Title：Water Management in Early Agriculture

　　As the first cities formed in Mesopotamia in the Middle East, probably around 3000 B.C., it became necessarily to provide food for larger populations, and thus to find ways of increasing agricultural production. This, in turn, led to the problem of obtaining sufficient water.

　　Irrigation must have started on a small scale with rather simple constructions, but as its value became apparent, more effort was invested in new construction to divert more water into the canals and to extend the canal system to reach greater areas of potential farmland. Because of changing water levels and clogging by waterborne particles, canals and their intakes required additional labor to maintain, besides the normal labor required to guide water from field to field. Beyond this,some personnel had to be devoted to making decisions about the allocation of available water among the users and ensuring that these directions were carried out. With irrigation water also came potential problems, the most obvious being the susceptibility of low-lying farmlands to disastrous flooding and the longer-term problem of salinization (elevated levels of salt in the soil). To combat flooding from rivers, people from early historic times until today have constructed protective levees (raised barriers of earth) between the river and the settlement or fields to be protected. This, of course, is effective up to a certain level of flooding but changes the basic water patterns of the area and can multiply the damage when the flood level exceeds the height of the levee.

　　Salinization is caused by an accumulation of salt in the soil near its surface. This salt is carried by river water from the sedimentary rocks in the mountains and deposited on the Mesopotamian fields during natural flooding or purposeful irrigation. Evaporation of water sitting on the surface in hot climates is rapid, concentrating the salts in the remaining water that then descends through the soil to the underlying water table. In southern Mesopotamia, for example, the natural water table comes to within roughly six feet of the surface. Conditions of excessive irrigation bring the water table to eighteen inches, and water can rise further to the root zone, where the high concentration of salts would kill most plants.

　　Solutions for salinization were not as straightforward as for flooding, but even in ancient times it was understood that the deleterious effects of salinization could be minimized by removing harmful elements through leaching the fields with additional fresh water, digging deep wells to lower the water table, or instituting a system of leaving fields uncultivated. The first two cures would have required considerable labor, and the third solution would have led to diminished productivity, not often viewed as a likely decision in periods of growing population. An effective irrigation system laid the foundation for many of the world’s early civilizations, but it also required a great deal of labor input.

　　Growing agrarian societies often tried to meet their food-producing needs by farming less-desirable hill slopes surrounding the favored low-lying valley bottoms. Since bringing irrigation water to a hill slope is usually impractical, the key is effective utilization of rainfall. Rainfall either soaks into the soil or runs off of it due to gravity. A soil that is deep, well-structured, and covered by protective vegetation and much will normally absorb almost all of the rain that falls on it, provided that the slope is not too steep. However, soils that have lost their vegetative cover and surface mulch will absorb much less, with almost half the water being carried away by runoff in more extreme conditions. This runoff carries with it topsoil particles, nutrients, and humus (decayed vegetable matter) that are concentrated in the topsoil. The loss of this material reduces the thickness of the rooting zone and its capacity to absorb moisture for crop needs.

　　The most direct solution to this problem of slope runoff was to lay lines of stones along the contours of the slope and hence, perpendicular to the probable flow of water and sediment. These stones could then act as small dams, slowing the downhill flow of water and allowing more water to infiltrate and soil particles to collect behind the dam. This provided a buildup of sediments for plants and improved the landscape’s water-retention properties.

　　Paragraph 2 Irrigation must have started on a small scale with rather simple constructions, but as its value became apparent, more effort was invested in new construction to divert more water into the canals and to extend the canal system to reach greater areas of potential farmland. Because of changing water levels and clogging by waterborne particles, canals and their intakes required additional labor to maintain, besides the normal labor required to guide water from field to field. Beyond this, some personnel had to be devoted to making decisions about the allocation of available water among the users and ensuring that these directions were carried out. With irrigation water also came potential problems, the most obvious being the susceptibility of low-lying farmlands to disastrous flooding and the longer-term problem of salinization (elevated levels of salt in the soil). To combat flooding from rivers, people from early historic times until today have constructed protective levees (raised barriers of earth) between the river and the settlement or fields to be protected. This, of course, is effective up to a certain level of flooding but changes the basic water patterns of the area and can multiply the damage when the flood level exceeds the height of the levee.

