Download Chapter 13 Soil and Its Uses

河 北 科 技 大 学 教 案 用 纸
第 17 次课 2 学时
上次课复习：
Many problems have resulted from unplanned growth.
1. Current taxation policies encourage residential development of farmland, which results in a loss of
valuable agricultural land .
2. Loss of property and life results when people build on floodplains
3.Transportation problems and lack of open space are also typical in many large metropolitan areas.
本次课题（或教材章节题目）
：Ch. 13 Soil and Its Uses
教学要求：了解土壤的基本情况；熟悉其形成、剖面、侵蚀等；掌握土壤的性质
重
点：土壤的性质
难
点：土壤的剖面
教学手段及教具：利用多媒体进行课堂讲授，图文并茂，增加认知的直观性；进行课堂讨论，活
跃课堂气氛。
讲授内容及时间分配：
Revision
13.1 Geologic Processes
13.2 Soil and Land
13.3 Soil Formation
13.4 Soil Properties
13.5 Soil Profile
13.6 Soil Erosion
Summary
课后作业
参考资料
3min
15min
15min
15min
15min
10min
14min
3min
任选课后讨论题，完成 50-80 字英文短文。
《Environmental Science》 Andrew R.W.Jackson．世界图书出版社，2001．
《Environmental Science》 William P.Cunningham．McGraw-Hill，1997．
注：本页为每次课教案首页
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Ch 13 Soil and Its Uses (pp288-310)
This chapter mainly discusses four topics:
How the soil is formed
Its properties and profile
Main environmental problem of soil erosion
How we use techniques to prevent soil erosion.
This Chapter Objectives (pp288)
After reading this chapter, you should be able to:
1/ Describe the geologic processes that build and erode (侵蚀)the Earth’s surface；
2/ List the physical, chemical, and biological factors involved in soil formation。
3/ Explain the importance of humus to soil fertility(肥力).
4/ Differentiate between soil texture and soil structure. (土壤质地和结构)
5/ Explain how texture and structure influence soil atmosphere and soil water.
6/ Explain the role of living organisms in soil formation and fertility.
7/ Describe the various layers in a soil profile(剖面)。
8/ Describe the processes of soil erosion by water and wind.
9/ Explain how contour farming (等高栽种), strip farming(带状种植),terracing(梯田),waterways(水
田),windbreaks(防风林) ,and conservation tillage(保护性耕种)reduce soil erosion.
10/ Understand that the misuse of soil reduces soil fertility, pollutes streams, and requires expensive remedial
(治理、补救治疗) measures.
11/ Explain how land not suited for cultivation(耕种)may still be productively used for other purposes.
13.1 Geologic Processes (p289)
●Structure
of the Earth: (见 figure 13.1 p289)
a. Crust: 地壳 an extremely thin, less dense, solid covering over the underlying (下伏的) mantle.
b. Mantle: 地幔 a layer that makes up the majority of the Earth and surrounds a small core made up
primarily of iron (an inner solid portion and an outer portion that is capable of flow).
Lithosphere 岩石圈 is made up of crust and outer mantle.
c. Core: 地核 central part of the planet earth.
The Earth is unstable with several events we can recognize happening: earthquakes, volcanic eruptions,
floods, and windstorms changing the surface of places we live.
The changing processes of the Earth: building and tearing down (拆毁、拆卸).
●One theory about the processes:
Plate tectonics (板块构造理论): (见 figure13.2 p290)
1.The composition of the plate: The outer surface of the Earth consists of large plates composed of the crust
and the outer portion of the mantle and that these plates are slowly moving over the surface of the liquid
outer mantle. 地球表面是由大的板块组成，这些板块由地壳和外层地幔构成，这些板块在内层地幔即
液层地幔的外表面上慢慢滑动。
2.Forces of plates’ movements: Heat from the Earth
3.The movements of the plates are independent of each other.
4.The movements includes:
A. Building movements:
a. Pulling apart (撕开、扯断) from one another:
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The liquid mantle moves upward to fill the gap and solidifies where the new crust is formed.
