Plant Growth Affects the Soil
Students define nitrogen, phosphorus, and potassium as soil nutrients, explain that plants use soil nutrients as they grow, discover that fertilizer replaces depleted nutrients, and analyze information on seed packets to determine the needs different plants have for growth. Grades 3-5
commercial fertilizer: commercially prepared mixtures with precisely measured plant nutrients that include nitrogen, phosphorus, and potassium applied to the soil to restore fertility and increase crop yields
fertilizer: any material of natural or synthetic origin that is applied to soils or plant tissues to supply one or more nutrients essential to plant growth
nutrient: a substance that provides nourishment essential for growth and the maintenance of life
nutrient deficiency: a condition where the amount of a nutrient essential to the health of an organism is lacking or present in an insufficient amount
organic fertilizer: a fertilizer that undergoes little or no processing and includes plant, animal, and/or mineral materials
Background Agricultural Connections
After completing this lesson, students will be able to:
- Describe how nutrient levels in the soil change after plants grow in the soil;
- Appreciate how fertilizers can replace nutrients in the soil;
- Predict how plant growth is affected by a lack of nutrients; and
- Analyze information about conditions for best seed germination and plant growth.
View the Plant Growth Affects the Soil Lesson Video to obtain background information for the lesson.
This lesson is one of a five part series. See the following titles for related lessons:
- Plants Around You: Students learn about the functions of plant parts and the environment plants need to grow.
- Properties of Soils: Students learn about the characteristics and components of soil.
- Plant-Soil Interactions: Students learn about the function of roots and how water and nutrients move through a plant.
- Plant Growth Affects the Soil: Students learn about how plant growth takes nutrients from soil and how nutrients can be replaced.
- How Does Your Garden Grow?: Students make a plan for a garden.
Interest Approach - Engagement
- Ask the students, "What are nutrients?" After hearing their responses, clarify that nutrients are mineral and non-mineral elements necessary for the health of organisms.
- Write the terms "Vitamin C" and "Calcium" on the board. Ask the students what they know about these terms. After the students express their ideas, summarize that vitamin C and calcium are types of nutrients that people need to be healthy, and we get these nutrients from the food and drink we consume. We cannot see nutrients, but they are needed for health.
- Ask the students to give examples of foods that contain specific nutrients. For example, oranges are a good source of vitamin C and milk is a good source of calcium and vitamin D. Guide the students to understand that food contains nutrients, but nutrients are not the same thing as food (food is important for providing energy).
- Ask the students, "How do plants get nutrients?" Explain to the students that they are going to investigate the nutrients necessary for plant health.
|A common misconception is that plants "feed" (gain energy) from nutrients in the soil. Plants use photosynthesis to create the sugars (energy) they need for plant growth and cell function. They take in nutrients from the soil to fulfill other functions. This is not completely analogous to how humans and animals eat food to gain energy and obtain nutrients.|
Activity 1: Plants, Soil, Nutrients, and Fertilizer
- Write the following words on the board or chart paper: nitrogen, phosphorus, and potassium. Help the students pronounce the words and explain that these nutrients are important for plant health. Remind the students that they can't see these nutrients in the soil, just like they can't see the vitamins in the food they eat.
- Project Master 4.1 onto a large screen. Read through the information on the master with the class, and use the example to teach students how to analyze this type of data. Explain to the students that, after working through the asparagus example, they will work with partners to analyze similar information on other plants.
- Help the students understand that the horizontal line marked “starting amount” represents the level of the nutrient before plants were grown in the soil. The bars indicate whether the amount of a nutrient in the soil either increased (more in the soil) or decreased (less in the soil) after the plants grew. If there isn’t a bar visible on the graph for a particular nutrient, the level in the soil didn’t change. (These numbers represent 50 pounds of crop harvest from an acre of soil.) Remember, the graph shows the change in the amount of these three nutrients after plants have grown in the soil compared with the amount before the plants grew. The graph does not show the specific amount of the nutrients in the soil.
- Ask the class to fill in the blanks of the statements at the bottom of Master 4.1. The students should observe that the amount of each nutrient removed from the soil was different.
- There was LESS nitrogen in the soil after the plants grew.
- There was LESS phosphorus in the soil after the plants grew.
- There was THE SAME AMOUNT OF potassium in the soil after the plants grew.
- Organize the students into groups of two. Give each pair of students a different page from Master 4.2. Explain that each group will look at data for a different plant to determine if there are changes in the soil after plants grow. As students work, circulate among the groups to assess their progress, answer questions, or help students that are struggling. Note: Because of the differences in data for particular vegetables, some of the y-axes have a different scale. An extreme example is the y-axis for the graph for peanuts. You may want to point out the scale as students are reporting their results. Including the larger values may make comparing the graphs slightly more challenging for students, but it is also an opportunity to point out details they should look at on graphs and to see how there are differences in plants and their effects on soil.
- After the students have had a chance to analyze their data, hold a class discussion to summarize the data. Ask the teams to report which vegetable they analyzed and what conclusions they made from the data. The main conclusion for students to draw from the data is that nutrients (nitrogen, phosphorus, and potassium) are removed from the soil when plants are grown. There is less of the nutrient in the soil after plants have grown than there was before (or no change for some nutrients). There are no examples given in which the nutrient level is higher after plants grow.
