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: 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: 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 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 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 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 morpho- species, 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 pre- weight. 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 Student Worksheet Student Lab Report Questions: 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? Explain the relationship between soil organic matter and biodiversity.
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