Percolation Test

Objective

In this activity, students will measure and record how long it takes water to soak into the soil at the selected field site, and then use these data to infer the degree of compaction of the soil.

Making the connection:

Activity

Hypothesize

How well does the soil at your field site drain? How compacted is the soil at your field site?

Plan it!

  • If you haven't already done so, choose a field site and map it in your field journal.
  • You also need to decide how many times to repeat the test. Before you begin, think about these questions:
    • How might your results be affected by the number of measurements you make?
    • Will you be more certain that your data are right if you do the test one time or many times?
  • Prepare your can before going into the field:
    • Remove both ends of the can.
    • Use a metric ruler to measure 3 cm from one end of the can, and then draw a line around the perimeter of the can using a permanent marker.
    • If you are working with a group or as a class, be sure to spread out over the field site. When you arrive at the field site, each student or group of students should set up a quadrant in which to work. If you are doing this activity with the Soil Temperature Test, Compaction Test, and the Texture Test, you should do all four activities in the same quadrant.
      Doing all four activities within the same quadrant allows students to put the results of all the tests together to form a more complete picture of the soil. By spreading out over the field site, students create an opportunity to compare results from different areas within their field site, to note differences and similarities in the soil properties, and to get a more representative sample of the entire field site.

Do it!

  1. Push the can 3 cm into the soil, until it reaches the line encircling the can.
  2. Pour water into the can until it reaches the top. Once you start pouring, be sure to fill the can quickly. Don't let the water overflow the can.
  3. Immediately use a stopwatch to measure how long it takes for the water to soak completely into the soil. If you do not have a stopwatch, you can use the second hand of a watch.
    Because timing is important here, it is a good idea for students to work in groups of two or three. One student can pour the water, while another watches and begins timing as soon as the water has been poured.
  4. Repeat this test several times in different spots within your quadrant.

Record it!

  • On the Soil Properties Data worksheet , record how long it takes for the water to soak into the soil for each test you do.
  • Record the average time on your worksheet.
    If students need a review of averaging, this can be done in the classroom either before or after the field study.
  • If the ground is frozen, write "frozen" on your worksheet.
  • Add the worksheet to your field journal.

Remember, be sci-wise!

  • The safest way to remove the end of a can is to use a can opener. If you are not used to using a can opener, ask an adult to help.
    It is best if you can prepare the cans for students or ask parents to send in prepared cans.
  • Use a water container that will allow you to pour water easily, such as a pitcher or a large water bottle.
    Empty soda or juice bottles with lids would work well.
  • It is important to pour water into the can as quickly as possible once you start in order to get an accurate time measurement.
  • You'll need to bring enough water to your field site to complete your tests. To be sure you have enough water, pour water into a large container using a can the same size as the can you prepared for the test. Add one can of water for each test you will do.
    To save classroom time, you can fill soda or juice bottles before class.
  • You'll need to prepare for dirt and mud that will be brought back on students' shoes. Consider having students bring in an old pair of sneakers or boots to use for your field activities. Students can leave their dirty shoes "at the door" and then shake or brush them off when the mud has dried.

Assessment and Reflection

  • Did the water soak into the soil quickly or slowly? What does this tell you about the soil compaction at your site? You can read about soil compaction and what it means at the Soil Properties Overview page.
    Students should understand that water will flow faster through lightly compacted soil and more slowly through highly compacted soil.
  • Based on the data you collected, do you think your hypothesis was correct or incorrect? Why?
  • How did your data compare with those of other students at other areas of the site?
    Results will vary according the overall composition of the soil at your field site. If some sections contain more clay than others, for example, students in that area would have very different results from students whose quadrant contains more sandy soil.
  • How do your results compare to the Compaction Test results? Would you expect the results of both tests to be the same or different?
    Both tests measure soil compaction and should therefore yield similar results.
  • How might the weather or season affect the data?
    If the ground is frozen or nearly frozen, that might make it more difficult for water to flow through the soil and to push the can into the soil. If the ground is extremely saturated, water might not soak into the soil as quickly as it normally would.
  • What other variables might affect the data? How?
    Some possible answers include soil temperature and soil saturation.
  • Now that you have measured the soil compaction at your site, would you expect to find many soil critters there or just a few? What kinds of critters would you expect to see?
    This answer will vary based on the site. In general, you would expect to find greater number and variety of creatures in soil that is less compacted. This is true because soil that is less compacted has more room for the air and water that organisms need to survive.
  • Based on the soil compaction at your field site, do you think it might be a good place to start a class garden? Why or why not?
    Again, this answer will vary. In general, soil that is less compacted is more hospitable for plants, especially garden plants, although various plants are adapted for growth in highly compacted soil.
  • Looking at the bigger picture, how might the data you collected here help you to answer your research question?
    Answers will vary based on the research question, but students should begin to connect the data they gathered in this activity with data from other activities to answer their question.
  • Fill in this section of the Soil Properties Overview worksheet .

Extensions

  • Have students brainstorm several factors that might affect how quickly water soaks into the soil. For example, the type of soil or how wet the soil is to start with might make a difference. Have students choose one of these variables and design an experiment to test it. They should use the Percolation Test as part of their experiment. What will the hypothesis be? The controls? How many times will they repeat the test? How will they record the data?
  • Have students conduct the Percolation Test at three different locations and note the differences. They should record the date, weather, and the time of day. Which site had the best drainage? The worst? Why? If you are in an urban area, have students conduct the tests at three different vacant lots. How might human actions have affected the compaction of the soil at the vacant lots? How might this affect plants and animals?
  • Ask students to come up with some similes to describe what it would be like to move through the soil when it is highly compacted and when it is not. For example: Moving through highly compacted soil is like _______________. Then, have them try some analogies. For example: Moving through highly compacted soil is to moving through lightly compacted soil as moving through _______________ is to moving through _______________. Challenge students see how many they can come up with!

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