Illinois 4-H

Exploring 4-H Plants & Soils
Spark Activity: Soil Layer Cake

 The mineral components of different soil types are made up of different amounts of sand, silt, and clay particles. This soil activity demonstrates the different types and proportions of mineral particles that make up different soils. Compare two or more topsoil samples from diverse locations to see the differences in soil types found in your neighborhood. Topsoil is specifically the upper 2 to 6 inches of the land surface in which plant roots grow.

1. From two or more areas, collect a quart of topsoil from a garden, flowerbed, woodland, or field. Label each sample by location. Please note that potting soil will not work for these purposes.
2. Predict which site will have the most sand and which will have the most clay. Write down your predictions.
3. Empty the soils onto an old newspaper to dry. Crush lumps between your thumb and fingers as the soil dries.
4. After removing trash, rocks, and roots from the soil, label quart jars for each site and fill them ¼ full with dry soil from that site.
5. Add water until each jar is ¾ full.
6. Add a tablespoon of non-foamy detergent or soap to each jar.
7. Close the lids and shake hard for about three minutes. Keep shaking until particles are well separated.
8. Set the jars on a table and watch very closely for a few minutes. Make observations and write down what you observe.
9. Do not disturb the jars for two days.
10. Place an index card alongside the jars. Mark off the depth of the clay (top layer), silt (second layer), fine sand (third layer), and coarse sand (last layer). Label a card for each layer. Fasten the card to the jar with tape. Draw a picture of the layers that have settled out in the jar. Be sure to label each card for the correct sample site.
11. Compare the soils. How are they the same or different? Discuss your observations with a parent or helper.
12. What percentage of the soil is clay? Silt? Sand? (Example: # mm sand ÷ # mm total soil sample = decimal fraction of the sand. Now convert the decimal fraction into a percentage.)
13. Record your observations and calculations. Do you have any small plant or insect materials floating in the water?
14. How do the results compare with your predictions? Discuss what you learned about the components of soil with a parent or helper.