1. Engage students in learning about soils and crop growth.

Tell students that plants grow better in high-quality soils than in lower-quality soils. Ask:

• Soil quality is a measure of the level of nutrients in soil and its structure. How does plant growth reflect the soil quality? (Plants grow better in high-quality soil because there are more nutrients in it. They grow less well in lower-quality soils because there are not sufficient nutrients.)

• How do you think humans could improve the quality of soils? (Answers will vary. Soil quality can be improved by adding more nutrients, which can be done by composting or leaving more roots in the soil year to year.)

2. Discuss the role of uncertainty in the scientific process.

Tell students that science is a process of learning how the world works and that scientists do not know the “right” answers when they start to investigate a question. Let students know they can see examples of scientists' uncertainty in forecasting crop yields. Show the Projection of Maize Crop Yields in France graphs. (Download the image from the media carousel above by clicking on the down arrow in the lower right corner of the carousel window.) Tell students these graphs show the average daily precipitation, number of hot days, and yield of maize. The gray line shows the predictions for crop yield based on technological improvements. The pink shading shows the expected yield based on temperature and precipitation influences. The total uncertainty is shown by the red lines outside the pink shading. Ask:

• Does the technology trend (gray line) accurately predict crop yields? (No, the technology trend does not adequately predict crop yields. This is because crop yields are dependent on temperature and precipitation as well as technological improvements.)

• Why do you think the crop models still have uncertainty even after accounting for precipitation and temperature differences year to year? (Student answers will vary. The crop yield could be affected by a pest infestation.)

Tell students that they will be asked questions about the certainty of their predictions. Let students know that they should think about what scientific data is available as they assess their certainty with their answers. Encourage them to discuss the scientific evidence with each other to better assess their level of certainty with their predictions.

3. Introduce the concept of stocks and flows in a system.

Tell students that materials flow into and out of systems. The flow of the materials over time can change and can be influenced by many different factors and interacting parts.

Scientists think about how one part of the system can affect other parts of the system. Give students a simple example of a stock and flow in a system, as described in the scenario below.

There is a bathtub with water flowing in from the faucet and water leaving through the drain. Ask:

• When the drain is plugged, what happens to the level of water in the bathtub? (The water level will increase because the outflow of water is stopped, but water keeps coming in from the faucet.)

• When the faucet is turned off, what happens to the level of water in the bathtub? (The water level will decrease because the inflow of water is stopped, but the water keeps leaving through the drain.)

• How can the level of water in the bathtub be kept at the same level? (The water in the bathtub can be kept at the same level by making the inflow equal to the outflow. Then the water that comes in through the faucet will be offset by the water that leaves through the drain.)

4. Introduce and discuss the use of computational models.

Introduce the concept of computational models and give students an example of a computational model they may have seen, such as forecasting the weather. Project the NOAA Weather Forecast Model, which provides a good example of a computational model. Tell students that scientists use weather models to predict future conditions based on current information about the energy and moisture in the atmosphere. There are many different types of models. Scientists can use soil models to predict the movement and quality of soil in a region. Let students know that they will be using models of soil movement and quality.

5. Have students launch the Soil Quality interactive.

Provide students with the link to the Soil Quality interactive. Divide students into groups of two or three, with two being the ideal grouping to allow groups to share a computer workstation. Tell students they will be working through a series of pages of questions related to the data in the interactive. Ask students to work through the interactive in their groups, discussing and responding to questions as they go.

NOTE: You can access the Answer Key for students' questions—and save students' data for online grading—through a free registration on the High-Adventure Science portal page.

Tell students that this is Activity 5 of the Can We Feed the Growing Population? lesson.

6. Discuss the issues.

After students have completed the activity, bring the groups back together and lead a discussion focusing on these questions:

• In Model 5: Landscape With Soil Quality Measurements, how could you treat the soil to improve its quality? (You can minimally till the soil, leaving roots in the soil year to year. This increases the soil quality.)

• How does constantly tilling the soil decrease its quality? (Lots of tillage breaks up the plant roots. This allows the soil to erode. When the soil erodes, it loses nutrients. That decreases the quality of the soil.)

Why does crop rotation work? (Different plants have different nutrient requirements. If you plant the same type of plant in a field year after year, the nutrients that it requires will be depleted from the soil. If you rotate other crops in, you have diversity in their nutrient requirements. Some plants add nutrients to the soil as they grow; legumes add nitrogen to the soil, for example. Using different crops to fertilize each other leads to less need for inorganic fertilizers.)