Conserving Land and Soil
Conserving Land and Soil D t scov ER How Does Míníng AÍJecl ¡he land? 3. After you have extracted the chunks of ore, break them open to remove the "minerals" inside. CAUTION: Do not eat the sunflower seeds.
;:iiilfifl';::å
and soil representing a mining site. There are at least 10 deposits of "ore" (sunflower seeds) buried in your mining
4. Observe your mining site and the surrounding area after your mining operations are finished.
site.
Ihink lt Over
2. Your goal is to locate and remove the ore from your site. You may use a pencil, a pair of tweezers, and a spoon as mining tools.
FOR
I i
EADING
How do people use land?
What kinds of problems occur when soil is not properly managed?
Reoding Típ Before you read, use the section headings
to
make an outline about land and soil conservation. Leave space in the outline to take notes.
Predíctíng How did mining change the land at your mining site? Predict whether it would be easy or difficult to restore the land to its original state. Explain.
I ess than a cuarter of Ear I a small am-ount tbrmed L.unnot be created. All th limited amount of land to produce their food, build shelter, and obtain other resources. Land is a precious resource. As the American author Mark Twain once said about land, "They don't make it anymore."
Types
of Land Use
People use land in many ways. Three uses that change the land are agriculture, development, and mining. Examples of these land uses are shown in Figure 1.
Agriculture
Land is the source of most food. Crops such as wheat, rice, and potatoes require large areas of fertile land. But less than a third of Earth's land can be farmed. The rest is too dr¡ too wet, too salty, or too mountainous. To provide food for the growing population, new farmland must be created by clearing forests, draining wetlands, and irrigating deserts. When people make these changes, organisms that depended on the natural ecosystem must frnd new homes. Many crops are grown to feed livestock such as hogs, chicken, and cattle. Other land serves as pasture or rangeland for grazinganimals.
Land Use in the United States
Development
People settled the flrst villages in areas that had good soil and were near a source of fresh water. As population grew, these settlements became towns and cities. People built more houses and paved roads. The construction of buildings, roads, bridges, dams, and other structures is called development. In the United States, about a million hectares of farmland (an area half the size of New |ersey) are developed each year. Development not onlyreduces the amount of farmland, but can also destroy wildlife habitats.
Mining Mining is the removal
of nonrenewable resources such as iron, copper, and coal from the land. Resources just below the surface are strip mined. Strip mining involves removing a strip of land to obtain the minerals and then replacing the strip. Strip mines expose the soil. It can then be blown or washed away more easily. Strip-mined areas may remain barren for years before the soil becomes rich enough to support the growth of plants again. For resources located deep underground, it is necessary to dig a tunnel, or shaft. The minerals are carried up through the shafts. This process is called underground mining.
I
e¿æøf¿*ø
Wilderness,
Cities
porks, ønd wildlife refuges
2o/o
9o/o
Figure
1
Land in the United
States is used in many ways. Clossifying Which of these lond uses chonge the notural ecosystems of the land?
Wlty isn't altlønd suitable for farming? Figure 2 Three major uses of land are agriculture, development, and mining.
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Eal15
Protecting the Soil Do you think of soil only as something that has to be washed off your hands or swept off the floor? Then you may not realize how much you depend on soil! Soil is a complex system made up of living and nonliving things. It contains the minerals and nutrients that plants need to grow. Soil also absorbs, stores, and filters water. Bacteria, fungi, and other organisms that live in soil break down the wastes and remains of living things. These decomposers recycle the chemical substances that are necessary for life. Figure 3 shows the structure of fertile soil. Notice that it is composed of several layers. The very top layer of dead leaves and grass is called litter. The next layer, topsoil, is a mixture of rock fragments, nutrients, water, air, and decaying animal and plant matter. The water and nutrients are absorbed by the many plant roots located in this layer. Below the topsoil is the subsoil. The subsoil also contains rock fragments, water, and air, but has less animal and plant matter than the topsoil. It can take hundreds of years to form just a few centimeters of new soil. All soil begins as the lnrecnnnxc Emrn Sqmcr
rock that makes up Earth's crust, called bedrock. Natural processes such
freezing and thawing gradually break apaft the bedrock. Plant roots wedge between rocks and break them into smaller pieces. Chemicals released by lichens slowly break the rock into smaller particles. Animals such as earthworms and moles help grind rocks into even smaller particles. As dead organisms break down, their remains also contribute to the mixture. Because rich topsoil takes a long time to form, it is important to protect Earth's soil. Poor soil management can result in three problems: erosion, nutrient depletion, and desertification.
