Keeping Soil in Its Place

Grade Level

3 - 5

Purpose

Students demonstrate rain drop splash (splash erosion) and determine its impact on bare soil by visually identifying types of erosion. Grades 3-5

Estimated Time

90 minutes

Materials Needed

Splash Zone Target (these could be made on a transparency, this way they could be washed and used year after year)
Graph handout
Soils on the Move, for handout or display
5 teaspoons of dry soil
Eyedroppers or dropper bottles
Water
Rulers
Erosion Control Practices, for handout or display

Vocabulary

erosion: the process by which the surface of the earth is worn away by the action of water, glaciers, winds, waves, and other natural forces

furrows: small ditches, usually 2-6 inches deep, between the rows of plants used to convey water

mulch: a covering placed on bare soil to keep it from eroding; loose leaves, straw, bark chips, etc.

row crops: plants grown in a row to facilitate harvesting and watering

Did You Know?

Soil creep is the extremely slow movement of soil down a steep hillside. It is caused by soil expanding and contracting, when it goes from wet to dry or frozen to unfrozen.
A slump is a mass movement that happens when a large section of soil or soft rock breaks away from a slope and slides downwards. Slumps often happen where the base of a slope is eroded by a river or by waves, or when soil or soft rock becomes waterlogged.
A lahar is a mudflow of water mixed with volcanic ash. The mud flows down river valleys and sets hard when it comes to a stop. Lahars can cause destruction on a massive scale.

Background Agricultural Connections

Erosion is a naturally occurring process. Erosion has given us some of our most beautiful landscapes. There are beautiful erosion formations such as the Grand Canyon and Bryce Canyon, Utah. Erosion is the loosening, transportation, and relocation of soil particles from one place to another. Erosion occurs primarily due to the action of wind and water. The rate and extent of erosion are determined by soil type and condition, slope of the land, plant cover, land use, and climate. Erosion does not occur only on wilderness landscapes, and the effects are not always positive, especially when you are talking about productive topsoil. Landslides, can bury towns and claim thousands of lives. Streams or rivers loaded with eroded soil can turn sources of clean drinking water into major health hazards.

Water erosion includes raindrop splash, sheet erosion, rill erosion, gully erosion, and slumping or mass erosion. Raindrop splash is the most obvious on bare ground during a torrential rainstorm. The raindrops strike the ground and upon impact break soil particles apart, splashing these particles into the air. The impact of raindrops can be lessened by plant cover. Plants break the fall of the raindrops and allow for water infiltration or percolation.

Sheet erosion is the washing away of a thin surface layer of soil over a large area of land. Because sheet erosion occurs evenly, it is generally not obvious until most of the topsoil is removed.

Rill erosion may be noticeable on sloping bare ground after a rainstorm. Water forms small, well-defined channels that carry soil away from the sides and bottom of these channels. The rills of channels erode more soil as they move downslope and increase in size. When rills become large, the process is called gully erosion. This severe form of soil erosion removes tons of soil from the sidewalls and bottom of the gully.

Streambank erosion (and similarly, coastal erosion) is the cutting away of the banks by water. It is generally a slow process which represents the normal situation occurring along most streams. It is most active during floods when the amount and velocity of water are the greatest and when the bank soils are submerged under water and saturated.

To control erosion, plant cover is usually the best solution. But to grow our food farmers make furrows in the land for row crops. A farmer can use a variety of methods to “keep soil in its place.” A farmer may plant his or her crops around the curve of a hill rather than up and down the hill, this is called contour planting. Plowing will also be done on the contour. Farmers may also build terraces. Terraces are wide ridges that go around a hill to prevent water from rushing down the hill too fast. On steep hillsides, rather than clear the area for cropland, farmers will maintain the area in forest and grass. Water always runs downhill, so farmers do not plow in low areas where water collects; instead they maintain low ditch areas as grassed waterways. Soils susceptible to wind erosion should be kept covered with some kind of vegetation. If this cannot be done year-round, a windbreak of trees and shrubs may be planted. Windbreaks are rows of trees planted to slow down the wind and prevent soils from blowing away in the wind.

Engage

Show your students pictures of famous landmarks that were created by erosion. Examples include the Grand Canyon, Zions National Park, or Arches National Park.
Ask your students how these unique rock and land formations were created. Allow students to offer their answers and use guided questions to lead them to the answer of erosion.
Explain that they will be learning about different types of erosion and methods farmers use to prevent erosion of their soil.

Explore and Explain

Activity 1: Splash Zone

Divide the class into five groups.
Give each group a Splash Zone Target, eyedropper, and a small container of water.
Instruct student to put enough soil (about ½ teaspoon of dry soil) in the center of their target to just cover the center circle.
Fill the eyedropper with water.
Hold the eyedropper about 18 inches (or 46 cm) above the soil sample.
Drop 5 drops of water directly onto the soil sample. If a drop misses the soil, continue until 5 drops hit the soil.
Record the number of water “splashes”—drops containing soil—in each zone.
Complete the graph to show your results.
Discuss the following questions:
- What did you observe? How did the soil particles move from the center of the target? (they were picked up and moved with the water)
- Which zone contained the most number of water drops with soil particles? Why?
- Which zone contained the least number? Why?
- What would happen if the drops were larger? (splashes would travel further)
- How might you prevent splash erosion? (plant vegetation, cover the soil with mulch)
- How do farmers decide which erosion control methods to use? (it depends on the slope, soil types, and what he or she wants to plant)
  - Note: You may want to repeat this activity with drops from 1 meter high or try the activity with wet soil.

Activity 2: Soils on the Move

Introduce students to the types of erosion using the erosion section in the Dirt: Secrets in the Soil video and the information found in the Background Agricultural Connections section of the lesson. (Play the first 3:44 of the video clip. The remaining portion will be used in the next activity.)
Project or provide each student with a copy of the Soils on the Move handout. Label the handout together and discuss how each type of erosion differs.

Activity 3: Methods for Controlling Soil Erosion

Introduce students to the methods for controlling erosion. Watch the remaining portion of the video, Dirt: Secrets in the Soil from Activity 2. This section discusses the methods that farmers use to protect soil and prevent erosion. You may choose to duplicate the video demonstration using erosion trays called “turkey pans.” You may also want to show students a movie of raindrops hitting soil, which can easily be found on YouTube.
Student should complete the Erosion Control Practices activity sheet, or project the graphic and label and discuss the practices together.
Discuss the various methods and why each practice is used.

Answers: 1) streambank erosion, 2) gully erosion, 3) wind erosion, 4) rill erosion, 5) sheet erosion.

Elaborate

Connect this lesson to Utah Studies by showing students the 14-minute video Dust Bowl: Grantsville Utah. This short documentary includes interviews from Utah residents who experienced the Grantsville Dust Bowl in the 1930s. Yes, Utah did experience its own dust bowl, but the cause was overgrazing rather than the turn of the plow.

Evaluate

After conducting these activities, review and summarize the following key concepts:

Soil is a valuable resource that needs to be conserved to allow farmers to grow our food.
Erosion is a process that moves soil from one place to another using water or wind.
Farmers use various methods such as furrows, row crops, terraces, and cover crops to prevent erosion of soil on their farms.