Biology of Soil - Lesson 1 - Why Are Soils Important

Biology of Soil - Lesson 1 - Why Are Soils Important

Target Grade Level / Age Range:

Grades 9-12

Estimated Time:

50 minutes


Students will understand that soil provides anchorage for roots, holds water and nutrients, is home to micro and macroorganisms, filters water, stores carbon, and is a foundation for humans to build and produce food.


  • Soil profile cups. One set per group. Each set is six Styrofoam cups. On each cup, write one of the following words on the lip of the cup so the word is visible when the cups are stacked: organic matter, topsoil, subsoil, parent rock, bedrock. Mix the cups up into a random order.
  • Markers
  • Flip chart paper

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

Vocabulary (with definitions)

  • Soil profile – the arrangement of horizons or layers of soil
  • Organic matter – carbon-based compounds found in soil that come from the remains of organisms
  • Topsoil – top layer of soil
  • Subsoil – soil layer immediately under the topsoil
  • Parent material – the geological material from which soil horizons are formed (glacial till, alluvium, colluvium, loess, lacustrine, or residual)
  • Bedrock – solid rock underlying loose deposits of soil
  • Overexploitation – also known as overcultivation or over harvesting, when crops are harvested and little or no biomass is returned to maintain healthy levels of organic matter
  • Overgrazing – when livestock are left on a section of land for too long and graze plants to a level where they can’t recover
  • Compaction – process in which a stress applied to a soil causes densification as air is displaced from the pores between the soil grains
  • Acidification – buildup of hydrogen cations, which reduces the soil pH
  • Salinization – process by which water-soluble salts accumulate in the soil

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

Soil is our life support system. Soils provide anchorage for roots, hold water and nutrients. Soils are home to a myriad of micro-organisms that fix nitrogen and decompose organic matter, and armies of microscopic animals as well as earthworms and termites. We build on soil as well as with it and in it.

Soil plays a vital role in the Earth’s ecosystem. Without soil human life would be very difficult.

  • Soil provides plants with a foothold for their roots and holds the necessary nutrients for plants to grow.
  • It filters the rainwater and regulates the discharge of excess rainwater, preventing flooding.
  • It can store large amounts of organic carbon.
  • It buffers against pollutants, thus protecting groundwater quality.
  • It provides humans with some essential construction and manufacturing materials.
    • Ex: We build our houses with bricks made from clay and we drink coffee from a cup that is essentially baked soil (clay).

It also presents a record of past environmental conditions.

The Importance of Soil: Historically, soil has been overlooked – seen as merely ground for holding plants while fertilizers, nutrients, and water help them grow. Over time, our topsoils have deteriorated due to erosion and some practices such as mono-cropping and over-tillage. A third of the planet’s land is severely degraded according to the United Nations (U.N.), and some experts consider most of the soil in the U.S. as very degraded or degraded. With global population growth expected to reach 10 billion in 2050, soils are becoming increasingly important.

Why Soil Health Matters: Good soil is alive with billions of microorganisms and it has the proper structure to hold water and nutrients. These attributes allow the soil to better absorb and retain water and nutrients for plants and to better protect against pests. Good soil health can improve farm productivity, improve the long-term sustainability of our soils, and help mitigate climate change. The impact of this degradation isn’t just on farmer’s economics but extends to American’s health. The U.N. considers soil degradation one of the central threats to human health in the coming decades.

Soil health has become a hot topic in agriculture and environmental circles:

  • The U.N.’s Food and Ag Organization declared 2015 the year of the soils.
  • The Paris Climate Agreement of 2015 included commitments from signatories to increase soil carbon by 0.4% each year.
  • The United Nations considers soil degradation one of the central threats to human health in the coming decades.

Recently, the Foundation for Food and Ag Research provided a $9.4M grant to the Soil Health Institute, Soil Health Partnership, and Nature Conservancy to work to improve soil health and support positive economic and environmental outcomes for American farmers. General Mills, Nestle Purina PetCare, and other companies matched the grant.

