Target Grade Level / Age Range:
3 rd grade
45 minutes – 90 minutes
Students will learn to sequence a plant life cycle using the soybean plant as an example.
- Soybean Sort worksheet
- Soybean Sort cards
- Compare and Contrast pictures
- My Family’s Soybean Farm by Katie Olthoff https://www.iowaagliteracy.org/Tools-Resources/Publications/My-Familys-Farm
Suggested Companion Resources (books and websites)
- My Family’s Soybean Farm by Katie Olthoff https://www.iowaagliteracy.org/Tools-Resources/Publications/My-Familys-Farm
Vocabulary (with definitions)
- Soybean: the seed of the soybean plant, used in a variety of foods and fodder, especially as a replacement for animal protein
- Germinate: when a seed begins to grow and put out shoots after a period of dormancy
- Seedling: a young plant
- Roots: the part of a plant that attaches the stem to the ground to support and supply water and nutrients from the earth to the rest of the plant
- Leaves: a flattened structure of a higher plant that is attached to a stem and is the main organ of photosynthesis and transpiration
- Pod: an elongated seed vessel of a leguminous plant
- Mature: fully developed
Background – Agricultural Connections (what would a teacher need to know to be able to teach this content)
This lesson was written to incorporate the book My Family’s Soybean Farm by Katie Olthoff. This book talks about two boys’ family farm, and how they grow soybeans. The book talks about different things the family does to take care of their soybeans during the different stages of development. This lesson will walk through some of the basic stages and will talk about how environment and care can impact the soybean plant at these different times.
This lesson talks about eight different stages of development. They include seed, germination, seedling, growing plant, flowering, small pod, large pod, and mature pod. Each one will be outlined below.
Seed: Most farmers today purchase their seeds each year. In the book, it mentions planning for next years’ crop. In this section, you can see Isaac looking at a seed catalog. In this catalog, there will be many types of seeds. Different varieties can have different technologies, like herbicide resistance, or built-in insecticide. Different varieties may also be better suited for different soil types, growing zones (subsections of climates), or have resistance to certain diseases. These seeds are also commonly coated with a treatment. This treatment can help protect the seeds against fungi or diseases that can damage the seed before it germinates.
Soybeans are planted in the spring. Farmers in Iowa tend to grow two main cash crops: corn and soybeans. Generally, planting will begin the last week in April, and will hopefully be done before June. Corn is usually planted first, because soybeans tend to be more forgiving in yield if planted later in the season. This is why farmers may plant more soybeans if the spring was especially rainy and they could not get in the field as early as they had hoped.
Germination: Seeds only need two things to germinate: water and warmth. This should hopefully happen less than a week after planting, given there is enough moisture in the soil and the weather has been warm enough. Soybeans need the soil to be at least 54° Fahrenheit to germinate. This will impact when farmers plant their seeds. If the seeds are planted in a cold, moist soil, they can become easy victims to disease and the germination in that field can be impacted poorly.
Seedling: If you are talking to an agronomist, they may refer to this as VE, or the development stage noted as “Vegetative, Emergence.” This happens about 5 – 21 days after planting. Because soybeans are a dicotyledon (broadleaf) plant, their two cotyledons will be the first thing to emerge. These cotyledons can be simply referred to as the first leaves, but in soybeans these cotyledons also give the embryo in the seed the nutrients and energy it needs to begin growing.
Soybeans are interesting crops in that they have a symbiotic relationship with a bacterium that makes atmospheric nitrogen available for them. The bacterium lives on the roots of the soybeans in nodules. When the plant has nodules, it needs far less nitrogen fertilizer, because the bacteria is helping to do that work instead. Usually, farmers don’t have to introduce this bacterium, but in cases where that is necessary (recent flooding, etc.), it is done during this stage or slightly earlier.
Growing plant: As the plant grows, it will create what is called a canopy. Farmers want this canopy to grow quickly, so that the sun cannot reach the ground in between rows. When the plants in neighboring rows grow canopies to meet, this is called “closing the canopy”. This helps prevent weeds in between rows from taking over the field and competing with the crop. As the plant gets larger, farmers will need to use special equipment to navigate through the field.
Some things farmers might look for during this time would be plant diseases, pest damage, and weed presence. They may look for these things themselves, but many farmers will hire an agronomist to scout the field for them. The agronomist may use equipment like a drone and an iPad or tablet to fly over the crop, or apps to help identify issues. The agronomist will also help the farmer decide if the current disease, pest, or weed problem has met an economic threshold where it would be cost effective to treat the issue. For instance, if there are only three weeds in the field, the cost of the herbicide, fuel, and time to spray the field may not be worth it. If there are three hundred weeds in the field, the cost to control the weeds may pay off in the end.
