Biology of Soil - Lesson 5 - Plant and Soil Interactions
Target Grade Level / Age Range:
Students will understand how soils help grow healthy plants, and the various ways plants help maintain healthy soils (including adding organic material and roots creating pore spaces).
- 7 punch cups
- 7 germinated soybeans (seeds available from IALF)
- Potting soil or garden soil
- Water source
- Plant food
- Permanent marker
- Labels, notecards, or paper
- Various potted plants with 1+ weeks growth (preferably different types of root systems)
- Plant dissection tools (tweezers, probes)
- Butcher paper or tarps
- Spray bottles with water
- Towels or paper towels
- Science notebooks
Essential Files (maps, charts, pictures, or documents)
- Substrate: an underlying substance of layer; the surface or material on which an organism lives, grows, or obtains its nourishment
- Macronutrient: a chemical element (e.g., nitrogen, phosphorus, potassium) required in large amounts for plant growth and development
- Micronutrient: a chemical element (e.g., chloride, iron, boron) required in trace amounts for the normal growth and development of plants
- Essential nutrient: a nutrient required for normal plant function that cannot be synthesized by the organism
- Cellular respiration: a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into ATP, and then waste products
- Hierarchy: a system or organization in which groups are ranked above one another
Background – Agricultural Connections (what would a teacher need to know to be able to teach this content)
A large piece of understanding soil biology is understanding how plants interact with the soil. This is a complex and varied area, and scientists continue to research this relationship.
A basic purpose of soil is to be used as a substrate in which plants grow and obtain nutrients. Plant roots reach into soil pores and collect nutrients that are held in the soil. The roots reach toward water sources and pull the water toward the stem and leaves. Without the correct access to air, water, and nutrients, a plant would not survive. Plants uptake nutrients through water. Not all nutrients are water soluble. Bacteria and fungus in the soil break nutrients from mineral and organic sources free making them water soluble for plants to use.
Plants need 17 essential nutrients. Of these, there are macronutrients and micronutrients. The Macronutrients are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Carbon, hydrogen, and oxygen are largely absorbed via the air and water. Nitrogen, phosphorus, and potassium (NPK) are primary nutrients, and are the main things fertilized for. The micronutrients are chloride, iron, boron, manganese, zinc, copper, molybdenum, and nickel. These are needed in very small amounts and are rarely fertilized for. The toxicity level for micronutrients is much closer to the deficiency level of those nutrients as compared to the same range in macronutrients. This same phenomenon is evident in animals, as well.
However, plants also give back to the soil. Different plants have different root structures. Think of the difference between a carrot’s taproot and the roots of the Kentucky bluegrass growing in your lawn. These roots interact with the soil differently, allowing different structures of soil to develop and take place. In agriculture, farmers may pay attention to differing root structures when planting cover crops or establishing crop rotations. For example, if a farmer is concerned about soil compaction, they may introduce turnips or radishes as a cover crop. Their large taproot will create more space in the soil and help combat soil compaction. However, if they’re more worried about erosion, they may choose a plant with a more fibrous root system (like rye) that holds onto more soil.
Plant roots also help create smaller pores in the soil, which help serve as water and air channels in the soil. A healthy soil is only about 50% solids (minerals and organic material). The rest is pore space for air and water. Air is important in not drowning the plants. Pore space for water is important so that water can have channels to leave the field and prevent ponding.
Many things can impact the root structure, however. If the soil is dense and clay heavy, it may be difficult for plant roots to grow, and they may adopt odd patterns or be abnormally short. You may be familiar with this phenomenon if you’ve tried to grow carrots at home and they end up with three or four stubby, crooked shoots on one root. On the other hand, sandy soils may result in very long roots, because it provides little resistance to the plant.
Nutrient and water availability also impact root structure. If nutrients and water are close by the plant’s roots when the plant is young, it will not need to grow very deep or wide. However, if it is a droughty spring, the roots will grow deeper and wider in search of water and nutrients. The deepest root system ever discovered (122 meters) was that of a fig tree in South Africa stretching for water! The longest total root length known is rye, which creates an extensive fibrous root system that can stretch over 350 miles in total growth. (Source: https://www.encyclopedia.com/science/news-wires-white-papers-and-books/record-holding-plants)
This lesson features two activities in which students should learn how soil impacts plants and how plants impact soil. The main ideas are as follows:
Soil’s impact on plants
- Provides support, nutrients, water, and air
Plants’ impact on soil
- Mitigates soil compaction
- Creates a variety of different networks in soil depending on plant grown
- Provides root exudates (sugars) and other organic material that feeds insects and microorganisms, and puts nutrients back into the soil
- Holds onto the soil, protecting it from erosion and building soil structure
- Can remove more nutrients than it gives back
These activities also encourage students to learn about the structure and function of plant roots and cellular respiration. The first activity encourages students to think about the purposes of roots and how they function. Review the attached PowerPoint before the lesson to review questions and graphics.
