Initial Publication Date: January 13, 2021

Explain: Plant Soil Interactions

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Part A. Nourishing the Planet

Lesson 3: Plant-Soil Interactions -- How do Plants uptake Nutrients?
In this activity set, students explore the important role of roots and other plant structures in the uptake of nutrients from the soil. 
Time required: 2-3 class periods to introduce the material and complete the experiment. Use the following Activities and Masters from Nourishing the Planet.

  • Activity 1. From Soil to Roots -- Master 3.1 "What Do You Know about Roots"
  • Activity 2. From Roots to Plant -- Master 3.2 "Moving Water and Nutrients into Roots"
  • Activity 2. Plant Vascular System -- Master 3.4 "The Plant Vascular System"

After completing the above activities, review soil formation and horizons. To do so, educators may either use the Nourishing the Planet Activity 3. materials or return to Module 2 of this Educator's Guide.

Part B. Cation Exchange

  1. Begin this segment of the lesson by showing the 5-minute animated video explaining Cation Exchange. The video is from the University of New Mexico. 
    Follow the video with these suggested questions:
    • What allows nutrients to "cling-on" to soil particle surfaces?
    • What defines a "cation" vs "anions"?
    • Describe the process of Cation Exchange.
    • How does it affect plants ability to uptake nutrients?
    • In regions of "low CEC" what strategies can farmers take to make sure that plants get the nutrients that they need, while not over-fertilizing?
      • What allows nutrients to "cling-on" to soil particle surfaces? 
        Answer: Electrostatic charges.
      • What defines a "cation" vs "anions"? 
        Answer: Cations are positively charged, anions are negatively charged.
      • Describe the process of Cation Exchange.
      • How does it affect plants ability to uptake nutrients? 
        Answer: Plants exchange Hydrogen ions (+ charged) for nutrients like Ca, Mg, and Fe.
      • In regions of "low CEC" what strategies can farmers take to make sure that plants get the nutrients that they need, while not over-fertilizing? 
        Answer: In areas of low CEC farmers need to fertilize in small quantities more frequently in order to prevent run-off.
  2. Next, Discuss CEC graphic and review Figures 4-3 and 4-4 from Know Soil, Know Life book.
  3. Following the video and discussion have students complete this reading and writing exercise from grownextgen.org which engages students in the relationship between plant nutrient needs and sources. Nutrients needed for proper crop development 
    Key point: There are 17 essential elements needed for plants to grow
  4. Lastly, divide the 17 elements among the students and ask them to present their element to the rest of the class. Record the student-generated information on a large whiteboard or sheet of paper.

Time required: 2-3 class periods to complete the reading and discussion.

Part C. Chemistry in Plant Nutrition

For homework, or to begin the next lesson, share the Chemistry in plant nutrition and growth handouts. 
Ask students to read the handouts and answer the included questions. 
Time required: 30 minutes to complete the reading and answer the questions.