3 Soil consists of several layers. Applying Concepts ln which loyer ore most plant roots located? What do the roots obsorb there?
Figure
iló.
E
Erosion The
as
process bywhich water, wind, or ice moves particles of rocks or soil is called erosion. Normall¡ plant roots hold soil in place. But when soil is exposed to wind and water, erosion occurs more rapidly. Many uses of land, including logging, mining, and farming, expose the soil and can cause erosion. Some farming methods that help reduce erosion are described in Exploring Soil Conservøtion.
Nutrient Depletion Plants make their own food through photosynthesis. But plants also require a variety of nutrients from the soil. Just as your body needs iron, zinc, and calcium to grow and function properl¡ plants need nitrogen, potassium, phosphorus, and other nutrients. Decomposers supply these nutrients to the soil as they break down the remains of dead organisms. Sometimes, a farmer plants the same crops in a field year after year. As a result, the plants use more nutrients than the decomposers can replace. The soil becomes less fertile, a situation that is called nutrient depletion. One way to prevent nutrient depletion is to periodically leave flelds fallow, or unplanted with crops. A second way to prevent nutrient depletion is to leave the unused parts of crops, such as cornstalks and watermelon vines, in the fields rather than
T
farming practices can help reduce soil erosion. hese
contour plowlng Farmers alternate strips of tall crops, such as corn, with short crops, such as squash. The
Conseruation plowing V Rather than plowing fields and leaving them bare, farmers use machines that break up only the subsoil. This method leaves the dead stalks and weeds from the previous year's crop in the ground
to hold the topsoil in place.
short crops prevent soil from washing out of the tall crop rows, which are less protected. Crops are planted in curving rows that follow the slope, or contour, of the land. Contour plowing can reduce soil erosion as much as 50 percent on gently sloping land.
Wlndbreaks Rows of trees are planted along the
edges of fields. These windbreaks
block the wind and also trap eroding soil. Using fruit or nut trees as windbreaks provides an extra benefit for the farmer and wildlife.
Terraclng Þ Steep hillsides are
built up into a series of flat "terraces." The ridges of soil at the edges of the terraces slow down runoff and
catch eroding soil.
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llT
clearing them away. The stalks and vines decompose in the fields, adding nutrients to the soil. Another method of preventing nutrient depletion is crop rotation. In crop rotation, a farmer plants different crops in a field each year. Different types of plants absorb different amounts of nutrients from the soil. Some crops, such as corn and cotton, absorb large amounts of nutrients. The next year, the farmer plants crops that use fewer soil nutrients, such as oats, barle¡ or rye. The year after that, the farmer sows legumes such as alfalfa or beans to restore the nutrient supply. Another benefit of crop rotation is that it limits the growth of pest populations from year to year.
øl
e¿"r¿f"*¿
Whøt causes nutrient depletion?
Desertification
Plants cannot grow without the moisture and nutrients in fertile soil. The advance of desertlike conditions into areas that previously were fertile is called desertification. In the past 50 years, desertification has occurred on about five billion hectares of land. One cause of desertification is climate. During periods of drought, crops fail. Without plant cover, the exposed soil easily blows away. Overgrazing of grasslands by cattle and sheep also exposes the soil. Cutting down trees for firewood can also cause desertification.
Desertification is a vety serious problem. People cannot grow crops and graze livestock where desertifrcation has occurred. People may face famine and starvation as a result. In central Africa, where desertification is severe, millions of rural people are moving to the cities because they can no longer support themselves on the land.
Figure
4
Large areas of the world
ATLANTIC OCEAN
are at risk of desertification. One cause is overgrazing. Without grass to hold the soil in place, the Senegal
plain is becoming a barren desert. lnterpreting Mops ln which biome
Eq!¿tor
PACIFIC OCEAN
ti
å
are most of the areas at risk of desertificotion located? (Hint: Refer
to Chopter 2.) ANTARCNCA
Areas Threatened by De¡ertlflcatlon Existing desert
il8 .
E
fHist'rirt
ffiHaoderaterisk
INDIAN OCEAN
Restoring the Land Fortunatel¡ it is often possible to restore land damaged by erosion or mining. The process of restoring an area of land to a more natural, productive state is called land reclamation. In addition to restoring lands for agriculture,land reclamation can restore habitats for wildlife. Many different types of land reclamation projects are currently underway all over the world. But it is generally more difflcult and expensive to restore damaged land and soil than it is to protect them in the first place. Figure 5 shows an example of land reclamation. When the mining operation in the first scene was completed, the mine operators smoothed out the sides of the mining cuts. Then they
Figure 5 lt's hard to believe that cows now graze on the same hillside that used to be an open mine. Thanks to land reclamation practices, many mining areas are being restored for other uses.
carefully replaced the subsoil and topsoil that had been removed before mining. Finall¡ they planted grass. The former mine is now agricultural land.
Section 1 Review 1. List three ways that people use land. 2. What are three problems that can occur when topsoil is not properly managed? 3. Describe the effects of strip mining on the land. 4. Why is it important to protect topsoil? 5. Describe two methods for reducing soil erosion.
6. Thinking Critically Relating Cause and Effect How may human activities be related to desertification?
Chopter4
E
a l19
;:iiilfifl';::å
and soil representing a mining site. There are at least 10 deposits of "ore" (sunflower seeds) buried in your mining
4. Observe your mining site and the surrounding area after your mining operations are finished.
site.
Ihink lt Over
2. Your goal is to locate and remove the ore from your site. You may use a pencil, a pair of tweezers, and a spoon as mining tools.
FOR
I i
EADING
How do people use land?
What kinds of problems occur when soil is not properly managed?
Reoding Típ Before you read, use the section headings
to
make an outline about land and soil conservation. Leave space in the outline to take notes.
Predíctíng How did mining change the land at your mining site? Predict whether it would be easy or difficult to restore the land to its original state. Explain.
I ess than a cuarter of Ear I a small am-ount tbrmed L.unnot be created. All th limited amount of land to produce their food, build shelter, and obtain other resources. Land is a precious resource. As the American author Mark Twain once said about land, "They don't make it anymore."
Types
of Land Use
People use land in many ways. Three uses that change the land are agriculture, development, and mining. Examples of these land uses are shown in Figure 1.
Agriculture
Land is the source of most food. Crops such as wheat, rice, and potatoes require large areas of fertile land. But less than a third of Earth's land can be farmed. The rest is too dr¡ too wet, too salty, or too mountainous. To provide food for the growing population, new farmland must be created by clearing forests, draining wetlands, and irrigating deserts. When people make these changes, organisms that depended on the natural ecosystem must frnd new homes. Many crops are grown to feed livestock such as hogs, chicken, and cattle. Other land serves as pasture or rangeland for grazinganimals.
Land Use in the United States
Development
People settled the flrst villages in areas that had good soil and were near a source of fresh water. As population grew, these settlements became towns and cities. People built more houses and paved roads. The construction of buildings, roads, bridges, dams, and other structures is called development. In the United States, about a million hectares of farmland (an area half the size of New |ersey) are developed each year. Development not onlyreduces the amount of farmland, but can also destroy wildlife habitats.
