Whats in Soil? | Texas Agriculture in the Classroom

Lesson Plan

What's in Soil?

Grade Level

3 - 5

Purpose

Students identify the components of soil and demonstrate that soil contains air and water. Grades 3-5

Estimated Time

50 minutes

Materials Needed

Engage:

Soil Ag Mag
Apple
Paring knife

Activity 1: Soil Inventory

2-cup soil samples, 1 per pair of students
Newspaper
Hand lenses

Activity 2: Soil Moisture

Tissue paper or thin paper towel (the thick, brown paper towels common in schools do not work)
Overhead projector

Activity 3: Soil Air

1-cup measuring cups, 1 per pair of students
2-cup containers, 1 per pair of students (preferably clear, e.g. plastic cups, mason jars)
Water
Soil Pie: Components of the Soil handout, for display
Piece of yarn

Vocabulary

infiltration: to pass through a substance by filtering or permeating

mineral matter: small pieces of weathered rock (parent material) that has been broken down into small particles over thousands of years

organic matter: a soil component derived from the decay of once-living organisms like plants and animals

percolation: the movement of water within and through the soil

pores: the spaces between soil particles and between soil aggregates; pores can be filled with air or water

saturation: occurs in a soil when all of the pores are filled with water, leaving no air

soil structure: the arrangement of soil particles into aggregates, which contain solids and pore space

Did You Know?

Soil contains all three states of matter; solids (minerals and organic matter), liquids (water), and gases (carbon dioxide, oxygen).¹
Soil is one of the most important natural resources known to man.³
Soil scientists study the upper few meters of the Earth’s crust.¹
A single shovelful of soil can contain more living things (organisms) than live in the Amazon rain forest.²
Just a teaspoonful of forest soil can hold more than 10 miles of fungi (mushrooms, mold, yeasts, and mildews).²

Background Agricultural Connections

Soil is a naturally occurring, loose material at the surface of the earth that is capable of supporting plant and animal life. In simple terms, soil is comprised of three phases: solid, liquid, and gas. The solid phase, which accounts for approximately 50% of the volume in a typical soil, gives soil its mass and is a mixture of mineral and organic matter. Soil particles fit together loosely (depending on particle size and aggregation), leaving “empty” pore spaces. The pore spaces are then filled with water (liquid) and air (gas). The water and air in an average soil make up the other half of the soil’s volume.

All soils are made up of mineral matter, organic matter, air, and water, although the proportions of each will vary. An average soil contains approximately 45% mineral matter by volume and 1 to 5% organic matter. The mineral component is derived from the weathering of rock at the earth’s surface. Mineral particles, which are classified as sand, silt, or clay based on their size, determine the texture of a soil. Weathering of minerals and decomposition of organic matter are key sources of nutrients for life in the soil.

The organic matter component of soil consists of decomposing plant and animal remains. Organic matter acts like glue, binding mineral particles together into aggregates that give a soil structure. Soils high in organic matter do not compress as tightly, meaning they have more pore space. Organic matter also absorbs water, improving the water holding capacity of a soil. Sand like you find in a sandbox does not hold water well because there is no organic matter and the pores between particles are all very large—the water just slips right through.

Pore space occupies approximately 50% of the volume in a typical soil. Water and air, which are both important to soil life, move through the pores in the soil. Larger pores allow air and water to move through the soil quickly, while small pores can hold reserves of air or water. In an “average” soil, half of the pore space is occupied by air and half by water. Of course, these proportions can change drastically during a drought or a flood. During a drought, plants will pull all the water that they can out of the soil, leaving pore spaces filled mostly with air. Water carries nutrients to plants and prevents them from wilting. Extended drought can wreak havoc on farmers.

Somewhat unintuitively, prolonged rain that saturates the soil can also wreak havoc on farmers. When a soil is saturated, all the pore spaces are filled with water, leaving no air. Most crop plants will drown if the soil is saturated for too long—their roots need oxygen from the air just like our lungs do. Some plants have adapted to growing in water. For example, rice has developed a special way to transport oxygen from its leaves to its roots. Rice is often grown in flooded fields, where soil saturation prevents weeds from growing.

Engage

Begin a discussion with students and ask, "Why is soil important?" Accept all answers and record them on chart paper or somewhere in the classroom where the responses are visible. Next, display the Illinois Ag in the Classroom Ag Mag, titled Soil on the whiteboard. Paper copies can be printed if a whiteboard is not available. Have a student read the section on the first page that addresses the importance of soil. Compare the students' responses to those found in the reading. Ask another student to read aloud the section on page 2 that addresses soil parts and add more information to the list as to why soil is important.
Review all responses and ask, "How much soil exists on earth that farmers can access to grow crops or raise livestock?" Accept all answers and add these responses to the chart paper. To respond to this question, refer the students to the section of the Ag Mag, titled A Slice of Soil found on page 3. You will need an apple and a paring knife to demonstrate the activity and answer the question as to how much farmable soil is available to farmers.
Challenge students to think of ways farmers can conserve soil to produce enough food to feed the world. If time permits, play one of the videos on the last page of the Ag Mag that interviews two individuals who work in the field of soil science to help students understand the importance of soil and ways farmers practice conservation. The videos can be shown from an interactive whiteboard. Look for the blue video cameras to play each video.

Explore and Explain