# Soil Porosity: Sand, Silt, and Clay

### Research Questions

• What is soil porosity and why is it important?
• How can porosity be measured?
• Which of the soil samples tested (sand, clay, and pebbles) has the greatest porosity?
• Which of the soil samples tested (sand, clay, and pebbles) has is the least pareses?
• Which particle size had the most amount of empty space? The least amount of space?
• Is there any relationship between particles size and pore space?

### Materials

• 3 metric measuring cups
• Water
• Permanent marker
• Soil samples: sand, clay and small pebbles (can be obtained from various field locations such as a rock quarry, road cuts, stream beds, etc.)

### Procedure

1. Fill one measuring cup to 200 ml with sand, the second cup with 200 ml of clay and the third with 200 ml with small pebbles.
2. Fill a graduated cylinder to 100 ml with water.
3. Slowly and carefully pour the water into the first cup until the water just reaches the top of the sand.
4. Pour slowly so no water spills out of the measuring cup. Record exactly how much water was used.
5. Use the formula below to calculate the percent porosity for the sand:

Porosity = (Amount of water added to sample ÷ Total sample volume) x 100

1. Repeat the same procedure with the clay and the pebbles.
2. Record the results in a table similar to the one shown

 Soil Type Total sample volume Amount of water added to sample Porosity Sand 200 ml % Clay 200 ml % Pebbles 200 ml %

### Digging Deeper

After measuring the porosity of sand and clay, make a mixture of these two samples by adding them together. Repeat the water addition procedure and calculate the % porosity then compare the results to that of the two individual soil samples.

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