Flowering: Flowering is the first stage in the reproductive portion of the plant’s life cycle. Soybean flowers are small (only about the size of a pinky nail), and are hidden underneath the leaves of the plant. Flowering will begin about 6 – 8 weeks after seedling emergence.
This is the beginning of the reproductive stages in soybean development. So at this point, nutrient needs will increase in order to grow the soybeans that farmers are hoping to harvest. The three main nutrients crops need are nitrogen (N), phosphorus (P), and potassium (K). Farmers may fertilize their soybean crops during flowering, and while the plant is starting the pod and filling the seeds.
Small pod: The pod is important in the soybean plant, because we harvest the plants for the beans that grow in the pod. Pods generally have 3-4 soybeans. Starting at this time, any stress to the plant can have a big impact on yield. The older the plant gets, the less able it is to compensate for stress. Farmers may pay extra attention to plant health during this time to make sure their plant is able to keep as many pods as possible. Iowans don’t typically irrigate their crops, since our rainfall patterns are generally adequate, but for soybean farmers in other regions, this is a key period to consider irrigation.
Large pod: At this stage, plant growth is all but finished. The seeds are now full, and pod weight will peak during this time. At this point, the plant will begin to mature. When a soybean plant matures, its leaves will first turn yellow, then will fall from the plant. Then, the plant will be essentially just a stalk with pods, that will be left in the field until it dries down. Grain should not be stored over about 15% moisture, and it takes energy to dry the grain down if harvested too early. So, this stage may be spent with the farmer monitoring the moisture of his grain so they can begin to decide when to harvest the crop.
Mature pod: The mature soybean pod is brown and hard. Once the seeds reach the target moisture content, the farmer will harvest the crop using a combine with a draper head, or a soybean head. The combine will cut the stalk, gather the pods, and sort the beans from the pods and other plant material. The extra plant material will be returned to the soil, while the combine holds the beans until a grain wagon or semi trailer comes for the grain to be deposited in.
After the plant’s life cycle, the grain can be stored or sold. Soybeans can be used for many purposes, including animal feed, soy biodiesel, vegetable oil, tofu, or even crayons, fibers, foam stuffing in car seats, and many other cool things! Each of these purposes has many jobs and careers associated with it, including livestock nutritionists, chemists, engineers, food scientists, marketers, economists, and many others.
The last activity in this lesson compares the corn life cycle to the soybean life cycle. In the attached document Compare and Contrast pictures.docx, a similar stage in development in the corn life cycle is paired next to the soybean equivalent. For the most part, these stages are very similar. The main differences are that (1) corn is a monocot (grass) while soybeans are a dicot (broadleaf plant), and (2) their flowers differ greatly.
The main differences between a monocot and a dicot are the shape of the leaves and the way the seed germinates. Corn has long, thin leaves, and soybeans have broad leaves with netlike veins.
The flowers on the soybean plant are very small, but they are perfect flowers, meaning they have both male and female parts on the same flower. Corn has imperfect flowers, because the male part of the flower is the tassel, located at the top of the plant, and the female part of the plant are the ears. However, we know that to reproduce, both plants make seeds.
Interest Approach or Motivator
Announce to the class that they will be learning about plant life cycles today. Introduce the idea by asking for examples of different organisms’ life cycles. Talk about how things start small and grow and develop until they mature.
- Turn the discussion towards soybeans. Ask students what they know about soybeans. Have any of them seen soybeans before? What about soy milk or tofu? Those are made from soybeans! Iowa grows more soybeans than any other state, and they are used for many things, including feed for animals, food for humans, and even soy biodiesel (used in school buses).
- Tell students that today they will be reading the book
My Family’s Soybean Farm.
- As a class, read the book aloud. If there are enough copies for every student, rotate through the classroom to allow students to read. Pause while reading to point out explanatory photos or answer questions.
- After finishing the book, ask students for the main idea of the book. What were some things they noticed or learned in the book? If specific pages are referenced, have students look back to find those topics.
- Next, write the eight specified growth and development stages (seed, germination, seedling, growing plant, flowering, small pod, large pod, mature pod) on the board. Walk through each stage with the class, having them describe what happens during each stage. Ask questions like, “What would a farmer do during this time?” or, “What might the plant need during this time?” Allow them to use the book as reference.
- Use this time to introduce information they do not volunteer. Information in the “background” section, worksheet key, or activity cards can be used to fill in gaps where you notice them.
- After the discussion, tell the students that they will be using this information to do an activity.
- There are two activities associated with this lesson. They can be used consecutively, or one instead of the other.