　　1. All of the following are mentioned in paragraph 2 as operations involved in the Mesopotamian irrigation system EXCEPT

　　determining how much irrigation water should be distributed to variousfarmers

　　widening existing canals so they could hold more water

　　removing undesirable materials from the intakes of irrigation canals

　　building new canals so irrigation water could be transported to distant areas Paragraph 2 is marked with an arrow [→]

　　2. According to paragraph 2, protective levees can have which of the following disadvantages?

　　They can greatly increase the destruction caused by floodwaters when floodwaters are higher than the levee.

　　They can fail even when the flood level remains below the height of the levee.

　　They can lead over time to a serious salinization problem.

　　They can cause damaging floods to occur more frequently by changing basic water patterns. Paragraph 2 is marked with an arrow [→]

　　3. Paragraph 2 suggests that irrigation increased the likelihood of destructive floods because

　　irrigated fields were often in locations that tended to flood naturally

　　the canal intakes for irrigation water often did not work

　　most irrigation canals were too narrow and thus overflowed

　　levees built to protect irrigation systems required maintenance

　　Paragraph 2 is marked with an arrow [→]

　　4. The word “potential” in the passage is closet in meaning to  serious  basic  new  possible

　　Paragraph 3 Salinization is caused by an accumulation of salt in the soil near its surface. This salt is carried by river water from the sedimentary rocks in the mountains and deposited on the Mesopotamian fields during natural flooding or purposeful irrigation. Evaporation of water sitting on the surface in hot climates is rapid, concentrating the salts in the remaining water that then descends through the soil to the underlying water table. In southern Mesopotamia, for example, the natural water table comes to within roughly six feet of the surface. Conditions of excessive irrigation bring the water table to eighteen inches, and water can rise further to the root zone, where the high concentration of salts would kill most plants.

　　5. The word “accumulation” in the passage is closet in meaning to

　　distribution

　　mixture

　　buildup

　　exchange

　　6. According to paragraph 3, excessive irrigation can destroy crops by

　　raising salty water to the level of the roots

　　forcing the roots of plants to grow close to the surface

　　taking the place of some natural flooding

　　creating salt deposits on the surface of the soil

　　Paragraph 3 is marked with an arrow [→]

　　Paragraph 4 Solutions for salinization were not as straightforward as for flooding, but even in ancient times it was understood that the deleterious effects of salinization could be minimized by removing harmful elements through leaching the fields with additional fresh water, digging deep wells to lower the water table, or instituting a system of leaving fields uncultivated. The first two cures would have required considerable labor, and the third solution would have led to diminished productivity, not often viewed as a likely decision in periods of growing population. An effective irrigation system laid the foundation for many of the world’s early civilizations, but it also required a great deal of labor input.

　　7. The word “straightforward” in the passage is closet in meaning to

　　successful

　　simple

　　common

　　complex

　　8. According to paragraph 4, which of the following is true of the more-likely-used solutions to the problem of salinization?

　　They resulted in a decrease in the amount of food that was produced.

　　They succeeded only on areas where the natural water table was especially low.

　　They often demanded much time and effort on the part of their users.

　　They often led to other technological advances.

　　Paragraph 4 is marked with an arrow [→]

　　Paragraph 5 Growing agrarian societies often tried to meet their food-producing needs by farming less-desirable hill slopes surrounding the favored low-lying valley bottoms. Since bringing irrigation water to a hill slope is usually impractical, the key is effective utilization of rainfall. Rainfall either soaks into the soil or runs off of it due to gravity. A soil that is deep, well-structured, and covered by protective vegetation and much will normally absorb almost all of the rain that falls on it, provided that the slope is not too steep. However, soils that have lost their vegetative cover and surface mulch will absorb much less, with almost half the water being carried away by runoff in more extreme conditions. This runoff carries with it topsoil particles, nutrients, and humus (decayed vegetable matter) that are concentrated in the topsoil. The loss of this material reduces the thickness of the rooting zone and its capacity to absorb moisture for crop needs.

　　9. According to paragraph 5, which of the following was the main challenge faced by early agricultural societies that wanted to grow crops on hill slopes?

　　Getting enough irrigation water to the hill slope

　　Growing crops without disturbing the natural vegetative cover

　　Retaining rainwater and thus preventing excessive runoff

　　Identifying crops that do not need a thick rooting zone

　　10. 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.

　　However, soils that are unable to absorb much water experience massive runoff during heavy rains.

　　However, where neither protective vegetation nor mulch covers the soil, much rainwater can be lost to runoff.

　　However, on extremely steep slopes there is no vegetative cover or mulch to prevent runoff.

　　However, in more extreme conditions water that runs off can carry away the vegetative cover and the surface mulch