Target Grade Level:
Three 40-minute lessons
Students will identify the many properties of soil and how it is made up many different types and textures (which can affect plants’ growth and development).
- Plastic bag filled with one –two cups of soil taken from field or garden
- One quart canning jar with a tight-fitting lid or one for each student
- Supply of water
- If desired, have students bring in ziplock bags of soil from their yard or a field near their house. Remind them that potting soil or sandbox sand or similar will not work.
- Large apple
- Cutting Board
- Clay: has the smallest sized particles (fine texture); clings together when wet, retains water for a long time
- Silt: has medium sized particles; grows plants well
- Sand: has the largest-sized particles (coarse texture) needs plenty of water for crops to grow well, low in plant nutrients; drains quickly after rain or watering and so is easy to cultivate: warms up very quickly.
- Loam: healthy (almost equal) combination of the three
- Pore spaces: spaces between particles of soil; water runs through here and removes harmful substances
Background – Agricultural Connections
There are three soil textures that make up a soil type. They are sand, silt, and clay. Each texture has different particle sizes which determine the pore space of the soil. Pore space is where roots can grow in the soil and it is also what hold water and air, which are two vital components of creating a soil profile and allowing a plant to grow.
Sand: Sandy soils drain very fast and do not hold water very well. They have the largest particle size and feels gritty to touch. Sand particles do not bind very well and easily warms up in the Spring because they have more pore spaces that fill with air. Its degree of aeration depends on the sizes of the particles, which vary a lot in size. Sand is usually formed from the weathering or disintegration of bedrock such as shale, limestone, granite and quartz.
Silt: Silty soils are finer, and smoother in texture and hold the most available water to plants. Sand does not hold any water and clay particles hold water so tightly to the particle surface that plant roots are unable to extract it from the soil. Silty soils are also heavier than sandy soils, and holds up nutrients and make it better for crop cultivation. Silt is formed when fine sediments (dust, organic matter, and debris) are carried by water or ice and deposited. When silt is deposited and cemented with time, it forms siltstone. Silt particles are very small and not easily seen by the eyes.
Clay: The particles that make up clay are the finest and they bind very well to each other and to water particles. Since they bind so well together they have very little air spaces. Clay is very sticky when it is wet and can be molded into any shape and form. When clay dries it is rock hard. Clay particles also do not drain water very well which can be a problem for plants. You do not want to underwater plants but you also do not want them to be submerged in water with no ventilation. Clay particles are so small that they are millions of clay particles that can fit in the size of your pinky fingernail.
- Show students a Ziploc bag of soil that you collected from a local source. Ask them the question, “What is this?”
- Have students brainstorm answers and write them in their journal.
- Some students may say that it is dirt. Remind them that dirt is what is found under your fingernails or what your shoes track into the house but soil is a substance that provides nutrients and allows plants to grow.
- Once soil is identified, have the class discuss why soil is important to humans and have students write their answers in their journal.
- Then ask students, “Is soil alive?” Have students brainstorm ideas and come up with a list of what soil is made up of and if anything lives in the soil?
Activity 1: What Soil Am I?
- Write the words and definition of sand, silt, and clay up on the board and have the students write down the words and their definition in their journals.
- S andy soil: contains particles that can be seen with the naked eye and feels gritty when rubbed between the thumb and forefinger. Sandy soils will generally not stick together when wet.
- Silty soil: contains particles, which are smaller than sand particles but larger than clay particles. Silt feels powdery when rubbed between the thumb and forefinger. Silty soil sticks together when wet, but will not hold its shape after it is dry.
- Clay soil: contains the smallest particle size. Clay particles form a sticky soil when wet and will generally hold a shape after drying.
NOTICE: Soils are rarely composed of just sand, silt, or clay. They are usually mixture of the three with a larger percentage of one of the textures.
- Show students a sample of each soil texture.
- Ask the students how much of the Earth’s soil is available to grow healthy plants? Hand out the What Soil Is This? WS.doc and have students color in the percentage of soil they think is available for growing crops on Earth in the apple drawing.
- Introduce the Apple Earth Activity:
- (Hold up the apple) This apple represents planet Earth. We’re going to cut the apple into pieces to see how much soil is left on planet Earth to grow food for more than 6.4 billion people and all the animals in our care.
- (Cut the apple lengthwise in four equal parts and take away three.) These three parts represent the water on Earth.
