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(2008-04-16 21:12:55)



Irrigation according to the principles outlined in the preceding paragraphs can achieve about 60% efficiency in the application of water. The other 40% is lost by evaporation, deep percolation in the upper ends of the rows and in the most permeable soil, and in waste water from the lower ends of the rows. The wastewater loss can be lessened if the irrigator will reduce the size of the irrigation streams when they approach the lower end of the rows. The extra water can then be used elsewhere.


Principles outlined for furrow irrigation apply to related methods of irrigation. Small furrows known as corrugations are used for uncultivated grain and forage crops. Such vegetation protects the soil better than row crops, but corrugations are too small to carry large streams of water.


Flood Irrigation  The three main type of flood irrigation are basin irrigation, border  irrigation,  and  wild  flooding. Basin irrigation is probably the oldest method of all. It was practiced in Egypt more than 5000 years ago. It is a simple method that is still widely used to keep land flooded for long periods for paddy rice production or for shorter periods for many other crops. (烟种)

淹灌  淹灌的3种主要类型是:格田淹灌、畦灌、漫灌。格田淹灌大概是最古老的方法,这种方法在埃及已经应用了5000多年。这种方法简便易行,现在仍然广泛使用,使土地长期淹水,种植水稻,或使土地短期淹水,种植许多其它作物。

Land preparation for basin irrigation is accomplished by forming a narrow ridge between 15 and 50 cm high on all sides of each area to be flooded. The elevations within any one basin should be as uniform as possible-certainly within a range of 5 or 10 cm. The area of a basin may be limited by elevation changes, by the size that can be covered uniformly by the available water supply on permeable soils, or by cropping factors. Basins range in size from those designed to irrigate individual trees or small areas of vegetable crop to rice paddies occupying several hectares.


A ditch or other water supply large enough to flood the basin must be available on one side. Water is turned in until the desired depth is reached, then cut back to just enough to hold a constant depth of about 10 cm for paddy rice or shut off completely for other crops. The water in the basin may be allowed to completely infiltrate or, in some low permeability soils, the excess may be drained onto a lower basin after a specified time.


Border irrigation can be described as elongated basins with a gentle slope in the long direction. Water is turned in at the upper end of the border and allowed to flow down its length as though it were a very wide furrow. Borders range from 3 to 30 m wide and must be nearly level across their width so the entire area will be irrigated uniformly. Their lengths are similar to the lengths of furrows on comparable soils and slope gradients.


Border irrigation can be used with slope gradients between 0.2 % and 2 % for cultivated crops, up to 4 % or 5 % for small grain or hay crops, and up to about 8 % for pastures. Extensive land leveling is often required because the topography must be smoother than for furrow irrigation. The cost of land leveling is offset by the low labor requirement for turning water into a few border rather than into many furrows or corrugations. The smooth topography is easy to work across at harvest time.


Several variations of border irrigation have been devised. Irrigation terraces made with surfaces that either slope like borders or are level like basins are one example. In another variation, ditches replace the ridge between borders and the area between is irrigated by blocking the ditches. Unfortunately, erosion can be a problem in the ditches, and uniform water application is often difficult to attain with this method.


Wild flooding is used to irrigate forage crops and sometimes small grains on uneven topography. Water flows down the ridges in ditches and is diverted to flood across the land. It is often necessary to have small spreader ditches to redistribute water that naturally accumulates in swales. The irrigator uses a shovel to make small furrows and ridges to guide water to any areas that would otherwise remain dry.


Wild flooding is inefficient in use of water and labor, but it irrigates land that can't be managed by other methods of surface irrigation. The soil may be too shallow or stony to have its surface smoothed by land leveling, and it may not be used intensely enough to justify a large investment. Rolling (起伏不平的)topography with slope gradients up to about 10% can be irrigated by wild flooding with permanent close-growing vegetation(多年生的茂密植被).


2.  Subsurface Irrigation

Subsurface irrigation, also called sub-irrigation, can be considered as a controlled drainage system. Ditches are usually used, but some systems use tile lines. The systems remove water during wet seasons and add it during dry seasons so the water table is always at a controlled depth. That depth might be as little as 30 cm for shallow-rooted vegetation in a coarse sandy soil or as great as 120 cm in some loamy soils. The surface soil should be dry but most of the root zone should be moist. The field can even be cultivated and irrigated at the same time. (yanzhong)

2。地下灌溉  "


The required conditions for subsurface irrigation are, so stringent that relatively little land is sub-irrigated. The land surface must be quite smooth and have a slope gradient of less than 0. 5%. The subsoil (底土) must be highly permeable, but it must have a shallow water table or be underlain by an impermeable layer that permits a perched (位置高的) water table to be maintained. Both the soil and the irrigation water must be low in salts to avoid the formation of saline and sodic soil. Suitable conditions for subsurface irrigation most often occur on glacial outwash plains(冰川冲积平原), terraces, or deltas in humid or sub-humid areas.


3. Sprinkler Irrigation

large-scale sprinkler irrigation is much newer than surface and subsurface irrigation because the necessary pipes, pumps, and power supply were not available until comparatively recent times.



Advantages such as portability, adaptability to a wide range of soil and topographic conditions with little or no land preparation, and good control of water application have made sprinkler irrigation popular. High efficiency of water application may result in energy savings and help avoid erosion and leaching nitrates from the soil. Disadvantages limiting its use include high equipment and operating costs, the need to move lines in muddy conditions, salt damage to some plants if poor-quality water is used, and disease problems with some plants.


