Irrigation

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irrigation,

in agriculture, artificial watering of the land. Although used chiefly in regions with annual rainfall of less than 20 in. (51 cm), it is also used in wetter areas to grow certain crops, e.g., rice. Estimates of total irrigated land in the world range from 543 to 618 million acres (220 to 250 million hectares), almost half of them in India, Pakistan, and China. The United States had almost 60 million acres (23.8 million hectares) of irrigated farmland in 1991.

Methods of applying water include free-flooding of entire areas from canals and ditches; check-flooding, in which water flows over strips or checks of land between levees, or ridges; the furrow method, in which water runs between crop or tree rows, penetrating laterally to the roots; the surface-pipe method, in which water flows in movable slip-joint pipes; sprinklers, including large-scale center-pivot and other self-propelled systems; and a variety of water-conserving drip and trickle systems. In many cases irrigation is correlated with drainagedrainage,
in agriculture, the removal of excess water from the soil, either by a system of surface ditches, or by underground conduits if required by soil conditions and land contour. Diesel or centrifugal pumps are sometimes used to drain large areas.
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 to avoid soil salinity, leaching, and waterlogging. Irrigation may also involve preliminary clearing, smoothing, and grading of land. Especially in areas of high evaporation rates, intensive irrigation can result in excessive quantities of salts accumulating in the upper layers of the soil as water evaporates from the surface, rendering the soil unfit for crop production.

Since prehistoric times water has been diverted from waterways to fields by ditching. Early improvements for raising water included counterbalanced poles with attached water vessels, and adaptations of the wheel and of a pump called the Archimedes' screw. The use of canals, dams, weirs, and reservoirs for the distribution, control, and storage of water was probably initiated in ancient Egypt. A system of gently sloping underground tunnels (qanats) to deliver water from a subterranean source to distant areas where it is accessed through shafts was developed in ancient Persia and has been widely used elsewhere. In modern times pumps have facilitated the use of underground as well as surface water, but overuse of water in aquifers can exhaust their usable water. Large-scale 20th-century irrigation projects commonly also include water supply, hydroelectric power, and flood control.

Many regions, notably in China, Egypt, Mesopotamia, and India, have been under continuous irrigation from ancient times. Today China, India, the United States, and Pakistan rank highest in irrigated land. In North America, where most of the arid and semiarid land lies west of the 100th meridian, irrigation was first practiced in the Southwest by Native Americans and later by the Spanish, especially in California. As agriculture expanded, early irrigation initiatives by individual farmers or local groups were soon supplemented by commercial projects, until more ambitious water conservation and development schemes involved state and federal governments in vast projects.

Bibliography

See J. Keller and R. D. Bliesner, Sprinkle and Trickle Irrigation (1990); B. A. Stewart and D. R. Nelson, Irrigation of Agricultural Crops (1990); W. F. Ritter, ed., Irrigation and Drainage (1991).

Irrigation

Supplying water to grass, trees, and other plants.

Irrigation

 

in medicine, a therapeutic procedure that consists in the flooding of inflamed tissue with a stream of water or medicinal fluid. It has been widely used in surgery (on wound surfaces and the rectum, for example) and also in urology, gynaecology, and other branches of medicine. The most frequent use of the term “irrigation” pertains to the rinsing of the urethra without a catheter. Cystoscopes and urethroscopes used for irrigation are called irrigation cystoscopes and urethroscopes. Enemas, syringes, and the like are called irrigators.


Irrigation

 

the supply of water to fields where a shortage of moisture exists, and also the increase of reserves of moisture in the root zone of the soil; a type of land reclamation.

Irrigation consists of a set of technical, scientific-farming, and organizational-management measures that are based on hydraulic-engineering methods for supplying standard quantities of water to the soil. Irrigation water improves water conditions in the soil, increases the water content of plant fibers, improves turgor, and dissolves nutrients and makes them available to plants. Irrigation affects temperature conditions by regulating the temperature of the surface layer of the soil and the ground layer of the air, and also makes possible control of the growth and development of plants, intensification of the growth of particular organs (including generative organs), and improvement of the quality of the harvest. In fruit and berry crops that receive optimum quantities of moisture, the sugar content of the fruit increases, and in oil crops the fat content in the seeds is greater. For wheat (with supplementary nitrogen feeding), the protein content in the grain increases, and for cotton the quality of the fiber is improved.