- After the students conclude that the soil contains fewer nutrients after plants grow, ask them to consider the following questions:
- What happened to the nutrients that were removed from the soil? (The plants took the nutrients up through their roots.)
- Where do these nutrients go when the plants are harvested and taken away from the soil? (The nutrients the plants take up through their roots are taken away with the plant.)
- If there are fewer nutrients in the soil after plants grow, and the nutrients are taken away with the harvest, what do you predict will happen the next year when someone plants a new crop in that soil? (The plants will not be as healthy and will not grow as well. Even though the amount of nutrients removed from the soil seems very small, if plants are grown year after year in the same soil, the soil can become depleted.)
- Project Master 4.3 onto a large screen. Ask for volunteers to read the information in the chart aloud to the class. Ask the students, "Can you draw a conclusion about what happens to plants when they don’t get enough of a specific nutrient?" (Crops don't grow well and aren't healthy when they are missing nutrients.)
- Continue the discussion by asking the students if they think there is anything that can be done to put nutrients back into the soil. Use the following information to guide the discussion:
- One way to replace the nutrients that come out of the soils is to use fertilizers. Fertilizers add nutrients back to the soil.
- The main nutrients in most fertilizers are nitrogen, phosphorus, and potassium. Different types of fertilizers have different amounts of each of these nutrients.
- Fertilizer is not plant “food.” This is not a scientifically accurate analogy, even though the term gets used this way in some popular media. A more appropriate analogy would be vitamins that humans take. People may take vitamins to replace nutrients that they don’t always get in their food.
- Ask the students to consider a scenario in which a farmer plants a crop in soil that is low in important nutrients. His plants aren’t doing very well so he puts fertilizer on the ground. Ask the students to predict what effect this might have on the plants. (The crop plants would get healthier after the fertilizer is applied to the land. Plants don’t distinguish between the nutrients that are natural in the soil and the ones added as fertilizer. Soils may be thought of as a “nutrient bank” that holds a limited amount of nutrients. Fertilizers put more “money” in the bank by restoring nutrient balance to farmed soils. The farmer needs to be careful not to use too much fertilizer. If the amount of a nutrient is too high, plants may not grow well.)
- Explain to the students that farmers and gardeners often do soil tests to find out which nutrients are present in the soil and what may be lacking. Ask the students to think of reasons why a soil test is helpful to farmers and gardeners. (A soil test gives the farmer or gardener specific information about whether the soil has low levels or high levels of certain nutrients, such as nitrogen, potassium, and phosphorus. This gives the farmer or gardener information that will help them make decisions about whether they need to use fertilizer, how much fertilizer to use, and what kind of fertilizer to use. It can also help them make decisions about which crop plants may grow best in their soil.)
Activity 2: What Should I Grow in My Garden?
- Ask students to make a list of environmental factors they would need to consider if they wanted to plant a garden outside. (soil, water, temperature, etc.)
- Hold a class discussion in which students identify categories of information they can find on seed packets. Write the categories on the board or chart paper. Categories may include:
- Name of the seed or plant
- Description of how the vegetable is used (prepared in dishes we eat)
- How deep to plant the seeds
- Type of soil in which the plant grows best
- How far apart to space the seeds when planting
- How far apart the plants should be (thinning space)
- How long it takes for the seeds to sprout
- How tall the plants get
- How long it takes until the plant is ready for harvest
- The type of weather the plant needs (temperature, sunlight)
- When to plant the seeds
- Organize students into groups of two. Give each group a different page from Master 4.4. Have each group find two pieces of information on their handouts that are specific to their seeds and ask them to share that information with the class. Ask the students why this information is important for growing the plants in a garden. (Plants have different needs. Knowing this information can help make a garden more successful.)
- Conclude the activity by asking students if the information on the seed packets makes them think of anything else they would need to know in order to plant these seeds in a garden. Have them add their ideas to the list they started in procedure 1. (how much space they have, whether or not the space gets full sun, what type of soil is in the space, what insects live in that area, date of last frost, etc.)
Concept Elaboration and Evaluation
After conducting these activities, review and summarize the following key concepts:
- Just like humans, plants need specific nutrients to grow and be healthy.
- Plants typically obtain their nutrients from the soil.
- Plants can use up all of the nutrients in the soil. Using fertilizer is one way to return nutrients to the soil.
- Farmers take care of their land by keeping a good balance of nutrients in their soil.
Read Issue 3 of Ag Today titled Our Invaluable Natural Resources. This reader can be printed or accessed digitally. It helps students understand how plants and animals raised on farms depend on natural resources, such as the sun, soil, water, and air, to live and grow. Learn methods farmers use to protect and preserve these natural resources while still providing the food, fiber, and fuel we need to live.
Have the students design an investigation to determine how the amount of fertilizer used affects plants. One basic design is to use different amounts (concentration) of fertilizer. For example, if growing peas, some containers could be treated with fertilizer at the recommended amount, while other containers would be treated with either a more dilute solution, a more concentrated solution, or no fertilizer at all. Safety Note: Be sure to label the fertilizer correctly and store it out of students' reach. Supervise student use of the fertilizer. Follow the package instructions for safe handling and storage.
- BSCS-Biological Science Curriculum Study
- Reviewed by Smithsonian Institution