4
4
Overview
READI NG WARM-U P
In this section, students will
learn the importance of soil.
Students will then learn about
the methods used to prevent
nutrient loss and erosion of soil.
Objectives
•
•
Describe three important benefits
that soil provides.
Describe four methods of preventing
soil damage and loss.
Terms to Learn
Bellringer
soil conservation
erosion
Tell students Franklin D.
Roosevelt’s quote: “The nation
that destroys its soil destroys
itself.” Lead a discussion on
the meaning of this quote.
READI NG STRATEGY
Reading Organizer As you read this
section, make a table comparing the
four methods of preventing soil damage
and loss.
soil conservation a method to
maintain the fertility of the soil by
protecting the soil from erosion and
nutrient loss
Discussion ----------------------------------g
Soil Engineering Students may
think that all soils are merely
dirt. Soils have different characteristics, which depend on soil
composition. Engineers study
soil types when planning roads
and buildings. Different types of
soils require different engineering considerations. For example,
soils high in clay swell when
they are wet and contract when
they dry. The expanding and
contracting can cause shifting
and cracking in roadbeds and
building foundations. Arrange
for an engineer, contractor, or
geologist to speak with the class
about the importance of understanding soil types. Have students prepare questions to ask
the guest speaker. l Auditory
Believe it or not, soil can be endangered, just like plants and
animals. Because soil takes thousands of years to form, it is
not easy to replace.
If we do not take care of our soils, we can ruin them or
even lose them. Soil is a resource that must be conserved.
Soil conservation is a method to maintain the fertility of the
soil by protecting the soil from erosion and nutrient loss.
The Importance of Soil
Soil provides minerals and other nutrients for plants. If the
soil loses these nutrients, then plants will not be able to grow.
Take a look at the plants shown in Figure 1. The plants on
the right look unhealthy because they are not getting enough
nutrients. There is enough soil to support the plant’s roots,
but the soil is not providing them with the food they need.
The plants on the left are healthy because the soil they live
in is rich in nutrients.
All animals get their energy from plants. The animals get
their energy either by eating the plants or by eating animals
that have eaten plants. So, if plants can’t get their nutrients
from the soil, animals can’t get their nutrients from plants.
✓
Reading Check Why is soil important? (See the Appendix for
answers to Reading Checks.)
Housing
Soil also provides a place for animals to live. The region where
a plant or animal lives is called its habitat. Earthworms, grubs,
spiders, ants, moles, and prairie dogs all live in soil. If the soil
disappears, so does the habitat for these animals.
Figure 1 Both of these photos
show the same crop, but the soil
in the photo on the right is poor
in nutrients.
CHAPTER RESOURCES
Chapter Resource File
CRF
• Lesson Plan
• Directed Reading A b
• Directed Reading B s
Technology
Transparencies
• Bellringer
294
Soil Conservation
Chapter 10 • Weathering and Soil Formation
Answer to Reading Check
Soil provides nutrients to plants, houses
for animals, and stores water.
Water Storage
Soil is also extremely important to plants for water storage.
Without soil to hold water, plants would not get the moisture
or the nutrients they need. Soil also keeps water from running
off, flowing elsewhere, and possibly causing flooding.
Soil Damage and Loss
What would happen if there were no soil? Soil loss is a serious problem around the world. Soil damage can lead to soil
loss. Soil can be damaged from overuse by poor farming techniques or by overgrazing. Overused soil can lose its nutrients
and become infertile. Plants can’t grow in soil that is infertile.
Without plants to hold and help cycle water, the area can
become a desert. This process, formally known as desertification, is called land degradation. Without plants and moisture,
the soil can be blown or washed away.
Answer to Math Practice
1 mm/y 500 y ! 500 mm
500 mm ! 50 cm
50 cm " 2 cm
Thus, the soil is eroding faster than
it is forming.
Making Soil
Suppose it takes 500 years
for 2 cm of new soil to form
in a certain area. But the
soil is eroding at a rate of
1 mm per year. Is the soil
eroding faster than it can be
replaced? Explain.
v------------------------------------------b
Uses of Soil Obtain three 4 in.
flowerpots. Fill one with gravel,
one with clay, and one with
potting soil. Place the pots on
a plank of wood over a sink.