Mining Mining is the removal
of nonrenewable resources such as iron, copper, and coal from the land. Resources just below the surface are strip mined. Strip mining involves removing a strip of land to obtain the minerals and then replacing the strip. Strip mines expose the soil. It can then be blown or washed away more easily. Strip-mined areas may remain barren for years before the soil becomes rich enough to support the growth of plants again. For resources located deep underground, it is necessary to dig a tunnel, or shaft. The minerals are carried up through the shafts. This process is called underground mining.
I
e¿æøf¿*ø
Wilderness,
Cities
porks, ønd wildlife refuges
2o/o
9o/o
Figure
1
Land in the United
States is used in many ways. Clossifying Which of these lond uses chonge the notural ecosystems of the land?
Wlty isn't altlønd suitable for farming? Figure 2 Three major uses of land are agriculture, development, and mining.
Chopter4
Eal15
Protecting the Soil Do you think of soil only as something that has to be washed off your hands or swept off the floor? Then you may not realize how much you depend on soil! Soil is a complex system made up of living and nonliving things. It contains the minerals and nutrients that plants need to grow. Soil also absorbs, stores, and filters water. Bacteria, fungi, and other organisms that live in soil break down the wastes and remains of living things. These decomposers recycle the chemical substances that are necessary for life. Figure 3 shows the structure of fertile soil. Notice that it is composed of several layers. The very top layer of dead leaves and grass is called litter. The next layer, topsoil, is a mixture of rock fragments, nutrients, water, air, and decaying animal and plant matter. The water and nutrients are absorbed by the many plant roots located in this layer. Below the topsoil is the subsoil. The subsoil also contains rock fragments, water, and air, but has less animal and plant matter than the topsoil. It can take hundreds of years to form just a few centimeters of new soil. All soil begins as the lnrecnnnxc Emrn Sqmcr
rock that makes up Earth's crust, called bedrock. Natural processes such
freezing and thawing gradually break apaft the bedrock. Plant roots wedge between rocks and break them into smaller pieces. Chemicals released by lichens slowly break the rock into smaller particles. Animals such as earthworms and moles help grind rocks into even smaller particles. As dead organisms break down, their remains also contribute to the mixture. Because rich topsoil takes a long time to form, it is important to protect Earth's soil. Poor soil management can result in three problems: erosion, nutrient depletion, and desertification.
3 Soil consists of several layers. Applying Concepts ln which loyer ore most plant roots located? What do the roots obsorb there?
Figure
iló.
E
Erosion The
as
process bywhich water, wind, or ice moves particles of rocks or soil is called erosion. Normall¡ plant roots hold soil in place. But when soil is exposed to wind and water, erosion occurs more rapidly. Many uses of land, including logging, mining, and farming, expose the soil and can cause erosion. Some farming methods that help reduce erosion are described in Exploring Soil Conservøtion.
Nutrient Depletion Plants make their own food through photosynthesis. But plants also require a variety of nutrients from the soil. Just as your body needs iron, zinc, and calcium to grow and function properl¡ plants need nitrogen, potassium, phosphorus, and other nutrients. Decomposers supply these nutrients to the soil as they break down the remains of dead organisms. Sometimes, a farmer plants the same crops in a field year after year. As a result, the plants use more nutrients than the decomposers can replace. The soil becomes less fertile, a situation that is called nutrient depletion. One way to prevent nutrient depletion is to periodically leave flelds fallow, or unplanted with crops. A second way to prevent nutrient depletion is to leave the unused parts of crops, such as cornstalks and watermelon vines, in the fields rather than
T
farming practices can help reduce soil erosion. hese
contour plowlng Farmers alternate strips of tall crops, such as corn, with short crops, such as squash. The
Conseruation plowing V Rather than plowing fields and leaving them bare, farmers use machines that break up only the subsoil. This method leaves the dead stalks and weeds from the previous year's crop in the ground
to hold the topsoil in place.
short crops prevent soil from washing out of the tall crop rows, which are less protected. Crops are planted in curving rows that follow the slope, or contour, of the land. Contour plowing can reduce soil erosion as much as 50 percent on gently sloping land.
