Chapter 9: Land

Section 9.2: Agriculture and Soil

Part 2

Topsoil Facts

• It takes about to 500 years to form one inch of topsoil.

• In the United States, about half of the topsoil has been lost to erosion in the last 200 years.

• Worldwide, it is estimated that about 11 percent of the soil has been eroded in the past 45 years.

Erosion is the wearing away of topsoil by wind and water.

Production Practices Causing Erosion

• Plowing produces a loose surface layer of soil.

• Harvesting may remove roots and other organic material.

• Clearing of forests to produce lumber.

World Map of Water Erosion

World Map of Wind Erosion

The loss of topsoil occurs all over the world, but is especially severe in dry

areas.

Dust Bowl • The name given to areas of the U.S. prairie

states that suffered ecological devastation in the 1930s and then to a lesser extent in the

mid-1950s.

• The problem began during World War I, when the high price of wheat and the needs of Allied troops encouraged farmers to grow more wheat by plowing and seeding areas in

prairie states, such as Kansas, Texas, Oklahoma, and New Mexico, which were

formerly used only for grazing.

Dust Bowl

Dust Bowl

• But as the droughts of the early 1930s deepened, the farmers kept plowing and

planting and nothing would grow.

Dust Bowl• The ground cover that held

the soil in place was gone. • The Plains winds whipped

across the fields raising billowing clouds of dust to

the skies. • The skies could darken for days, and even the most well sealed homes could have a

thick layer of dust on furniture.

How was the Dust Bowl Fixed?

• Proper Farming Techniques!

• And the return of the rains!

• Planted trees!

Due to increased populations, several

crops a year may now be planted, and fallow

periods may be shortened or

eliminated, causing the soil to lose its fertility.

Soil fertility can deteriorate so much that the land becomes desert-like in a process

called desertification.

Worldwide, an area the size of Pennsylvania becomes desert each

year.

Ways to Conserve Topsoil and Reduce Erosion

• Contour Plowing – is plowing across the slope of a hill.

                                      

    

Ways to Conserve Topsoil and Reduce Erosion

• Contour Plowing – is plowing across the slope of a hill.

• No-till farming – the seeds of the next crop is planted in slits that are cut into the soil, straight through the remains of the previous crop.

Ways to Conserve Topsoil and Reduce Erosion

• Using organic material instead of inorganic fertilizers.

Another way of farming and not depleting the world’s resources is

low-input farming – farming without using a lot of energy, fertilizer, and

water.

Two Types of Low Input Farming

• Organic Farming – growing plants without any synthetic pesticides or inorganic fertilizers.

• Aquaculture – raising fish in artificial environments.

Aquaculture

SALINIZATION

Although all soil naturally contains some salts, more salts are added when land is irrigated in a process called salinization.

This is because water for irrigation is taken from rivers or

groundwater, which contain more salt than rainwater.

When land is irrigated, much of the water evaporates, leaving behind the

salts it contained.

Eventually the soil may

become so salty that

plants cannot grow in it.

Means of Controlling Salinization

• Careful irrigation methods.

• Planting salt-tolerant plants that absorb the salt from the soil.

• Planting trees to decrease the evaporation rate.