coco的BLOG

 

Lesson 2   The Characteristics of Soil

 

New Words and Expressions

nature n. inherent character 内在本质

acidity  n. the degree of being acid or sour 酸度

prerequisite  n. something that is necessary before something else can happen 先决条件

texture  n. the degree of roughness or fineness of a material 质地

wafer  n. thin slices 薄片, 薄饼

diminish  v. become smaller or less 变小, 变少

minute  a. very small or tiny 微小的

tenaciously  adv．holding firmly, persistently 坚持地

adsorption  n. the adhesion in an extremely thin layer of molecules to the surfaces of solid bodies or liquids with which they are in contact 吸附(作用)

leach  v. to separate (sth) from a material by passing water through the material 沥滤

eutrophication  n. the process of making a body of water rich in nutrients 富营养化过程

resin  n. thick sticky liquid that comes from certain trees 树脂

macronutrient  n. nutrient with a big quantity 大量营养元素

micronutrient  n. nutrient with a small quantity 微量营养元素

molybdenum  n. a silver-white metal 钼

trace element 微量元素

protract  v. prolong, extend 延长

waterlog  v. have excessive water 渍水

inhale  v. breathe in 吸入

exhale  v. breathe out 呼出

aerate  v. allow air to flow around 使通气

solvent  n. a liquid able to turn a solid into liquid 溶剂 (solute 溶质)

low-lying  低洼的

field capacity 田间持水量

permanent wilting point 永久萎焉点

Text

The major characteristics of soils are texture, acidity, nutrient content, gaseous content, and moisture content. An understanding of the nature of these characteristics is an essential prerequisite to the study of soil profiles, soil types, soil productivity, and soil management.

土壤的主要特性有质地、酸度、养分含量、气体含量和含水量。了解这些特性是对土壤剖面、土壤类型、土壤生产力和土壤管理进行研究的一个必要的先决条件。

1. Soil Texture

Texture is the size and shape of the individual soil particles as well as the proportions in which they occur. For convenience and efficiency in the study of mineral particles, the U.S. Department of Agriculture (USDA) has classified soil particles in categories of diminishing size as gravel (砾石), sand, silt (粉沙粒), and clay (粘粒).

1．土壤质地

质地是指单个土壤颗粒的大小、形状以及它们存在的比例。为了方便有效地研究矿质颗粒，美国农业部把土壤颗粒依大小顺序分为砾石、砂粒、粉砂粒和黏粒。

CLAY. Clay particles are so small (less than 0.004 mm) that they are not even visible under an ordinary microscope. Each clay particle has the shape of a flat, many-sided wafer.

黏土黏粒很小(小于0.004mm)甚至于在普通显微镜下也看不见。每个黏粒都呈扁平的、多面的片状。

The total amount of air space in clay is somewhat greater than in sand; however, because much of the air space is represented by extremely minute pores, the actual rate of water and air movement through clay is much slower than through sand. Water is held so tenaciously that most plant root systems cannot absorb it. Moreover, because young plant rootlets do not readily penetrate poorly oxygenated clay, soil composed exclusively of clay is poor for raising crops.

黏土中的气隙的总量在某种程度上要比砂土中的大。然而，由于大量的气隙都以极其微小的孔隙形式存在，水和空气通过黏土运动的实际速度要比通过砂土慢得多。水被牢牢地吸住以至于不能被大多数植物根系吸收。另外，因为幼苗的小根不能轻易扎入含氧少的黏土中，所以只是由黏土构成的土壤不适合种植作物。

Clay serves as an important reservoir of plant food, a function that largely depends on two characteristics of clay particles: ( 1 ) their very large surface area and (2) their negative electrical charge. It has been estimated that the aggregate surface area of the clay particles in the topsoil of only five acres of an Iowa cornfield is roughly equal to the entire surface area of the North American continent. The negatively charged surface of the clay particle attracts positively charged atoms (cations) of nutrient elements such as calcium, potassium, magnesium, phosphorus, zinc, and iron. Those nutrient particles then form a loose chemical bond with the clay particles. This process is called adsorption. From the standpoint of soil fertility, it is of fundamental importance.

