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
29
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://kaotiyun.com/show/mjyO777K
0
托福(TOEFL)
相关试题推荐
DothefollowingstatementsagreewiththeviewsofthewriterinReadingPassage1?Inboxes8-13onyouranswersheet,writeY
REVIEWOFRESEARCHONTHEEFFECTSOFFOODPROMOTIONTOCHILDRENThisreviewwascommissionedbytheFoodStandardsAgencytoex
REVIEWOFRESEARCHONTHEEFFECTSOFFOODPROMOTIONTOCHILDRENThisreviewwascommissionedbytheFoodStandardsAgencytoex
DothefollowingstatementsagreewiththeviewsofthewriterinReadingPassage3?Inboxes31-36onyouranswersheet,write
Answerthequestionsbelow.ChooseNOMORETHANTWOWORDSfromthepassageforeachanswer.Writeyouranswersinboxes10-13on
Completethesummarybelow.ChooseNOMORETHANTHREEWORDSfromthepassageforeachanswer.Writeyouranswersinboxes31-35
DothefollowingstatementsagreewiththeinformationgiveninReadingPassage2?Inboxes19-23onyouranswersheet,writeTR
Whichtwothingsareuncommoninruralareas?Whichareasgenerallyhavemoreconservativepopulations?
"ResearchMethodology"Closescientificmethodbasedonempiricalevidence(=(21))Findaresearchproblemorques
随机试题
苏某系某市制药厂的职工,受该厂委托去某限价区收购当地农民采挖的麻黄草,收购后苏某雇佣了个体运输户陈某的汽车,将麻黄草运往所属的制药厂。在运输途中,被该县草原监理所工作人员发现,经检查,苏某、陈某并未持有采药许可证及调运、货运的合法批准手续,该县草原监理所遂
Dr.Smith,togetherwithhiswifeandtwosons,______toarriveontheeveningflight.
Makeanoteofit______youshouldforgetit.
患者,女,63岁。腰部冷痛重着,转侧不利,逐渐加重,静卧病痛不减,寒冷或阴雨天则加重,舌质淡,苔白腻,脉沉而迟缓。其方药宜选
关于执业药师资格考试和注册管理的说法,正确的是()。
深证综合指数的样本股是在深圳证券交易所上市的全部股票,计算权数为()。
甲、乙两家旅行社都是享有盛名的国家承办境外游客到国内观光的经济组织。2010年,两旅行社均接待海外游客20万人次,经济效益不相上下。2013年上半年,甲旅行社以高薪为条件,致使乙旅行社海外部15名工作人员全部辞职,转入甲旅行社工作a甲旅行社为此成立海外旅行
显示ARP缓存的命令是(61),清除ARP缓存病毒的命令是(62)。(62)
•Youwillhearfiverecordings.•Foreachrecording,decidewhatthemainreasonisforthephonecall.•Writeoneletter(A—H)
A、Every6years.B、Every2years.C、Every4years.D、Wheneveronedies.A
最新回复
(
0
)