chapter 9: land section 9.2: agriculture and soil part 2
Post on 05-Jan-2016
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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.
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.
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
• 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.
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.
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