Soil Health Management Methods: Promoting soil health has traditionally come down to three basic practices: cover cropping, crop diversification, and no-till.

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

Students will likely have some basic knowledge of soil. Or, through context clues they can probably figure this activity out to review previous knowledge or learn it as new knowledge. Break the class into groups of two to four. Give each group a set of soil profile cups. Instruct the groups to stack the cups in order of the lowest soil profile layer to the uppermost soil profile layer. Give students two minutes to create their stacks. Review the correct order with them (top to bottom: organic matter, topsoil, subsoil, parent rock, bedrock). You can also review what each of those terms means. Use slide #2 to review and discuss with students.

Next, present students with the pie chart in the PowerPoint slide deck (slide #3) with the displayed percentiles. Explain that each of the percentiles represents a different component of what soil is made up of. Have the students brainstorm what those components are. After some discussion, reveal the answers and review how soil is made up of these different components.

From an agricultural perspective, the plant growth on the surface of the soil provides the cash flow to drive the business. But, the health of the soil beneath the surface can be viewed as stored capital for future year’s productivity.


  1. Students should have some previous knowledge with how soils are formed. Break students into partners or small groups and have them work together to do a “brain dump” and write down everything they know about how soil forms. As a full class, have each of the groups report out. Create a KWL (Know, Want, Learn) chart on a large writing surface. Fill in the first column - What I Know. Then prompt student to share what they Want to Know and capture responses in the second column. Leave the third column blank to be filled in at the end of the lesson – What I Learned.
  2. Review the soil formation process (slides #4-5 of the PowerPoint presentation). Note: Depending on student’s level of pre-knowledge on this, there may need to be additional review of concepts.
  3. Post six large sheets of poster paper around the classroom. Each one should have the heading: ‘Key Soil Function’ and a subheading of one of the following six items.
    1. Food and other biomass production
    2. Environmental Interaction: storage, filtering, and transformation
    3. Biological habitat and gene pool
    4. Source of raw materials
    5. Physical and cultural heritage
    6. Platform for man-made structures
  4. Give students markers and ask them to walk around the room writing down examples of each of the soil functions. Allow for five minutes to complete this activity. Responses will vary greatly. You might need to provide an example to get students started thinking. Monitor student progress and help facilitate the brainstorm process. Here are some examples:
    1. Food and other biomass production
      1. Growing corn
      2. Growing trees
      3. Growing soybeans
      4. Anchors plant roots
    2. Environmental Interaction: storage, filtering, and transformation
      1. Filtering drinking water
      2. Storing garbage (landfill)
      3. Stores carbon in the form of living and non-living organic matter
      4. Transforming atmospheric nitrogen (N2) to plant available nitrogen (NO3)
    3. Biological habitat and gene pool
      1. Seeds can grow – soil provides insulation for warmth, nutrients, water, etc.
      2. Habitat for worms, moles, insects, bacteria, fungi, etc.
      3. Soil bacterium was naturally absorbed into sweet potato DNA to protect the sweet potato from insect predation
    4. Source of raw materials
      1. Ancient ceramic production
      2. Mining for minerals
      3. Building material for houses
    5. Physical and cultural heritage
      1. Effigy Mounds
      2. Acts as cover to protect and preserve physical artifacts from past cultures
    6. Platform for man-made structures
      1. Building houses
      2. Building highways
  5. Pose the following questions and facilitate discussion. Through this conversation, students should realize that our modern and current form of life is largely dependent on soils. If we didn’t have soils, many things would have to be drastically different.
    1. Could we produce food without soil? (Yes, through things like hydroponics and aeroponics food production is possible. But not at the scale needed to feed more than seven billion people. Soil is essential to food production.)
    2. Could we filter water and store garbage without soil. (Yes, water filtration can be achieved without soil, but again not at the scale needed considering the amount of water present on Earth. Garbage management systems could be designed, we could burn garbage, but both have limitations or environmentally negative impacts.)
    3. Where would moles and worms and similar creatures live without soil? (Those creatures are uniquely adapted to living in soil and could not survive elsewhere.)
    4. Is there a source of raw material that could replace soils in how we are currently using them? (No.)
    5. If we didn’t have soil, could we build the same types of buildings, roads, and other structures? (No. Soil allows us to dig basements and pour foundations for buildings. Soils allow us to level roadways for smooth driving.)
  6. Check for student understanding regarding the importance of soils. Explain to the class that even though soils are vital to human existence, approximately 17% of the Earth’s land surface is considered degraded and soils are under threat. Present slides 6-10 in the PowerPoint presentation. Facilitate a student conversation and answer any questions about the topics presented in the slides.
  7. Revisit the KWL chart from the beginning of the class. Fill out the third column and what the students learned
  8. As an assignment, break students into teams of two. Instruct them to conduct internet research to answer and address the questions posed. Have students write a two-page paper in which they:
    1. Identify in what ways soil impacts daily life, and
    2. identify data they find that indicates how a change in soil can cause change to other Earth systems.
      1. For example: soil erosion from Midwest fields and soil deposits in the delta in the Gulf of Mexico.
      2. For example: soil compaction from tractors, livestock, or construction and the decrease in productivity for crop growth.

