How Much Is Dirt Worth?
9 - 12
Students will understand that topsoil is a limited resource with economic value. Activities include slicing up an apple to demonstrate the distribution of Earth’s soil resources and exploring scenarios involving the dollar valuation of soil. Grades 9-12
Essential File (map, chart, picture, or document)
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: 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 2013, more than 16 million people had farm- and agriculture-related jobs. 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.
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.
Interest Approach - Engagement
- Ask your students to name some items that they would consider valuable. Students may list items that are of monetary or sentimental value.
- 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 learning why soil is valuable.
Activity 1: Slicing Up Earth’s Land Resources
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.
- Ask students to fill in the Earth’s Soil Resources Pie Chart activity sheet while you perform the following demonstration:
- Cut the apple into four equal wedges. Three of these quarters represent the oceans, which occupy 75% of Earth’s surface. Set these aside.
- The remaining quarter represents land area, which occupies 25% of Earth’s surface. Take this quarter, and cut it in half, so you have two, one-eighth sections.
- One of these sections represents deserts, swamps, mountains, and polar regions; this half of our land, or one-eighth (12.5%) of Earth’s surface, is not suitable for people to live or grow crops on. Set this section aside.
- The other eighth represents land where people can live. There are some places where people can live, but crops can’t be grown. Slice this section lengthwise into four equal parts. Now you have four 1/32nd pieces of an apple, each representing 3.1% of Earth’s surface.
- The first section represents the areas of the world with rocky soils that are too poor for any type of food production. Set this section aside.
- The next two sections represent land that is too wet or too hot for food production. Set these sections aside also.
- The fourth section represents the area of the world that is most suitable for development and agricultural cultivation. The best lands for agriculture are often desirable places to build homes and towns as well.
- Carefully remove the peel of the last 1/32nd section. This small bit of peel represents all the soil of our earth upon which humans depend for food production.
Activity 2: Cost versus Value
- Discuss the economic, environmental, and societal value of soil. Then demonstrate some scenarios involving the dollar valuation of soil. Use the following examples or develop your own.
- Say you have 1 acre of land and 7 inches of topsoil. If every inch is worth $10 (use round numbers to 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?
- Discuss the following questions:
- 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?
Concept Elaboration and Evaluation
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.
Adapted from materials provided by Oklahoma Agriculture in the Classroom.
Suggested Companion Resources
- Nutrients for Life eLessons
- Apple Land Use Model
- Apple as Planet Earth video
- Dust Bowl: CBS 1955 Documentary
- FDR's Fireside Chat: Dust Bowl
- Living Soil Film
- Soil Science Videos
- Soil, Not Dirt
- School Gardens: A Guide for Gardening and Plant Science
- Dirt-to-Dinner: Food Matters
- Soil Health Education Resources
- Soil Science Society of America
- Unlock the Secrets in the Soil
- Web Soil Survey
Utah Agriculture in the Classroom