuals?
Which habitat had the greatest and least species richness?
List 3 hypothesis to explain why species diversity differs between habitats.
Is the data representative of the total diversity of the habitats? Why or why not?
What is the advantage and disadvantage of using species richness as an estimate of
diversity?
What would happen if the diversity of arthropods was suddenly reduced by 50%? 95%?
Does this type of experiment have a control?
Does diversity affect soil processes, such as decomposition and nutrient recycling?
What is the function of the different soil invertebrates?
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Explain the relationship between soil organic matter and biodiversity.