This lesson introduces agriculture as a managed system that has environmental impacts, and how farmers employ practices such as growing pulses to minimize these impacts. Grades 6-8
Essential Files (maps, charts, pictures, or documents)
break crop: a secondary crop grown to interrupt the repeated sowing of cereals as part of crop rotation
cover crop: a crop grown for the protection and enrichment of the soil
crop rotation: the successive planting of different crops in the same field over a period of years to maintain or improve soil quality and reduce pest problems
inter-cropping: growing two or more crops in the same field; often in the space between rows
legume: a type of plant which has seeds contained in a pod such as a soybean, pea, or alfalfa plant
pulse: the edible, dry seeds of various crops of the legume family
Did You Know? (Ag Facts)
- Beans have been grown by humans for almost 6,000 years.
- Chickpeas were grown in the Hanging Gardens of Babylon (one of the seven wonders of the ancient world).
- An archaeologist working in New Mexico found a clay pot with bean seeds that were 1,500 years old. When the seeds were planted, they grew!
Background Agricultural Connections
Pulses are the edible, dry seeds of plants in the legume family. Examples of pulses include dry beans, dry peas, chickpeas, cow peas, pigeon peas, lentils, Bambara beans, vetches, and lupins. Pulses grow within a pod that can vary in shape, size, and color. Pulse pods can contain between one and 12 grains, or "seeds" depending on the plant variety.
Pulses provide crucial nutrients to our diet. Pulses are low in fat, high in fiber, and a good source of protein, vitamins, and minerals. In comparison to other plant-based foods, they have the richest supply of protein. They are a healthy part of any balanced diet, especially in developing countries with little access to meat or for people who choose a vegetarian or vegan diet. Pulses are very versatile and can be used in entrees, salads, breads, and desserts.
Most pulses are planted from seed in the early spring. They grow throughout the summer and are harvested in the late summer or fall. In addition to the health benefits of consuming pulses, growing pulses is also beneficial to the environment. As part of the legume family, the growth of pulses improves the quality of farm land by returning nitrogen to the soil through a process called nitrogen-fixing. Plants within the legume family contain symbiotic bacteria called rhizobia within the nodules of their root system. When the plant dies, the fixed nitrogen is released which fertilizes the soil and makes it available to other plants. As a result, pulses are a beneficial crop to include in a crop rotation to manage and balance soil nutrients. Watch the video, Science of Nitrogen Fixation to learn more about the discovery of nitrogen fixation by George Washington Carver and the benefits of crop rotation. Other cultivation practices that take advantage of the benefits of pulse/legume crops include:
- Inter-cropping: Growing two or more crops in the same field; often in the space between rows.
- Cover crops: Growing a crop for the protection and enrichment of the soil.
- Break crops: The practice of growing a secondary crop to interrupt the repeated sowing of cereals as part of a crop rotation.
Farming, provides the food, fiber (fabric), and fuel that we use in our every-day lives. Farming requires the use of natural resources such as water and fertile soil. These natural resources are limited and must be managed properly to preserve them for future generations. This is generally referred to as sustainability, or the ability to farm using techniques that protect the environment, public health, and animal welfare. Growing and consuming pulses has a high level of sustainability.
In this lesson, students will:
- understand how nutrients are passed from the soil to the plant through its root system;
- understand nitrogen-fixing as a concept; and
- learn about symbiosis through the role of rhizobia in growing pulses.
Interest Approach - Engagement
- Recall student's prior knowledge by asking, "What is symbiosis?" Review the concepts to identify what students already know. Provide clarification and explanation as necessary.
- Give examples of symbiosis in the natural world. Explain the various animal relationships such as between the hippopotamus and oxpecker bird.
- After giving examples of symbiosis in the animal kingdom, tell students that there are also symbiotic relationships in the plant kingdom. Ask students if they can think of examples. Allow them time to think and offer their ideas.
- Prompt the students by asking them what a legume plant is and how it differs from other non-legumes. If possible, allow students to perform a Google search to discover how the relationship between legumes and the soil they grow in is different than other plants. (legumes are nitrogen-fixing plants which means they return nitrogen to the soil rather than just depleting it like other plants)
- Watch Science of Nitrogen Fixation to learn how agricultural scientist, George Washington Carver helped discover the importance of nitrogen fixation.
- Discover what students already know about how plants grow. Ask, "What are the basic needs for seed germination and growth?" (water, sunlight and nutrients)
- If students already know about plants needing sunlight to create their energy, ask them what else they need?
- "What role does the soil play in feeding the plants?" (soil contains the nutrients, or 'food' necessary for plant growth.)
- "How do plants get water and nutrients from the soil?" (nutrients and water from the soil are absorbed through the root system and circulated through the plant through the xylem tissue.)
- "What would happen to the plants if the soil had no water or nutrients?" (the plant would not grow.)
- Have students follow instructions found in the How to Grow Pea Shoots handout to plant and grow pulse plants in pots or tin cans, which they can observe growing over a period of time.
- Using the Diagram of Pulse Plant Nitrogen-Fixing, introduce students to the concept of nitrogen fixing and explain how rhizobia bacteria works with a plant to improve soil quality.
- Ask students the following questions:
- "How can pulses and nitrogen-fixation help other crops?" (They replenish the soil with nitrogen, a necessary nutrient for plant growth.)
- "How can growing crops together such as inter-cropping like the Three Sisters help? (The bean plant is a legume. When planted with corn and squash the bean replenishes the nitrogen that the corn and squash use.)
- Display the Example 4-step Crop Rotation diagram. Teach students how rotation (growing different crops one after the other) and using ‘break crops’ like pulse crops can improve and manage the available soil nutrients.
- Distribute Crop Cards 1 to 4, giving one set to each group of four students. Ask each group to read out loud what the card says about the crop. Have the students work in their groups to decide which order they will plant the crops over a four year cycle. Remind them that the soil must be left in a suitable state for their first crop to be planted again in the fifth year.
- Ask students to present their crop rotation plan and explain why they chose their particular order.
- To conclude, ask students to again define symbiosis and explain how legumes such as pulses have a symbiotic relationship with the soil and environment. Show the video clip, Pulses and the Environment.
Concept Elaboration and Evaluation
After conducting these activities, review and summarize the following concepts:
- Understanding the process of nitrogen-fixation helps farmers manage and preserve their soil and natural resources.
- Farmers use cultivation practices such as crop rotation, cover cropping, break cropping, and inter-cropping to utilize the benefits of growing legume plants.
- Growing legumes improves the sustainability of agriculture.
Share the Food and Agriculture Organization's infographic, Surprising Facts About Pulses You Might Not Know.
Visit a local farm or invite a farmer to speak in class.
Have students research the impact that pulses in crop rotation have on sustainability.
Ask students to record how their plants grow over a period of time – making observations recorded as diagrams/graphs etc.
Grow alternative pulse plants such as chickpeas and navy beans and compare rates of growth.
Research how to give plants the highest yield through different watering and nutrient feeding techniques or even planting different crops together.
Show the video clip, Pulses Around the World to give students a basic introduction to what pulses are, the food dishes they are found in, and the benefits of growing pulses.