Soil Quality

Soil is a renewable?resource, but only on a very long time?scale, as it takes hundreds or thousands of years for the natural processes of?erosion,?organic?decay, and?accumulation?to create soils.?Soil?quality?and the?potential?to produce crops can?vary?enormously from?region?to?region?and among various soil types.

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One important?factor?affecting the?productivity?of soils over time is?agriculture.?Top-?quality?lands are brought into production earlier because of their higher?potential?to produce food.?As more and more land has been brought under agricultural production, the?average?quality?of land has decreased, reducing?potentialproductivity?per?hectare.?Crops?deplete?soil?fertility?by consuming nutrients, and this?eventually?reduces crop yields.?Poor?management?practices?lead?to soil compaction and soil pollution as well as loss of soil cover.?Without?proper?management?and the?constant?addition?of nutrients and energy in the form of fertilizers and?irrigation, crop production falls over time.

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Within?the?scientific?community, there is little?doubt?that soil?quality?is diminishing in many areas around the world.?Scientists have found that the?quality?of one quarter of the world’s soils has experienced some?degradation, and the pace of?degradation?has?accelerated?over the past 50 years.?The loss of soil?fertility?has caused a slowing in the growth of agricultural?productivity.?Annual?crops?tend?to?degrade?soils more than?perennial?crops, and?common?property?lands generally suffer more?degradation?than private lands.

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Today, irrigated?cropland?produces about one-third of the world’s food.?Approximately?18 percent of the world’s?cropland?is irrigated, and scientists?project?this?amount?to double by 2020.?Irrigation?can increase crop yields per?hectare?to two or three times the yields of land watered only by rain.?However, there are also some harmful side effects.?Besides?increasing crop?productivity?in the short run,?irrigation?can?lead?to sharp drops in crop?productivity?in the long run by causing?excessive?salt buildup and rising water tables.

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One of the most?critical?soil?quality?problems related to?irrigation?is the increase in?concentration?of dissolved salts.?This?process,?salinization, affects an estimated one-fourth of the world’s irrigated?cropland.?In some places,?irrigation?water contains as much as 3.5 tons of salt per 1,000 cubic meters.?As the water flows over and?through?the ground, it dissolves salts, increasing the?salinity?of the water.?Since some crops?require?6,000 to 10,000 cubic meters of water per?hectare, land can receive tens of tons of salt per?hectare.?As the water evaporates, high concentrations of salts such as?sodium?chloride are left behind in the?topsoil.?Salt buildup can?stunt?crop growth,?decrease?yields, kill crop plants, and?eventually?make the land unproductive.

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A problem that often accompanies?salinization?in dry regions is waterlogging, which often occurs when farmers?apply?heavy amounts of?irrigation?water in an?attempt?to prevent salts from accumulating.?However, unless the water drains properly, it collects?underground?and?gradually?raises the water table closer to the surface,?thereby?bringing salts to the surface and concentrating them.?Saltwater then envelops the?fragile?root?systems of plants, killing the plants and converting?fertile?fields to wet deserts.?This is a particularly serious problem in California’s heavily irrigated San Joaquin?Valley, where soils?contain?a?clay?layer?that prevents water from flowing?through?the ground.?Worldwide, at?least?one-tenth of all irrigated land is?subject?to waterlogging.

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Another serious soil problem is?erosion, the loss of soils from water and wind?action.Soil?erosion?occurs on agricultural land without?vegetative?cover for protection or because of poor agricultural?management.?Scientists?estimate?that?topsoil?on?cultivated?land is being lost 16 to 300 times faster than it is being replaced.?In many parts of the world, a?shift?away from?traditional?agricultural practices is placing greater?pressure?on the soil, which in turn is causing an increase in soil?erosion?rates.?Studies in the United States suggest that the loss of just 2.5 centimeters of?topsoil?reduces corn and wheat yields by 6 percent.

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Glossary:

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degradation: loss of quality

1

According to the passage, all of the following contribute to soil degradation EXCEPT

A. poor agricultural management

B. rotation of annual crops?

C. accumulation of salts?

D. lack of water drainage

2

The word?deplete?in paragraph 2 is closest in meaning to

A. reduce

B. attract

C. prepare

D. create

3

Within?the?scientific?community, there is little?doubt?that soil?quality?is diminishing in many areas around the world.

Which sentence below best expresses the essential information in the highlighted sentence in paragraph 3? Incorrect choices change the meaning in important ways or leave out essential information.

A. The scientific study of soils is improving soil quality in many regions worldwide.

B. Few people would disagree that soil quality is as diminished as scientists say it is.

C. The number of scientists who specialize in the study of soils has been decreasing.

D. Most scientists agree that soil degradation is occurring in many parts of the world.

4

What can be inferred from paragraph 3 about annual crops and common property lands?

A. They have been part of agriculture for only the past fifty years.

B. They are not considered to be significant causes of soil degradation.

C. They produce more income than perennial crops and private lands do.

D. They may decrease soil fertility and agricultural productivity.

5

According to the passage, which of the following is a serious consequence of irrigation?

A. Loss of fresh water for drinking

B. Decrease in the level of rivers

C. Excessive buildup of salts in the soil?

D. Increase in the rate of soil erosion

6

In what way is salinization a serious problem for agriculture?

A. ?Soils with high salt concentrations are destructive to crop plants.

B. ?Salinization can lead to soil compaction or to loss of soil cover.

C. ?Excessive amounts of water are required to prevent salinization.

D. ?Adding salt to fertilizer raises the operating costs of agriculture.

7

How are waterlogging and salinization related?

A. Salinization occurs only where waterlogging is a problem.

B. Waterlogging raises and concentrates salts near the surface.

C. Farmers add salts to irrigation water as a way to fertilize soil.

D. Both waterlogging and salinization contribute to soil erosion.

8

Why does the author mention corn and wheat yields in paragraph 7?

A. To illustrate the effect of a small amount of erosion

B. To explain why erosion affects only certain crops?

C. To describe the result of a shift from traditional practices?

D. To show how poor management influences crop yields

9

One of the most?critical?soil?quality?problems related to?irrigation?is the increase in?concentration?of dissolved salts.?This?process,?salinization, affects an estimated one-fourth of the world’s irrigated?cropland.?In some places,?irrigation?water contains as much as 3.5 tons of salt per 1,000 cubic meters.?[■]As the water flows over and?through?the ground, it dissolves salts, increasing the?salinity?of the water.?[■]Since some crops?require?6,000 to 10,000 cubic meters of water per?hectare, land can receive tens of tons of salt per?hectare.?[■]As the water evaporates, high concentrations of salts such as?sodium?chloride are left behind in the?topsoil.?[■]Salt buildup can?stunt?crop growth,?decrease?yields, kill crop plants, and?eventually?make the land unproductive.

Look at the four squares[■],A, B, C, and D, which indicate where the following sentence could be added to the passage. Where would the sentence best fit?

Unless they are flushed or drained from the soil, their buildup may cause a number of serious problems. .

10

Read the first sentence of a summary of the passage. Complete the summary by selecting the?THREE?answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.?Several factors are responsible for the degradation of the world’s soils.

A.Soils are created through the processes of erosion, organic decay, and accumulation.

B.Contamination of the soil from air and water pollution is a growing threat.

C.Agriculture and poor land management practices decrease the quality of soils over time.

D.Irrigation can diminish soil productivity by causing salts and water to accumulate.

E.The soils in the San Joaquin Valley contain a clay layer that contributes to waterlogging.

F.The erosion of topsoil on agricultural lands is a growing problem that affects crop yields.