Duration: 30 to 60 minutes
Vocabulary: sand, silt, clay, humus, texture, organic
Summary: Students will use different tools to explore the different parts of soil on school grounds, and if possible compare it to soil from another area.
Objectives: Students will learn about the different characteristics of soil, compaction, percolation, temperature, and texture, as well as the impacts these qualities have on plant growth.
Materials: hand trowels, magnifying glasses, steel percolations cans, water, cups, paper bowls, compaction dowel rods, thermometers
Soil is one of the most important parts of the natural world, but it is also one that we don’t usually think of! Think about it—soil supports almost all of the plants growing on this earth, and almost all of the things human have built are on top of the soil!
Soil provides nutrients and holds water for plants, which in turn feeds animals, including humans! Many different factors influence the soil. Soil in a forest may feel differently than soil in an open field or a wetland. It may also have different things living in it and water may move through it differently.
Soil is made up of sand, silt (the grain size between sand and clay), clay, and humus (decaying organic material). Different types of soil have different amounts of each of these “ingredients.” For example, a forest should have more humus in the soil than open grassland because of all the leaves and organic matter that fall off the trees onto the ground.
Wetlands have a special type of soil called “gleyed” soil. It is one of the biggest indicators that you are in a wetland! Gleyed soil is greenish-bluish-grey in color, and represents a waterlogged soil that is low in oxygen (oxygen is low because the area is filled with water–this makes the bluish colors).
You can test the texture of soil by taking a round ball of soil into your hand and squeezing it into a ‘ribbon.’ The longer the ribbon can stick out the top of your hand without breaking off, the more clay is present in the soil. The grittier the ribbon feels, the more sand is present.
Ask students what they think about soil. Is it what they bring into the house stuck to the bottom of their shoes? Why is it important? Do they think they need it to live?
Show students the different tools they will use to study soil qualities. Hold up each tool, explain what it is and show how to use it. Explain to students that they will be completing a few different activities related to soil.
Students will work in groups of two or more. Each group will have a trowel for digging, a magnifying lens, a steel can for the percolation test, a wooden dowel for the compaction test, and a thermometer to take the temperature. They should record their findings as they go.
Have students study different types of soil if possible. This could be done by giving some students a forested area while others have a grassy path, or by studying soil on school grounds and then in a different location on a field trip.
Have students dig up a small pile of soil into a small container and make observations (what is the texture? Are there roots or insects present? What color is it?) Encourage them to use descriptive words. Next, have students place their thermometers in the bottom of the soil and leave it there to adjust. While they are waiting, have them perform the compaction test. Have students try to push the dowel into the ground. If it is hard to push down, the soil is very compacted. If it is easy to push down into the soil, it is less compacted. If the wooden dowel goes into the soil, have them record how far.
Next is the percolation test. Have students press their steel cans about a half-inch into the ground (optional: marking a line on the side of the cans will be easier for this age group). Then, have students take the same amount of water, and all pour the water in their cans at once. Time this! Have students record how long it takes for all of the water to go into the ground. The longer the water takes to go into the ground, the more water is already present in the soil. The faster it goes in, the drier the soil was.
Have students share results. How do the results you found in one area compare to another?
Ask students to explain the main “ingredients” in soil, and what test they could do to see how much there is of each in a sample. Have them explain what the results of their tests they did tell about the soil they are studying.
Ask students to bring in soil from home and compare what they find. Ask them what might affect what the soil is like. How would animals living in the soil change it? What about plant roots?
What difference does temperature make in a soil?
Demonstrate the way water moves through organic matter (collection of dead leaves) and clay, and how they are different.