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# Soil

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Source:
Author: Janice VanCleave

### Purpose

To determine the volume of air in soil.

### Materials

• Spoon
• 4 cups (1 L) soil
• 2 measuring cups marked in ounces and milliliters-one 2-cup (l6-ounce, 480-mL), one 1-cup (8-ounce, 240-mL)
• Tap water
• Writing paper
• Pencil

### Procedure

There are 4 ounces (120 mL) of air in the soil sample.

1. Use the spoon to put 8 ounces (240 mL) of soil in the larger measuring cup. Do not press against the surface of the soil as you gently add the soil to the cup.
2. In the smaller measuring cup, put 8 ounces (240 mL) of tap water. Slowly add this water to the cup of soil. Record the starting volume of soil and water as 16 ounces (480 mL) in an Air Volume in Soil Data table like the one shown.
3. Allow the soil and water to stand 2 or more minutes. Then read the volume on the measuring cup and record this measurement as the final volume in the data table.
4. Subtract the final volume from the starting volume to determine the volume of air that was in each soil test sample. For example, the starting volume (the volume of soil by itself plus the volume of water by itself) is 16 ounces (480 mL) and if the final volume (the volume of soil and water together in the cup) is 12 ounces (360 mL), then the volume of air in the soil sample would be calculated as follows:
• starting volume 16 ounces (480 ml) - final volume 12 ounces (360 ml) = 4 ounces (120 ml)
5. Discard the soil-and-water mixture, then clean and dry the measuring cup.
6. Repeat steps 1 to 5 three times.
7. Average the volume of air in the soil sample.

### Results

The volume of water and soil combined is less than the starting volume of water plus soil.

### Why?

Soil particles are irregularly shaped, and as they stack together there is space between them that fills with air. When soil and water are combined, the air between the soil particles is displaced (pushed out of the way) by water. When you subtract the final volume from the starting volume of soil and water, you get the volume of air that was displaced.

### For Further Investigation

Some soils have larger particles than others. The texture of soil depends on the size of its particles. A coarse-textured soil has large particles, and a smooth-textured soil has small particles. Is there more air in coarse or smooth soil? A project question might be, How does texture affect the amount of air in soil?

1. Repeat the investigation with soils of different textures.
2. Display soil samples in plastic jars with lids.
3. Examine the soil samples with a magnifying lens and make drawings to compare the sizes and shapes of the particles.

### References and Project Books

Campbell, Ann-Jeannette, and Ronald Rood. The New York Public Library Incredible Earth. New York: Wiley, 1996.

Farndon, John. How the Earth Works. Pleasantville, N.Y: Reader's Digest, 1992.

Parsons, Alexandra. Make It Work! Earth. Ocala, Fl: Action, 1992.

Potter, Jean. Nature in a Nutshell for Kids. New York: Wiley, 1995.

Redfern, Martin. The Kingfisher Young People's Book of Planet Earth. New York: Kingfisher Books, 1999.

Time-Life Books. Planet Earth. Alexandria, Va: Time-Life Books, 1997.

VanCleave, Janice A Janice VanCleave's A+ Projects in Earth Science. New York: Wiley, 1999.