This lesson is designed to take place outside
Students will be digging in soil to make educated guesses about the amount of organisms in soil, and they will be making their own soil mixes out of sand, humus, and clay. It will get messy!
Alternative options in case of rain: you can bring the soil inside of the classroom with ample newspaper or butcher paper to lay out for easy cleanup. Keep soil inside of containers, and have a large container of soil directly from the garden for the soil life activity.
|NGSS 2-LS4-1 Compare the diversity of life found in different soil types or in different areas of the same soil type.
NGSS 3-LS4-3 What soil type is best for growing vegetables? What types of life do you find in different areas of soil?
For this lesson you will need:
- Hand trowels (1 per group of 4 students)
- Magnifying glasses (1 per group of 4 students)
- Copy of Soil Organisms in One Square Meter of Soil
- Copy of ID Soil Organisms
- Copy of Which Soil Is Best? Student Lab Sheet, enough for each group of 4 students to have 1 lab sheet.
- Set up an outside station for the sensory soil activity. Set out three containers with different types of soil for each group: clay, sand, and humus. If your garden has multiple picnic benches you can set up a container of each of the three soils at each table. Students could also sit with their groups on the ground around the three containers of soil.
- Have the Soil Mixture Experiment supplies organized ahead of time to be passed out to students at their stations.
- Set up three chimneys as in the diagram below. Add an equal amount of a different soil to each one ie. one sand chimney, one clay chimney, and one humus chimney. Label each of the soils (sand, clay, humus)!
Begin with a classroom discussion in the seating area in your garden or in the classroom. Elicit students’ ideas about soil by holding up a jar full of soil. Write the following bolded questions on the board, record answers, and discuss with the class:
What ingredients make up soil? Many students will list among their ingredients “dirt” or “brown stuff”. Challenge them to figure out what the brown stuff is. The simplest answer: It’s just smaller pieces of all the other ingredients: crushed rocks, crumpled leaves, twigs, bugs, sand, and so on.
How important is soil? Soil grows the food that all creatures depend on! It is also the habitat for decomposers, which are a vital part to the nutrient cycle and help convert all of our “dead scraps” into usable matter again. Do you think all soils are alike? In nature, soil types greatly influence the kind of plants that grow in an ecosystem. Cacti seem to thrive in sandy soil while dandelions do well in clay soil.
How is soil created? Can we manufacture soil? What explains how rocks, branches, leaves, sand, and other natural materials develop into soil? (Cause and Effect; Construct Explanations and Design Solutions). Explain that each inch (2.5 cm) of topsoil requires more than 100 year to form, by the processes of weathering and decomposition. Our hands and tools cannot equal the power of weathering and decomposers!
Take a hand raising survey
How many of you believe that there is life inside of soil? Is soil alive? Who/what lives inside of soil? We are going to find out!
Divide the class into groups of four students. Explain that each group is going to estimate how many organisms live within one square meter of soil. How long is a meter? What does a square meter indicate? Using student responses, draw a cube on the board showing the dimensions of a cube meter. Brainstorm how students could estimate the area of one square meter using their bodies. (Each group of 4 can stand in a square with each of their arm spans extended out to a 90 degree angle.)
Instruct each group to find an area of the garden and create a square meter. Provide each group with 1 hand trowel for them to observe the soil in their area. Instruct students to not try to dig up a square meter, but rather estimate through digging a smaller area. Within your square meter, how many organisms do you think live in the soil? Remember your square meter also extends down.. how many feet? You may use your hand trowel and magnifying glasses to dig and observe.
Call students back to the group and discuss their observations and estimates. What living creatures did your group find within your square meter? How does that organism contribute to the soil? Who else might live in the soil that we cannot see? Ask students to take 30 seconds to discuss with their groups how many total organisms live in one square meter of soil on average. Record each group’s guess on the board.
Show students the large laminated copy of Soil Organisms in One Square Meter of Soil and ID Soil Organisms. Point out organisms and numbers, starting from the top of the pyramid down. Did anyone see this living creature? Do these numbers surprise you? What do the vertebrates eat in this pyramid? We are looking at the soil food web, comprised of organisms eating decomposing matter and returning nutrients to the soil!
Soil is alive!
With more than 100 billion microorganisms living in a pound (0.45 kg) of soil, in addition to the roots, insects, worms, and other living things we can see in the soil. There is no recipe that could duplicate this substance so full of life and so necessary for life.