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Sustainable Agriculture  It All Starts with the Soil

Sustainable Agriculture It All Starts with the Soil

The idea for "Sustainable Agriculture — It All Starts with the Soil" grew out of a desire by Screenscope, Inc., the producer of the PBS television series Journey to Planet Earth, and South Carolina ETV to expand on the idea of sustainable agriculture and to teach youngsters about its importance in their lives. This educational package combines video excerpts from the third program in the Journey to Planet Earth series, Land of Plenty, Land of Want, with solid background information on soil and two fun hands-on activities. Soil was selected as the focus because, as Pennsylvania farmer Steve Groff says in Land of Plenty, Land of Want, "Soil is my number one asset."

"Sustainable Agriculture It All Starts with the Soil" is available in PDF (This file is 104K)

Along with teaching kids about soil, "Sustainable Agriculture — It All Starts with the Soil" also demonstrates to youngsters how agriculture is real science, just like chemistry or biology (See "Agriculture Is Science"). In addition, while youngsters are learning about soil and science, they are acquiring new "life skills." The hands-on activities will teach them to solve problems, to make decisions, and to work together. (See "Life Skills")

Teaching Suggestions

"Sustainable Agriculture — It All Starts with the Soil" is full of in-depth information about soil. This package is designed to be used with a wide range of age groups and knowledge levels; therefore, you need to pick and choose what is appropriate for your group. You may decide to show your youngsters one of the video segments, briefly discuss the different types of soil, and do just one of the Learning Activities. Remember, the video is an important part of this package. It adds an extra dimension to the activities by introducing youngsters to real-life farmers. Watching the video reinforces the importance of soil to youngsters. Take a few minutes to carefully read over all the information in the package and then decide what will work best for you and for your group.

Why Is Soil So Important?

Although soil is a renewable natural resource, it is only renewable over long periods of time, measured not in days or years but in decades and even centuries. The livelihood of farmers worldwide is dependent upon their management and nurturing of the soil. In turn, so too is the world's supply of food and fiber, and, ultimately, the well-being of the planet's population. The production of food and fiber for both humans and animals requires an underground plant environment that is favorable for plant growth. Soil affects the growth and development of all plants, whether for human or animal consumption. Soil provides an anchor, or medium, for plant roots to take in oxygen, moisture, and minerals, which are all vital to plant life.

What Is Soil?

Soil is made up of sand, silt, clay, organic matter, living organisms, and pore spaces which hold water and air. The percentage of sand, silt, and clay determines how soils are categorized. Soil particles vary greatly in size. A sand particle is much larger than a silt particle. Clay particles are by far the smallest and hold moisture and plant food elements much more effectively than larger particles. A certain amount of clay in all soil is important for this reason.

Depending on their origin, soils vary greatly in general composition. Some soils were formed as a result of rock breaking down over thousands of years; others developed as certain materials were deposited by water. A normal soil profile consists of three layers:

  • topsoil
  • subsoil
  • soil bedrock (or if rock is not present, lower subsoil)

The depth of topsoil represents that soil which is normally plowed or tilled and contains the most organic matter or decaying plant parts. Deep-rooting plants send roots down into the subsoil, which is a well-defined layer immediately below the topsoil. If the soil is well drained, roots penetrate deeper into subsoil since oxygen is available at greater depths.

An ideal soil is about 50 percent solid material, consisting mainly of minerals and a small percentage of organic matter. The other 50 percent of this ideal soil is pore space, which consists of small holes between soil particles that are filled with water and air in different amounts. After rain or irrigation, the pores may be nearly filled with water and the air is pushed out. As the soil dries, the amount of water decreases and the pores gradually fill with air again. The ideal water-to-air ratio in the pores is about half and half, 50 percent air to 50 percent water.

The amount of moisture and air a soil holds depends on the soil structure and the type of soil. Sandy soils with large particles have large pore spaces. Pore space can be illustrated by comparing a door or window screen to nylon stockings. The screen represents the large pore spaces found in sandy soil, and the nylon represents clay soil with small pore spaces. If you dip each into water, you can observe the differences in the two as to how they hold water. Water is lost more quickly from these large pores as the force of gravity drains the water out; these are well-drained soils. As the content of clay in the soil increases, more water is held. If soils contain too much clay, they may not drain well enough to allow enough oxygen in the pore space for good plant growth.

Soil Types
SANDY SOIL: Sandy (or light) soils are soils in which silt and clay make up less than 20 percent of the material by weight. These soils drain well, but have little capacity to hold moisture and plant food. Sandy soils have comparatively large particles that permit good aeration, quick passage of water, and quick warming.

CLAYEY SOIL: A clayey soil must contain at least 30 percent clay and is known as a heavy soil. Heavy soils have relatively poor drainage and aeration capabilities. Because of this, heavy soils tend to hold more moisture than is good for plants. However, this type of soil also holds fertilizer and plant food well, which can be beneficial to plant growth.

LOAMY SOIL: This is the most desirable soil for agricultural use. Loam is a mixture of approximately equal parts of sand, silt, and clay. If loamy soil has more sand than silt or clay, it is known as a sandy loam; more clay, it is known as a clayey loam; more silt, a silty loam.

Learning Activities

To introduce realistic examples of the differences between clayey, sandy, and loamy soils to youngsters, try the following activity.

Activity 1
What you will need:

  • 1 cup of sugar/salt
  • 1 cup of flour
  • modeling clay
  • 1 cup of water

What you will do:

1. Rub sugar or salt between your thumb and finger to give you an idea of what sand feels like.
2. Add a few drops of water to the sugar or salt. Describe how it feels. Do the crystals stick together?
3. Feel some flour between your fingers. Describe how it feels. This is the way silt feels.
4. Add a few drops of water to the flour. How does it feel now? Does it stick together?
5. Feel the modeling clay. This is how clay in the soil feels.
6. Add a few drops of water to the clay. How does it feel now? Is there any difference?

Activity 2: An Experiment
What you will need:

  • 1 cup of dry, finely crushed soil (remove grass, sticks, stones, and leaves)
  • 1-quart clear glass jar with lid
  • dishwasher detergent
  • pencil
  • water
  • ruler
  • index card or a white sheet of paper

What you will do:

1. Fill the quart jar 2/3 full of water and pour the cup of soil into the jar.
2. Add 3 tablespoons of detergent, cover the jar tightly, and shake well for 5 minutes.
3. Let the jar sit for 24 hours.

4. Place the index card next to the jar and mark on the card where each layer of soil has settled.


How many total inches of soil are in the jar? _____________________________________

How many inches of sand are in the jar? _______________________________________

How many inches of silt are in the jar? _________________________________________

How many inches of clay are in the jar? ________________________________________

Bonus Activity: The Textural Triangle

The Texture Triangle

A triangle can be used to determine the textural name of a soil by actually measuring the percentage of sand, silt, and clay found in the soil. After the percentages of silt and clay are determined, these amounts can be plotted on the textural triangle. To do this, project lines inward from the point on each side of the triangle that represents the percentage of that particular type of soil. The line drawn from the silt side of the triangle is placed parallel to the sand side of the triangle. The line projected from the clay line runs parallel to the silt line. The location of the point at which these two lines intersect indicates the name of the soil. The name of the section of the triangle in which the point is located is the name of the soil.

Using the Textural Triangle, determine what soil type was used in the experiment.

HINT (Sand is heavier than clay, which is heavier than silt.)

Explain how you determined this.

Agriculture Is Science

The first step in the scientific process teaches youth to put forth an idea (formulate a hypothesis) and can be incorporated into both Activity 1 and Activity 2: An Experiment. What happens when...? What happens if...? I think this soil is...(particular type).

The second step in the scientific process is to construct a real-life simulation to prove or disprove the hypothesis or idea. Youth can still practice deductive reasoning — using general facts or knowledge to arrive at specific examples — in the experiment.

In the third step, youngsters collect scientific information (data) to support or refute their idea or hypothesis. This is the results from the experiment. Finally, based upon the data collected, youth can conclude or present facts regarding their hypothesis.

Life Skills

Life skills are tools for coping with daily circumstances, making important decisions, and enhancing the quality of our lives. As youngsters in your group acquire life skills, they not only become prepared to deal with a wide variety of situations, but they are also better prepared for social, academic, career, and leisure settings throughout their lives.

These activities are very rich in the life skills of problem-solving and decision-making. Youngsters can choose to work with others, or by themselves, and to use the basic steps in problem-solving:

  • defining the problem
  • diagnosing
  • formulating alternatives
  • deciding on and implementing a solution
  • evaluating the action taken and
  • identifying who has the problem.

Personal development life skills can also be enhanced in these activities. Encouraging youngsters to share skills and knowledge in mentoring (helping) roles, sharing feelings and ideas, and receiving acceptance for them while recognizing and appreciating differences are life skills that are of immense benefit to youngsters at this age.

Using Video with These Activities

If you decide to have your group watch all of Land of Plenty, Land of Want, below are suggestions of where to break the program and insert the Learning Activities. Have the students watch a portion of the video, then pause to discuss it or to do an activity.

(time in minutes from opening title)

12:30-end of Zimbabwe segment
20:00-end of Auvergne segment
25:00-end of Brittany segment
34:00-end of China segment
43:00-end of Iowa segment
46:00-end of erosion in Lancaster County segment

If you use the specifically selected video segments, explanations about each follow.

Introduction to Iowa Segment (6 minutes and 52 seconds)
This segment introduces youngsters to one of America's high-tech, large-scale farming operations. The bulk of the food produced on this Iowa farm run by Bill and Joe Horan will feed people outside the United States. To oversee an operation like this, these farmers need to keep on top of the latest technological developments; they even need to learn how to depend on satellites.

As seen in this excerpt from "Land of Plenty, Land of Want," the large-scale intensive agriculture practiced in the Midwest is highly variable due to weather conditions and heavily dependent upon the soil. The Dust Bowl conditions observed on the Great Plains earlier this century are, thankfully, now history as a result of the new sustainable agricultural and soil management practices farmers are using today. The quality and quantity of topsoil enables U.S. farmers to provide not only our citizens, but also the inhabitants of the rest of the world, with high-quality food and fiber. Agriculture's dependency on topsoil has produced the highly mechanized and scientific management practices used in Iowa today. The family farmers in Iowa use high-tech practices and machinery to maximize the production of corn from their farms. Yet, as can be observed from the scenes of the Dust Bowl, the use of this technology is for nought without topsoil.

Introduction to Lancaster County, Pennsylvania Segment (4 minutes and 23 seconds)
Even farmers running smaller operations face the same problems as their large-scale counterparts — how can they protect their soil? This excerpt from "Land of Plenty, Land of Want" focuses on the agricultural practices used in southern Pennsylvania, which epitomize the wisest and best use of one renewable natural resource — the soil. With the loss of 4 million tons of topsoil each year and half of their original topsoil already washed into rivers and streams, these farmers are utilizing the latest technology to prevent further erosion.

Farmer Steve Groff, who is profiled in this excerpt, is using a different type of technology. It may not depend on satellites but it is an effective method of preserving the soil. Groff uses cover crops and specialized seed-planting equipment to prevent further erosion. Called no-till farming, this is another example of how sustainable agriculture has changed the face of agriculture through increased crop yield, decreased loss of topsoil to erosion, and improvement of the soil. Groff's success with no-till farming won him national recognition as a "No-Till Innovator" in January 1999.

Practical Applications and Discussions

Some practical applications can be made from the soil science activities that deal with the same issues that the farm families in Iowa and Pennsylvania face on a daily basis.

1. For example, questions could be asked of youngsters about the "dirt and mud" that often is brought into homes on the bottoms of shoes or the "soiled, muddy knees" on pants. Which particle(s) of soil is this? Is it sand? Is it silt? Or is it clay? (Chances are good that youngsters can relate to this fairly well.)

2. On a bank by a river or stream and on the beach by the ocean, which particle(s) of soil is found there? Do youngsters ever see any silt or clay laying on top of the beach? Probably not, because silt and clay are comprised of smaller particles that are carried downstream and deposited at the bottom of the body of water.

3. After a rainfall, ask the youngsters to observe and touch the "mud" in a puddle of water (or where the puddle was). What is it they feel? Is it slippery and gooey or is it sandy? Chances are that it will feel slippery because the sand, being a larger and heavier particle, is at the very bottom; what is at the top comprises the "topsoil." Although sand is needed in topsoil, the Textural Triangle reveals that the ideal "topsoil" has a relatively small proportion of sand in it, less than 50 percent. Activity 2: An Experiment can be used to confirm the youngsters' observations about how much sand, silt, and clay have been found in their soil sample.

4. If you have shown your group the entire Land of Plenty, Land of Want program, even more questions can be asked and discussions can be started about the various types of soils found in agriculture in Zimbabwe, France, and China.

For example, the soils of Zimbabwe require large amounts of water to remain productive. Why is that? Could it be that the soils "drain" too well and too quickly due to the large particle size of sandy soils? What role does the climate and weather play in sustainable agriculture in this country, or in the other countries? What similarities/differences are there in the soils where agriculture is practiced in France and in Zimbabwe? Are the soils "good" or not? Why? What type of soil enables China to grow large quantities of rice while Iowa grows corn almost exclusively? What can be done to prevent future disasters, such as the Dust Bowl, from occurring in Zimbabwe, France, and China?


"Sustainable Agriculture — It All Starts with the Soil" was created by Dr. Timothy J. Rollins, 4-H and Youth Development Specialist and Associate Professor of Agricultural and Extension Education at The Pennsylvania State University.

Learning Activities Credit
Vegetable Gardening. 1990. Rollins, Timothy J. et al. Pennsylvania State University, College of Agricultural Sciences, University Park, Pa.

Special Thanks
South Carolina ETV thanks the National 4-H for its assistance in the development and promotion of this outreach activity.

The Journey to Planet Earth series and these teaching materials were made possible by major funding from:

NASA Earth Science Enterprise
The W.K. Kellogg Foundation
The Arthur Vining Davis Foundations
Continental Airlines, Inc.
The World Bank

with additional support from:

The Rockefeller Foundation
U.S. Department of Agriculture, SARE
American Honda Foundation

For additional copies of these materials, contact:

Journey to Planet Earth
Outreach Department
South Carolina ETV
PO Box 11000
Columbia, SC 29211

Fax: 803/737-3544

Journey to Planet Earth is available for educational use. Purchase price includes public performance rights for classroom use. Please contact:

Screenscope, Inc.
4330 Yuma St., NW
Washington, DC 20016

Phone: 202/364-0055
Fax: 202/364-0058

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