Degradation and Erosion of Soil
Land without soil can support only very small primitive plants such as lichens and mosses that can cling onto a rock surface. The rest of the world’s terrestrial vegetation has to be rooted in soil, which gives it physical support. The soil also serves as a store of essential mineral nutrients and water that are extracted by the roots during plant growth. Soil develops by the accumulation of finely divided mineral products of rock weathering and decomposing organic residues from previous vegetation. The characteristics of the soil under natural vegetation in any particular climatic region and on any particular rock type depend on the balance between these processes of accumulation and forces that degrade and remove the soil.
The formation and persistence of soil in a region depend on local natural checks and balances. Soil may be lost by being washed or blown away, perhaps to be redeposited as an accumulation of fine-textured “loess” somewhere else. Soil is best protected when it contains organic matter, is always wholly covered with vegetation, is finely interwoven with roots and rootlets, and is on horizontal ground. Natural soil systems are probably always too fragile to be fully sustained when land is brought into cultivation. Dramatic evidence of unsustainable land use came from the “dust bowl”disaster in the Great Plains of the United States in the 1930s, when years of severe dust storms occurred due to misuse of land and drought.
Almost all (perhaps all) agricultural land will support higher yields if artificial fertilizers are applied to supplement the nitrogen, phosphorus, and potassium supplied naturally by the soil. Fertilizers are cheap, easy to handle, and of a guaranteed composition, and they allow even and accurate application and higher and more predictable yields. When there is an overwhelming reliance on them, however, maintaining the organic matter within the soil tends to be neglected and has declined everywhere.
The degradation of soil by agriculture can be prevented, or at least slowed down, by incorporating farmyard manure, crop residues, and animal wastes; by alternating years under cultivation with years of not growing anything; or by returning the land to grazed pasture or rangeland. Such practices conserve soil quality in technologically sophisticated agricultures in temperate regions.
But soil degradation is most serious and least easily prevented in tropical areas of the world. The problems are greatest in high rainfall areas and on steeply sloping ground in the tropics where organic matter in the soil also decomposes more rapidly. The most cost-effective technology used in reducing soil erosion is considered to be contour-based cultivation. In India, contour ditches (ditches cut at right angles to the line of the slope) have helped to quadruple the survival chances of tree seedlings and quintuple their early growth in height. Deeply-rooted, hedge-forming grass, planted in contour strips across hill slopes, slows water runoff dramatically, reduces erosion, and increases the moisture available for crop growth. Currently 90 percent of soil conservation efforts in India are based on such biological systems. Simple technologies involving rock embankments (raised structures) constructed along contour lines for soil and water conservation have also been successful. Embanked fields in Burkina Faso (in West Africa) yielded an average of 10 percent more crop production than traditional fields in a normal year and, in drier years, almost 50 percent more. Such terracing provides a very high level of soil conservation but is possible only where labor is cheap. On lesser slopes, by plowing and cultivating in strips along the contours, runoff of soil can be significantly reduced.
In arid and semiarid regions, agricultural land is also highly susceptible to degradation. Both overgrazing and excessive cultivation expose the soil directly to erosion by the wind and to rare but fierce rainstorms. In the process of “desertization,” land that is arid or semiarid but has supported subsistence or nomadic agriculture gives way to desert. The process has often been slowed down for a time by irrigating the land. This gives a temporary improvement but lowers the water table, and salts accumulate in the topsoil (salinization). Once salts have started to accumulate, the process of salinization tends to spread and leads to an expansion of sterile, white salt deserts. This has been a particular hazard in irrigated areas of Pakistan.
1
Land without soil can support only very small primitive plants such as lichens and mosses that can cling onto a rock surface. The rest of the world’s terrestrial vegetation has to be rooted in soil, which gives it physical support. The soil also serves as a store of essential mineral nutrients and water that are extracted by the roots during plant growth. Soil develops by the accumulation of finely divided mineral products of rock weathering and decomposing organic residues from previous vegetation. The characteristics of the soil under natural vegetation in any particular climatic region and on any particular rock type depend on the balance between these processes of accumulation and forces that degrade and remove the soil.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
Sentence Simplification Questions句子简化题
ARegardless of climate or rock type, the processes of accumulation and the forces that degrade and remove soil will be in balance.
BThe characteristics of the soil depend on the particular climatic region and rock type in the area in which it is found.
CThe balance between processes of soil accumulation and forces that degrade and remove soil is determined by the particular climatic region and rock type where the soil is located.
DThe balance between processes of soil accumulation and forces that degrade and remove soil determines the characteristics of the soil.
