6th Grade Earth Science
Ch. 7.3: Soil Conservation
Suppose you were a settler traveling west in the early 1800s. Much of your
journey would have been through vast, open grasslands called prairies. After the
forests and mountains of the East, the prairies were an amazing sight. Grass
taller than a person rippled and flowed in the wind like a sea of green.
Prairie=
Draw a picture of a prairie in the box:
The prairie soil was very fertile. It was rich with humus because of tall grass. The
sod—the thick mass of tough roots at the surface of the soil—kept the soil in
place and held onto moisture.
Humus=
What role did grass play in conserving the soil of the
prairies? (Think of our erosion demonstration)
Sod=
Color the area cover by the prairies green on the
map:
The prairies covered a vast area. They included the eastern parts of Kansas,
Nebraska, North and South Dakota, as well as Iowa and Illinois. Today, farms
growing crops such as corn, soybeans, and wheat have replaced the prairies. But
the prairie soils are still among the most fertile in the world.
Challenge: Why do farmers grow corn, soybeans,
and wheat?
6th Grade Earth Science
The Value of Soil
Soil is one of the Earth’s most valuable resources because everything that lives
on land depends directly or indirectly on soil.
Soil=
Plants depend directly on the soil to live and grow. Animals depend on plants—
Renewable
or on other animals that depend on plants—for food. Soil is a renewable
resource=
resource that can be found wherever weathering occurs. But soil formation takes
a long time. It can take hundreds of years for just a few centimeters of soil to
form. The thick, fertile soil of the prairies took many thousands of years to
develop.
Ch. 7.3: Soil Conservation
Why is soil one of Earth’s most valuable resources?
Draw a simple food chain that demonstrates the
statement, “Everything that lives on land depends
directly or indirectly on soil.”
Fertile: producing or
capable of
producing abundant
vegetation or crops
Fertile soil is valuable because there is a limited supply. Less than one eighth of
the land on Earth has soils that are well suited for farming. In many areas,
farming is difficult and little food is produced. The reasons for this include low
soil fertility, lack of water, steep slopes, or a short growing season.
How much of the land on Earth has soils that are
well suited for farming?
Soil Damage and Loss
Soil is one of the Earth’s most important resources. But soil can be lost or
damaged. For example, soil can become exhausted, or lose its fertility. This
occurred in large parts of the South in the late 1800s. Soils in which only cotton
had been grown were exhausted. Many farmers abandoned their farms. Early in
the 1900s in Alabama, a scientist named George Washington Carver developed
new crops and farming methods that helped to restore soil fertility in the South.
Peanuts were one crop that helped make the soil fertile again.
Exhausted soil=
Soil can be lost to erosion by water and wind. Water erosion can occur whenever
soil is not protected by plant cover. Plants break the force of falling rain, and
plant roots hold the soil together. Wind erosion is another cause of soil loss.
Wind erosion, combined with farming methods that were not suited to dry
conditions, caused the Dust Bowl on the Great Plains.
Erosion=
Fill out the table:
Human activities that
can harm the soil:
Restore: bring back
Human activities that
can help save the soil:
6th Grade Earth Science
The Dust Bowl
Toward the end of the 1800s, farmers had settled most of the prairies. New
settlers moved on to the Great Plains farther west. This region sweeps eastward
from the base of the Rocky Mountains across the western parts of North and
South Dakota, Nebraska, Kansas, Oklahoma, and Texas.
Ch. 7.3: Soil Conservation
Color the region of the Great Plains brown on the
map:
The soil of the Great Plains is fertile. But there is an important difference
between the Great Plains and the prairie. Rainfall decreases steadily from east to
west across the Great Plains. The tall grass gives way to shorter, thinner grass
needing less moisture.
Plowing removed the grass from the Great Plains and exposed the soil. In times
of drought, the topsoil quickly dried out, turned to dust, and blew away.
What is the difference between the Great Plains and
the prairie?
Drought: a
prolonged period of
abnormally low
rainfall
By 1930, almost all of the Great Plains had been turned into farms or ranches.
Then, several very dry years in a row turned the soil on parts of the Great Plains
to dust. The wind blew the soil east in great, black clouds. The clouds turned the
sky dark as far away as Chicago, and even New York City. Eventually, the soil
blew out over the Atlantic Ocean, where it was lost forever.
Soil Conservation
The Dust Bowl helped people appreciate the value of soil. In the 1930s, with
government support, farmers in the Great Plains and throughout the country
began to take care of their land. They adopted methods of farming that helped
save the soil. Some of the methods were new. Others had been practiced for
hundreds of years.
Farmers in the United States adopted modern methods of soil conservation. Soil
conservation is the management of soil to prevent its destruction.
Where did the wind blow the soil of the Great
Plains?
What caused the Dust Bowl?
Why did farmers think it was important to adopt
methods to save the soil?
Soil conservation=
6th Grade Earth Science
Two ways that soil can be conserved include contour plowing and conservation
plowing.
Ch. 7.3: Soil Conservation
What are two ways that soil can be conserved?
Contour plowing is the practice of plowing fields along the curves of a slope. This
helps slow the runoff of excess rainfall and prevents if from washing the soil
away.
Conservation plowing disturbs the soil and its plant cover as little as possible.
Dead weeds and stalks of the previous year’s crop are left in the ground to help
return soil nutrients, retain moisture and hold soil in place. This method is also
called low till or no-till plowing.
In grasslands such as the Great Plains, grazing livestock is an important use of the
land. But if too many cattle graze on the grass during dry periods, the grass cover
protecting the soil may be damaged. This exposes the soil to both wind and
water erosion. To prevent damage to the soil, ranchers must limit the size of
their herds.
Challenge: If you had to plant corn on a steep
hillside, how would you do it so that rain would not
wash the soil away?
How can grazing livestock contribute to soil erosion?