黏土作为植物养分的一个重要贮存库，其功能主要取决于黏粒的两个特征；(1)它们很大的表面积。(2)它们带有负电荷。据估计在耶阿华一块仅五英亩的玉米田的表土层上黏粒的聚合表面积大约等于北美大陆的整个表面积。黏粒带负电荷的表面吸引营养元素的带正电荷的原子(阳离子)如钙、钾、镁、磷、锌和铁等。那些营养粒子与黏粒形成一个松散的化合键，此过程叫做吸附作用。从土壤肥力的角度来看，这是极其重要的。

On the other hand, clay particles have a relatively poor ability to retain negatively charged nitrate particles (anions). As a result, nitrates are leached from the soil by rainfall or washed away with runoff waters. The nitrates then fertilize lake and pond waters and eventually convert open-water, game-fish lakes to weed-grown, trash-fish lakes ---- a process called eutrophication.

另一方面，黏粒保留带负电荷的硝酸根离子的能力相对较弱，结果硝酸盐由于降雨而被淋失或由径流而被冲洗掉。那么硝酸盐使湖水和池水肥沃，最终将开放水域和游钓鱼类的湖变成生长杂草和垃圾鱼的湖。这一过程被称为水体的富营养化过程。

To prevent such excessive nitrate loss from farmlands, James Bonner of the California Institute of Technology has suggested adding a resin to the soil in order to increase its ability to hold the negatively charged nitrate particles. Such a proposal, of course, would have to be studied very carefully, lest this new technological "fix" create a more serious problem than the one it was supposed to cure.

为了阻止硝酸盐从农田中大量损失，加利福尼亚技术研究所的James Bormer建议在土壤中加入树脂以提高对带负电荷的硝酸根离子的保持能力。当然这个建议还必须进行认真研究，以免这种新技术的“固定”导致产生比要解决的问题更为严重的问题。

LOAM. Very few agricultural soils are composed exclusively of one textural class; usually they represent a mixture in which all four of the major classes (gravel, sand, silt, and clay) are represented in varying proportions. The most desirable soil from an agricultural standpoint is loam, which represents a mixture of heavy and light soil materials in the following proportions: sand, 30%-50%; silt, 30%-50%; and clay 0-20 %. In the best loams the most desirable qualities of sand and clay are combined and their undesirable traits are minimized.

壤土  农业土壤很少是由一种质地粒级组成，通常它是由四种主要粒级{砾石、砂粒、粉砂粒、黏粒)以不同比例混合而存在的。从农业角度上来说，最理想的土壤是壤土。它是以轻重土质按下列比例混合而成的：砂土占30%-50%，粉砂粒占30％-50％，黏粒占0-20％。在最好的壤土中，砂质土和黏质土最理想的特性结合到一起，而它们的不利特性减小到最低程度。

2. Soil Acidity (pH)

Soil scientists employ the symbol pH as a quantitative measure of hydrogen ion concentration. (The hydrogen ion is a positively charged hydrogen atom.) Soils may vary from a pH of 4.5 (strongly acid) to 9 (strongly alkaline). Soils having a pH of 7 are considered neutral. Most vegetables, grains, trees, and grass grow best in soil that is very mildly acid (about 6.8). A few species of plants, such as the valuable long-leaf pine of the South, prefer a more acidic soil. Hardwood-forest soils are usually more alkaline than coniferous-forest soils.