2
The formation and persistence of soil in a region depend on local natural checks and balances. Soil may be lost by being washed or blown away, perhaps to be redeposited as an accumulation of fine-textured “loess” somewhere else. Soil is best protected when it contains organic matter, is always wholly covered with vegetation, is finely interwoven with roots and rootlets, and is on horizontal ground. Natural soil systems are probably always too fragile to be fully sustained when land is brought into cultivation. Dramatic evidence of unsustainable land use came from the “dust bowl”disaster in the Great Plains of the United States in the 1930s, when years of severe dust storms occurred due to misuse of land and drought.
The word”fragile” in the passage is closest in meaning to
Vocabulary Questions词汇题
Aeasily damaged
Bconstantly changing
Cshort-lived
Dinferior
3
Almost all (perhaps all) agricultural land will support higher yields if artificial fertilizers are applied to supplement the nitrogen, phosphorus, and potassium supplied naturally by the soil. Fertilizers are cheap, easy to handle, and of a guaranteed composition, and they allow even and accurate application and higher and more predictable yields. When there is an overwhelming reliance on them, however, maintaining the organic matter within the soil tends to be neglected and has declined everywhere.
The word”supplement”in the passage is closest in meaning to
Vocabulary Questions词汇题
Aadd to
Btake in
Cactivate
Dcombine
4
Almost all (perhaps all) agricultural land will support higher yields if artificial fertilizers are applied to supplement the nitrogen, phosphorus, and potassium supplied naturally by the soil. Fertilizers are cheap, easy to handle, and of a guaranteed composition, and they allow even and accurate application and higher and more predictable yields. When there is an overwhelming reliance on them, however, maintaining the organic matter within the soil tends to be neglected and has declined everywhere.
According to paragraph 3， which of the following is a disadvantage of using artificial fertilizers?
Factual Information Questions事实信息题
AThey have an inconsistent composition.
BThey can reduce organic matter in soil when overused.
CThey can be difficult to apply evenly.
DThey are relatively expensive to use.
5
But soil degradation is most serious and least easily prevented in tropical areas of the world. The problems are greatest in high rainfall areas and on steeply sloping ground in the tropics where organic matter in the soil also decomposes more rapidly. The most cost-effective technology used in reducing soil erosion is considered to be contour-based cultivation. In India, contour ditches (ditches cut at right angles to the line of the slope) have helped to quadruple the survival chances of tree seedlings and quintuple their early growth in height. Deeply-rooted, hedge-forming grass, planted in contour strips across hill slopes, slows water runoff dramatically, reduces erosion, and increases the moisture available for crop growth. Currently 90 percent of soil conservation efforts in India are based on such biological systems. Simple technologies involving rock embankments (raised structures) constructed along contour lines for soil and water conservation have also been successful. Embanked fields in Burkina Faso (in West Africa) yielded an average of 10 percent more crop production than traditional fields in a normal year and, in drier years, almost 50 percent more. Such terracing provides a very high level of soil conservation but is possible only where labor is cheap. On lesser slopes, by plowing and cultivating in strips along the contours, runoff of soil can be significantly reduced.
According to paragraph 5， what is one reason that soil degradation is especially problematic in tropical areas?
Factual Information Questions事实信息题
AHeavy rainfall has gradually created slopes that are too steep.
BOrganic matter breaks down more quickly in tropical areas.
CThe roots of plants are not very deep in tropical areas.
DSoil conservation systems are currently not effective in tropical areas.
6
But soil degradation is most serious and least easily prevented in tropical areas of the world. The problems are greatest in high rainfall areas and on steeply sloping ground in the tropics where organic matter in the soil also decomposes more rapidly. The most cost-effective technology used in reducing soil erosion is considered to be contour-based cultivation. In India, contour ditches (ditches cut at right angles to the line of the slope) have helped to quadruple the survival chances of tree seedlings and quintuple their early growth in height. Deeply-rooted, hedge-forming grass, planted in contour strips across hill slopes, slows water runoff dramatically, reduces erosion, and increases the moisture available for crop growth. Currently 90 percent of soil conservation efforts in India are based on such biological systems. Simple technologies involving rock embankments (raised structures) constructed along contour lines for soil and water conservation have also been successful. Embanked fields in Burkina Faso (in West Africa) yielded an average of 10 percent more crop production than traditional fields in a normal year and, in drier years, almost 50 percent more. Such terracing provides a very high level of soil conservation but is possible only where labor is cheap. On lesser slopes, by plowing and cultivating in strips along the contours, runoff of soil can be significantly reduced.
In paragraph 5,why does the author compare embanked fields in Burkina Faso with traditional fields?
