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Soil Ecology

based on 6 ratings
Author: Lynsey Peterson

Grade Level: 5th - 12th; Type: Life Science

Objective:

Student finds and identifies invertebrates in soil samples to determine which soil has greater biological activity.

Research Questions:

  • What organisms are found in soil?
  • What are nematodes?
  • What role do nematodes play in soil?
  • How do soil organisms help plants grow?

Though it may appear to be only dirt, soil is actually a complex ecosystem composed of living and nonliving parts. The soil ecosystem is based on plant roots and decomposing organisms, which are eaten by fungi and invertebrates. Healthy soils have many invertebrates that recycle nutrients in decomposing organisms so that plants can use the nutrients again. In this experiment, the student will discover the organisms present in soils. Based on the number and variety of organisms found, the student will compare the soil samples to each other.

Materials:

  • Shovel or spade
  • Bags or containers to hold soil samples
  • Window screening, fine wire mesh, or cheesecloth
  • 3 funnels (or 3 gallon jugs to make funnels)
  • 3 lamps
  • 3 jars that funnel can fit on top of
  • Magnifying lens and/or dissecting or digital microscope

Experimental Procedure:

  1. Obtain soil samples from outside. Choose three different locations with different plant communities. Keep the soils from different locations separate and place them into labeled containers. Make sure that the sample comes from the top portion of the soil (not deep in clay, etc.). Obtain about 4 cups of soil for each sample. Bring the soil samples inside. Write down a hypothesis as to which soil will contain the most organisms and the most species and why you think so. 
  2. Set up three stations with a light/heat source. Label three jars with the names of the soil samples. Put enough water in each jar to adequately cover the bottom (about a ¼ inch of water). 
  3. Obtain or create your funnels (using gallon jugs as described in the fourth link in the bibliography). For each funnel, cut a piece of screen, mesh, or cheesecloth (4 layers thick for cheesecloth). Place the screen, mesh, or cheesecloth in the funnel and press down. Hold the funnel with cheesecloth over the trashcan and pour one of the soil samples into it. Carefully place the funnel over the correct labeled jar and place it under your light/heat source. Repeat with the other soil samples.
  4. If you find any earthworms or other large invertebrates while placing the soils into the funnels, remove them and record the number and type in your results. Return the organisms outside where they were found.
  5. Turn on the lamp and make sure that the lights are centered over the soil sample. Leave for 1-4 days. The heat and light from the lamp will drive the organisms down and through the funnel into the water below. Once the soil samples are completely dried out, you may proceed.
  6. Turn off the lamp. Remove the funnel setup. Place the soils back into your collection containers. Take your jars and observe the organisms inside. You can pour the water and organisms into shallow containers for easier viewing. Use a magnifying glass and/or a microscope to view the organisms. 
  7. Count the number of each type of organism for each soil sample. If you can identify the different species (nematode, tardigrade, springtail, etc), that would be helpful. If not, just record descriptions of the different types of organisms. Return the organisms to the soil samples and place outside where they were found.
  8. Create a bar graph showing the total number of organisms and total number of species for each soil sample. Compare your results to your hypothesis.

Terms/Concepts: Soil macroinvertebrates; Soil organisms; Soil ecology; Nematodes; Tardigrades; Earthworms; Berlese funnel; Soil food web

References:

 

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