Students will recognize that fertile soil is a limited resource, describe the role fertilizer plays in increasing food productivity, distinguish between organic and commercial fertilizers, describe how excess nutrients are harmful to the environment, and identify different sources of nutrient pollution. Grades 9-12

• Lesson Handouts: Masters 5.1 - 5.7

algal bloom: a rapid increase in the population of algae in a given area of water, which often causes the water to look green

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

non point source: nutrient pollution that results from runoff and enters surface, ground water, and the oceans from widespread and distant activities

nutrient: a substance that provides nourishment essential for growth and the maintenance of life

point source poluution: nutrient pollution that comes from a specific source that can be identified such as a factory or a wastewater treatment plant

1. Ask your students if they think we have adequate land to grow and produce enough food for a growing population.  Can every acre of farm land be used to grow food crops or raise animals? 
2. Students may picture areas where there is a lot of open space. However, do they realize that not all land is suitable for growing crops?
3. Introduce the lesson to students. After completing this lesson, they will be able to:
   • recognize that farmland is a finite resource;
   • appreciate that the world’s growing population demands an increase in food productivity;
   • describe the role fertilizer plays in increasing food productivity;
   • distinguish between organic and commercial fertilizers;
   • describe how excess nutrients are harmful to the environment; and
   • identify different sources of nutrient pollution.

Activity 1: The Big Apple

Teacher Note: This activity uses an apple as a model of Earth. The Apple Land Use Model can be used as an alternative demonstration option. Students discuss the various ways people use land and make predictions about what percentage of Earth’s land is needed to grow our food. After discussing the ways in which land is used (Step 2), you may consider having the students create their own pie charts where they predict the percentages associated with different land uses, especially farming. Later, their predictions can be compared with the actual values revealed by the apple demonstration.

1. Explain to the class that this activity is concerned with how we as a society use land. The amount of land on Earth stays the same, so as the world’s population gets larger, it becomes even more important that we make wise decisions about how it is used.
2. Explain that land is used for many different reasons. Ask, “What are some of the most important uses for land?” Write students’ responses on the board or an overhead transparency. Students’ responses may include the following:
   • Farming
   • Homes
   • Industries or places where we work
   • Pastures or land for livestock.
   • Parks, sports, and recreation.
   • Wildlife habitat (wetlands,mountain ranges, forests, deserts, beaches, and tundra).
     • If one of these uses is not mentioned by a student, ask guiding questions to bring it out. A student may point out that some land such as a desert has no use. Of course, any land that is not being used by humans can be considered a habitat for wildlife and provides a variety of other economic services for people. For example, wetlands help remove nutrient pollution from rivers, lakes and estuaries.
3. Call attention to the apple and the knife. Explain that the apple represents Earth. Ask, “How much of the total Earth’s surface do you think is devoted to farming?” Students’ responses will vary. Some may remember that about 70 percent of the surface is water.
4. Use the knife to cut the apple into 4 equal parts. Set 3 parts aside and hold up 1 part. Explain that the surface of the world is about 70 percent water, so this 1 piece represents that part of the surface that is land. Remind students of the many different uses for this relatively small amount of land.
5. Use the knife to cut the 1/4 piece of apple in half 3 more times, each time discarding 1/2. Finally, hold up 1 of the smallest pieces and explain that it represents 1/32 of the surface of Earth or 1/8 the land where we live. This is the amount of land available for farming. Point out that the skin on this small piece of apple represents the tiny layer of topsoil that we depend on to grow food.
6. Explain that because we put land to so many different uses, the amount devoted to farming has hardly changed during the past 50 years. Scientists are worried about how we will feed the world’s growing population in the next 50 years.

Activity 2: Using Land Wisely

In this activity, students use a world population projection to consider how much additional farmland will be needed to feed humans in the year 2050.

