What's Our Soil Worth?
Students determine that topsoil is a limited resource with economic value and use an apple to represent how Earth’s land resources are used. Grades 3-5
Activity 1: Slicing Up Earth's Land Resources
- Slicing Up Earth's Land Resources Slide Deck
- Slicing Up Earth's Land Resources Activity Sheet
- Large apple
- Cutting Board
- Apple Land Use Model, available for purchase from agclassroomstore.com (optional)
Activity 2: The Value of Soil
conservation tillage: farming methods that reduce the intensity or frequency of tilling in order to maintain some ground cover throughout the year and disturb the soil as little as possible while still providing the conditions needed to grow a productive crop
contour planting: tilling and planting crops on the contour, or at a right angle to the slope, which slows water flowing downhill and reduces erosion
cover crop: a crop grown for the protection and enrichment of the soil
nonrenewable resource: limited natural resource that cannot be replaced or reproduced within a generation and cannot be managed for renewal; examples include oil, soil, mineral resources (lead, iron, cobalt, zinc, etc.)
strip cropping: planting in strips or bands of alternating crops that serve as barriers to erosion; crops that have fibrous roots hold the soil better than crops with tap roots, and taller crops act as wind buffers
sustainable agriculture: an approach to agriculture that focuses on producing food while improving the economic viability of farms, protecting natural resources, and enhancing quality of life for farmers and society as a whole
value: usefulness or importance of something; also, the amount of money that something is worth
Background Agricultural Connections
Agriculture is an important part of the economy of the United States. In 2020, 19.7 million full- and part-time jobs were related to the agricultural and food sectors—10.3 percent of the total U.S. employment.1 Agricultural exports are translated into billions of dollars for United States trade. On poor soil, it costs farmers more to produce good crops, and this cost is passed on to the consumer—you—in higher prices at the grocery store. Erosion reduces agricultural productivity and washes sediment into rivers, lakes, ocean gulfs and bays, affecting fisheries and recreation opportunities in these water bodies. Soil loss affects our country’s economy and our lives.
The United States has more high-quality agricultural land than any other country in the world. Just over half of our land is used for agricultural production, and that production depends on good soil. It can take 100 to 500 years to make one inch of topsoil. From the perspective of a human lifetime, soil is a nonrenewable resource. Fertile topsoil produces the highest yields of food per acre, and farmers will work hard to protect their soil, but erosion can be complicated and expensive to address.
In the United States, cropland erosion decreased by more than 40% between 1982 and 2007. During this time, more and more farmers implemented practices like strip cropping, contour planting, conservation tillage, and planting cover crops to help mitigate wind and water erosion. Erosion has slowed over the past 30 years, but we are still losing millions of tons of topsoil each year at a rate much faster than the natural replenishment rate. Farmers don’t always have the resources needed to implement soil conservation practices. For example, cover crops effectively reduce erosion, but the seed for the crop costs money, takes time to plant, and needs water to grow, and the cover crop doesn’t directly generate any income for the farmer. When topsoil is lost, crops are less productive, income is reduced, fewer people might be fed, and sediment may wash into lakes and rivers downstream impacting water quality.
Soils produce our food, keeping us alive. How do we put a value on soil or land? Many would say it is simply invaluable, but farmers have to make economic decisions about the soil every day. They cannot spend more to protect the soil than they earn from selling their crops, or they will go out of business. Yet, if farmers don’t protect the soil, many years of erosion could destroy the productivity of our valuable agricultural soils. The field of sustainable agriculture has grown out of problems like this. Agricultural scientists, policy makers, engineers, and many others are working to help farmers develop techniques that are economically viable, produce the food we need, and protect natural resources like soil and water over the long term.
- Ask the students to think about an item that is valuable to them. Ask them to answer the following questions to themselves:
- Was your item expensive to buy?
- Can it be easily replaced?
- Does it perform a function that has value?
- Could another item perform the same function?
- Next, ask students if they believe that soil is valuable. Discuss why or why not. Guide the class discussion to help students begin to understand that soil is a valuable resource. Inform students that they will be exploring why soil is valuable.
Explore and Explain
Activity 1: Slicing Up Earth’s Land Resources
Teacher Note: The following activity uses an apple to demonstrate the distribution of Earth's soil resources. Alternatively, you can provide the same demonstration using the Apple Land Use Model.
- Project the Slicing Up Earth's Land Resources Slide Deck. This slide deck provides step-by-step instructions in the notes section. It also provides images to illustrate the type(s) of land discussed in each step.
- Provide each student with a copy of the Slicing Up Earth's Land Resources activity sheet. Instruct them to fill in the chart while you perform the following demonstration:
- Step 1: Hold up the apple. Explain to the students that this apple represents planet Earth.
- Step 2: Cut the apple into four equal wedges. Three of these quarters represent the oceans, which occupy 75% of Earth’s surface. Set these aside.
- Step 3: The remaining quarter represents land area, which occupies 25% of Earth’s surface. Take this quarter, and cut it into three equal wedges, so you have three 1/12 sections.
- Step 4: Hold up one of these sections. This piece represents inhospitable land including deserts, mountains, and polar regions. This land is not suitable for people to live or grow crops. Set this section aside.
- Step 5: Hold up the other two sections. These sections represent habitable land. This is land where people can live. Set one section down (it will be used in Step 7).
- Step 6: Show one of the sections. This section represents habitable land where people live but crops are not grown. This includes nature preserves, public lands, and developed areas like roads, schools, houses, etc.
- Step 7: Hold up the last section. This section represents the Earth's agricultural land, all the land on Earth that is used to grow food. Cut this section crosswise into four equal pieces, so you have four 1/48 sections.
- Step 8: Hold three sections up. This land is used to graze livestock like dairy cows, beef cattle, pigs, and sheep and to grow crops to feed the livestock.
Teach with Clarity
Cattle, sheep, and goats spend the majority of their lives grazing grasses and other forages for feed. Their unique ruminant digestive system allows them to obtain nutrition from plants that other animals (or humans) cannot. Livestock animals also consume grain-based feeds consisting of field corn, soybeans, barley, oats, sorghum, etc. Step 8 of this activity illustrates the land used to feed the livestock that produce our meat, milk, eggs, and other animal-source products. More details can be found in the Background Agricultural Connections section of the lesson.
- Step 9: Hold up the last section. This 1/48 section represents the amount of agricultural land on our Earth used to grow food crops for humans to eat. Examples of these crops include beans, fruits, vegetables, and grains.
- Lead a discussion about land use and food production. Use the following questions to guide the discussion:
- Why can't we grow food on all of the land on Earth? (Most crops cannot grow in soil that is too rocky, wet, or dry or in places that are too hot or cold.)
- Does our food only come from agricultural land? Where else does food come from? (Most of our food comes from agricultural land, but food like fish and shellfish come from water like oceans, rivers, and lakes. Food can also be grown in home gardens and greenhouses.)
Teach with Clarity
As students are thinking about land and its connection to the production of our food, they may wonder about aquatic food sources that do not rely on land. Aquatic food sources include those harvested from the ocean (lobster, salmon, shrimp, shellfish, and some species of fish) and those grown and harvested in freshwater (trout, catfish, and tilapia). Explore FAO's Consumption of Aquatic Foods report to explore foods grown and harvested from the water.
- What can we learn from this demonstration? (The amount of habitable land where we can live and produce our food is extremely limited. We need to use it wisely and protect it.)
Activity 2: The Value of Topsoil
- Refer to the apple demonstration from Activity 1. Project the Agricultural Land Apple Slice image. Remind the students that almost all of our food is produced on this relatively small portion of Earth. Ask, "What non-renewable natural resource covers the surface of agricultural land?" (topsoil) The peel of the apple can represent topsoil. For added effect, peel the segments that represent agricultural land in the demonstration.
- Lead a discussion about the economic, environmental, and societal value of soil. Include the following points and questions in the discussion:
- Topsoil is what makes agricultural land valuable and capable of growing crops or supporting livestock for our food.
- Crops grow best in fertile topsoil.
- Soil is a nonrenewable resource because it can take 100 to 500 years to make one inch of new topsoil.
- It is important to protect topsoil. Farmers use conservation practices to protect topsoil from erosion.
- Say you have 1 acre of land and 7 inches of topsoil. If every inch is worth $10 (round numbers simplify the math), your topsoil would be worth $70.
- Suppose you lose ½ inch of topsoil each year to erosion. How much money would you be losing each year? ($5.00 of topsoil from one acre) What is your topsoil now worth? ($65.00) At your current rate of topsoil loss, how many years will it take to lose all seven inches? (14 years).
- Discuss other losses that would occur (crops will be less productive, your income will go down, you will feed fewer people with the crops grown on your acre, sediment will wash into lakes and rivers downstream). How much would you be willing to pay to prevent erosion of your topsoil?
- Since soils provide our food, how can we place a value on them? Who pays for soil conservation? Who benefits from soil conservation?
- What is an acre of farmland worth? What is an acre of city worth?
Read Issue 3 of Ag Today titled Our Invaluable Natural Resources. This reader can be printed or accessed digitally. It helps students understand how plants and animals raised on farms depend on natural resources to live, such as the sun, soil, water, and air to grow. Learn methods farmers use to protect and preserve these natural resources while still providing the food, fiber, and fuel we need to live.
After conducting these activities, review and summarize the following key concepts:
- Soil is a natural resource necessary to grow the crops that provide our food.
- Soil is a valuable and limited resource that is not renewable.
- It is important to preserve soil through conservation practices.
Recommended Companion Resources
- A Handful of Dirt
- Ag Today
- Apple Land Use Model
- Dig In: Hands-On Soil Investigations
- Dirt: Secrets in the Soil (DVD)
- Dirt: The Scoop on Soil
- Dust Bowl: CBS 1955 Documentary
- Dust Bowl: Grantsville, Utah
- Farming in a Glove
- First Peas to the Table
- Jump Into Science: Dirt
- Mountains of Jokes About Rocks, Minerals, and Soil
- Nutrients for Life eLessons
- Rocks and Soil
- SOIL Reader
- School Gardens: A Guide for Gardening and Plant Science
- Soil Health Education Resources
- Soil Life
- Soil Science Society of America
- Soil Science Videos
- Soil! Get the Inside Scoop
- The Dirt Book: Poems About Animals That Live Beneath Our Feet
- Under Your Feet: Soil, Sand and Everything Underground
- You Wouldn't Want to Live Without Dirt!