2．土壤酸度(pH)

土壤科学家用符号pH作为氢离子浓度的一种数量衡量标准。（氢离子是一个带正电荷的氢原子）土壤pH值从4．5(强酸)变化到9(强碱)。土壤pH值为7时被认为是中性的。大多数蔬菜、谷物、树木和草在弱酸性(pH值大约为6．8)的土壤中生长得最好。有几种植物比较喜欢酸性土壤，如南方宝贵的长叶松。与针叶林土壤相比阔叶林土壤常常偏碱。

Soil pH is an important factor in determining the distribution of vegetation in natural ecosystems. Extreme acidity (low pH) or alkalinity (high pH) may exceed the tolerance range of all but a few highly specialized species.（烟）

在自然生态系统中，土壤pH值大小是决定植物分布的一个重要因素。除了几种高度特化的植物外，过酸(pH值低)或过碱(pH值高)，可能会超过植物对酸碱的忍耐度。

Acid Rain. One of the most serious environmental problems plaguing our nation is that of acid rain. It has had harmful effects on both terrestrial and aquatic organisms. The severity of the effects depends to a large degree on the soil pH. If the pH is high (alkaline soil) the acid rain will tend to be neutralized and the adverse effects will be minimized.

酸雨  困扰我国的最严重的环境问题之一是酸雨。它对陆生生物和水生生物都有害，在很大程度上，其影响的严重性取决于土壤的pH值。如果pH值高(碱性土壤)，酸雨会被中和，有害程度会降低。

3. Nutrient Content

Of the 89 naturally occurring chemical elements, about 17 are required by plants and about 19 are required by animals, including humans, for health, growth, and reproduction. Mineral nutrients that are used by organisms in large quantities are classified as macronutrients; those that are needed in only extremely small amounts are called micronutrients.

3．养分含量

自然界中存在的89种化学元素中，大约有17种是植物健康、生长、繁殖所需要的，大约有19种是动物包括人所需要的。被有机体大量利用的矿质养分为大量营养元素，而那些需要量极少的称为微量营养元素。

MACRONUTRIENTS. The macronutrients essential for plants include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, magnesium, and sulfur. Carbon, hydrogen, and oxygen are usually abundantly present in air and water. As a result they do not ordinarily represent limiting factors for plant development. Nitrogen is required by plants for the synthesis of proteins, which are needed as enzymes and as structural components of cells. Nitrogen is also required for the synthesis of nucleoproteins(核蛋白)--the chemicals of heredity.  Nitrogen is necessary for growth, respiration, photosynthesis, and seed production. Although there is 34,500 tons of gaseous nitrogen in the air column above each acre of the earth's surface, this cannot be used by plants until it has been fixed by nitrogen-fixing bacteria and algae.

大量营养元素  对植物来说所必需的大量元素包括碳、氢、氧、氮、磷、钾、镁和硫。在空气和水中常常存在大量的碳、氢、氧，因此，一般情况下它们对植物发育不是限制因素。氮是植物合成蛋白质所需要的，蛋白质又是酶和细胞结构的组成成分。氮也用于合成核蛋白—一种遗传化学物质。氮对于生长、呼吸、光合作用和种子生产是必要的。虽然在地球表面每英亩空气柱中有34，500吨气态氮，但是如果这些气态氮不被固氮菌和藻类固定，是不能被植物利用的。

Phosphorus. Phosphorus is obtained by plants in the form of phosphate (PO₄) ion. Some phosphate is derived from the weathering of rock; however, the amount obtained from this source is small. Plants get most of their phosphorus from the decomposing remains of dead plants and animals ---- in other words, from organic compounds.

磷  磷以磷酸根离子的形式被植物吸收。某种磷酸根来自岩石风化；然而，此来源的磷酸根量很小。植物获得的大部分磷是来自动植物残体的分解，换句话说是来自有机化合物。

Magnesium. Magnesium is essential for the synthesis of chlorophyll, the green pigment of photosynthesis. It is usually fairly abundant and does not ordinarily represent a limiting factor.