A correct irrigation schedule creates favorable conditions for microbiological processes in the soil, particularly nitrification. With irrigation, land in arid zones may be fundamentally improved and drawn into the agricultural cycle; in addition, farmlands in regions with adequate moisture may be used more productively. Irrigation is of great importance for the development of cotton, rice, and grain production (establishment of large irrigated areas of grain crops), as well as for animal husbandry (repeated plantings of fodder crops on irrigated lands; establishment of irrigated crop pastures).

By the early 19th century the world area of irrigated land was 8 million hectares (ha), and by the turn of the 20th century it was 48 million ha (irrigation construction in India, Egypt, the USA, and Italy). In Russia irrigation work was financed mainly by private capital; by 1913 the irrigated area was not more than 4 million ha. In the 20th century, irrigation is developing in many countries, particularly China, India, Pakistan, Iran, Japan, Egypt (the entire sown area is irrigated), the USA, Mexico, Italy, Bulgaria, and France. In the 1950’s, irrigated land occupied 121 million ha; in 1972, more than 225 million ha. In the USSR the irrigated area is about 12 million ha (1972); during the ninth five-year plan (1971–75) there was a significant increase in irrigated lands (in Middle Asia, the Volga Region, the Northern Caucasus, and the southern Ukraine).

A distinction is made between regular irrigation (gravity-flow and with mechanical water-lifting using pumping stations), in which the water is supplied to the fields at set times and in the required quantity, according to an irrigation schedule, and periodic (one-time) irrigation, in which water is supplied to the irrigated area once (for example, during spring floods or after being released from a reservoir). Irrigation systems are built to provide irrigation. The water intake structures of such systems draw water from irrigation sources—rivers, large canals, lakes, reservoirs, and subterranean waters collected by means of wells or karezes (underground irrigation canals)—into irrigation canals, which transport it to the irrigated areas and distribute it among the irrigated plots. Sewage and water with dissolved fertilizers (fertilizer irrigation) are also used.

Present-day irrigation involves not only the modernization of old irrigation systems but also the construction of new, large-scale systems in which the irrigated area reaches tens and hundreds of thousands of hectares (for example, the Karshi system in the USSR, the Saskatchewan River system in Canada, and the system in the region of the Aswan Reservoir in Egypt). Technical advances in irrigation include the introduction of remote control and automation of intake, distribution, and metering of water and waterings; replacement of open canals in earthen channels by pipelines and trough canals; the use of facing and screens for protection against seepage, and also the use of polymers (pipes and films for screens in canals and reservoirs); more efficient methods of watering (for example, sprinkling, subsoil irrigation, and surface watering); better designs for watering equipment; and the development of irrigation with mechanical water-lifting.

The raising of agricultural crops with irrigation has distinctive features; among them are specific methods of tilling the soil, increased dosages of fertilizer, and coordination of watering with tillage of the fields. Prevention of salinization of the soil is very important; in many countries (for example, Iran, Iraq, Syria, India, and Egypt), salinization has assumed catastrophic proportions. The problem is combated by flushing and the construction of drainage networks.

REFERENCES

Kostiakov, A. N. Osnovy melioratsii, 6th ed. Moscow, 1960.
Kostiakov, A. N. Izbr. trudy, vols. 1–2. Moscow, 1961.
Askochenskii, A. N. Oroshenie i obvodnenie ν SSSR. Moscow, 1967.
Mamedov, A. M. Irrigatsiia Srednei Azii. Moscow, 1969.
Shumakov, B. A. Oroshenie ν zasushlivoi zone Evropeiskoi chasti SSSR. Moscow, 1969.
Shubladze, K. K. Melioratsiia zemel’. Moscow, 1970.
Oroshaemye kul’turnye pastbishcha. Moscow, 1970.

K. K. SHUBLADZE

irrigation

[‚ir·ə′gā·shən]
(civil engineering)
Artificial application of water to arable land for agricultural use.
(medicine)
Therapeutic washing out by means of a continuous stream of water.
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