Interest Approach – Engagement (what will you do to engage students at the beginning of the lesson)
Ask students what the purpose of soil is to a plant. Can plants live without soil? If they can, what else do they need to replace soil?
Soil is a substrate for plants to grow in. Soil provides support, nutrients, and a network of water and air to the plant’s roots. Plants can grow without soil, but they will need structures to support them, the correct amount of water and air to their roots, and ample nutrients. This can be done in hydroponic and aquaponic systems.
Ask students what the purpose of plants are to the soil. Do plants help the soil? Can they hurt the soil? Is this a symbiotic relationship or more parasitic?
Plants protect soil. They can use the nutrients in the soil, in some cases degrading it. However, plant material then fertilizes the soil when the plant dies, thus giving nutrients back to the soil. Plant material keeps soil healthy. This is a symbiotic relationship when managed correctly.
Activity: Analyzing the role of soil in plant growth
- In this activity, students will maintain a series of plants and observe how their growing medium effects their growth. They will observe the need for nutrients, support, water, and air. This will help them understand cellular respiration and the nutrients needed to support various processes.
- Create an experiment on plant growth. Follow the below chart to set up the experiment:
- Seven soybean plants will be planted in punch cups. Four will be planted in soil (either potting soil or garden soil). Two will be planted in only water. The control will have no substrate, nutrients, or water. All plants should be in a similar area with similar temperature and access to sunlight.
- Engage students in this experiment by splitting the class into seven groups and assigning each group to construct one of the planters. Tell students they will be observing the effect of different variables on each plant.
- Provide each group one punch cup, one germinated soybean (germinate ~7 days prior), and their designated substrate. Give each group a permanent marker to write their group number or label on the cup. Have them create a small label with nutrient and water usage for their plant, as well.
- *note: this step should be done a few days (5-7) before observations on the impact should begin. This step may take 15-20 minutes.
- As a class, analyze the experiment. Take note on the board of what constants and variables there are. Why does this matter? What will it tell us?
- Constants: Punch cup, soybean plant, access to light, air quality, temperature
- Variables: Substrates, nutrients, water
- Discuss with students what they
will happen. How will each of the plants fare? Why do they think that?
- Have students journal their hypotheses overall and with each individual plant in their science journal. Tell them to hypothesize reasons for their guesses as best as they can, as well.
- Five to seven days after the seedlings are planted, have the class re-analyze how each plant fared. What do they notice?
- Before discussing as a whole group, allow students to walk up to each plant, analyze, and take notes in their science journal. Again, have them make observations overall, and for each specific plant.
- Prompt them to look for changes in color, shape of plant, texture, etc.
- After each student has made observations, bring the group back together for a class discussion. How do the plants look?
- The Control plant is likely dead, as may be the plants in only water. This is because roots need water and air to survive.
- The plants without nutrients likely did worse than those with extra nutrients. However, the plants in soil likely still had enough nutrients and maybe didn’t need extra nutrients. Can students tell a difference between plants in soil with nutrients and without? Discuss the potential issues with using too many nutrients (toxicity to plant, loss to environment, additional cost).
- Discuss with students what they can glean from the experiment overall. They can see that plants growing in a solid substrate like soil have support to stand tall. Plants with nutrients and the correct amount of water and air grow better. But why do plants need nutrients? Don’t they make sugar from photosynthesis (sunlight and air)?
- Plants do photosynthesize, but they need more types of nutrients to survive.
- When plants photosynthesize, they make glucose (C6H12O6). Then, the glucose is transformed into ATP via cellular respiration. ATP stands for adenosine triphosphate, which includes nitrogen and phosphorus in addition to carbon, hydrogen, and oxygen. The plant needs these nutrients to grow and create plant matter but cannot get them from the air or water. The plant must absorb these nutrients via its roots.
- Introduce students to the idea of essential nutrients. There are 17 nutrients essential for plant growth. Some of these are micronutrients. Some are macronutrients. This essentially means that some are needed in small amounts and others are needed in large amounts. Nitrogen and phosphorus (found in ATP) are macronutrients and are needed in large amounts. Farmers generally pay attention to nitrogen, phosphorus, and potassium as fertilizers in their field to maintain plant growth.
- Review with the class why the plants look the way they do. What does soil provide for plants? Why does that matter?
- It provides a substrate that supports the plants, and provides nutrients, air, and water, through a network of pore spaces, minerals, and a realm of living and organic material.
- Have students write some wrap-up notes either accepting or declining their original hypotheses about what happened to the plants.
Activity: Exploring root structures
- This activity will encourage students to explore root structures and observe differences in plants. This will help them understand the differences in plants, the differences in soils/growth substrates, and plant structures and functions.
- Start class with a dissection activity. Have full-grown potted plants (a variety of plant types would be ideal – have them labeled for identification) for small groups of students (2-4 students per group). Distribute the plants with a large piece of butcher paper or tarp, spray bottle of water, paper towels, and various dissection tools (such as probes and tweezers).
- Tell the class that they will be responsible for showing the root structure of the plant. They will need to remove the plant from the pot as carefully as possible and clean away all soil and substrate from the roots. Remind students that roots can be very delicate, so this will need to be done carefully. Allow students to use any tools available to them.
- Give students about 15-20 minutes to work. Walk around to observe groups and answer questions as they arise.
- Towards the end of their work time, encourage students to wrap up their work and begin small group discussion and science journaling. Have each group review what their plant is, what it was growing in, and describe the root patterns they see. Have them sketch the root patterns in their science notebook. What is the overall shape of the root structure? Are the roots fine or large?
Bring the large group together. Have students give observations of the root structures of different plants. Allow students to hold up their plants or let students walk to see the different plants. What might influence the different root structures? What are the purposes of roots?
- Different plant types, different growing mediums, different access to water and nutrients, container size and shape may all contribute to root structure.
Roots support the plant. Roots absorb water and nutrients for the plant to use. Roots are connected to the xylem and phloem in the plant’s stem to send necessary materials to all parts of the plant from the roots.
- Tell students to sketch in their science journal the flow of nutrients and water from the roots to the rest of the plant.
Ask students why we may care about root structure. Why do we care?
- Roots benefit soils by creating new pore spaces. This aerates the soil and creates networks for water. New research suggests these pores may also help store or sequester atmospheric carbon. Roots hold onto the soil, keeping it in place. When plants die, roots return organic matter directly back to the soil, which decomposes and feeds insects and microorganisms that live in the soil.
- Different plants have different root structures. These structures may be better suited for different kinds of soils (think onions grow better in sandy soil where the bulbs can grow with little resistance) or may help repair soils (think planting turnips as a cover crop to aid in reducing soil compaction).
Have students wrap up their thoughts by journaling in their science notebook. Have them answer a few key questions:
- What are the purposes of roots?
- How can root structures differ?
- How can roots impact soil?
Extension Activities (how students can carry this beyond the classroom)
Have students research native prairie plants and their root structures. Iowa has many native prairies. These plants would have been thick a few hundred years ago. How would those prairie grasses’ root structures have impacted the soil? How would the prairie soil impacted the plants?
Suggested Companion Resources (books and websites)
- Nutrients for Life: www.nutrientsforlife.org
- 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
- Soil Pore Structure as Key to Carbon Storage: https://www.morningagclips.com/soil-pore-structure-as-key-to-carbon-storage/
- Plant-Soil Interactions: Nutrient Uptake: https://www.nature.com/scitable/knowledge/library/plant-soil-interactions-nutrient-uptake-105289112/
- Soil Fertility and Fertilizers; An Introduction to Nutrient Management, Seventh Edition, by John L. Havlin, Samuel L. Tisdale, James D. Beaton, and Werner. L. Nelson.
- Photosynthesis and Cellular Respiration: https://photosynthesiseducation.com/photosynthesis-and-cellular-respiration/
- Xylem and Phloem: https://basicbiology.net/plants/physiology/xylem-phloem
- How Do Trees Transport Water from Roots to Leaves? https://www.youtube.com/watch?v=9-dicqNoODg
- How Plants Get Their Nutrients, and What Nutrients Plants Need to Survive: https://www.plantsnap.com/blog/plant-nutrients/
- Soil-Plant Interactions: https://openoregon.pressbooks.pub/envirobiology/chapter/9-2-soil-plant-interactions/
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-LS1-2: Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
- HS-LS1-7: Use a model to illustrate that cellular respiration is a chemical process whereby the bonds of food molecules and oxygen molecules are broken and the bonds in new compounds are formed resulting in a net transfer of energy.
This work is licensed under a Creative Commons Attribution 4.0 International License.