Most field sprinklers use a rotating sprinkler head of the general type. Although the sprinklers may be fixed in permanent locations for limited areas of high-value crops, they are usually mounted on either moving or movable lines.


4. Trickle Irrigation

Trickle irrigation, also called drip irrigation, is the newest method and the one that achieves the highest irrigation efficiency: about 90% of the applied water is available to the plants. High efficiency is achieved by supplying water to individual plants through small plastic lines. Water is supplied either continuously or so frequently that the plant roots grow in constantly moist soil.



Trickle irrigation is especially suitable for watering trees or other large plants. Much of its use has been in orchards and vineyards but it has also been used to irrigate a variety of row crops including several kinds of vegetables and fruits. Its advantages are greatest where areas between plants can be left dry. It has no advantage for close-growing vegetation such as lawns, pastures, or small grain crops.


An Israeli engineer named Symcha Blass developed the idea of trickle irrigation in the 1930s, but it had to wait until plastic tubing was available to make a practical system. Trickle irrigation in the United States increased from 40 ha in 1960 to over 50,000 ha in 1976 out of a worldwide total of about 160,000ha. Nearly half of the trickle irrigation in the United States is in California, some of it in avocado orchards with slopes up to 50% to 60%. Erosion is not a problem because there is no runoff.


A bonus with trickle irrigation is its ability to use water with a higher salt content than any other method up to about 2500mg/liter. The constant flow of water from the trickle emitter toward the outer edges of the plant root zone carries the salt along with it. Salt concentrations become very high in the dry areas between plants but not in the actual root zone.


Trickle irrigation saves water, is able to use water high in salt, functions well in all but the extremes of coarse-and fine-textured soils, works on almost any topography without causing erosion, and required little labor. The disadvantages are mainly high equipment costs and plugging of the lines by sediment, salt encrustation, or algae.


A trickle irrigation system normally includes a control box that regulates the water pressure, filters the water, and provides for the addition of fertilizer and herbicides. Chlorine may be added to eliminate algal growth. The water pressure for trickle irrigation is normally 0.4 to I kg/cm2 as compared to I to 8kg/cm2 for sprinkler irrigation. Some trickle controls are set to increase the pressure periodically and flush the lines to reduce clogging.

滴灌系统一般包括一个控制箱,用以调节水压力、过滤灌溉水、并添加化肥和除草剂。也可以加入氯以排除藻类的生长。滴灌的水压力一般是0.4-1.0千克/平方厘米, 而喷灌要求的水压一般为1—8千克/平方厘米。一些滴灌控制设施被安装,用于周期性增加压力、冲洗管道,以减少堵塞。

Exercise 1

Decide whether the following statements are true or false.

  1 ) Surface irrigation is the oldest type of irrigation and it is out of use today.

  2) Trickle irrigation is the most efficient type of irrigation.

  3) Subsurface irrigation can be used in any condition and in any climate.

  4) For any type of irrigation, we can only use fresh water.

  5) Sprinkler irrigation is advantaged and can be used in most kinds of condition.





New words

Salinization n. treating or impregnating with salt 盐化



1. What percent of all cropland is irrigated according to UNFAO? How much food is produced by the irrigated land?

2. What is the problem with the irrigated land? Where is the problem most severe?

3. What is salinization? By what rate does it reduce the world’s irrigated land?

4. What is the worst danger to the soil? What will happen when the ground is too wet?

5. How to prevent or reduce salinization? 



New Words

Nitrate  n. a salt of nitric acid硝酸盐

Ammonium  n. an ion NH4+ derived from ammonia铵


1. What are the two effects caused by higher levels of carbon dioxide in the atmosphere?

2. Who reported the findings regarding the changes in the use of N fertilizer.

3. How much has the carbon dioxide level in the atmosphere increased during the past two centuries?

4. By what percent did the carbon dioxide levels increased in the experiments? What was the plant response?

5. What are the scientists at the University of California at Davis studying?

6. What did the scientists at the University of California at Davis find?




New Words

Catch  n. the total quantity caught at one time 捕捞量

Eel  n. long thin snake-like fish 鳝

Salmon  n. a large fish from northern ocean with silvery skin and pink flesh 大马哈鱼

Aquaculture=aquiculture  n. the cultivation of the natural produce of water 水产养殖



1. Why have many nations turned to fish farming?

2. How much did the farmed fish account for the world’s in 1970 and in 2000, respectively?

2. How much farmed fish was harvested in China in the year 2000?

3. What are the possible problems connected with the fish farming?

4. Why do the fish farmers feed their fish with antibiotics?

5. What did the scientist say positively about the farmed fish?





New Words

Larvae n. the immature, wingless feeding form that hatches from the egg of many insects〔单larva〕〔昆虫〕幼虫

Ladybug (ladybeetle) n. any of numerous small nearly hemispherical often brightly colored beetles of temperate and tropical regions 瓢虫

Pecan n. a large hickory that is widely grown in the warmer parts of the U.S. and in Mexico for its edible nut [植]美洲山核桃(树)



1. Why do farmers like some of the insects?

2. In what ways do aphids damage plants?

3. How many aphids could an adult lady beetle and a young beetle larva eat?

4. Why did American scientists import the multicolored Asian lady beetle?

5. Is there any ladybeetle that is bad? What are they?

6. What kind of ladybeetle is mentioned most in this passage? Where does it come from probably?

7. In what ways could the Asian lady beetles help farmers?


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