(The bottom of the Atlantic and Pacific Oceans and the Rift Valley and Red Sea area of Africa)
Rift Valley (大裂谷): depression southwest Asia & east Africa extending with several breaks from valley of
Jordan River south to central Mozambique
b. Colliding (碰撞):
(a)One of the plates slides (滑动) under the other and is melted, while some of the liquid mantle goes
up to the surface where the volcanoes are formed. This results in the formation of mountains. (The west
coasts of North and South America)
(b)When the collision occurs under the ocean, the volcanic islands are formed. (Aleutian Islands, many
of the Caribbean Islands)
(c)When two continental plates collide，neither plate slides under the other and the crust buckles(变形)
to form mountains. (the Himalayan, Alp，and Appalachian mountain ranges)
The characters of building movements:
c. Associated with earthquakes
d. Damageable for humans
B. Tearing down processes:
Weathering processes (breakdown of parent material):
a. Mechanical weathering processes:（见 figure13.3 p291）
Caused by physical forces:
Changes in temperature
Repeat freezing of water and thawing (融化) of ice
Forces that move and rub (摩擦) rock particles against each other (glacier, wind and moving water)
Exposure of new surfaces caused by wind and moving water (Painted Desert in the Southwest of United
States)
Action of plants and animals
b. Chemical weathering processes: (oxidization and hydrolysis)
c. Erosion: The process of loosening and redistributing 重新分配 particles.侵蚀
13.2 Soil and Land (p291)
Geological processes include those of land and soil.
Soil and land are not the same.
Land is the part of the world not covered by the oceans.
Soil is a thin covering over the land consisting of a mixture of minerals, organic material, living organisms,
air, and water. There are many kinds of soil. A typical, “good” agricultural soil is about 45 percent mineral,
25 percent air, 25 percent water, and 5 percent organic matter.(见 figure13.5 p291)
To understand how soil can be protected, we must first understand its properties 性质 and how it is formed.
13.3 Soil Formation (p292)
A combination of physical, chemical, and biological events acting over time is responsible for (是造成…的
原因) the formation of soil.
1.First step: Fragmentation (破碎作用) of the parent material
2.Factors in the formation of soil:
a. The size and chemical nature of the particles
b. Plants and animals:
(a)Organisms: Decomposition of dead organisms provides acids causing further fragmentation.
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(b)Humus: An important soil component and contains nutrients, enhances the water-holding ability and
the acidity of the soil, sticks other soil particles and help to create a loose soil for keeping more water and air
(c)Burrowing 会打洞的 animals: Such as earthworm, nematodes, mites, pill bugs, and tiny insects, they
mix the organic and inorganic material providing more nutrients for plants and add more organic material to
the soil by collecting dead organic from the surface.
(d)Soil bacteria 细菌 ,fungi 真菌: They enhance the quality of the soil by breaking down the organic
material to smaller particles and releasing nutrients.
(e)The roots of plants: Its dead and decay provide more nutrients to the soil and more space for air and
water.
a. Slope: Steep slopes do no good for soil formation because the materials tend to be moved downslope
by wind and water.
b. Climate: Humid and warm climates are good because they accumulate more organic materials and
the chemical weathering process is slow.
c. Time: Anyway the time for soil formation is long (15-hundreds years)
d. The amount of rainfall 降雨量 and the organic matter influence the PH of the soil. High rainfall and
more organic materials can enhance the acidity of the soil. The appropriate PH for plants is 6-7. Lime and
Sulfates can be used to adjust the PH of the soil to desired level for specific plants.
13.4 Soil Properties (p292)
Soil properties include soil texture, structure, atmosphere, moisture, biotic (生物的生命的) content, and
chemical composition.
1.Soil texture: 土壤结构
Categories of soil particles according to their size:
Gravel (砾): Diameter > 2.0 millimeters
Sand: Diameter between 0.05 and 2.0 millimeters
Silt: Diameter between 0.002 and 0.05 millimeters
Clay: Diameter < 0.002 millimeters
Soil consists of different kinds of particles.
Texture depends on the percentage of clay, silt, and sand, see figure 13.6 p293
A best soil for agricultural use is a loam (壤土) which contains both the good aeration (透气性) and drainage
properties of large particles and the good nutrient-retention (保持保留) and water-holding ability of clay
particles.
2.Soil structure: 土壤构造
a. It refers to the way various soil particles clump together in a specific kind of soil.指特定类型土壤的
各种颗粒结合的方式
For examples:
Sandy soil-granular (颗粒状的) structure; Clay soil-large aggregates; Mixture (混合)-smaller aggregates (集
合体)
b. A good soil for agricultural use is friable (易碎的) which means crumble easily(易碎的)and has
spaces for air and water.
