ũѧרҵӢ
˾ڲ룺[OPPTR-OPPT28-OPPTL98-OPPNN08]
Unit 1
basic parts of a plant a the root system, which is below the ground , and the shoot system above. һֲɲǵ¸ϵͳ͵Ͼϵͳ
takes in, or absorbs, water and mineral from the soil through the root hairs, which are single cells near the tip of each rootëǿ˵ĵϸԴˮֺͿ
addition, plants such as clover and Lucerne, known as legumes have special bacteria which live on the roots. ⣬һЩҶݺޣļڸϸ
important function is to enable water and mineral to pass up from the roots to the leaves and flowers.һҪĹʹˮͿʴӸ䵽ҶƬͻ
main job is to make food for the plant by the process known as photosynthesis.ǵҪǹΪṩӪ
from the soil and carbon dioxide from the air are converted into sugars and other carbohydrates.еˮԴеĶ̼תǺ̼ˮ
stamens produce the male sex cells, or spermatic, which are carried in the pollen grainsϸӣDZЯ.
fruit, the ripened ovary of the flower, encloses the seeds and protects them while they are developingʵгӷΧӣǷʱ
seed itself consists of an embryo and foodstoreߺ.鹹ɵ
embryo is the part which will develop into anther plant and the foodstore is necessary to provide nourishment for the young plant while it is growing.ܷ٣ΪеṩҪӪ Unit 2
remain dormant, or in a resting state, if they are kept cool and dry.ڵº£״̬
the amount of moisture and the temperature level are right, the seeds germinate and start growing.¶Ⱥʪʱӷѿʼ
is because wet soils remain cold for a longer period of time than drier, well-drained soils.Ϊʪȸˮõָܱʱĵ
seeds require very little oxygen in order to stay alive, but when they start to germinate they require more. ״̬ʱΪֻҪo2ǷѿʱҪ϶o2
the early stages of development the seedling depends entirely on the
foodstore in the seed but as soon as the first leaves are produced, it is able to manufacture food for itself.ڣȫе飬һһƬҶΪԼʳ
the process of pollination the pollen is carried by wind or insects from the stamens to the stigma of the carpel.۹У۱ﴫͷ
germinates on the stigma and grows down the style into the ovary, where fertilization takes place.ͷϲӷзܾ Unit 3
material originates from dead plants and animals and material other than this are derived from rocks of various kinds. лʷԴĶֲ֮ͬIJֽ⣬Դڲͬʯ
rocks are broken down into small particles by mechanical disintegration and chemical decomposition.ЩʯͨͻѧֽС
arid regions weathering is mostly by physical means.ڸɺ绯Ҫ
in humid regions chemical processes of weathering are equally importantʪĵʴĻѧͬҪ.
, the insoluble mineral residues in the soils have less resemblance to the original rocks. ˣܽIJԭʼʯʲôƴ
of them contain various proportions of sand, silt and clay and these varying proportions make up a soils textural class.ҪɳӣɰճDzͬıͬʵصȼ
principle classes in order of increasing fineness of material are sand, loamy sand, loamy, silt loamy, silty clay loam, clay loam, silt and clay.տʴ˳Ϊɳɰ ɰճɰճ is to say, smaller sized particles can react or combine with water,
nutrients and humus more sassily than larger sized particles.˵СˮӪֳʱȴ
from decomposed organic matter is vital to a soil as it makes a heavy soil lighter. ԴڸлʵĸֳʣҪΪʹĸ Unit 4
2.The ease with which water san pass through a soil depends on the
proportions in it of coarse and fine particles such as sand and clay.ˮϸɰճ
10.Another advantage is that a well-drained soil will have enough air for aerobic bacteria to break down humus and so provide food for the plant.һŵˮܺõ㹻ĿΪϸȥֽⸯֳʣȻΪṩӪ
12.Ditches can be cut at certain intervals between the crops.֮乵иضļ
16.Porous drainage tiles may be laid in or on the land and these will help draw off the surplus water. ˮƽ»£ڷŵˮ
17.The distance between the drains will depends on the level of the land, the permeability of the soil, and the amount of rainfall.ˮľȡصƽ̶̹ȣԺĶ
22.We should distinguish between the collection of water and its applicationӦˮļϺ֮.