Have three students slowly
pour 500 mL of water into
each pot simultaneously. Ask
students to note which pot
begins to leak first. Explain
that the gravel started to leak
first because the pores or spaces
between pieces of gravel are
too large to hold the water. The
potting soil has much smaller
spaces, where water can be
stored. The clay has very small
spaces between the soil particles
and does not allow water to
pass through. Have students
then explain in writing which
material they would choose
for the following activities:
Soil Erosion
When soil is left unprotected, it can be exposed to erosion.
Erosion is the process by which wind, water, or gravity transport
soil and sediment from one location to another. Figure 2 shows
Providence Canyon, which was formed from the erosion of
soil when trees were cut down to clear land for farming. Roots
from plants and trees are like anchors to the soil. Roots keep
topsoil from being eroded. Therefore, plants and trees protect
the soil. By taking care of the vegetation, you also take care
of the soil.
erosion the process by which wind,
water, ice, or gravity transport soil
and sediment from one location to
another
Figure 2 Providence Canyon
has suffered soil erosion from the
cutting of forests for farmland.
• lining the foundation of a
house so that it drains
quickly (gravel)
• sowing grass seed (potting soil)
• lining the bottom of an artificial pond so that it doesn’t
leak (clay)
l Kinesthetic
CONNECTION to
Life Science -----------------------------------g
CONNECTION v
Math ----------------------------------------------------------------------------g
Soil for Plants Loam is a type of soil
that, depending on the amount of humus,
is best for plant growth. Because loam
contains an ideal balance of varied soil
particles (sand, silt, and clay), the soil can
retain the air and water in the pore spaces
between the particles. The air and water
stored in these pore spaces are essential
for plant growth. Have students research
plants that have adapted to live in less
hospitable soils.
All soils contain varying amounts of water,
air, minerals, and organic matter. A 200 cm3
soil sample ideal for plant growth may
contain 40 cm3 of water, 50 cm3 of air,
70 cm3 of mineral fragments, and 40 cm3
of humus. Have students create a pie
chart showing this composition by
percentage. l Logical
e
Section 4 • Soil Conservation 295
Figure 3
Soil Conservation Techniques
Reteaching -------------------------------------b
Soil Conservation On the
board, write the headings
“Soil erosion” on one side
and “Nutrient depletion” on
the other. Ask students to suggest different soil conservation
methods, and have them state
which problem (soil erosion or
nutrient depletion) the method
of conservation addresses. After a
brief discussion of each method,
write the method under the
appropriate head. l Verbal
Contour plowing helps prevent
erosion from heavy rains.
Terracing prevents erosion from heavy
rains on steep hills.
No-till farming prevents erosion by
providing cover that reduces water runoff.
Soybeans are a cover crop which restores
nutrients to soil.
Quiz ---------------------------------------------------------------------g
1. What is one way that nutrients are removed from soil?
(Sample answer: by planting the
same crops every year)
2. How do contour plowing and
terracing help prevent soil
erosion? (by interrupting water
flow across the topsoil)
Alternative
Assessment ---------------------------g
Contour Plowing and Terracing
Raising Awareness Declare
“Soil Conservation Awareness
Week.” Have students create
posters that alert your school to
the importance of soil and that
highlight some ways to protect
and conserve soil. l Visual
If farmers plowed rows so that they ran up and down hills,
what might happen during a heavy rain? The rows would act
as river valleys and channel the rainwater down the hill, which
would erode the soil. To prevent erosion in this way, a farmer
could plow across the slope of the hills. This is called contour
plowing. In contour plowing, the rows act as a series of dams
instead of a series of rivers. Figure 3 shows contour plowing
and three other methods of soil conservation. If the hills are
really steep, farmers can use terracing. Terracing changes one
steep field into a series of smaller, flatter fields. No-till farming,
which is the practice of leaving old stalks, provides cover from
rain. The cover reduces water runoff and slows soil erosion.
CHAPTER RESOURCES
Technology
Transparencies
• Soil Horizons
296
Chapter 10 • Weathering and Soil Formation
h -----------------------------a
Indigenous Agriculture The ancient Maya
of Central America used specialized agricultural techniques to maximize their corn
crops. The Maya intentionally planted their
crops over sinkholes. Soil over sinkholes is
ideal because it is rich and all surface water
drains into the sinkhole. Have students
find out more about the agricultural innovations of other indigenous cultures and
prepare a five-minute speech on the topic.
