- Which Retain More Water
- Sand or Potting Soil?
- Help students soak up knowledge about soil with earthy investigation!
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- Purpose
- To observe how the texture of a soil affects how much water it can hold
Materials For The Teacher
- Clean, empty two-liter plastic bottle for each group
- Scissors
- 1/2 C. Measuring Cup
- 1/2 C. Sand for each group
- 1/2 C. Potting Soil for each group
- Two coffee filters for each group
- Materials for Each Group
- Download and print the Earth Science Data Collection Sheet
- 2 clear plastic cups
- black crayon
- 2 prepared coffee filters
- prepared funnel
- access to water and paper towels
- Liquid measuring cup
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- Background for the Teacher
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- A soil's texture affects its ability to retain water. Soils are made up of rock pieces and animal and plant materials. The size of the rock pieces helps determine the soil's texture. Soil with larger rock pieces is considered sand. Soil with smaller rock pieces is considered silt. Soil with the smallest rock pieces is considered clay. Soils made up of larger rock pieces have more space between the pieces, which allows water to drain off quickly. Soils made up of smaller rock pieces have less space between the pieces and retain more water.
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- Getting Started
- In advance, cut the tops from the palstic bottles to make funnels. Next, place half of a cup of sand and a half of a cup of potting soil on seperate coffee filters for each group. Begin the activity by showing students each type of soil and asking them to describe the chracteristics of each. Discuss students' responses and explain that they will conduct an investigation to find out which soil retains more water. Divide studenst into groups of four and give each group the materials listed above. Guide each group through the steps below to complete the investigation.
The Investigation
- Step 1 - Have each group study its soil samples and reflect on the question "Which retains- sand or potting soil?" Direct each group to formulate a hypothesis that answers the question and record it on the Data Collection Sheet.
Step 2 - Direct each group to use a black crayon to label one clear plastic cup "sand" and the other cup "potting soil." Have students place the bottle funnel in the plastic cup labeled "sand" and put the sand-filled coffee filter in the funnel as shown. Then have them measure one cup of water in the liquid measuring cup. On your signal, direct the group to pour half of a cup of water over the sand. Allow one minute for the water to drain through the sand.
Step 3 - Direct the group to repeat Step 2 using the coffee filter filled with potting soil and the other labeled cup.
Step 4 - Have each group compare the amount of water that drained through the sand with the amount that drained through the potting soil. Next, have the group use the liquid measuring cup to measure the water fvrom each plastic cup. Direct the group to record the data and then complete the results and conclusions sections on the data collections sheet. Set aside time for each group to share its findings with the class.
Case File Conclusion
Because the sand is made up of larger rock pieces than the potting soil, more water should drain through the sand. potting soil is made up of smaller rock pieces than sand. Students should observe that the water drains through the potting soil more slowly.
- Further Investigation
- If desired, continue this investigation by posing the following questions:
- Does wet soil hold more water than dry soil?
- Would a mixture of sand and potting soil hold more or less water than potting soil only? Why?
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