Factual Information Questions事实信息题
ATo argue that rock embankments conserve water more effectively in West Africa than in other areas
BTo provide evidence that rock embankments effectively conserve soil for traditional fields but not for trees
CTo support the claim that rock embankments can successfully conserve water and soil
DTo suggest that rock embankments are less effective in dry years than in rainy years
7
But soil degradation is most serious and least easily prevented in tropical areas of the world. The problems are greatest in high rainfall areas and on steeply sloping ground in the tropics where organic matter in the soil also decomposes more rapidly. The most cost-effective technology used in reducing soil erosion is considered to be contour-based cultivation. In India, contour ditches (ditches cut at right angles to the line of the slope) have helped to quadruple the survival chances of tree seedlings and quintuple their early growth in height. Deeply-rooted, hedge-forming grass, planted in contour strips across hill slopes, slows water runoff dramatically, reduces erosion, and increases the moisture available for crop growth. Currently 90 percent of soil conservation efforts in India are based on such biological systems. Simple technologies involving rock embankments (raised structures) constructed along contour lines for soil and water conservation have also been successful. Embanked fields in Burkina Faso (in West Africa) yielded an average of 10 percent more crop production than traditional fields in a normal year and, in drier years, almost 50 percent more. Such terracing provides a very high level of soil conservation but is possible only where labor is cheap. On lesser slopes, by plowing and cultivating in strips along the contours, runoff of soil can be significantly reduced.
Paragraph 5 suggests that which of the following is a problem with using rock embankments to prevent soil degradation?
Inference Questions推理题
AThey are less effective than terracing.
BThey require a great deal of labor to build.
CThey can be used only on very steep slopes.
DThey are effective only in relatively dry areas.
8
In arid and semiarid regions, agricultural land is also highly susceptible to degradation. Both overgrazing and excessive cultivation expose the soil directly to erosion by the wind and to rare but fierce rainstorms. In the process of “desertization,” land that is arid or semiarid but has supported subsistence or nomadic agriculture gives way to desert. The process has often been slowed down for a time by irrigating the land. This gives a temporary improvement but lowers the water table, and salts accumulate in the topsoil (salinization). Once salts have started to accumulate, the process of salinization tends to spread and leads to an expansion of sterile, white salt deserts. This has been a particular hazard in irrigated areas of Pakistan.
According to paragraph 6,what is a drawback to irrigation in arid and semiarid regions?
Factual Information Questions事实信息题
AIt reduces the effectiveness of erosion-protection measures.
BIt increases the damage that can be caused by fierce rainstorms.
CIt immediately speeds up the process of desertization.
DIt leads to a buildup of salts in the topsoil.
9
But soil degradation is most serious and least easily prevented in tropical areas of the world. [■] The problems are greatest in high rainfall areas and on steeply sloping ground in the tropics where organic matter in the soil also decomposes more rapidly. [■] The most cost-effective technology used in reducing soil erosion is considered to be contour-based cultivation. [■] In India, contour ditches (ditches cut at right angles to the line of the slope) have helped to quadruple the survival chances of tree seedlings and quintuple their early growth in height. [■] Deeply-rooted, hedge-forming grass, planted in contour strips across hill slopes, slows water runoff dramatically, reduces erosion, and increases the moisture available for crop growth. Currently 90 percent of soil conservation efforts in India are based on such biological systems. Simple technologies involving rock embankments (raised structures) constructed along contour lines for soil and water conservation have also been successful. Embanked fields in Burkina Faso (in West Africa) yielded an average of 10 percent more crop production than traditional fields in a normal year and, in drier years, almost 50 percent more. Such terracing provides a very high level of soil conservation but is possible only where labor is cheap. On lesser slopes, by plowing and cultivating in strips along the contours, runoff of soil can be significantly reduced.
Look at the four squares [■] that indicate where the following sentence could be added to the passage
However, even under such conditions, certain measures can limit degradation.Insert Text Questions句子插入题
Where would the sentence best fit？Click on a square sentence to the passage.
10
Soil develops as a result of decaying organic material and the products of rock weathering and is lost through erosion.
Prose Summary Questions概要小结题
Select 3 answers
ASoil is best protected from being washed or blown away when it contains ample organic matter and is covered by vegetation, and it is at greatest risk in tropical areas with high rainfall and steep slopes.
BIn temperate areas where soil is conserved using suitable natural organic materials and appropriate cultivation technologies, artificial fertilizers generally do not produce higher yields.
CLand in dry regions has typically supported only subsistence or nomadic agriculture, but with the introduction of irrigation systems, large-scale grazing and cultivation begin to dominate.
DMaintaining soil’s organic matter is often neglected on cultivated land, especially when there is heavy use of artificial fertilizers, but degradation can be minimized through proper land-use practices.
EThe most effective biological systems for soil conservation-those developed in India and in West Africa-have reduced erosion by as much as 90 percent, while significantly increasing crop yields.
FSimple technologies can reduce erosion in tropical areas, where soil is at great risk of degradation, but in arid and semiarid regions, heavy use of the land can lead to desertization and salinization.
