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
Weed Communities In an intact plant community, undisturbed by human intervention, the composition of a community is mainly a
Weed Communities In an intact plant community, undisturbed by human intervention, the composition of a community is mainly a
admin
2010-07-19
29
问题
Weed Communities
In an intact plant community, undisturbed by human intervention, the composition of a community is mainly a function of the climate and the type of soil. Today, such original communities are very rare—they are practically limited to national parks and reservations.
Civilization has progressively transformed the conditions determining the composition of plant communities. For several thousand years vast areas of arable land have been hoed, ploughed, harrowed and grassland has been cut or grazed. During the last decades the use of chemical substances, such as fertilizers and most recently of weed killers (herbicides) has greatly influenced the composition of weed communities in farm land.
All selective herbicides have specific ranges of activity. They control the most important weeds but not all the plants of a community. The latter profit from the new free space and from the fertilizer as much as the crop does; hence they often spread rapidly and become problem weeds unless another herbicide for their eradication is found.
The soil contains enormous quantities of seeds of numerous species—up to half a million per m2 according to scientific literature--that retain their ability to germinate for decades. Thus it may occur that weeds that were hardly noticed before emerge in masses after the elimination of their competitors. Hence, the knowledge of the composition of weed communities before selective weed killers are applied is not only of scientific interest since the plant species present in the soil in the form of seeds must be considered as potential weeds. For efficient control the identification of weeds at the seedling stage, i. e. at a time when they can still be controlled, is particularly necessary; for the choice of the appropriate herbicide depends on the composition of the weed community.
A knowledge of the composition of the weed community ______.
选项
A、is essential to the efficient control of weeds
B、may lead us to be aware of the fact that the soil contains enormous quantities of seeds of numerous species
C、helps us to have a good idea of why seeds can lie dormant for years
D、provides us with the means to identify weeds at the seedling stage
答案
A
解析
转载请注明原文地址:https://kaotiyun.com/show/W8lO777K
0
专业英语八级
相关试题推荐
"Ineveryknownhumansocietythemale’sneedsforachievementcallberecognized...Inagreaternumberofhumansocietiesmen’
ThethirdparagraphexaminesAmerica’sfuture-mindednessfromthe______perspective.Accordingtothepassage,peopleatpres
ItcanbeinferredfromthefirstparagraphthatcosmologistsAccordingtothepassage,theauthorthinksWMAP’sfindingsare
WhichofthefollowingstatementsabouttheAmericanDefenseDepartmentisTRUE?
Storytellingisanancientandhonoredart.Storytellersentertainedduringthelongdarkhoursbeforesleeparrivedafterthe
WhichoneisnotthereasonwhyAfghanistangovernmentcannoteliminateopiumquickly?Whatistheauthor’sattitudetowardsA
Thestudyofthementalprocessesoflanguagecomprehensionandproductionis______.
Themostimportantroleforgovernmentincreatingtheconditionsforcommercialinnovationistosupportuniversitiesintheir
TheUnitedNationsConferenceonDrugAbusethattookplaceearlierthisyearinVienna,wasaveryproductivemeeting.Asnever
A、worldtravelB、educationC、knowledgeoftheworldD、serviceA
随机试题
给婴儿添加辅食的原则有哪些?
A.黑色素瘤B.脂肪瘤C.纤维瘤D.血管瘤E.皮脂腺囊肿好发于皮下、界限清楚、分叶状、生长较慢的肿瘤是
临床医生申请血浆时,输血前相容性检测项目不包括
(2007)压气机最理想的压缩过程是采用()。
设置会计科目时,不仅要能全面正确地反映企业的财务状况和经营成果,满足外部投资者和债权人的需要,还应当有利于企业内部管理活动的开展,这是设置会计科目的()原则
TothewestofAmericaliesthe______Ocean;totheeastofAmericaliesthe______Ocean.
我区医疗救助对象患重大疾病医疗救助年封顶线是()万元。
某日深夜,甲喝醉酒后,叫上乙外出找乐,乙应邀开车载甲前往一娱乐场所。当车行至一昏暗的路上时,甲看见路边有一女子丙(21岁)正在等车,遂对乙说:“停车下去看看,找那个女的玩玩。”乙便下车,跟丙搭讪,发现丙神情恍惚,有点发呆,顿觉无趣,便上车对甲说:“那个女的
InDecember,WaymoLLC,theleadingdriverlesscarcompany,broughtouttheworld’sfirstcommercialrobo-taxiservice.Butfor
Whydomostparentsfeelembarrassedwhentheirchildrengraduatefromhighschool?
最新回复
(
0
)