Imagine that you planted flower seeds in your backyard
garden. What might heavy rainfall do to the seeds and soil?
Soil—An Important Resource
Rain flowing off a farm field often looks muddy. The
water picks up some of the soil and carries it away. The
process in which sediment is moved is called soil erosion.
Soil erosion is caused mainly by water and wind. Soil
erosion is harmful because plants do not grow well when
topsoil has been removed.
Causes and Effects of Soil Erosion
Soil erodes when it is moved from the place where it
formed. Water flowing over Earth’s surface and wind
blowing across the land erodes soil. Soil erosion is more
severe on steep slopes than on flat land. Erosion is also
worse in areas where there are few plants. Vegetation, such
as trees and grasses, helps hold soil in place.
When soil erosion occurs naturally, there is a balance
between the amount of soil that is eroded and the amount
of new soil that forms. This means that in any particular
place, soil forms at the same rate that it is eroded. However,
humans sometimes upset this balance causing soil erosion to
occur faster than new soil can form.
How does soil erosion affect farming?
Soil erosion is a serious problem for agriculture. Topsoil
holds water and contains nutrients that plants need. Topsoil
also has pores, or open spaces, that are good for plant
growth. But when topsoil erodes, the quality of the soil
decreases. The eroded soil has fewer nutrients that plants
need and may not hold enough water for plants.
In nature, decaying plant parts add nutrients to the soil,
while plant roots take some nutrients out of the soil. This is
called nutrient balance. Soil erosion upsets this balance. If
topsoil erodes rapidly, there are not enough nutrients for
plants to grow. Farmers may have to add fertilizers to the
soil to make up for the lost soil nutrients. It is more
difficult for plants to take root and grow well in
poor-quality, eroded soil.
How does removing forests affect erosion?
Trees protect the soil from erosion. In large forests, soil
is protected from erosion by trees and roots that hold soil
in place. But, when trees are cut down, soil is exposed and
erosion increases. Erosion of forest land is a problem in
many parts of the world, but it is especially severe in
tropical rain forests.
Each year, huge areas of rain forest are cut down for
lumber, farming, or grazing. In rain forests, most of the
nutrients are in only the top few centimeters of soil.
Farmers can grow crops in rain forest soil for only a few
years before the topsoil is gone. Then they must clear more
rain forest land somewhere else to grow their crops. The
cycle continues. More trees are cut down, more topsoil
erodes, and then more soil needs to be cleared.
How does overgrazing affect erosion?
Sheep or cattle feed on grasses. In many places, sheep
and cattle can graze on the land without causing much
damage to soil. In areas that get little rain, grasses do not
grow quickly. If grazing animals eat too much of the
vegetation, there is no ground cover to protect the soil. The
topsoil is exposed and may blow away in the wind before
new grasses have a chance to grow. The exposed soil also
loses moisture. In time, an overgrazed grassland can become
like a desert where the poor, dry soil cannot support plants.
How does sediment affect the environment?
In places where soil erosion is severe, sediment can
damage the environment. Severe erosion may occur when
land is exposed at large construction sites or strip mines.
The soil removed from these sites is moved to a new
location where it is deposited. Huge mounds of soil deposits
are easily eroded by rain and wind. The soil may be carried
into streams, or people may deposit it directly in a stream.
Large amounts of sediment might fill the stream channel,
damaging or destroying the stream environment and the
fish and wildlife that depend on it.
Preventing Soil Erosion
Every year more than 1.5 billion metric tons of soil are
eroded in the United States. Soil is a natural resource that
must be protected and managed. There are several things
people can do to protect soil.
How can managing crops protect the soil?
Farmers use several methods to slow down soil erosion.
They plant rows of trees, or shelter belts, to break the force
of the wind that would otherwise erode topsoil. They plant
crops to cover the ground and hold the soil after the main
crops are harvested. In dry areas, farmers do not plow
under their crops because this disturbs the soil and
increases erosion. Instead, they graze animals on the leftover
vegetation. If grazing is controlled, the animals leave enough
vegetation on the land to reduce erosion.
No-till Farming In the past, farmers would till or plow their
fields one or more times each year. When the soil was
plowed, loose soil was turned over. Wind and water eroded
the loosened soil. In recent years, many farmers have begun
to practice no-till farming to reduce erosion. No-till farming
is a farming method in which the plant material left after
harvesting remains in the field to decay over the winter. When
it is time to plant again, the farmers plant their crop seed
without plowing the land or clearing away last year’s plants.
No-till farming leaves plant cover on the land all year, so
topsoil erosion by wind and water is greatly reduced. One
study showed that no-till farming leaves up to 80 percent of
the soil covered and protected by plants or plant remains.
Another benefit of no-till farming is that plant remains keep
weeds from growing in farm fields.
Contour Farming Soil erosion occurs more quickly on slopes
than on flat land. Farmers who plant crops on slopes take steps
to limit soil erosion on their land. They plant crops using
contour farming. Contour farming is planting crops along the
land’s natural contour, or slope shape. The figure below shows
an orchard planted along the natural contours of a slope. The
curving rows catch water that would otherwise flow downhill,
carrying a lot of topsoil with it. Contour farming helps prevent
water and sediment from flowing down the slope.
Terracing Where slopes are steep, farmers use terracing
(TER uh sing) to conserve water and prevent soil erosion.
Terracing is a method of farming in which steep-sided,
flat-topped areas are built into the sides of steep hills so
crops can be grown on the level areas. The flat-topped areas
that are planted with crops are like terraces of land. The
terraces reduce runoff of rainwater by creating flat areas and
short sections of sloping land. The terraces also help prevent
topsoil from eroding down the hill or mountainside.
How can erosion be reduced in exposed soil?
There is a variety of ways to control erosion on soil that
is exposed. During large construction projects, water may be
sprayed on exposed soil to weigh it down and prevent erosion
by wind. When the construction is complete, topsoil is
added to the land and trees and other vegetation are planted
to protect the soil. Soil removed at strip mines may also be
protected so that it can be put back in place when mining
stops. After mining is complete, vegetation may be planted
to hold the soil and limit erosion on the reclaimed land.