首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
SOIL QUALITY 1 Soil is a renewable resource, but only on a very long time scale, as it takes hundreds or thousands of years fo
SOIL QUALITY 1 Soil is a renewable resource, but only on a very long time scale, as it takes hundreds or thousands of years fo
admin
2012-01-14
56
问题
SOIL QUALITY
1 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.
2 One important factor affecting the productivity of soils ever 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 potential productivity 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.
3
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.
4 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.
5 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.
6 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
.
7 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.
Glossary:
degradation: loss of quality
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.
选项
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.
答案
D
解析
Within the scientific community, there is little doubt...is paraphrased in Most scientists agree...; ...that soil quality is diminishing in many areas around the world is paraphrased in...that soil degradation is occurring in many parts of the world. (1.7)
转载请注明原文地址:https://www.kaotiyun.com/show/mjyO777K
0
托福(TOEFL)
相关试题推荐
DothefollowingstatementsagreewiththeclaimsofthewriterinReadingPassage3?Inboxes33-40onyouranswersheet,write
TheHistoryoftheGuitarTheword’guitar’wasbroughtintoEnglishasanadaptationoftheSpanishword’guitarra,’whichwas,
TheInnovationofGroceryStoresA.Attheverybeginningofthe20thcentury,theAmericangrocerystoresofferedcomprehen
Completethefollowingsentences.UseNOMORETHANTHREEWORDSforeachanswer.Thespeakeridentifiesthefollowingtwo
"ResearchMethodology"Closescientificmethodbasedonempiricalevidence(=(21))Findaresearchproblemorques
WriteNOMORETHANTWOWORDSforeachanswer.BeWellOnlineProgramme=interactivewebsitewithresourcestohelpreach
Wherewouldyougoforinformationorresources?Writethecorrectletter,A,B,orCnexttoquestions15-20.A.fromanI
ChooseTWOletters,A-E.WhatTWOchangeswillbemadetothecompetitionnextyear?AAnewwayofjudging.BAdifferentlen
ChooseTHREEletters,A-G.WhichTHREEcompulsorycoursesmustbetaken?AMedicalScienceBComputingCMathematicsDLaborator
随机试题
赵某在公共汽车上因不慎踩到售票员而与之发生口角,售票员在赵某下车之后指着他大喊:“打小偷!”赵某因此被数名行人扑倒在地致伤。对此应由谁承担责任?()
对于非重点污染源的调查与评价时,一般采用()的方法。
【背景资料】某施工企业承包了一段36.8km的四车道高速公路沥青混凝土路面工程,路面单幅宽11.25m。路面结构形式为:基层为两层18cm的石灰粉煤灰稳定碎石;底基层为一层18cm的石灰粉煤灰稳定碎石;沥青混凝土面层为7cm的下面层,6cm的中面层和5c
报关人指的是向海关报关并承担由此而引起的经济、法律责任的法人或自然人。()
在计算国别风险时,一般都采用风险因素加权打分方法,其优点包括()。
我国现存规模最大、保存最完整的古清真寺是()。
由垃圾渗出物所导致的污染问题,在那些人均产值为每年4000至5000美元之间的国家最严重,相对贫穷或富裕的国家倒没有那么严重。工业发展在起步阶段,其污染问题都比较严重,当工业发展能创造出足够多的手段来处理这类问题时,污染问题就会减少。目前X国的人均产值是每
为了把观众从电视节目里夺回来,好莱坞推出了一种新玩艺——立体电影。戴着特殊眼镜的观众像在观看《布瓦那魔鬼》及《蜡屋》这类惊险片那样,发现自己躲在魔鬼及逃跑的火车的后面,感受真实刺激。2010年由著名导演詹姆斯.卡梅隆执导3D电影《阿凡达》更是大获成功,立体
Whichsporthasthemostexpenses______trainingequipment,players’personalequipmentanduniforms?
Withoutcomputers,we______thetremendousmedicaladvancementinthelastfewdecades.
最新回复
(
0
)