Biology of Soil - Lesson 4 - Issues of Soil Degradation

Biology of Soil - Lesson 4 - Issues of Soil Degradation

Target Grade Level / Age Range:

Grades 9-12

Estimated Time:

Two 50-minute class periods

Day 1: Presentation of concept and instructional materials. Start and complete student experiments. Homework: develop presentation.

Day 2: Students finalize their presentations and present to the class.

Purpose:

Students will understand the issues that can affect soil health and reduce fertility, biodiversity, and/or overall soil health.

Materials:

  • Stakes
  • Twine
  • Scissors or shears
  • Two soil thermometers
  • Timer / watch
  • Optional: high wattage lights or other heating element
  • Mass scale
  • 1,000 grams of dry topsoil
  • Two 500-gram beakers
  • Spoon, weight, or press
  • Water
  • Worms
  • Plastic container (margarine or cottage cheese containers or other Tupperware containers work well)
  • Subsoil with little or no organic matter
  • Potting soil with a high amount of organic matter including peat moss, bark, and other composted vegetation
  • Large measuring beakers. Beaker mouth should be larger than the base of the plastic container.
  • Popsicle sticks
  • Drill
  • Four Nitrate test strips
  • All-purpose fertilizer with high nitrogen content (i.e. 24-0-0 NPK)

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

Vocabulary (with definitions)

  • Extensification – the geographic spread of farming into woodland areas. Using more land and fewer inputs per acre to produce the same amount of production.
  • Intensification – increase in agricultural production per unit of inputs (which may be labor, land, time, fertilizer, seed, feed or cash)
  • Urbanization – changing land use from agricultural production to homes and buildings due to an increase in human population
  • Climate change – any significant long-term change in the expected patterns of average weather of a region (or the whole Earth) over a significant period of time
  • Deforestation – clearance, clearcutting or clearing of a forest or stand of trees from land, which is then converted to a non-forest use
  • Desertification – the process by which fertile land becomes desert, typically as a result of drought, deforestation, or inappropriate agriculture
  • Erosion – the process of soil being moved or carried away by wind, water, or other natural agents
  • Soil compaction – compression of soil particles into a smaller volume, which reduces the size of pore space available for air and water

Background – Agricultural Connections

Soil is the earth’s fragile skin that anchors all life on Earth. It is comprised of countless species that create a dynamic and complex ecosystem and is among the most precious resources to humans. Increased demand for agricultural commodities generates incentives to convert forests and grasslands to farm fields and pastures. The transition from natural vegetation to agriculture can play a role in soil erosion and the soil’s ability to maintain itself.

Half of the topsoil on the planet has been lost in the last 150 years. In addition to erosion, soil quality is affected by other aspects of human activity. These impacts include compaction, loss of soil structure, nutrient degradation, and soil salinity. These are very real and at times severe issues.

The effects of soil erosion go beyond the loss of fertile land. It has led to increased pollution and sedimentation in streams and rivers, clogging these waterways and causing declines in fish and other species. And degraded lands are also often less able to hold onto water, which can worsen flooding. Sustainable land use can help to reduce the impacts of agriculture, livestock, and other human activity preventing soil degradation and erosion and the loss of valuable land to desertification.

The health of soil is a primary concern to farmers and the global community whose livelihoods depend on well-managed agriculture that starts with the dirt beneath our feet.

Interest Approach – Engagement (what will you do to engage students at the beginning of the lesson)

After gaining the student’s attention, ask students what they know about the Dust Bowl. Play one of the YouTube clips of the Dust Bowl.

Continue to discuss the Dust Bowl based on student’s prior knowledge. Facilitate responses and a short discussion. The Dust Bowl was a perfect storm of weather (drought) and poor soil management (plowing). What kind of management practices might have prevented this? What kind of soil management practices can we implement now to prevent something like this from happening in the future?

Procedures

Present the PowerPoint on soil degradation to give students an overview of the potential issues.

Break the class into four groups. Each group will be responsible for conducting one of the following experiments. Each group will be responsible for presenting an overview of the experiment as well as their findings to the rest of the class.