Factors that decide whether the soil is friable: soil structure and moisture (水分温度) content.
Sandy soils are friable.
In good soil, about one-half to two-thirds of the spaces contain air after the excess water has drained.
The relationship between the air and water is not fixed and both are important in determining the numbers
and kinds of the soil organism.
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Soil organisms:
a) Protozoa (原生动物): Parasites (寄生动物) and Predators (捕食者) on the others and regulating the
populations of those organisms.
b) Nematodes(线虫类): Wireworms or roundworms breakdown the dead organic matter.线虫或蛔虫分
解死的有机物 Some are parasitic(寄生) on the roots of plants.
c) Insects and other soil arthropods(节肢动物): Burrowing(打洞), consuming and fragmenting organic
materials of these organisms are helpful but they are also crop pests that feed on plant roots.
d) Algae(海藻): They carry on photosynthesis(光合作用) and are consumed by other organisms.
e) Bacteria and fungi: They change complex organic materials to simple ones which are suitable for
plant uses such as nitrogen-fix process.
c. The soil contains a complicated food chain in which all organisms are subject to the being consumed
by others.
13.5 Soil Profile (p294)
Concept: Distinct horizontal layers in the soil that differ in chemical composition, physical properties,
particle size, and amount of organic matter.
Each recognizable layer is known as a horizon. Composition:
1. The top layer: (见 fig.13.9 p295)
a) A horizon(A 层), or topsoil(表土层)which consists of small mineral particles mixed with organic
matter.
The thickness is small on steep slopes and big on rich grasslands.
There are most living organisms and nutrients.
b) O horizon: There is a layer of litter (undecomposed or partially decomposed organic matter 未被分
解的和部分分解的有机物质)on the surface. It usually exists in the forests.
c) E horizon: Lighter-colored layer containing few nutrients which is caused by the removing of darker
minerals such as iron compounds of leaching process and is not always developed in all soils.
Leaching process happens in this horizon: water carries dissolved organic material and minerals to
lower layers.
2. B horizon or subsoil (底土):
With less organic material and fewer organisms but more suspended nutrients.
Support a well-developed root system
Rainfall is main factor decide the quality of this horizon: grasslands soils with poorly developed B
horizon, woodlands soils with well-developed B horizon.
3. C horizon:
Consists of weathered parent material(被风化的原始物质)
With no organic materials
The chemical composition of the minerals of this horizon affects the PH of the soil(两种影响的情况：
原始物质是石灰石 limestone 会中和酸，若是花岗岩 granite 则不能中和酸)
The characteristics of the parent materials affect the soil’s rate of water absorption and retention.
4. R horizon: Bedrock(基岩)on which C horizon rests
Factors affect the soil profile: difference of vegetation, climate (the cold wet and the hot humid climates tend
to have poorly developed soil horizons.
Classification of soils according to different soil profiles and soil development factors:
a. Grassland soils: thin topsoil and subsoil, when the plants die and the roots rot, a deep layer of topsoil
develops.
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b. Forest soils: clay is accumulated here. This limits the growth of roots and prevents water from
reaching the soil’s deeper layers.
c. Desert soils: very poorly developed horizons
13.6 Soil Erosion 土壤侵蚀(p297)
1. Concept: Erosion is the wearing away and transportation of soil by water, wind, or ice.
2. Conditions accelerating the erosion rate:
a. Agricultural practices that leave the soil exposed
b. Disappearing of vegetation: deforestation and desertification (wind erosion leaves a degraded area,
bury and kill vegetation, and fill drainage and irrigation ditches. Water erosion will also pollute the runoff by
the chemical pesticides and fertilizers remained in the water-carried particles.)
c. Wind is an important mover of soil. It may not be as evident as water erosion, since it does not leave
gullies (冲沟). Wind erosion is most common in dry, treeless areas where the soil is exposed.
3. Future trend: 前景
Worldwide, erosion removes about 25.4 billion tones of soil each year.
Fortunately, many soil conservation practices have been instituted that protect soil. Traditional
labor-intensive, small-scale soil conservation efforts combines maintenance of shrubs and trees with crop
growing and cattle grazing
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