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

Nourishing Plants with Fertilizers

See the Background section of the lesson Plant Nutrient Deficiencies for further information.

Fertilizers and the Environment

Nutrients provide the basic building blocks of life for all organisms. Proper nutrient application, through fertilizer, improves plant growth and crop yield. However, the nutrient cycle is very complex and humanity is still developing an understanding of the scientific details. Because nutrients occur naturally in the environment, fertilizer application augments nature’s processes. Challenges arise when nutrients, through nitrogen-containing fertilizer, are applied improperly. If nutrients are applied at the wrong rate, in the wrong place, from the wrong fertilizer source, or at the wrong time, then the nutrients may be lost to the environment before the plant(s) can take them up and use them for growth. In such cases, nutrients can be lost from the field either through runoff (water) or through gasification and evaporation (air). In the case of runoff, nutrients can be lost to streams, rivers, lakes, and eventually the oceans. While the hydrologic cycle is very complex, excess nutrients in surface waters can promote growth of algae, which in turn can reduce oxygen concentrations in the water and degrade the overall water quality. In the case of gasification and evaporation, nitrogen is broken down by soil bacteria, is converted to N2O, and moves into the atmosphere as a greenhouse gas.

Nutrient Pollution

Nutrients are a natural part of the environment and enter the biosphere from weathering and erosion processes. Nutrients can enter the environment through agriculture, sewage and wastewater treatment plants, coal-burning power plants, storm water runoff, and automobile exhaust. Nutrient sources vary greatly between urban and rural areas. Controlling nutrient loss means identifying its various sources and implementing policies that limit the loss of nutrients to the environment.

As discussed earlier, organisms require essential nutrients to survive, but they must be present in the proper amounts. Either too little or too much can adversely affect health. A similar situation exists with regard to the environment. The U.S. Environmental Protection Agency (EPA) estimates that almost 20 percent of the nation’s lakes and 30 percent of streams have high levels of nitrogen and phosphorous pollution. This type of nutrient pollution can cause massive overgrowth of algae. These so-called algal blooms also damage water quality. When large populations of algae die and decompose, they deplete the dissolved oxygen in the water. Marine animals that depend on this oxygen either die or leave the area.

Some species of algae emit toxins that can cause rashes, stomach aches and more serious problems for humans. The most severe acute health effect is methemoglobinemia, often called “blue baby syndrome”. Recent evidence suggests that there is not a simple association between nitrate and blue baby syndrome, rather that nitrate is one of several interrelated factors that lead to methemoglobinemia. The disease is uncommon in the United States because potential exposure to high levels of nitrate is limited to a portion of the population that depends on groundwater wells, which are not regulated by the EPA. Public drinking water systems should contain nitrates at a level safe for consumption as nitrates can be removed by water filtration. Nitrogen pollution from cultivated soils, industry, and other sources contributes to global warming because a portion is released into the atmosphere as nitrous oxide (N2O), a powerful greenhouse gas.

Excess nutrients can enter the environment through both natural and human-induced mechanisms. Sources of nutrient pollution are classified as being either point sources or non point sources.

Nutrient Pollution Point Sources

Point sources of nutrient pollution can be tied to specific locations. Typical point sources include factories, power plants, and wastewater treatment plants. In urban areas, wastewater treatment facilities can be the largest contributors to nutrient pollution. For example, in Long Island Sound off the East Coast, an estimated 60 percent of the nitrogen that enters the water comes from sewage discharge leaving New York City.

Nutrient Pollution Non point Sources

Non point sources of nutrient pollution are general sources such as agricultural areas, cities, and automobiles (golf courses, lawns, anything without a distinct discharge point). A major non point source of nutrient pollution is urban development. For example, clearing of land for housing and industry creates sealed surfaces that do not absorb water and increase nutrient-laden runoff. A related non point source of nutrient pollution is the septic systems that have proliferated as the suburbs extend beyond the reach of urban sewer systems. Automobile exhaust is another non point source. This exhaust releases nitrogen into the atmosphere, but it returns to Earth’s surface with the rain. Although definitive information is hard to come by, it has been estimated that up to 40 percent of the nitrogen entering aquatic environments in some areas can come from nitrogen in the air. Agriculture is also a non point source for nutrient pollution. Use of fertilizers can send excess nutrients into the environment, particularly when best practices are not used. To avoid introducing nutrient pollution, fertilizers must be applied using the right source, rate, time, and place. Increasingly, farmers are adopting nutrient management and precision agriculture measures that minimize the amount of this pollution.

Regulation of Nutrient Pollution

During the past 40 years, antipollution laws have been enacted to reduce the amounts of toxic substances released into our waters. States, territories, and tribes set water-quality standards. They classify a given water body according to the human uses the water quality will allow—for example, drinking water supply, contact recreation (swimming), and aquatic life support (fishing)—and the scientific criteria to support those uses. The Federal Clean Water Act mandates that if a water body is impaired by a pollutant, a total maximum daily load (TMDL) must be created. Total maximum daily load is a calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards, and an allocation of that amount to the pollutant’s sources. A TMDL is the sum of the allowable loads of a single pollutant from all contributing point and non point sources. The calculation must include a margin of safety to ensure that the water body can be used for the purposes the state has designated, such as swimming and fishing. The calculation must also account for seasonal variation in water quality.

Today, scientists and policy-makers are working with farmers to develop more-effective and extensive nutrient management strategies. Solving the nutrient pollution problem will involve establishing emission regulations, compliance incentives, and federal oversight.