Group 1 Experiment: Soil compaction.
  1. Using a mass scale, weigh out 1,000 grams of a sample of dry topsoil. Put 500 grams into two beakers or another clear-sided container.
  2. Using a spoon, weight or other method of compaction, firmly press down the soil into one of the beakers. Try to remove any pore space. Total volume of the compressed soil should be much less than the other sample.
  3. Add 250 ml of water to the surface of the compressed sample. Using a timer or stopwatch, record how long it takes the water to reach the bottom of the soil sample. Repeat this procedure with the sample that was not compressed.
  4. If necessary, add more water to both samples so they are damp but not sodden. Different soils will take different amounts of water. Try to create a moisture level that would be hospitable to worms.
  5. Place two or three worms on the surface of each soil sample. Time how long it takes for the worms to start burrowing into the soil samples and if they are able to burrow into the samples.
  6. Record your observations.
Group 2 Experiment: Deforestation / desertification effect on temperature
  1. Identify a patch of lawn or other plant covered area on school grounds or area with permission.
  2. Mark out two patches of lawn that are each one square foot in area adjacent to each other. Use sticks, nails, or other material to mark the corners.
  3. Insert a thermometer into the soil to record the soil temperature with the plant cover. Ensure that both patches provide a similar soil temperature reading to establish a baseline.
  4. On one of the patches, use a pair of scissors or clippers and cut as much of the plant matter off as possible. Try to cut down to the roots of the plant or the surface of the soil. Do not pull the plants as you want to keep the soil intact.
  5. Leave the marked patches to sit in direct sunlight for 5 minutes. Take a temperature recording of both marked areas. Repeat this procedure taking temperature recordings every five minutes for a total of 30 minutes. Note: if there is no direct sun, a similar experiment could be done using high wattage light bulbs that produce heat or another heating element positioned close to the surface of the soil.
  6. Record your observations.
Group 3 Experiment: Organic matter water holding capacity
  1. Fill a plastic container with a sample of 500 grams of subsoil with little to no organic matter.
  2. Fill a plastic container with a sample of 250 grams of subsoil and mix in 250 grams of potting soil. Potting soil is made of things like peat moss and bark and will provide a high amount of organic matter.
  3. Press both soils down into the containers to remove as much of the pore space as possible.
  4. Drill or poke holes into the bottom of each container.
  5. Set or hold the containers over two large beakers that can catch water. Use long popsicle sticks to create a suspension platform that will hold the container but still allow for water to drain.
  6. Slowly pour 1,000 milliliters of water onto each soil sample. Let sit for 10 minutes.
  7. Measure the amount of water that was collected in each beaker.
  8. Record your observations.
Group 4 Experiment: Organic matter nitrate holding capacity
  1. Fill a plastic container with a sample of 500 grams of subsoil with little to no organic matter.
  2. Fill a plastic container with a sample of 250 grams of subsoil and mix in 250 grams of potting soil. Potting soil is made of things like peat moss and bark and will provide a high amount of organic matter.
  3. Press both soils down into the containers to remove as much of the pore space as possible.
  4. Drill or poke holes into the bottom of each container.
  5. Set or hold the containers over two large beakers that can catch water. Use long popsicle sticks to create a suspension platform that will hold the container but still allow for water to drain.
  6. Slowly pour 1,000 milliliters of water onto each soil sample. Let sit for 10 minutes.
  7. Using nitrate test strips, measure the amount of nitrate in each of the collected water samples.
  8. Record your observations.
  9. Repeat steps 1-5.
  10. Mix two solutions of 1,000 milliliters of water and one tablespoon of all-purpose fertilizer 24-0-0 NPK or higher nitrogen content. Slowly pour the solutions on each of the soil samples. Let sit for 10 minutes.
  11. Using nitrate test strips, measure the amount of nitrate in each of the collected water samples.
  12. Record your observations.

Have each group prepare a poster, PowerPoint, or other presentation to describe their experiment and their results to the rest of the class. Students should be prepared to make a 10-minute presentation and answer questions about their experiment.

Did You Know? (Ag facts)

  • The FAO (2011) suggests the relatively small area of the earth's surface devoted to agriculture (about 11%), is 25% highly degraded.
    • About 10% of that highly degraded land is improving.
  • The Global Assessment of Human-Induced Soil Degradation estimates soil erosion is responsible for 83% of global land degradation.

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

Suggested Companion Resources

Sources/Credits

  • This material is based upon work supported by the Natural Resources Conservation Service, U.S. Department of Agriculture, under number NR196114XXXXC003. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.
  • The grant by which this project is funded is administered by the Conservation Districts of Iowa.

Author(s)

Will Fett

Organization Affiliation

Iowa Agriculture Literacy Foundation

Agriculture Literacy Outcomes

  • T1.9-12.b. Describe resource and conservation management practices used in agricultural systems (e.g., riparian management, rotational grazing, no-till farming, crop and variety selection, wildlife management, timber harvesting techniques)

Iowa Core Standards:

  • HS-LS1-3. Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.  
  • HS-LS2-1. Use mathematical and/or computational representations to support explanations of factors that affect carrying capacity of ecosystems at different scales.
  • HS-ESS2-2. Analyze geoscience data to make the claim that one change to Earth’s surface can create feedbacks that cause changes to other Earth systems.
  • HS-LS2-2. Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales.
  • HS-LS2-6. Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem.