FOCUS: Life abounds in the soil, from plant roots to earthworms to moles and millipedes. All these organisms play important roles in the flow of energy and matter through an ecosystem. Many soil critters act as decomposers, breaking down plant and animal materials and returning them as nutrients to the soil where other living things may use them again. The soil is a rich ecosystem teeming with life in a complex food web.
Objective: To begin to explore and ask questions about life in the dirt.
Give small groups of children worms to observe and draw, and ask what they notice about them.
Materials: earthworms, one for each pair of children (any kind of garden worm is fine; night-crawlers are less active but larger so the parts are easier to view; smaller worms are often more active and so more fun); water mister, paper plate and damp paper towel for each worm; magnifying lenses.
EARTHWORMS UP CLOSE
Objective: To view some special characteristics of earthworms and consider how these make them well suited to life in the soil.
Bring in a container of worms in soil. Have children work in pairs or small groups. Before you start, have children rinse their hands to remove any soap, sanitizer, or hand cream as this could injure the worms. Have them wet their hands before handling worms or dampen them with the water mister. Set out paper plates covered with damp paper towels at each table. Review how to use a magnifying lens. Place a worm (rinsed in clean water if needed) on each plate.
Things to Look for with a Lens:
Body segments – notice how the body seems to be made of many rings
The worm’s digestive tract full of dirt
The front end or mouth of the worm; the tail end – can you tell which is which? Does the worm have eyes? (No, though it can sense light through its skin.)
The top and bottom side of the worm – how can you tell which is which?
The worm’s protruding lip (prostomeum)
The band or clitellum, a thickened area around the worm – easier to see in nightcrawlers than in some smaller worms where it can look like an indentation rather than a bulge.
Pick Up the Worm
Feel the worm’s skin. Is it smooth on both top and bottom of the worm? (Smooth on top, rough on the bottom.) Why might it feel prickly on the underside? (It has little bristles called setae.)
Look at the bristles with a magnifying lens (easier to see on night crawlers than smaller worms). Feel the bristles by rubbing a finger gently one way and then the other on the worm’s underside. Why would a worm have bristles? (To hold onto the soil so it cannot be easily pulled out.)
Watch the Worms Move
What do you notice about changes in the worm’s shape as it moves? (Gets longer, then wider, then longer.)
Show the Worm Innards diagram and practice squatting down and then stretching up as high as you can reach.
Keep an eye on the worms; as they warm up, they may get very active and crawl off the plates. Afterward, collect the worms and return them to their container of soil. Store in a cool place.
How could we test if worms prefer a damp or dry place? One way would be to place a dry and a damp paper towel into a basin, about a half-inch apart, and then put some worms in the space between them. After ten minutes, count how many worms are on each side. Combining the results for the class, was there evidence for a preference? Did many of the worms end up underneath the paper towels? Why might that be?
Materials: earthworms, one for each pair of children (any kind of garden worm is fine; night-crawlers are less active but larger so the parts are easier to view; smaller worms are often more active and so more fun); water mister, paper plate and damp paper towel for each worm; magnifying lenses, Worm Innards diagram; dish basin, paper towels; optional: Worm Life diagram, Earthworm Guided Exploration.
PUPPET SHOW “Worm Wonderings”
Objective: To learn about the four components of soil, meet some inhabitants, and think about their roles in the soil food web.
Perform the puppet show or have a group of children perform it for the class. Afterward, ask questions to review the key ideas and vocabulary in the play. What are the four components of soil? (Air, water, rock bits, organic matter.) What does “decompose” mean? (To break down.)
Why are worms called “decomposers”? (They eat dead leaves and grind them up into tiny bits.) What else do worms do for the soil? (They dig tunnels that make spaces for air and water and roots to grow.) Which animal was a predator (meat-eater)? (The mole.) What food chains can you make with characters in the puppet show? (Dead leaves–worms–mole, or dead leaves–millipede–mole.) Hold up the puppets as the children list the food chains in the puppet show.