镁  镁对叶绿素(光合作用的色素)合成是必要的，常常很丰富，一般不是限制因素。

Micronutrients. The micronutrients essential to plants include molybdenum, boron, zinc, manganese, iron, copper, and chlorine. The amounts of these trace elements required by crops are exceedingly small. A clover field, for example, requires only one ounce of molybdenum per acre. Boron requirements are met with a concentration of only one part boron per million parts water. Seven tons of Maine potatoes may possess 143 pounds of nitrogen but only 0.2 pound of boron!

微量营养元素  植物所必需的微量元素包括钼、硼、锌、锰、铁，铜和氯。作物对这些微量元素的需求量非常小。例如一块三叶草田地，每英亩(6.07亩)只需1盎司（28.35g）的钼。对硼的需要量是每一百万份水中只需一份硼这样的浓度。7吨缅因马铃薯可能拥有143磅（0.907斤）氮，但只有0.2磅硼。

The range of tolerance that some plants have for trace elements may be extremely narrow. For example, for some plants a one part per million concentration of boron in the soil may be optimal. However, an increase to five parts per million may exceed the plant's tolerance and cause death.

一些植物对微量元素的耐性范围很窄。如对于有些植物，土壤中万分之一的硼的浓度可能是最适宜的，当增加到5 ppm时，可能会超过植物的耐性而引起死亡。

4. Gaseous Content

Only about 50% of soil volume is actually represented by solid materials such as minerals, plant and animal bodies, and organic residues. The remaining 50% is represented by pore spaces, which occur between the individual soil particles. When soil is extremely dry because of a protracted drought, the spaces are filled with air. When soil is waterlogged after a violent thunderstorm, they may be filled with water.

4．气体含量

土壤体积中实际上大约只有50％是固体物质，如矿物质、动植物体及其有机残体，余下的50%则是单个土粒间的空气空隙。由于长期干旱使土壤非常干燥时，空隙充满空气。一场暴风雨过后，当土壤渍水时，这些空隙内充满水。

In a sense, soil can be considered to "inhale and exhale" continuously. Oxygen, which is present in greater concentration in the atmosphere than in the soil, diffuses into the soil pores. Carbon dioxide continuously moves from soil into the atmosphere. When soil is poorly aerated, the activity of nitrogen-fixing bacteria is slowed down. This results in reduced soil fertility. Moreover, an oxygen-deficient soil slows the development of crop roots and may hamper their ability to absorb water and nutrients.

在某种意义上，土壤可被看做不断地进行“吸入”和“呼出”。在大气中的氧气浓度要比土壤中的浓度大得多，氧气扩散进入土壤空隙内。二氧化碳不断从土壤进人大气。当土壤通气不良时，固氮菌的活性降低，导致土壤肥力降低。而且，缺氧土壤可减慢作物根的发育，并会影响它们吸收水和营养的能力。

5. Moisture Content

Water serves several important plant functions. It is an essential raw material for photosynthesis; it is the solvent medium by which minerals are transported upward to the leaves and sugar is transported downward to the roots; and it is an essential component of protoplasm(原生质)forming 90% of the weight of actively growing organs such as buds, roots, and flowers.

5. 含水量

水对植物有几种重要功能。它是光合作用的必要原料；是矿物质向上运输到叶、糖向下运输到根的溶剂媒介；是原生质必要组成成分-占生长旺盛器官如芽、根和花重量的90％。

Soil is said to be saturated when the air in all the pores has become replaced with water. This may occur after low-lying fields have been flooded following a severe thunderstorm or intensive irrigation.

当所有空隙中的空气被水取代后，我们说此时土壤是饱和的。这可能发生在一场大雷雨或集中灌溉使低洼田被淹没之后。

Most upland crops such as corn and cotton cannot survive in soils that are water-saturated because of the greatly reduced oxygen content. Rice, however, grows well under these conditions. The amount of water that remains after the excess has drained away from the saturated soil is known as the field capacity.

