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.
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 crops: crops grown between periods of regular production for the purpose of protecting and improving the soil; generally a crop with fibrous roots (like clover, various grasses, vetch, etc.) that will hold soil and often a legume that will add nitrogen to the soil
nonrenewable resource: a limited natural resource that cannot be replaced or reproduced at a rate that will meet demand over the long term
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
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.
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Explain how the availability of productive resources and technology limits the production of goods and services.
Agricultural Literacy Outcomes
Agriculture and the Environment
Describe resource and conservation management practices used in agricultural systems (e.g., riparian management, rotational grazing, no till farming, crop and variety selection, wildlife management, timber harvesting techniques) (T1.9-12.b)
Discuss the value of agricultural land (T1.9-12.d)
Reason abstractly and quantitatively. Students make sense of quantities and their relationships in problem situations. They bring two complementary abilities to bear on problems involving quantitative relationships: the ability to decontextualize—to abstract a given situation and represent it symbolically and manipulate the representing symbols as if they have a life of their own, without necessarily attending to their referents—and the ability to contextualize, to pause as needed during the manipulation process in order to probe into the referents for the symbols involved. Quantitative reasoning entails habits of creating a coherent representation of the problem at hand; considering the units involved; attending to the meaning of quantities, not just how to compute them; and knowing and flexibly using different properties of operations and objects.