Did You Know? (Ag facts)

  • Wetlands deliver a wide range of ecosystem services that contribute to human well-being, such as fish and fiber, water supply, water purification, climate regulation, flood regulation, coastal protection, recreational opportunities, and, increasingly, tourism. Despite these important benefits, the degradation and loss of wetlands is more rapid than that of other ecosystems.
  • Through natural processes, such as soil adsorption, chemical filtration and nutrient cycling, the Catskill Watershed provides New York City with clean water at a cost of $1-1.5 billion, much less than the $6-8 billion one-time cost of constructing a water filtration plant plus the $300 million estimated annual operations and maintenance cost.
  • U.S. agriculture produces about 500 million tons of crop residue annually, most of which contributes to maintaining soil organic matter. Plans to use crop residues for bioenergy production could deprive agroecosystems of important inputs for future soil productivity, potentially upsetting existing agroecosystem balances.
  • Arsenic from smelter emissions and pesticide residues binds strongly to soil and will likely remain near the surface for hundreds of years as a long-term source of exposure.
  • Archaeologists have determined that the demise of many sophisticated civilizations, such as the Mayans of Central America and the Harappan of India, resulted directly from the mismanagement of their soils.
  • Covering just 6% of Earth's land surface, wetlands (including marshes, peat bogs, swamps, river deltas, mangroves, tundra, lagoons and river floodplains) currently store up to 20% (850 billion tons) of terrestrial carbon, a CO2 equivalent comparable to the carbon content of today's atmosphere.
  • There are more living individual organisms in a tablespoon of soil than there are people on the earth.
  • Almost all of the antibiotics we take to help us fight infections were obtained from soil microorganisms.
  • Agriculture is the only essential industry on earth.
  • Soil is a nonrenewable natural resource.
  • The best china dishes are made from soil.
  • About 70% of the weight of a textbook or glossy paged magazine is soil.
  • Putting clay on your face in the form of a "mud mask" is done to cleanse the pores in the skin.

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

  • Challenge students to create a song and/or a music video to highlight what they’ve learned. See this example for inspiration.
  • Soil is a mineral resource. Have students conduct research to evaluate competing design solutions for developing, managing, and utilizing soil resources based on cost-benefit ratios.

Suggested Companion Resources (books and websites)


  • 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.
  • Why Is Soil Important? Soil Science Society of America:


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 Science Standards:

  • 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-ESS3-2. Evaluate competing design solutions for developing, managing, and utilizing energy and mineral resources based on cost-benefit ratios.