Materials: puppets, script, stage.
EXPLORING THE SOIL FIELD WORK
Objective: To examine the soil and its inhabitants and to investigate the number of earthworms present.
Ahead of time, ask the children to think about what you might find if you dig up a shovel-full of soil and sod. Make a list of their predictions. Keep the list and add to it as children make discoveries. One question that the group could investigate is: “How many animals live in each cubic foot of soil on the playground?”
Dig a Hole
In teams of four or five children and an adult, have each group dig a small hole on the edge of the school grounds. If space is limited, carefully mark spots ahead of time. These can be in different kinds of places for comparison. The holes should be one foot square and one foot deep and far enough apart so there is room by each one for the group, their equipment, and a plastic sheet on which to sort through the soil. If there isn’t a place to make holes at the school, an alternative is to dig a hole at home and bring in the plug of dirt and sod in a plastic bag or basin for each group. Use the Exploring the Soil Field Work sheet as a guide for the investigation.
Before digging, have children look at the plants that are growing in their section of ground. Catch and gently place any animals in bug jars to share later, keeping them out of the sun. Part the grass to look for any dried or decaying plant material. Are there any dead leaves? Are there any holes? Are there ants or other insects? Are there worm holes or worm castings? What else is there of note?
With shovel, dig a hole six to twelve inches deep and about a foot on a side. Remove the sod and dirt and place it on a piece of white plastic to one side for further study.
Explore the Hole
Have children examine the hole itself, and the soil and sod you removed, for signs of layers or differences from top to bottom. Note where there are rocks, different colors, large roots, or anything else of interest. Look for large and small tunnels. Have children take turns putting their faces into the hole and sniffing. What does it smell like?
Examine the Contents
Help the children to carefully take apart the soil plug, spreading it out and sifting through it on the plastic sheet. Sort the contents into piles of similar-sized stones, different colors or textures of soil, and plants. It helps to use a kitchen strainer for sifting the soil. Gently catch any worms, ants, millipedes, and other creatures in bug jars and examine with magnifying lenses; compare to the Soil, Litter, and Log Critter guide to identify them, if possible. Place some of the topsoil in the corner of a clean white dish basin. After a few minutes, some of the tiniest soil creatures may be more visible as they walk out onto the white surface. Look closely! Have the children in each group count up the number of earthworms in their soil sample and enter their result on a chart.
Count the Earthworms
As a group, look at the chart and compare the number of earthworms in each sample. Which one had the most? Fewest? What is the average number per sample? What might affect the number in one sample compared to another? (Temperature, shade, type of soil, etc.) How could you test this?
With an adult, older children can try to estimate how many worms there would be in the whole playground by estimating the area in square feet and multiplying by the average number of earthworms per sample.
Sort the Roots (Grades 4-6)
Have the students soak the plant roots and then gently separate them, laying them out for comparison. Which plants have tap roots (a single tapering root that grows vertically downward) and which have fibrous roots (like many branching threads)? Which have the deepest roots, the shallowest, the finest small roots? If there is any clover, look for swellings on the roots; these nodules contain nitrogen-fixing bacteria, which help the plant grow dark-green, healthy leaves.
Before You Leave!
Carefully replace the material that was removed from the holes. Gently return any animals you collected, or do this after the Dirt Painting activity (below). Scatter grass and clover seed over the soil you replaced. Pat it down and sprinkle with hay or dead grass as mulch.
Materials: sharp spade; for each group: white plastic sheet (about 4’x5′), white dish basin, magnifying lenses, bug jars, small amount of grass seed mix, Soil, Litter, and Log Critter guide, Exploring the Soil Field Work sheet; optional: field guides, Critter Information Sheet, bucket of water for older students to rinse plant roots, kitchen strainers.
EARTH PAINTING (Grades K-3)
Objective: To visually depict life in the soil, noting plants and animals above and below the ground.