Ask students if any of these techniques
are still being used today. l Verbal
Answer to Reading Check
They restore important nutrients
to the soil and provide cover to
prevent erosion.
Cover Crop and Crop Rotation
In the southern United States, during the early 1900s, the
soil had become nutrient poor by the farming of only
one crop, cotton. George Washington Carver, the scientist
shown in Figure 4, urged farmers to plant soybeans and
peanuts instead of cotton. Some plants, such as soybeans
and peanuts, helped to restore important nutrients to the
soil. These plants are called cover crops. Cover crops are
crops that are planted between harvests to replace certain
nutrients and prevent erosion. Cover crops prevent erosion by providing cover from wind and rain.
Another way to slow down nutrient depletion is
through crop rotation. If the same crop is grown year
after year in the same field, certain nutrients become
depleted. To slow this process, a farmer can plant different crops. A different crop will use up less nutrients
or different nutrients from the soil.
✓Reading Check
Answers to Section Review
Figure 4 George Washington Carver
taught soil conservation techniques to
farmers.
What can soybeans and peanuts do for
nutrient-poor soil?
Review
Summary
is important for
• Soil
plants to grow, for ani-
•
mals to live in, and for
water to be stored.
Soil erosion and soil
damage can be prevented by contour plowing, terracing, using
cover crop, and practicing crop rotation.
Using Key Terms
Math Skills
1. In your own words, write a definition for each of the following
terms: soil conservation and
erosion.
Understanding Key Ideas
2. What are three important benefits that soil provides?
Critical Thinking
3. Practicing which of the following soil conservation techniques
will replace nutrients in the soil?
a.
b.
c.
d.
cover crop use
no-till farming
terracing
contour plowing
5. List four methods of soil conservation, and describe how each
helps prevent the loss of soil.
George Washington Carver By the
early 20th century, Southern cotton cultivation had so depleted soil nutrients that
the area faced an agricultural crisis. George
Washington Carver convinced farmers to
plant peanuts and soybeans instead of cotton.
These crops helped restore nitrogen to the
soil. The soil recovered, and Carver’s work
helped revitalize the agricultural economy of
the South. Ask students to learn more about
the life of this remarkable scientist.
7. Applying Concepts Why do
land animals, even meat eaters,
depend on soil to survive?
Developed and maintained by the
National Science Teachers Association
4. How does crop rotation benefit
soil?
CONNECTION to
History ---------------------------------------------------------------g
6. Suppose it takes 500 years to
form 2 cm of new soil without
erosion. If a farmer needs at least
35 cm of soil to plant a particular crop, how many years will
the farmer need to wait before
planting his or her crop?
For a variety of links related to this
chapter, go to www.scilinks.org
Topic: Soil Conservation
SciLinks code: HSM1409
1. Sample answer: Soil conservation is a method used to protect
soil from erosion and nutrient
depletion. Erosion is a process
by which soil is moved from one
location to another by wind,
water, ice, or gravity.
2. Sample answer: Soil supplies
support and nutrients to plants,
provides housing for animals,
and stores water.
3. a
4. Crop rotation helps prevent soil
nutrients from being depleted.
Alternation of crops in the same
soil reduces nutrient loss.
5. Contour plowing prevents erosion by plowing across a slope
so that plowed rows act like a
series of dams to prevent erosion by rain. Terracing prevents
erosion by dividing a hillside
into a series of flat fields. No-till
farming prevents erosion from
water runoff by leaving cover
over the soil. Cover crops prevent erosion from water runoff
by providing cover for the soil.
6. 500 y $ 2 cm ! 1 cm/250 y
1 cm/250 y 35 cm !
8,750 years
7. Land animals depend on the
soil to support and grow plants.
Animals get their energy by eating the plants or by eating the
animals that eat the plants.
CHAPTER RESOURCES
Chapter Resource File
CRF
• Section Quiz g
• Section Review g
• Vocabulary and Section Summary g
• Reinforcement Worksheet b
• Critical Thinking a
• SciLinks Activity g
Section 4 • Soil Conservation 297