Soil Erosion

Author

Joanne Maynard

Published

1/2/2016

Topics:

Lesson Plans - 6th - 8th

Target Grade Level / Age Range:

6 ^th Grade

Time:

45-50 minutes

Purpose:

Students will compare three types of groundcover to see which provides the best defense against soil erosion.

Materials:

Three empty 2-liter bottles
Three empty water bottles
Soil
Rye grass seed (or other quick growing seed)
Dead leaves or other plant debris
String
Water
Newspapers or plates
Magnifying glasses

Suggested Companion Resources (books and websites)

Fun Science Demos Soil Erosion

Vocabulary (with definitions)

Runoff: the draining away of water (or substances carried in it) from the surface of an area of land, a building or structure
Cover crop: a crop grown for the protection and enrichment of the soil.
No-till: a management practice in which the farmer doesn’t till the land

Background – Agricultural Connections (what would a teacher need to know to be able to teach this content)

This lesson focuses on environmental science, physics, and geology through the practical lens of soil conservation on a farmer’s field.
- This lesson focuses on three types of field management; conventional till, no-till, and no-till with cover crops. However, these are not the only management systems out there. Here is a brief outline of various systems including pros and cons:
  - Conventional till: Conventional tillage is how people describe the use of a moldboard plow (think John Deere’s first piece of equipment) as primary tillage, paired with secondary tillage like discs, harrows, cultivators, or others.
    - Pros: A tilled seedbed can have some beneficial impacts as far as plant growth. This can help “ warm up” the soil, create better seed-to-soil contact, counteract soil compaction, and can help control weeds. This was especially important before herbicides were used. Today, tillage is a way for farmers to create a better seedbed, primarily.
    - Cons: Conventional tillage requires more equipment (multiple kinds of tillage tools), time in the field, fuel usage, and drastically increases potential for erosion.
  - No-till: No-till, like it sounds, means that the soil is not tilled. This is made possible because of herbicides and special attachments on planters.
    - Pros: No-till’s biggest benefit is that erosion is cut down drastically. It also cuts down on necessary equipment, and time. No-till can help increase organic matter content in the soil, as more plant material is left to decompose. This can help improve soil structure as well as soil tilth.
    - Cons: One of the larger cons is that no-till doesn’t lend an ideal warm, soft seedbed for crops. To counteract this, farmers can use planters with “row cleaners” that help move residue out of the way of the seed. No-till can also cause soil compaction concerns if not monitored and managed effectively. Farmers may attach multiple pieces of equipment to one another to counteract this. For instance, some may apply nitrogen at the same time that they plant seeds.
  - Cover crops: Cover crops are plants that farmers seed in the offseason. In Iowa, common cover crops could be cereal rye, winter wheat, or even turnips and radishes. Their primary purpose is to hold soil together and provide extra protection, but there are many other benefits.
    - Pros: Plants’ root structure help keep the soil together, provide added organic matter, added roots decrease soil compaction, can provide added cost benefit, and many others.
    - Cons: Cost and time are two very prominent concerns. Cover crop seed costs money, and cover crops are rarely harvested. Some producers may use cover crops to graze cattle or other livestock on, but that may mean that added tillage is necessary to create an even seedbed after animals create tracks in mud. In Iowa with our wet springs, it can also be tricky to find time to put the cover crops down and still have adequate time to plant in the spring of the year. This is a larger problem for producers who want to use rye (the most common crop) and plant corn afterwards (Iowa’s largest crop). If corn is planted within a couple weeks after the rye has been killed, it can cause a major yield reduction for the corn crop. That extra two weeks between the two crops may or may not be possible for many Iowa farmers.
  - Conservation tillage: Conservation is a broad term used to describe when farmers use some tillage, but far less than conventional systems would imply. One type of conservation tillage is strip tillage. Like it sounds, this means that the field is only tilled in strips, where the seeds will be planted.
    - Pros: Farmers gain the benefit of seed bed preparation, counteracting soil compaction, incorporating fertilizer and organic matter, etc., without becoming as vulnerable to erosion.
    - Cons: While this could be the best option for some farms in some areas, tillage still takes time, equipment, fuel, and creates more potential for soil erosion.
  - Contour farming: While this is not a tillage method, it is another form of conservation. This means that instead of creating straight rows along the fenceline, the crop rows are instead oriented around hillsides. This helps slow water as it runs down the hills and has to pass through many rows of crops, instead of running down the center of two rows.
    - Pros: Helps slow erosion without added machinery or cost.
    - Cons: Can be more difficult if the farmer is not used to the system.