大多数旱地作物，如玉米和棉花不能在被水饱和的土壤中存活，因为氧的含量大大减少了。然而水稻在这种情况下却长得好。当过量的水从饱和土壤中排出后，余下的水量被称为田间持水量。

Crops continuously remove soil moisture. As the soil drys out a critical point is reached when the "pull" of the plant roots for water is not sufficient to prevent permanent wilting. This is known as the permanent wilting point--a condition experienced by many a farmer or suburban gardener who has seen his plot of beans and lettuce (莴苣)wilt and shrivel(皱缩) during a late summer drought.

作物不断消耗土壤水分。随着土壤变干，达到一个临界点，这时植物根对水的吸力不足以阻止永久萎蔫发生，这就是永久萎蔫点。这是一种许多农场主或郊区园丁经历过的情况。他们在夏末的干旱期，目睹田里的菜豆和莴苣萎蔫并卷曲。

EXERCISE 1

Choose the best answer for each of the following.

1. Which of the following is not the characteristic of the soils?

   a. Acidity  b. Moisture content  c. Acid rain  d. Nutrient content

2. Why cannot most plant root systems absorb the water in clay?

   a. Because it is held firmly to clay particles.

   b. Because there is much water in clay.

   c. Because there is no water in clay.

   d. Because there is little water in clay.

3. Which of the following is the characteristic of clay particles.

a. Their negative electrical charge   b. Their air space

c. Their positive electrical charge    d. Their size and shape

4. What is formed between clay particles and some nutrient particles such as calcium, potassium and so on?

a. A tight chemical bond             b. A loose chemical bond

c. A tight substance                 d. A loose substance

5. _________should be added to the soil to increase its ability to hold the negatively charged nitrate particles.

a. Charge       b. Colloid           c. Resin         d. Cation

6. The most desirable soil from an agricultural standpoint is

a. clay          b. loam             c. sand         d. gravel

7. What is used to measure hydrogen-ion concentration in soil acidity?

a. ppm         b. N                c. M            d. pH

8. About how many chemical elements are required by plants

a. 89           b. 19               c. 17          d. 36

9. In which form is phosphorus obtained by plants?

a. PO₄^3-         b. H2PO₄^-           c. HP0₄^2-     d. P

10. Which of the following is not micronutrient?

a. Zinc          b. Iron              c. Copper       d. Carbon

EXERCISE 2

Amswer the following questions.

 1. What are the important plant functions of water?

 2. What will happen when soil is poorly aerated?

3. What are the differences between clay and sand according to the passage?

4. How do soil scientists use pH to determine soil acidity?

5. Why is nitrogen important in plant physiology?

1) Water serves three important plant functions. First, it is an essential raw material for photosynthesis. Second, it is the solvent medium by which minerals and sugar are transported. Third, it is an essential component of protoplasm.

2) It causes the activity of nitrogen-fixing bacteria to be slowed down. It also slows the development of crop roots and it hampers their ability to absorb water and nutrients.

3) The total amount of air space in clay is greater. The actual rate of water and air movement through clay is slower.

4) When pH =7, the soil is considered neutral. When pH≤4.5, strongly acid. When 4.5 <pH <7, acid. When 7 <pH <9, alkaline. When pH> 9, strongly alkaline.

(5) It is essential for the synthesis of proteins; for the synthesis of nucleoproteins - the chemicals of heredity; for growth, respiration, photosynthesis and seed production.

VOA 1

New words

Till v. to cultivate 耕作

Low-till=low-tillage 少耕 no-till

Bangladesh n. 孟加拉

Questions

1. Where is International Maize and Wheat Improvement Center located?

2. What is blamed on plowing according to the passage?

3. What is low-till farming? How are seeds and fertilizers put into the soil?

4. What good effects does the low-till farming have?

5. How many people in South Asia are depending on local rice and wheat crops.?

6. How do farmers in South Asia grow wheat and rice?