- Activity 1, Picture sort:
- Break students into 8 separate groups, and give each group one of the photo cards. Place the card picture side up, and instruct them to not turn the card over.
- Instruct the class to look at their photo and spend two minutes discussing that the photo is, and what it represents.
- Once the two minutes are up, tell the groups to organize themselves in consecutive order based on the pictures.
- Tell each small group to pick one volunteer to hold the picture, and have the rest of the students take their seats.
- Ask the class if the order seems correct to them. If someone doesn’t think so, have the class discuss and decide if the order should be changed.
- When the class is satisfied, start at the beginning and walk through each picture. At teach stage, have the student turn the card around. The back will have the stage and more information. At the bottom, there will be a letter. The order of the cards should go alphabetically A-H.
- Once each stage is presented, collect the cards and have the volunteers take their seats.
- To close, ask the students to summarize what they learned about the life cycle of soybeans.
- Activity 2, Worksheet:
- After students have been introduced to the life cycle of soybeans and each stage, give every student a copy of the Soybean Sort Worksheet.
- Instruct students to use the word bank at the top of the worksheet to label each stage. Then, use the box in the corner of each picture to number the stages from 1-8.
- Then, have students turn their worksheet over. Tell them to list the stages in order there. In three stages, instruct them to write something a farmer might do during this time.
- When students have completed their worksheets, talk together as a class about what each answer is. Refer back to the notes on the board or the book as necessary.
- Activity 3, Compare and Contrast:
- Next, relate what the students have learned about life cycles to a different plant. Show students the side-by-side comparison pictures of corn and soybean life cycles (Compare and Contrast pictures.docx).
- Draw a Venn Diagram on the board with corn on one side and soybean on the other. Have students talk through some ways that their life cycles are alike and different.
- The two plants are different in a lot of ways, so try to focus the students on the ways the life cycle in particular is alike and different.
- Point out that the two plants have similar stages, but they look differently while they accomplish the same goals. This is because corn is a grass and soybeans are a broadleaf plant. Their flowers are also different in many ways, but they both do have flowers.
- Fill in the Venn Diagram as students give more examples.
Essential Files (maps, charts, pictures, or documents)
- Soybean Sort – Cards
- Soybean Sort – Worksheet
- Soybean Sort – Worksheet Key
- Compare and Contrast pictures
Did you know? (Ag facts)
- Iowa grows more soybeans than any other state!
- Soybeans are a popular ingredient in feeds for animals like cattle and pigs!
Extension Activities (how students can carry this beyond the classroom)
- Have students brainstorm another organism and research their life cycle. Then, have them write about, draw about, or describe for the class how that life cycle is similar to or different from the soybean plant’s life cycle.
- Soybean Physiology, Purdue: https://www.agry.purdue.edu/ext/soybean/Arrivals/10SoyDevt.pdf
- Soybean Growth and Management Quick Guide, North Dakota State University: https://www.ag.ndsu.edu/pubs/plantsci/rowcrops/a1174.pdf
- Identifying Soybean Growth Stages, University of Kentucky: http://www2.ca.uky.edu/agcomm/pubs/AGR/AGR223/AGR223.pdf
- Tall Beans? How to tell if your soybeans are too tall, and what to do. IL Soy Advisor: http://ilsoyadvisor.com/diagnostics/2014/august/tall-beans-how-to-tell-if-your-soybeans-are-too-tall-and-what-to-do/
- Soybean Growth and Development, Iowa State University Extension. PM 1945. Dec. 2009.
Iowa Agriculture Literacy Foundation
Agriculture Literacy Outcomes
- Agriculture and the Environment Outcomes:
- T1.3-5.b: Explain how the interaction of the sun, soil, water, and weather in plant and animal growth impacts agricultural production
- Plants and Animals for Food, Fiber, and Energy Outcomes:
- T2.3-5.c: Explain how the availability of soil nutrients affects plant growth and development.
- T2.3-5.e: Understand the concept of stewardship and identify the ways farmers/ranchers care for soil, water, plants, and animals
- Science, Technology, Engineering and Math Outcomes:
- T4.3-5.d: Provide examples of science being applied in farming for food, clothing, and shelter products
Common Core Connections
- 3-LS1-1. Develop models to describe that organisms have unique and diverse life cycles but all have in common birth, growth, reproduction, and death.
- Social Studies:
- SS.3.13: Identify how people use natural resources, human resources, and physical capital to produce goods and services.
- Language Arts:
- RI.3.3: Describe the relationship between a series of historical events, scientific ideas or concepts, or steps in a technical procedure in a text, using language that pertains to time, sequence, and cause/effect.
This work is licensed under a Creative Commons Attribution 4.0 International License.