Interest Approach or Motivator

Ask students if they have watched the ground when it rains. What happens in your yard when it rains? What about your garden? Are they different?

Procedures

To create display:

Take three two-liter bottles, and cut a large, oval shape out of one side.
Fill the bottles about halfway up with soil .
Set one bottle aside. It is complete. It will represent a fully tilled field .
Plant ryegrass seed in one bottle. Cover the seeds lightly, and water it .
Place leaves or decomposing plant matter on top of the seeds. This step should be completed at least one week in advance, if not two. This bottle will represent a no-till field with cover crops .
Place the same plant matter on top of the soil of the remaining bottle. This bottle will represent a no-till field .
Next, take three large water bottles, and cut the bottoms off of them. They should be 3” or taller, and should be able to hold some water.
- Take these plastic “bowls” and poke holes in either side at the top. This will be where you tie the string through.
Tie a piece of string through the sides of the bowls. Try to keep the string length the same on all. This will be how you hang them over the cap of the 2-liter bottles.
- Write on each of the bowls 1, 2, and 3. These labels will help students identify the bottles more easily in the lesson.
Lastly, drape the string handles over the cap end of the 2-liter bottles. Before you perform the experiment, be sure to remove the caps from the bottles.
This display could be made as little as once for the whole class to look at, or as many times as one display per student. If you would like students to have hands-on interaction with the display, the class could be split into groups of 3-5, and each group could use their own display.
If possible, try to find a way to stabilize the bottles so they don’t roll during the experiment. You could go so far as to build a tray for them, or you could try using pencils or popsicle sticks to hold the bottles steady.

Lesson:

Ask the students what they know about erosion. Have they heard about it in the news? Have they seen it? What causes erosion? Have a short discussion.
Show students the display. Ask them what they notice about it. How are the bottles different?
Explain to the students that they will be gently pouring one liter of water over the soil in all three bottles.
1. If the display is not possible, show the students this video: https://www.youtube.com/watch?v=im4HVXMGI68. It will help illustrate the same topics.
Tell the students to take out their science notebooks. Have them write down their predictions about what they will see in each runoff cup.
Pour water over the first bottle. Discuss and record the results. Were their predictions correct? Have students draw and label a picture of the setup and its results.
Pour water over the second bottle. Discuss and record the results. Were their predictions correct? Have the students draw and label a picture of the second setup and its results.
Pour water over the last bottle. Discuss and record the results. Were their predictions correct? Have the students draw and label a picture of the third setup and its results.
Compare the runoff cups. Have students turn to a partner and talk about what they saw and what they predicted.
Ask students why this experiment might be important. Take some ideas if students have them (learning about water movement, how erosion happens, how the earth changes over time, etc.).
1. Guide students to the idea of soil conservation. Talk about why it’s important, and how all food starts from the soil.
Talk with students about different ways that farmers try to prevent erosion. Point to the bottle with bare soil, and talk about how farmers used to till their fields multiple times a year. All of the soil would be turned over and bare. Point to the bottle with plant debris on top, and talk about how some farmers now use no-till systems, so they don’t have to turn over all of the soil in their fields. This helps keep plant material on the soil surface. Then, point to the last bottle with grass growing in it. Talk about how farmers are now planting more cover crops over winter months. Not only is the ground covered, but something is growing in it.
Take out the grass and soil sample and lay it carefully over newspapers or paper plates. Tell students to look closely at the roots of the grass. Each student should record why they think this sample conserved the most soil.
Wrap up class with a summary discussion. Talk about which of the three conserved soil the best and why conserving soil is good for all of us.
Have students write a conclusion paragraph in their science journal summarizing what they learned.

Essential Files (maps, charts, pictures, or documents)

N/A

Did You Know? (Ag facts)

In 2012, nearly 35% of cropland acres in the U.S. were under no-till operation.
In 2012, more than 10 million acres of cover crops were planted.

Extension Activities (how students can carry this beyond the classroom)

Encourage to do more research on no-till and cover crop operations. Have them dig into more of the issues and learn more about the complexities of the issue. Have them write a research paper citing at least one credible source.

Sources/Credits

Fun Science Demos, published February 28, 2015, Jared, video: https://www.youtube.com/watch?v=im4HVXMGI68
Iowa Environmental Focus
Natural Resources Conservation Service

Author(s) (your name)