Give each child a clipboard with a piece of card stock or other heavy paper and light-colored crayons to draw with. Ask them to draw a line across the middle of the paper to represent the surface of the ground. Now have them draw everything but the dirt in the scene above and below, including things that they found while doing the soil study such as rocks, plants with their roots, worms, and other creatures. When the crayon drawings are done, the children can finger-paint with some mud over the underground part of their drawings. (The crayon, being waxy, will repel the wet dirt.) Prepare the mud by mixing finely sifted dirt with water to make a smooth slurry. Have children share their pictures, then dry and display in the classroom. Be sure to return any animals you collected to the soil.
Materials: card stock on clipboards, one per child; light-colored crayons; kitchen strainer for sifting the soil to make watery mud for finger-painting, small plastic containers; water and an old towel for washing and drying hands.
JOURNAL ACTIVITY (Grades 3-6)
Objective: To record observations about a soil organism.
Ask the children to draw and describe something they found in their soil samples. Include as many details as possible about the appearance and behavior of the critter (if they choose an animal). If possible, try to count the number of legs on the animal and then compare to the Soil, Litter, and Log Critter guide. Try to identify the group to which the animal belongs. Have students share their journal entries in small groups. Afterward, gently return any animals to the soil, using the release poem below.
I’m glad you shared this time with me,
But now I’ll gently set you free
So you can hop or crawl or fly.
It’s time for us to say goodbye.
Materials: science journals or clipboards and paper, pencils, soil animals in bug jars from Exploring the Soil activity, Soil, Litter, and Log Critter guide, copy of Goodbye Poem in plastic cover.
UPPER GRADES CHALLENGE: Two Tests of Soil Conditions (Grades 5-6)
Objective: To test whether soil is compacted or has room for water and air, and to compare percolation rates at different sites.
Have the students work in small groups. Each group will test the compaction of the soil by pushing a sharpened pencil into the ground at various locations on the school grounds. Discuss what it means when the pencil goes in far (lots of spaces between soil particles) and when it is hard to push in (soil is compacted, few spaces between the particles).
Have students record the depth that the pencil penetrates, testing different kinds of places (e.g. playing field, lawn, garden, flowerbed, near a pathway, in a parking area, etc.) and listing the depth for each location on the Two Tests of Soil Compaction data sheet. Gather the students and review their findings. What kinds of places were compacted? Where was the soil the loosest?
Based on the findings of the compaction test, ask students to make a prediction about percolation. At which of the locations would rainwater soak into the ground the fastest? Where would it go the slowest? Have students test their predictions with a percolation test (see below) at different sites, comparing places where the pencil went in easily and where it was hard to push in.
At each site, have students push the prepared soup can (or tomato paste can) into the soil to the one-inch mark by rotating it while pushing down hard or by placing a small board over the top of the can and hammering it in. Quickly fill the can up to the top with water and time how long it takes the water to sink to the one-inch mark inside the can. Repeat at the second site and at other sites if time permits. Did the times differ? How did this compare to their predictions? What does this tell you about spaces in the soil? (The more spaces in the soil, the more easily water can soak in, unless it’s already water-logged or if it’s completely dry.) What might happen when rain falls on the most compacted sites? (It might puddle up or run off, carrying soil with it.) What makes compacted soil a difficult place for plants and animals to live? (It has fewer spaces for air and water and roots.)
Materials: small soup cans or tomato paste cans with ends removed and a line marked 1″ from the bottom on the outside and 1″ from top on the inside; 4″x4″ board to fit over can; hammer; water container; timer; for each group of students: pencils (at least 6″ long) with sharpened points for compaction test, ruler, clipboard, Two Tests of Soil Compaction data sheet, pencil for recording data.
Objective: To reflect on the discoveries made while investigating the soil.
Have children complete the sentence: My favorite soil discovery today was ______________ because of the way it _________________.