Lesson #2: Soil
Last week, students reviewed the role seeds play in the life cycle of a plant. This week, students will learn about the soil requirements that support plant growth throughout the life cycle. Students will learn how the ratio of different particle sizes determines the soil type and how the soil type dictates how soil is agriculturally managed. Students will also learn about the macronutrients (Nitrogen, Phosphorus, and Potassium) required for healthy plant growth. One of the vegetables most closely associated with the soil are root vegetables, because they are harvested from beneath the soil surface. Root vegetables are generally storage organs, enlarged to store energy in the form of carbohydrates. They absorb water and nutrients directly from the soil to feed the rest of the plant, making them extra healthy for us to eat. Students will prepare and try a wide variety of roasted root vegetables, which can include yams, beets, parsnips, turnips, rutabagas, carrots, yuca, kohlrabi, onions, and garlic. Are there any root vegetables the students haven’t tried before? What’s their favorite root vegetable?
Soil characteristics determine what plants can be grown in an area.
SWBAT describe differences in soil texture, color, and the capacity to retain water.
SWBAT explore the connection between soil nutrients and plant needs.
SCIENCE 7 (A) examine properties of soils, including color and texture, capacity to retain water, and ability to support the growth of plants.
- Board with markers or poster board
- 3 Soil samples – enough for each small group to have a plastic cup of soil
- Large clear plastic cups or glass jars, 3 per group
- 3 soil balls (1 mostly sand, 1 mostly silt, 1 mostly clay)
- Observing Soil Samples sheet, 1 section per student
- Funnels, 3 per group
- Large clear plastic cups, 2 per group
- How Do Plants Affect the Soil?, 1 worksheet per student (note: there are 14 variations of this worksheet, so try to give each student a different plant. If more than 14 students, make sure only 2 students share the same plant)
- Varieties of root vegetables to peel and cut (carrots, turnips, onions, radishes, beets, etc..)
- Cutting boards
- Adult sharp knife
- Root vegetable stew recipe, 1 per student
- Stew ingredients (prepared beforehand): olive oil, butter, yellow onion, carrots, celery, parsnips, beets, thyme, curry, tomato paste, flour, water, cilantro, lime, yogurt, salt and pepper)
Different types of soil hold different amounts of water, minerals, and air. Sandy soils drain well because they have large air spaces. Water is lost more quickly from the large spaces between sand particles, as the force of gravity drains the water out. Also, sandy soils have little capacity to hold plant growth minerals.
Sandy soil is made up of large round particles with relatively large spaces of air between them. Since sandy soil contains a lot of air (or space), it cannot hold water well and tends to lose soil and nutrients quickly.
Silty soil is intermediate in texture between clay and sand. It feels smooth and is slippery to the touch when wet.
Silt prevents water and minerals from leaching (or draining) out of the soil.
Clay soil is made up of microscopic, flattened mineral particles. These tiny particles pack closely together, becoming sticky when wet and leaving little space for air and water.
Clay soils have poor drainage and air holding spaces. Because of this, clay and other heavy soils often hold more water than is good for plant growth. On the other hand, clay soils may be richer in nutrients, because they can hold plant minerals more effectively than soils composed of larger particles.
-Why is soil classification [ratio of clay, silt, and sand] important?
Farmers, gardeners and anyone else growing plants need to know what kind of soil is present. For example, sandy soils require less fertilizer and more frequent applications of water than clay soils.
Print Observing Soil Samples sheet, 1 section per student
Print How Do Plants Affect the Soil?, 1 worksheet per student
Print Root vegetable stew recipe, 1 per student
Cook root vegetable stew
This lesson is messy. Prep 2 stations- one for the lesson and the other for peeling, slicing, and dicing.
Timeline (1 hour total):
5 min Introduction to Soil
5 min Observing Soil Samples
5 min Soil Particles (sand, silt, and clay)
10 min Soil and Water Experiment
15 min How Do Plants Affect the Soil?
10 min Make It – Peeling and Cutting Root Vegetables
5 min Taste It – Roasted Root Vegetables
5 min Clean-up
- Introduction to Soil – Draw a circle on the board – this will become a pie graph. Title the graph “what’s in soil?” Ask the students what they think is in soil. When they identify one of the correct elements of soil, help them determine the percentage. As they name correct percentages, fill in the pie graph.
- Minerals – 45%
- Air – 25%
- Water – 25%
- Organic matter – 5%
- Observing soil samples – Tell the students that they are going to have the chance to look at some soil samples. Give each group a large clear plastic cup or glass jar with each of the three types of soil samples, making sure they are labeled 1, 2, and 3. Have the students write their observations of each soil sample before feeling it with their hands. When they are ready, they may use pipettes to drop water on the soil and observe any changes in texture. Have them observe if they can make a ball with the soil when wet and which soil was the best.
- Soil Particles – Hold up three soil balls- small, medium, and large. Explain that soil particles – the pieces that make up soil – can be described as large (sand), medium (silt), and small (clay). Share the following with the students:
- The smallest particles, clay, is made up of tiny flakes of minerals. They pack closely together when wet and have very little space to hold water and air. This can mean that clay soil can have poor drainage and drown plants. On the other hand, clay soils can also hold lots of nutrients.
- The medium particles (silt), feel smoother than sand but rougher than clay. It feels smooth and slippery when wet and does a better job at holding water and nutrients than sand.
- Sand is the roughest, largest particle of soil. It loses water and nutrients easily and can hold lots of air.
- Soil and Water Experiment – Give each group of students a cup with water. Have them pour an equal amount on each of the jars of soil. Have students observe differences between each container. Typically the clay container has water pool on top and takes a long time to absorb the water, while the silt slowly absorbs the water and the sand has water penetrate through quickly. Next, distribute one funnel to each group and another plastic cup or jar. Have students pour samples one at a time into the funnel to observe how much water passes into the cup. They can repeat with each sample. This shows how much water is passing by the plant deeper into the soil, or lost in runoff. The goal for farmers is to have the soil hold enough water to slowly give water to the plants and not have it all leave as runoff.
- How Do Plants Affect the Soil? – Distribute one worksheet per student. Have them look at their plant (there are 14 varieties so each student might have a different plant) and determine how the levels of Nitrogen (N), Phosphorous (P), and Potassium (K) in the soil, were affected by the plant. They can fill this information out on the worksheet individually. As a class, discuss which plant took the most N, P, and K, and which plants had no effects. Did any plant leave the soil with more nutrition than when it was planted?
- Make It – Peeling and Cutting Root Vegetables. Distribute cutting boards, peelers, and knives. Review how to safely use a peeler – peel away from you and keep your fingers away from the blade. Even kid-friendly peelers can cut when misused. Tell students that they will just be peeling the outermost part of the root to get the tough skin off of the vegetable. Otherwise students will try to peel the entire thing! Safe cutting should include an adult cutting the root in half with a sharp knife and having students put the flat end on their cutting boards to slice into half rounds. Students can sample the washed roots raw.
- Taste It –Root Vegetable Stew. Distribute copies of the root vegetable stew recipe to the class. While we don’t have time to make this in class, this is an example of how delicious root vegetables can be. Give each student a small serving of the stew in a cup to cut down on spilling. If they like the stew, suggest they bring the recipe home to the parents and prepare it together.
- Clean-Up – Students will return the classroom to its previous state, including washing bowls and spoons, and wiping down tables and floors as necessary.