Activity: Soil and Erosion Objective: To examine the effects of rainfall-induced erosion on bare soil versus vegetated soil. Grade level: 6 th Format: Lab experiment Materials: Per student or student group 2 aluminum or plastic pans (at least 2 cm deep and sturdy; I used 8 in by 8 in aluminum cake pans set in a large plastic tub then raised the tub on a block so that pans would be the same height), block or book to raise pans 5-6 cm, loose soil, square of sod (I couldn t find sod so bought some groundcover plants instead), paper cup, sharp pencil (or scissors), 100 ml beaker, water. Materials available in grocery stores and nurseries. Total cost of supplies was about $25. Description: This is a great scientific inquiry activity, especially for a discussion of controlling variables. In the experiment, students have to control the amount of soil in both trays, the amount of water and the way it falls on the two soils, and the slope of the land surface. We also had students write hypotheses, then evaluate their hypotheses based on the results of the experiment. Lab procedure: Students set up the experiment in two aluminum pans (for detailed instructions, see attached student handout). One pan contains loose soil whereas the other contains sod or other soil with plants and roots. Pans are raised several cm (raised end contains soil or sod). Next, students use a paper cup with holes in the bottom to create rain on each of the soil types. The loose soil washes to the bottom of the pan, but the sod looses very little soil. Setting up and performing the experiment takes 15-20 min. Words of wisdom: I was unable to purchase sod, so I bought Lobelia plants; I think just about any type of plants sold in individual containers would do, as the important thing is that the soil is bound up by the root system. Be sure to tell students not to make the holes in the paper cup too large 4 holes made by once scissors blade or the tip of a sharp pencil seemed to work best. Depending on how much loose soil you use, it may take more than 100 ml of water to saturate the soil and cause it to wash down the pan. Finally, you might want to have a large tub handy for disposing of the used soil. I let students take the plants home after the experiment. Modifications: Because several variables must be controlled in the experiment, it could easily be modified to investigate one or more of these other variables for example, raising pans to different heights to study effects of slope on erosion, compacting one sample of soil, changing the duration or hardness of rain on the soil, or even using different types of soil. Resources: This activity was adapted from Save that soil in Science Explorer: Environmental Science (Teacher s Edition), Prentice Hall, Needham, MA: p. 120E. Your name and Fellow year: Heather Petcovic, 2000-2001
School or outreach event where activity was used: Gregory Heights Middle School, Portland
Name: Date: Period: A. What is soil? SOIL AND EROSION Soil is a mixture of air, water, and small pieces of inorganic and organic material. Soil is difficult to describe because it is changing all the time due to weather, plants and animals, and human activity. Inorganic (non-living) parts of soil are: Organic (living or formerly living) parts of soil are: B. A soil profile: Soil forms into different layers. If you dug a deep hole in the soil you would see the different layers, which is called a soil profile. The layers in a soil profile are called: Duff: Topsoil: Subsoil: Parent Material: Bedrock: C. Erosion: Erosion is the wearing away of soil by wind, water, gravity, or human impact. It occurs naturally but can be made worse by human activities such as farming, logging, and mining. The most common type of erosion happens when soil is washed off a slope by rainwater. What are some factors that control how much soil is washed away by rain?
D. Erosion Activity: In today s activity we will investigate how rainfall affects soil erosion on different types of land surfaces. We will compare the erosion of bare soil to erosion of soil covered with vegetation. PROCEDURE 1. Read through the entire lab procedure, then answer the pre-lab questions. 2. Place the two aluminum dishes side by side in the plastic tub. 3. Place a handful of loose soil along one side of the aluminum dish. Do not push down on the soil! 4. Place a piece of sod along the edge of the other aluminum dish. 5. Raise the long side of the plastic tub (the side containing the sod and loose soil) up 5-6 cm by placing it on a book. 6. Construct your rainmaker (this controls how much rain falls on the soil) by punching 4 or 5 SMALL holes in the bottom of a paper cup. 7. STOP!! Check with your teacher that you have set your lab up correctly before you do anything else! 8. Let it rain! First test the loose soil. Pour 100 ml water from the beaker into the rainmaker and observe the effects of the rain on the soil. 9. Repeat step 7 with 100 ml of water falling on the vegetated soil. 10. CLEAN UP your table and work area. 11. Answer the follow-up questions. E. Pre-lab questions: 1. Write a question that expresses the purpose of this experiment what are we trying to find out? 2. Write a hypothesis that predicts what will happen during the experiment. Remember that a hypothesis is a testable, if-then statement.
3. What are the variables that we have to control in the experiment? 4. What is the manipulated variable in the experiment? F. Follow-up questions 1. Briefly describe what you observed in each tray during the experiment. What effects did the rainwater have on the soil in each tray? 2. This experiment models soil erosion. What does the experiment tell you about the effects of rain on loose soil in the real world. 3. How could scientists and farmers use the information from this experiment to prevent erosion? 4. Suppose you want to investigate the effects of a different variable on erosion (for example, slope steepness, soil compaction, soil type, or kind of rain). Choose one variable and describe how you would change the experiment to study it.