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.