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How Does Moisture Affect the Color of Soil?

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Talk It Over

What color is the soil in your yard, in the park, by the beach, or the lake? When it gets wet, does its color change? How? Why?

Get

  • Soil samples (take along small jars or ziptop bags, trowel or spoon, and a ruler)
  • Marker
  • Small baking dishes, 1 for each sample
  • Tablespoon
  • Cookie sheet
  • Oven
  • Camera (digital or film)
  • Access to a computer or photocopier (to make black-and-white pictures)
  • Grayscale (see "How to Make a Grayscale" in Part III)
  • Water
  • Measuring cup
  • Spoon

Go

  1. In jars or ziptop bags, collect small samples of soil from places near your home or school. (Be sure to ask permission.) Label each sample with a letter of the alphabet so you don't get mixed up. Keep good records. Write down where you got each sample and how deep you dug (use a ruler!).

  2. Using the marker, label small baking dishes with the same letters as your samples. Put 2 tablespoons of each sample in its labeled dish. Put the dishes on a cookie sheet.
  3. Ask an adult to put the dishes in a warm oven (about 150°F). Leave them for several hours. This will bake the water out of your samples. Remove and let cool.
  4. On a white piece of paper, write the letters of your samples. Put a teaspoon of each soil sample next to its letter.
  5. Take a picture of the paper and samples. Use your computer to print a black-and-white copy, or make a black-and-white picture on a photocopier.

  6. Compare the colors of the soils to the grayscale. Assign each soil a number from the grayscale that matches its color best.

  7. Add ¼ cup of water to each of the soil samples left in the baking dishes. Stir with a spoon to mix well.
  8. Repeat steps 4–6. Did the soils change color? How? Did some soils change more than others?

Stay Safe

Let an adult use the oven for you, and don't touch the baking dishes until they cool. You might burn your fingers!

Go Easy

Compare potting soil and sand. Use the grayscale to compare their colors when dry and wet.

Go Far

Online or in your library, find out about the Munsell system for describing the hue, value, and chroma (intensity) of colors. Use the system to compare and contrast soil samples taken from different locations or from different depths at the same location.

Expand your project by testing for different compounds in soil using soil test kits available from gardening centers and scientific supply houses. Does soil chemistry relate to color?

Show Your Results

Put numbers in a data table like this for "Go" and "Go Easy":

Soil Tested Dry Grayscale Value (1–10) Wet Grayscale Value (1–10)
     
     

For "Go," display your wet and dry samples, along with maps of where you collected them. For both "Go Easy" and "Go," make bar graphs that compare the grayscale values of wet and dry colors for each sample.

For "Go," subtract the dry grayscale value from the wet grayscale value to measure how much each sample changed and reveal which sample changed most. Try to explain any similarities and differences you find.

For "Go Far," display the Munsell system along with your samples and data tables. If you use a soil test kit, display your results. Try to explain the similarities and differences you observed.

 

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