OBJECTIVE

Students will understand what soil is made of, how it erodes, and why it matters. Students will understand how the rock cycle affects soil structure and soil conditions.

ESSENTIAL QUESTIONS

What is soil? What is it made of?

Why do we need soil?

Why does soil structure matter?

How can we build soil?

MATERIALS

• Prepared soil shake tests for observation
• Soil particle cards for each student (Sand, silt, clay)

PROCEDURE

1. Discussion – What is soil? What is soil made up of? Why does soil matter to us?

• Soil is made of rock particles and organic matter (living and nonliving parts)
• Allow students to offer reasons why soil is important: food, resources, clothes 

             How are we losing soil? Take responses and follow up with clarifications: 

• Natural erosion from weather events, tides, etc.
• Irresponsible land use: deforestation (tree roots hold soil in place), tilling, overgrazing all cause further erosion. 

            We can build soil, too! To understand how, we need to know what soil is made of: The living 

            and non-living parts (rock particles & organic matter). Today we will talk about the non-living

            parts – Rock particles!

2. The non-living part of soil is weathered rock particles of different sizes. There are three main classifications of particles: Sand, Silt, Clay

Explain and draw on the board:

Sand particles are the biggest. 

             Silt is medium-sized particles. Smaller than sand, bigger than clay. 

             Clay is the smallest particles – the small size of the rock particles are the reason that clay

             binds together so well and can be molded into shapes!

      Some soils are mostly made up of one type, but some others are made up of two or all of these

      types, with diffferent proportions of each. 

3. The size of the soil particles matters to use because it effects how well soil can hold on to water and nutrients, how susceptible it is to erosion, and what kinds of plants can live in it. 

Draw: A cluster of sand particles (big particles with space in between), a cluster of silt particles (smaller particles with some small gaps between them), a cluster of clay particles (tiny dots all very close together)

Ask: Which of these types of particles do you think hold on to the most water? Which type do you think loses water really easilly?

4. Play the Soil Particle Game:

• Split the class up into groups of clay, silt, sand, and water. 
• Sand particles stand at arms-length from each other; water tries to move through. Was that easy? (yes)
• Silt particles stand at elbow’s distance; water tries to move through. Was that easy? (harder than before)
• Clay particles stand very close, almost touching; water tries to move through. Was that easy (no!)

5. Each particle type has good qualities and challenges.

Clay: can become too compact (particles tightly squished together), water cannot move through, it becomes water-logged, difficult for plants to root into. Strenths: that it holds onto nutrients well and does not erode easilly. 

Silt: drains poorly, easilly compacted, doesn’t hold nutrients well. Strengths: very fertile. 

Sand: Loses water and nutrients easilly. Strengths: warms up early, easy to work. 

6. Show shake tests to students and pass them around. Explain how the layers indicate soil structure:

• Clay is settles at the bottom
• Silt is in the middle
• Sand is the top
• Organic Matter floats on the top of the water. 

Pass shake tests around and as students if they can identify the different layers of the soil. Do any have a lot of one type? Or a lot of organic matter?

Extensions:

• Do ribbon tests with different soil tests to show the differences in soil structure. 
• Conduct shake tests with soil from the school garden to determine soil conditions.
• Follow up with a worm-bin building or composting lesson to highlight the organic part of soil and how that can be built. 
• Apple As the Earth activity to illustrate topsoil loss. 
• Deeper discussion:

How can we prevent erosion and water run-off in sandy soil? Plant trees, deep-rooted plants,  add organic matter

How can we loosen up clay soil? Plant trees or introduce other living creatures like worms, ants, millipedes to burrow in and break up soil.