Wlndbreaks Rows of trees are planted along the
edges of fields. These windbreaks
block the wind and also trap eroding soil. Using fruit or nut trees as windbreaks provides an extra benefit for the farmer and wildlife.
Terraclng Þ Steep hillsides are
built up into a series of flat "terraces." The ridges of soil at the edges of the terraces slow down runoff and
catch eroding soil.
Chopter4
E
a
llT
clearing them away. The stalks and vines decompose in the fields, adding nutrients to the soil. Another method of preventing nutrient depletion is crop rotation. In crop rotation, a farmer plants different crops in a field each year. Different types of plants absorb different amounts of nutrients from the soil. Some crops, such as corn and cotton, absorb large amounts of nutrients. The next year, the farmer plants crops that use fewer soil nutrients, such as oats, barle¡ or rye. The year after that, the farmer sows legumes such as alfalfa or beans to restore the nutrient supply. Another benefit of crop rotation is that it limits the growth of pest populations from year to year.
øl
e¿"r¿f"*¿
Whøt causes nutrient depletion?
Desertification
Plants cannot grow without the moisture and nutrients in fertile soil. The advance of desertlike conditions into areas that previously were fertile is called desertification. In the past 50 years, desertification has occurred on about five billion hectares of land. One cause of desertification is climate. During periods of drought, crops fail. Without plant cover, the exposed soil easily blows away. Overgrazing of grasslands by cattle and sheep also exposes the soil. Cutting down trees for firewood can also cause desertification.
Desertification is a vety serious problem. People cannot grow crops and graze livestock where desertifrcation has occurred. People may face famine and starvation as a result. In central Africa, where desertification is severe, millions of rural people are moving to the cities because they can no longer support themselves on the land.
Figure
4
Large areas of the world
ATLANTIC OCEAN
are at risk of desertification. One cause is overgrazing. Without grass to hold the soil in place, the Senegal
plain is becoming a barren desert. lnterpreting Mops ln which biome
Eq!¿tor
PACIFIC OCEAN
ti
å
are most of the areas at risk of desertificotion located? (Hint: Refer
to Chopter 2.) ANTARCNCA
Areas Threatened by De¡ertlflcatlon Existing desert
il8 .
E
fHist'rirt
ffiHaoderaterisk
INDIAN OCEAN
Restoring the Land Fortunatel¡ it is often possible to restore land damaged by erosion or mining. The process of restoring an area of land to a more natural, productive state is called land reclamation. In addition to restoring lands for agriculture,land reclamation can restore habitats for wildlife. Many different types of land reclamation projects are currently underway all over the world. But it is generally more difflcult and expensive to restore damaged land and soil than it is to protect them in the first place. Figure 5 shows an example of land reclamation. When the mining operation in the first scene was completed, the mine operators smoothed out the sides of the mining cuts. Then they
Figure 5 lt's hard to believe that cows now graze on the same hillside that used to be an open mine. Thanks to land reclamation practices, many mining areas are being restored for other uses.
carefully replaced the subsoil and topsoil that had been removed before mining. Finall¡ they planted grass. The former mine is now agricultural land.
Section 1 Review 1. List three ways that people use land. 2. What are three problems that can occur when topsoil is not properly managed? 3. Describe the effects of strip mining on the land. 4. Why is it important to protect topsoil? 5. Describe two methods for reducing soil erosion.
6. Thinking Critically Relating Cause and Effect How may human activities be related to desertification?
Chopter4
E
a l19