1. Remind students that the purpose of diagnosing plant nutrient deficiencies is aimed toward increasing food production for both local and world wide inhabitants.
2. Display Master 5.1, Newspaper Articles and reveal only the top article. Ask a student volunteer to read the article aloud.
3. Explain to students that they will continue in their roles as agricultural experts concerned with increasing crop yields on farms. Ask students to summarize the content of the article.
   • Try to focus the discussion on the world. Most students in the United States do not have direct experience with severe hunger. Help them understand that in addition to human suffering, hunger can also lead to unstable governments, wars, and threats to national security—including that of the United States. It is in everyone’s best interest to eliminate world hunger.
   • The article states that population growth contributes to the problem of world hunger. Do not dwell on population control measures. The students are working as agricultural experts and need to focus on how to grow more and better food. The article also mentions availability of freshwater and increasing temperatures as challenges for growing more food. If students do not understand why increasing temperatures cause lower crop yields, explain that it takes more energy for plants (and people) to maintain themselves at higher temperatures. Using humans as an example, you can point out that marathon records are usually set at cooler temperatures.
4. Now uncover the bottom article and ask a second volunteer to read it aloud. Ask students to summarize the article.
   • Students should recognize that there are many factors that influence world hunger and that addressing the problem requires the skills of many different types of professionals including social scientists, climatologists, water management experts, and agricultural experts.
5. Divide the class into teams of 3 students . Explain that their first task is to investigate how population growth is expected to affect farming in the future.
6. Pass out to each team a copy of Master 5.2, Population and Land Use Graphs and Master 5.3, Needs of the Future. Briefly review the information with students .
   • The population graph provides data about the world population from 1950 and projections for the population in the year 2100. The high, medium, and low estimates of the future world population are based on fertility rates (the number of children that people have). Instruct some teams to use the high estimate in their calculations, others the medium estimate, and the rest the low estimate.
   • The value of 12 percent of land devoted to farming refers to the world as a whole. Obviously, the corresponding figures for different countries vary considerably. This activity is designed to examine the problem of feeding the world and not to explore the situations within individual countries.
7. Instruct teams to use the graphs on Master 5.2, Population and Land Use Graphs to perform calculations on Master 5.3, Needs of the Future about how much farmland will be needed in the year 2050.
   • Give teams 10 minutes to perform their calculations. The numbers needed to perform the calculations can be estimated from the population graph.
8. Ask each team to report the results of their calculations. Write their answers on the board or chart paper.
   • If any answers are out of the expected range, go through the calculation systematically, identify the mistake, and correct it. Obtain answers using the high, medium, and low population estimates.
9. Ask students to summarize the results .
   • If students do not point this out, emphasize that if crop yields stay the same between now and 2050, then perhaps an extra 1 billion acres of farmland will need to be set aside and cultivated.
10. Ask the students to remember the different uses of land that they described in Step 2 of Activity 1, The Big Apple.
    • Point to the list of land uses that students created in Activity 1.
11. Ask, “If a billion acres of extra farmland are needed to feed the world’s population, from where should it come? What are you willing to sacrifice?”
    • Students likely will believe that people must have adequate land for the places where they live and work. They may suggest taking the land from parks or wildlife habitats. Some may suggest that if more people became vegetarians, the extra farmland could come from pastures where livestock graze.
    • These questions are not intended to settle the issue. Instead, they are intended to prompt a discussion that helps students see the scope of the problem and to consider some of the difficult decisions that may lie ahead.
    • This step gives you a sense of the students’ awareness of the tradeoffs associated with the reallocation of limited resources.
12. Explain that in the next activity, they will consider how farming practices can influence land use and crop yields.

Activity 3: Fertilizers and the Future

In this activity, students identify advantages and disadvantages of using organic and commercial fertilizers. They also consider how to minimize nutrient pollution.

Teacher note: The readings about organic and commercial fertilizers are brief. The information is not meant to be comprehensive. Rather, it is designed to challenge students’ critical-thinking skills and provide opportunities for them to construct explanations supported by evidence.

