Lab: Soil Composition and Soil Erosion
Part I: Soil Composition Analysis
Materials:
3 glass jars
soil samples from 3 different locations
water
a sieve (screen or mesh, optional)
microscope (optional)
Procedure:
Follow these instructions and keep a written record of precisely what you do and do not do. The record should be detailed enough that someone else could perform the same procedure just using what you have written.
1. Collect soil samples from three different locations. The locations should be obviously different from each other in terms of vegetation composition (the amount of plant growth) or geological origin. For instance, you can get one from your back or front yard, one from a garden, and one from an area without much plant growth. You only need enough soil to fill a quarter of the jars you are using.
2. Label the jars so you know which jar contains the soil sample from which location. Fill about a quarter of the jar with the soil sample.
3. Fill the jars with water.
4. Put the lid on the jar and shake each jar vigorously for 2 to 3 minutes or until the soil is totally loosened up (falls apart) and let it sit until all the particles (sediments) settle. Depending on your soil composition, this may take some time since the smallest particles will settle very slowly.
5. There should be different layers of sediment in the jars. Measure the thickness of each layer and figure out the ratio of each layer. The thickness of the sediment layers and their ratio determines the soil composition.
Note: Remember the particle size for gravel is between 10 to 2 mm in diameter, the particle size for sand is 2.00 mm 0.05 mm in diameter, 0.05 to 0.002 mm in diameter is for silt, and clay’s particle size is smaller than 0.002 mm in diameter.
6. Compare the soil composition of the 3 jars.
7. You can “screen” the sediment layers and observe them under the microscope to determine their sizes if you have access to a microscope. If not, you can determine the soil texture by the feel method. You can find the method here: SOIL TEXTURE FEEL TEST (pdf file)
Part II: Soil Erosion
Materials:
1 cup of topsoil, sand, clay, gravel, and rocks each (for procedure 1)
3 cups of top soil (for procedure 2)
6 cups of sand (for procedure 3)
enough soil to make 2 little mounds (for procedure 4)
tissues
2 -3 bottle caps
water
water hose or watering can with sprinkle head
Procedure:
Follow these instructions and keep a written record of precisely what you do and do not do. The record should be detailed enough that someone else could perform the same procedure just using what you have written.
1. Mix one cup each of the topsoil, sand, clay, gravel and rocks and pat it into a bread loaf like shape. Water it evenly across the top (simulate the way actual rain falls as closely as you can). Observe and record what happens.
2. Shape one cup of topsoil into a little mound and press the bottle caps into the top of the mound. Water the mound simulating rain with a water hose or watering can. Observe and record what happens.
3. Make two mounds of sand of similar sizes. Put a tissue on top of one mound to simulate grass. Water the mounds simulating rain. Observe and record what happens.
4. Make one mound with loose soil and another one with packed soil. Water them, observe, and record what happens.
Analysis Questions:
1. Were there obvious differences among the soil composition from your soil samples? Explain what they were.
2. What did you learn about the relationships between the soil composition, the other factors, and the rate of soil erosion?
3. What do you think we can do to prevent soil erosion?
– Submit a report of your procedure and the data you collected. Use paragraphs with complete sentences and proper English grammar. You do not need to submit your data sheet, those are for your own convenience, but the information you collected should be part of your report.
– Submit your data analysis. Be sure that your analysis addresses the questions and directions listed in the instructions above. Also record any other conclusions you have reached. Use paragraphs with complete sentences and proper English grammar.