Managing Lawn Fertilizers

Growing concern about algae in surface waters has led some local municipalities to begin regulating lawn fertilizers. Areas in Florida, Illinois, Maine, Maryland, Michigan, Minnesota, New Jersey, New York, Vermont, Virginia, Washington, and Wisconsin have enacted ordinances limiting the phosphorus in lawn fertilizers. In Ontario, Canada, the township of Georgian Bay passed a bylaw banning the application of fertilizer. The merit of such legislation is still under debate. However, manufacturers are responding by offering fertilizer grades with lower amounts of phosphate. Will these approaches be effective in improving water quality in our rivers, lakes, and reservoirs? The principles of nutrient management that have been developed for agricultural fertilizers also apply to lawn fertilizers. With soil testing and wise application, such as more frequent applications at lower doses, nutrient losses can be reduced.

Land Use

Perhaps surprisingly, fertilizers can have a positive impact on the environment with regard to land use. Land is a finite resource, and human societies use it for a variety of purposes. We need land for residential living, for industries, for recreation, for wildlife habitats, and of course, for growing food and fiber. Land cultivation worldwide has remained about the same for the past 50 years. Although subsistence farmers in developing countries have brought some additional land into production, land has also been lost to expanding cities in the developed countries. Even so, starting in the 1960s, farmers have increased food production about 400 percent. The Green Revolution was made possible largely by three innovations: better crop varieties, use of commercial fertilizers, and better water management practices. The economist Indur Goklany calculated that if we needed to feed today’s population of over 6 billion people using the organic methods in use before the 1960s, it would require devoting 82 percent of Earth’s land to farming.

The United States produces a surplus of food, but the world does not. By 2050, the world’s population is expected to number well over 9 billion people. Food production will need to keep pace. If the world’s population used the world’s farmland evenly, then each person would use 1.8 hectares. Instead, each person in North America uses 9.6 hectares and each European uses 5.0 hectares.

Technology and Nutrient Management

Clearly, if we are going to produce adequate food for our growing population, then crop yields will need to further increase. Strategies will have to be developed to meet the challenges of the future. Some farmers are using technology in a variety of ways to increase crop yields. While the utilization of these new technologies is growing, it is not occurring today on most of the nation’s farms, although adoption is growing. The rest of this section describes some of these technologies.

• Geographic information systems (GIS) allow farmers to use map-based information about natural resources, soils, water supplies, variability in crop conditions throughout the year, and crop yields to ensure the that amount of nutrients being used matches crop needs Even information about the amount of crop residue (which still contains nutrients) left at the end of the year and the amounts of nutrients removed by the crop can be “mapped” and stored in a GIS database. Once this information is gathered into one database, it can be integrated with other GIS databases such as rainfall records (taken from Doppler radar).
• Global positioning system (GPS) is critical to the development of GIS databases and is used to identify the locations of equipment and people in the field. GPS is also useful in assessing general crop conditions and for scouting fields for problems such as nutrient deficiencies. GPS can help farmers return to the same field sites when problems are being addressed.
• Auto-guidance is a feature of mechanized agriculture. It ties together GPS, GIS, and robotics technologies, allowing a driver to sit and watch as the machine does the work. This technology is being used in various types of farm equipment such as tractors, combines, sprayers, and fertilizer applicators. For example, by using auto-guidance systems, farmers can ensure that applications of fertilizers are not on overlapping tracks. The best of these systems can apply fertilizer to an accuracy of less than one inch.
• Remote sensing uses satellite images of fields to help farmers know what is happening to their crops. The satellite images can be analyzed to detect variability in the reflection of visible, infrared, and other wavelengths of light. Some images show thermal (heat) radiation from the ground below, which helps estimate soil moisture conditions. These images and data, linked with the GIS data mentioned earlier, offer a means of detecting problems developing in the field and comparing successive images over time. The rate of change can be determined to illustrate how a problem is spreading.
• Enhanced efficiency fertilizers help reduce nutrient losses and improve nutrient-use efficiency by crops while improving crop yields. These products provide nutrients at levels that more closely match crop demand leaving fewer nutrients exposed to the environment. Slow- and controlled-release fertilizers are designed to deliver extended, consistent supplies of nutrients to the crop. Stabilized nitrogen fertilizers incorporate nitrification inhibitors and nitrogen stabilizers, which extend the time that nitrogen remains in a form available to plants and reduces losses to the environment.
• Gene modification technology is another strategy with potential implications for the future. One of the main factors that limit crop growth is the efficiency of nitrogen uptake and usage by the plant. If crop plants can be made to more efficiently use nitrogen, more fertilizer will be converted into biomass. This means less fertilizer will run off into the environment.

The ultimate goal of this research is to give non legume plants the ability to obtain their own nitrogen from the atmosphere (i.e., to “fix” nitrogen from the atmosphere) and not rely as heavily on added fertilizers. However, giving a corn plant the ability to fix nitrogen would involve adding a large number of genes not only from nitrogen-fixing bacteria but also from an appropriate host plant. The prospect of achieving this anytime soon is remote. Scientists have succeeded in helping plants better use nitrogen by increasing the expression of a single gene. For example, plants that highly express the enzyme glutamate dehydrogenase have been shown to grow larger than those that were not modified to do so. Of course, genetic scientists are not limiting their efforts to nitrogen fixation. A wide variety of crop plants have been engineered to grow faster, tolerate unfavorable environments, resist pests, and have increased nutritional value.

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