Soil Temperature

What We're Doing

In this activity, you will measure and record the soil temperature at your field site over time.

Why We're Doing It

Soil temperature is one of the many variables that can affect the types of creatures and soil you find at your field site. By measuring and recording the soil temperature over a period of time, you can discover how it varies at your field site.

Making the connection:

Getting Our Hands Dirty

Hypothesize

What will the soil temperature be at your field site?

Plan it!

  • If you haven't already done so, choose a field site and map it in your field journal.
  • If you are doing this activity along with the Compaction, Percolation, and Texture tests, Air Temperature, or Cloud Cover, you should do all of the activities at the same time and place. If you haven't yet done so, decide how often to take soil temperature readings. If you are working with a group or as a class, you should decide together. As you decide, think about these questions:
    • How might your results be affected if you take daily readings?
    • How might your results be affected if you take monthly readings?
    • How might your results be affected if you take annual readings?
    Most scientists would agree that taking readings at least once a week will give you the most accurate record of changes in temperature over time.

Do it!

  1. Choose a spot in your field area in which to measure the soil temperature. If you are also measuring the air temperature, you should take air and soil temperature readings at the same place and time. You will need to take your soil temperature readings in the same spot and at the same time of day each time you do it.
  2. On your soil thermometer, measure 2.5 inches from the tip and mark the spot with the permanent marker or tape.
  3. Gently insert the soil thermometer in the soil until your mark is just touching the ground. You should try to take readings at this same depth each time.
  4. Hold the thermometer in place for two to three minutes in order to get an accurate reading.
  5. Remove your soil thermometer from the ground and store it in a dry place.

Record it!

  • Record the soil temperature on the Soil Properties worksheet . Be sure to mark the date.
  • If the ground is frozen, write "frozen" on your worksheet.
  • On the field site map you drew in your field journal, mark the spot where you took the temperature reading.

Remember, be sci-wise!

  • Do not allow the direct heat of the sun to warm up the thermometer. This could affect the temperature reading.
  • Store the thermometer in a cardboard tube when it is not in use, and take the temperature reading right after pulling it out of the tube.
  • If your results seem unusual, double-check them by taking another reading. If your results still seem unusual, try using a different thermometer.
  • Do not force the thermometer into the ground. If the ground is too hard or dry to insert the soil thermometer, try carving out a small hole with a pencil before inserting the thermometer. If the ground becomes crumbly, move a few inches away and try again.
  • Do not leave your soil thermometer outside for long periods of time. Soil thermometers should be stored in a dry place out of direct sunlight when not in use.

Thinking About It

  • How did the soil temperature at your site change over time? This will vary depending on where you are and the duration of your study.
  • Based on the data you collected, would you revise your hypothesis before testing again? Why or why not?
  • How did the soil temperature compare with the air temperature?
  • What were some of the possible variables that could affect the data?
  • Which of these variables did you control? How?
  • What patterns or links did you notice between the season and the soil temperature?
  • What patterns or links did you notice between the weather and the soil temperature?
  • If you continued taking the soil temperature for a whole year, what differences would you expect to find?
  • Looking at the bigger picture, how might this data help you to answer your research question?
  • Fill in this section of the Soil Properties Overview worksheet .

Still Interested?

If you liked this activity, try these:

  • Take the soil temperature in different locations in the field site, such as under trees, bushes, leaves, or bricks. Will the readings vary? What do you predict?
  • Take the soil temperature at different depths. For example, take the temperature at 2 inches down and then at 6 inches down. Will the readings vary? What do you predict?
  • To see how soil helps to keep us cooler in the summer, take the following temperatures each day for a week: soil temperature, surface temperature of grass-covered soil, surface temperature of blacktop and air temperature. After a week, graph your data. Which surface was the coolest each day? Which was the hottest? Looking at your graph, make a hypothesis about what the temperatures would be for each material if the air temperature went up to 100°. How does the concept of thermal mass explain the data you collected?

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