Target Grade Level / Age Range:


Estimated Time:

Two to four 45 min. class periods


Students will understand the complexity of the soil biome, including the interaction of all organisms, from microorganisms, to plants, to insects and vertebrates.


  • Science journals
  • Computers or tablets with internet access
  • Relevant reference books about soils, plants, microbes, and soil-dwelling insects
  • Poster paper or butcher paper
  • Markers, pens, colored pencils, etc.
  • Optional: craft supplies like pipe cleaners, popsicle sticks, colored paper, pop poms, etc.

Vocabulary (with definitions)

  • Legume: a member of the pea family; a crop that has a symbiotic relationship with soil bacteria that form nodules and fix atmospheric nitrogen
  • Nonliving: inanimate; inorganic
  • No-till: an agricultural field management system in which the soil is not plowed or tilled
  • Tillage: a management practice in which the soil is broken up to prepare a seedbed, kill weeds, or reduce soil compaction
  • Acre: a unit of land equal to 4,840 square yards (about the size of a football field)

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

Thus far, students have learned about many different types of organisms that interact with the soil. This lesson will include how all of those organisms work together to build and maintain a healthy soil, and what those interactions look like.

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

Write the following bell-ringer question on the board for students to answer quickly in their science journal.

“Name three living and three nonliving elements in soils.”

Some examples of living things in soil include plants/plant roots, insects, microbes, bacteria, fungi, worms, and rodents. Some examples of nonliving elements in soil include manure, soil particles, rocks, ag lime (calcium carbonate), and fertilizer. 


  1. Show students the following graphic. Ask them to take out their science journals and write about what is happening. What do these numbers suggest? Why might they suggest it?

  2. After a few minutes, bring the class together and review some things they noticed about the data set. Students may notice that pasture ground was home to many more worms than continuous corn tilled fields. Fields that are not tilled seem to have a higher population than fields that are. Why might that be? Fields planted with legumes (soybeans and clover) have higher populations than corn. Why might that be?
  3. Tell students that their project today will be to start researching the interactions between all of the different pieces of the soil biome. Students will need to create a poster (either individually or in groups of 2-3) where soil particles, plants, organic material, invertebrates, fungi, and bacteria are all represented and labeled. Other organisms or materials can also be represented if they would like. Each item represented on the poster should be labeled, and information should be included about what impacts that aspect of the soil biome. These will be called impacting factors.
    1. For example, worms (invertebrates) can be labeled on the poster with a note saying that tillage and nitrogen availability in the soil impact worm populations.
    2. This poster can be as creative or as bare-bones as the student would like, but must include all previously discussed aspects of the soil biome, and at least one impacting factor for each of them. Any further labeled items or impacting factors are options.
  4. Break the students up either individually or in their small groups to start their poster and research. If reference books are available to them, bring those out for their research. Allow students to bring out laptops or set aside time to visit a media center to allow online research.
    1. Review with the class what a reputable source looks like. State Extension services, like Iowa State University Extension and Outreach are good sources for information. Individuals’ blogs may be good sources of information but can also be much less reputable.
    2. Each lesson in this unit has sources listed near the end of the lesson plan. Consider choosing a few key links per topic for students to review for their research.
  5. Offer one to three class periods for students to research and compile their information. Once students have a firm grasp on their posters, have students share their posters with the class.
    1. Set up areas to post each of the posters. Have each student stand by their respective poster. Tell students that each one of them will give a highlight of their poster and will mention one specific interaction they find the coolest or most surprising in the soil biome.
    2. Encourage students to engage with each other during the presentation. Take one to two questions from other students for each presentation.
  6. Once the poster presentation is complete, have students take their seats. Review with them some of the things they learned. Returning to the initial chart they saw, why do they think now that worm populations were lower in tilled fields and in corn?
    1. Tillage disturbs the worm’s habitat, and legumes like soybeans and clover fix nitrogen and leave a lower carbon to nitrogen ratio in the soil that worms like to eat. However, soybeans leave less organic material in the soil for worms to eat than corn, so a rotation of the two may benefit worms the best in a row crop field.
  7. Other interactions students may mention:
    1. Organic matter feeding invertebrates: a higher organic matter content will help feed and sustain a higher invertebrate population
    2. Soil particle size impacting plant growth: in the plants in soil lesson, students learned that soil texture can impact root growth, among other things
    3. Fungi networks pass nutrients, impacting plant growth: one of the more newly discovered interactions is that of mycorrhizae fungi networks, which can pass nutrients across a field when left undisturbed.
    4. Bacteria break down organic material: The Natural Resource Conservation Service notes that one teaspoon of productive soil generally contains between 100 million and one billion bacteria! These bacteria can break down organic material, suppress disease, fix nitrogen, or do many other things.
    5. Bacteria living symbiotic with plant roots: leguminous plants like soybeans have a symbiotic relationship with certain kinds of bacteria that form nodules on their roots and fix atmospheric nitrogen for the plant to use. This results in less fertilizer needed for the plant to grow its best.
    6. Invertebrates creating macropores in the soil: worms and bugs crawling through the soil aerates it, creating passageways for air, water, and roots.
    7. Microbes creating “glues” that build soil structure: as a byproduct of living, microbes give off glues that can help hold soils together and make them stronger and more resilient.
    8. Or more!
  8. Take any final suggestions from students regarding these interactions.
  9. Next, have students take their science notebooks back out. Have them summarize some key ways living and nonliving things interact in the soil biome.
    1. Once they have done this, pose the question, “What would happen to the biome if we changed one key characteristic?” Have them journal a sentence or two, then have them think about how each of the following factors would impact a soil biome:
      1. Soil texture?
      2. Types of plants grown or crop rotation?
      3. Tillage system?
    2. Would a change in one of these key aspects change much about the biome? Would it continue as normal, or would the entire dynamic change?
  10. Wrap up class by jotting final notes in science journals and storing the soil biome posters properly.

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

  • To prove there is a rich microbial life in soil, take a Mason jar and fill it with topsoil outside of the classroom. Have students smell the soil before the jar is sealed. Seal the jar’s lid tightly and let sit for several days. Then, open the jar and let students smell it again. Does it still have the nice, earthy smell it did before? No, it likely smells more like decaying organisms because that microbial life we cannot see needs air to survive.

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.
  • Earthworms, PennState Extension:
  • The Living Soil: Bacteria, NRCS:


Chrissy Rhodes

Organization Affiliation

Iowa Agriculture Literacy Foundation

Agriculture Literacy Outcomes

  • T2.9-12.b: Compare similarities and differences between organic and inorganic nutrients (i.e., fertilizer) on plant growth and development; determine how their application affects plant and animal life.

Iowa Core Science Standards:

  • 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.

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.