23.There are two main sources of irrigation water: surface water and ground water.Ҫ ĹˮԴرˮ͵ˮ
31.By this we mean the amount of water which is needed to bring the soil to full capacity.˼ Ҫˮʹﵽֵĵ
32.It also depends on the type of crop, the stage of growth of the crop and the amount which it will use at that particular time.Ҳȡͣʱںʱڵʹ
34.Most plants require larger quantities of water during the later stages than in the earlier stages.ںڱǰҪˮ Unit 5
8.Finally, it makes up for the plant nutrients which have been removed by crops or lost by leaching and soil erosion.գֲգʴʧӪ
14.So, they maybe grouped as nitrogenous fertilizers, phosphatic
fertilizers, potassic fertilizers and so on.ˣDZΪʣ طʵ
15.The most commonly used fertilizer which contains nitrogen is ammonium sulphate, which is made from ammonia and sulphuric acid, and which
contains 21% nitrogenʹձķǺģҪ淋ȣɰɣкٷֶʮһ.
16.This element encourages rapid vegetative growth and gives plants a healthy green colour.Ҫشٽһɫ
19.Phosphorous stimulates the formation of a plant's root, and promotes fruit and seed production.״̼ϵγɣٽӲ
21.finally, wherever high crop yields are expected, potash is used together with nitrogen and phosphorous.գĸ߲DZģͨkn,pʹ
23.This help plant to withstand mechanical damage such as broken branches and torn ֿе˺֦Ҷ
27.It is usually supplied in the form of muriate of potash (potassium chloride), which contains 50 to 60% potassium oxide (K2O) and sulphate of potash (potassium sulphate).kĻʽʹãٷʮ60k2ok2so4
32.If a soil is very acid, with a pH value of less than , lime can be added to correct this acidity.ԣphС5ʯܹ 35.Nitrogen, phosphorous and potassium are more easily available in a well-limed soil than in an acid soil.ʯҴбԵиױ Unit 6
1 In crop production the control of weeds, diseases and pests is essential to obtain high yields.Ӳݺͳ溦Ŀƶڻø߲бҪ
5 Weeds reduce crop yields on account of the fact that they compete with crops for water.Ӳʹ͵ԭᄎˮ֣Ӫ
7 Most weeds are aggressive and invasive, they grow quickly and spread far, and so are difficult to get rid of.Ӳо ԺֺԵģѸ٣Զ˺Ѱ
8 One recommended way of eradicating many persistent weeds is first to plough up the roots and underground parts of the plant.һֵƼĸӲݵķȸϵ²
11 Weeds may also be killed by means of chemicals which have the collective name of herbicides.ӲҲԱΪݼĻѧҩɱ
17 They must be used extremely carefully for the simple reason that they will eradicate all plants on contact-which includes the crop itself.ʹõʱ൱Сģԭܼǻ֮Ӵֲﱾ
18 They are usually used before sowing or before the emergence of the crop itself.DZڲǰǰ
23 Micro-organisms are reproduced and spread by minute bodies such as spores, fungi and bacteria.ͨѿߣϸСзֳɢ
25 It is very difficult to kill the fungi and bacteria, or to make the virus which is inside the host plant inactiveϸʹڼвԾIJǷdzѵ.
26 But the evolution of plant varieties which can resist disease has
completely changed methods of disease controlֿܹĽѾȫı˲Ƶķ
36 One way is to use chemicals that easily change into a gas or vapour, which enter the soil and kill the harmful organisms. һַʹױ״Ļѧҩܽк