- Ask students,
Where do we find water on planet E
- In oceans, rivers, lakes, ponds, streams, etc.
- The piece that is left, one-fourth of the apple, represents the land on Earth.
- Yes, most of the land in our state is owned by farmers. They work to plant crops and food to feed the world.
- Ask students, Where do we find water on planet E arth?
- (Cut the remaining quarter in half lengthwise and take away half.) This half represents the areas on Earth that are too hot, too cold, or too wet for the plants we eat to grow.
- Ask students,
What places are too hot?
- Deserts and places near the equator
- What places are too cold?
- The poles, places where there is frozen ground
- What places other than bodies of water are too wet?
- What places are too cold?
- Deserts and places near the equator
- Ask students, What places are too hot?
- (Cut the remaining portion crosswise into four equal parts and take away three.)
These three parts represent areas of Earth where the plants we eat can’t grow roots into the ground. We call these surfaces impervious, which means incapable of penetrating or being passed through.
- Ask students
, What things cover soil and make the ground impenetrable?
- Roads, houses, businesses, shopping malls, schools, parking lots, mountains, forests, etc.
- Ask students , What things cover soil and make the ground impenetrable?
- The fourth portion – only 1/32 of Earth – represents the land that can grow crops for the more than 6.4 billion people and all the animals in our care.
- Ask students
, Do plants grow into the core of the earth?
- What do you call the layer of soil where plants grow?
- Ask students , Do plants grow into the core of the earth?
- (Peel the skin off the remaining section.) This skin represents topsoil, the part of the soil that plants grow in. This is the amount of soil on planet Earth that grows the food to feed all the people and animals that live around the world.
- Ask students if they think,
there very much topsoil on planet E
arth to grow our food?
- Do you think I owa has a large portion of that valuable topsoil?
- Ask students if they think, is there very much topsoil on planet E arth to grow our food?
- To end the demonstration, ask students to bring a Ziploc baggie (about 2 cups) of soil from their fields, their garden, or from a parent approved location near them.
Activity 2: Shake and Wait: Students’ Procedures
- Have students bring in their Ziploc bag full of soil that they collected from home.
- Have students examine their Ziploc bag with soil. Remind students of the three types of soil textures: sand, silt, clay.
- Have students make observations on their soil on the What Soil Is This WS.doc
- Once students have made their observations and predicted which type of soil they have, have students place their soil in a clear glass jar.
- Fill the jars with 2/3rds full of water.
- Have students place their lid snuggly on the jar and then have them shake the jar until the ingredients are thoroughly mixed.
- Have students place their jar on their desks and leave it undisturbed for two to three days.
Activity 3: And the Answer is…
- On day three, the students will revisit their jar of soil and water. On day three you should see some separation of the three soil textures.
- Have students guess which soil texture will be found at the bottom, middle, and top of the jar and write their guess in the What Soil Is This WS.doc. Also have them draw what they see on that worksheet.
- Sand will drop to the very bottom of the jar because it is heavy and it does not suspend in water. Silt will accumulate on top of the sand and clay will stay in suspension the longest and will deposit on top of the silt.
- Using a ruler, have the students measure the length of each layer vertically. Record data on What Soil Is This WS.doc worksheet.
- The layer that is the thickest determines the type of soil. Example: if there is a lot of sand at the bottom and the middle and top layers do not have much then that soil is classified as a sandy soil. It is possible to have two types of layers that are equal. You could have a sandy-silt soil or a silty-clay soil.
Activity 4: Wrap up
Analysis: Students will discuss and journal these questions in their notebook or on the back of the What Soil Is This WS.doc:
- What kind of soil particle was the most common in the soil sample?
- From what kind of rocks do you think your soil was formed?
- How did your soil sample compare from the soil samples of your friends?
Did you know…? (Ag facts)
- That one shovel of soil has more living species than the Amazon Rain Forest has living species above ground?
- One cup of soil has almost 6 billion species of bacteria
- Ask an agronomist to come in and talk to the class about soils, what they do in their career, and how learning about the soil is important for plant growth.
Iowa Agriculture Literacy Foundation
Hull Prot. Ref. Christian School
National Agriculture Literacy Outcomes
- T2. 3-5 c. Explain how the availability of soil nutrients affects plant growth and development
Iowa Core Standards
- 4-LS1-1. Construct an argument that plants and animals have internal and external structures that function to support survival, growth, behavior, and reproduction
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