1. Remind students that in Activity 2, Using Land Wisely, they calculated that approximately 1 billion extra acres of farmland would be needed to feed the world’s population in 2050. Ask, “What were two assumptions made in reaching this conclusion?”
   • Students’ answers will vary. Some may focus on assumptions associated with the rate of population growth. This is a good answer, but you should guide the discussion to remind students that their calculations assumed that the crop yields from farms would remain constant between now and 2050.
2. Ask, “What will be the effect of increasing the amount of food that an acre of farmland can produce?"
   • Students should realize that if farmland becomes more productive, then fewer acres would be required to meet the world’s food needs.
3. Explain that in their roles as agricultural experts , they are going to make recommendations to the Earth Food Bank about how to farm in the future. Explain to students that when considering the proper use of fertilizer, they want to increase crop yields, while at the same time minimizing harm to the environment. Proper application of fertilizer means the following:
   • Fertilizer is added at the right time. Fertilizers should be applied during that part of the plant’s life cycle when the nutrients are needed.
   • Fertilizer is added at the right place. Fertilizers should be applied in a location where the nutrients can be taken up by the plant’s root system.
   • Fertilizer is added at the right rate. Fertilizers should be applied at the rate at which the plant can use the nutrients.
4. Explain that students need to learn more about fertilizers and their effects on the environment.
   • Pass out to half of the teams a copy of Master 5.4, Thinking about Fertilizers and a copy of Master 5.5, Pros and Cons of Different Fertilizers.
   • Pass out to the other teams a copy of Master 5.6, Nutrient Pollution and a copy of Master 5.7, Nutrient Pollution Discussion Questions.
   • Instruct the teams to read the information found on the first handout (either Master 5.4, Thinking about Fertilizers or Master 5.6, Nutrient Pollution) and to discuss within their teams their understanding. Students should relate the ideas of “right time, right place, and right rate” when considering the use of fertilizers and their impacts on the environment.
   • Students should use the second handout (either Master 5.5, Pros and Cons of Different Fertilizers or Master 5.7, Nutrient Pollution Discussion Questions) to record their conclusions.
   • Students reading about fertilizers should be able to identify 3 or 4 advantages and disadvantages of each type of fertilizer. Students reading about nutrient pollution should be able to describe how excess nutrients can produce algal blooms that use up oxygen in waterways, leading to suffocation of other plants and animals. They should be able to identify wastewater treatment facilities and industrial plants as point sources of nutrient pollution. They should identify urban development, septic systems, the burning of fossil fuels, and agricultural runoff as non point sources of nutrient pollution. Student suggestions for limiting non point sources of nutrient pollution will vary. There is no simple correct answer. Look for logical responses that students can defend using evidence. The idea is to get them thinking about the multiple sources of nutrient pollution and for them to realize that minimizing it will require a complex set of regulations, incentives, and government oversight.
5. After the teams have completed their tasks, ask volunteers to read their conclusions.
   • Make a list of the advantages and disadvantages of each type of fertilizer on the board or on chart paper.
   • Discuss answers to the questions about nutrient pollution.
6. Ask, “Why do you think that some farmers use organic fertilizers and others use commercial fertilizers?”
   • Student responses will vary. Try to bring out in the discussion that the farmers in the United States have more options than farmers in poorer countries who may have no choice but to use organic fertilizers that they produce for themselves. One consequence is that farmers in poorer countries often obtain lower crop yields as compared with farmers in the United States.
   • Teacher note: Try to avoid getting bogged down in debating whether or not food that is organically grown is safer or tastes better than food grown using commercial fertilizers. This is not the focus of the lesson. Scientific studies have not been able to find consistent taste, health, or safety differences between foods grown using the two types of fertilizers.
7. Conclude the lesson by asking students to hold on to their handouts. Explain that they will refer to them during the next lesson when they will be making recommendations for farming in the future.

After conducting these activities, review and summarize the following key concepts:

• Fertile soil that is adequate to grow crops for our food and fiber is a limited natural resource.
• Nutrients are required in the soil to grow healthy plants just like people need nutrients in their diet.
• When nutrients are not available in the soil, they can be added through the use of fertilizer.
• With a growing population, properly using and balancing soil nutrients is very important to the stability of our food supply.
• Farmers use various conservation techniques and technologies to manage their use of fertilizers and diminish negative impacts such as algal bloom or water pollution.

• Nutrients for Life Foundation
• BSCS-Biological Science Curriculum Study
• Reviewed by Smithsonian Institution

• Apple Land Use Model
• Nutrients for Life eLessons
• Phosphate Mining Video
• Potash Mining Video
• Soil Health Education Resources