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Irrigation

2007 Schools Wikipedia Selection. Related subjects: Environment; General
Geography

   Irrigation is the artificial application of water to the soil. In crop
   production it is mainly used to replace missing rainfall in periods of
   drought, but also to protect plants against frost. Additionally
   irrigation helps to suppress weed growing in rice fields. In contrast,
   agriculture that relies only on direct rainfall is sometimes referred
   to as dryland farming or as rainfed farming.
   High-altitude aerial view of irrigation in the Heart of the Sahara (
   22°16′21″N, 28°44′55″E)
   High-altitude aerial view of irrigation in the Heart of the Sahara (
   22°16′21″N, 28°44′55″E)

History of irrigation

   An example of irrigation system common in Indian subcontinent. Artistic
   impression on the banks of Dal Lake, Kashmir, India.
   An example of irrigation system common in Indian subcontinent. Artistic
   impression on the banks of Dal Lake, Kashmir, India.
   A double waterwheel lifting water for irrigation at the Fayûm oasis,
   Egypt.
   A double waterwheel lifting water for irrigation at the Fayûm oasis,
   Egypt.
   Inside a quanat tunnel at Turpan, China.
   Inside a quanat tunnel at Turpan, China.

   Archaeological investigation has identified evidence of irrigation in
   Mesopotamia and Egypt as far back as the 6th millennium BCE, where
   barley was grown in areas where the natural rainfall was insufficient
   to support such a crop.

   In the Zana Valley of the Andes Mountains in Peru, archaeologists found
   remains of three irrigation canals radiocarbon dated from the 4th
   millennium BCE, the 3rd millennium BCE and the 9th century CE. These
   canals are the earliest record of irrigation in the New World. Traces
   of a canal possibly dating from the 5th millennium BCE were found under
   the 4th millennium canal. ( Dillehay, et al., 2005)

   The Indus Valley Civilization in Pakistan and North India (from circa
   2600 BCE) also had an early canal irrigation system.

   There is evidence of the ancient Egyptian pharaoh Amenemhet III in the
   twelfth dynasty (about 1800 BCE) using the natural lake of the Fayûm as
   a reservoir to store surpluses of water for use during the dry seasons,
   as the lake swelled annually as caused by the annual flooding of the
   Nile.

   The Qanats, developed in ancient Persia in about 800 BCE, are among the
   oldest known irrigation methods still in use today. They are now found
   in Asia, the middle east and north Africa. The system comprises a
   network of vertical wells and gently sloping tunnels driven into the
   sides of cliffs and steep hills to tap groundwater.

   The irrigation works of ancient Sri Lanka, the earliest dating from
   about 300 BCE, in the reign of King Pandukabhaya and under continuous
   development for the next thousand years, were one of the most complex
   irrigation systems of the ancient world. In addition to underground
   canals, the Sinhalese were the first to build completely artificial
   reservoirs to store water. The system was extensively restored and
   further extended during the reign of King Parakrama Bahu (1153–1186
   CE).

   In the Szechwan region ancient China the Dujiangyan Irrigation System
   was built in 250 BCE to irrigate a large area and it still supplies
   water today.

   In fifteenth century Korea the world's first water gauge, woo ryang
   gyae ( Korean: 우량계), was discovered in 1441 CE. The inventor was Jang
   Young Sil, a Korean engineer of the Choson Dynasty, under the active
   direction of the King, Se Jong. It was installed in irrigation tanks as
   part of a nationwide system to measure and collect rainfall for
   agricultural applications. With this instrument, planners and farmers
   could make better use of the information gathered in the survey.

   By the middle of the 20th century, the advent of diesel and electric
   motors led for the first time to systems that could pump groundwater
   out of major aquifers faster than it was recharged. This can lead to
   permanent loss of aquifer capacity, decreased water quality, ground
   subsidence, and other problems. The future of food production in such
   areas as the North China Plain, the Punjab, and the Great Plains of the
   US is threatened.

Present extent of irrigation

   At the global scale 278.8 Mha (689 million acres) of agricultural land
   was equipped with irrigation infrastructure around the year 2000. About
   68 % of the area equipped for irrigation is located in Asia, 17 % in
   America, 9 % in Europe, 5 % in Africa and 1 % in Oceania. The largest
   contiguous areas of high irrigation density are found in North India
   and Pakistan along the rivers Ganges and Indus, in the Hai He, Huang He
   and Yangtze basins in China, along the Nile river in Egypt and Sudan,
   in the Mississippi-Missouri river basin and in parts of California.
   Smaller irrigation areas are spread across almost all populated parts
   of the world.

Types of irrigation

   Basin flood irrigation of wheat
   Basin flood irrigation of wheat

   Various types of irrigation techniques differ in how the water obtained
   from the source is distributed within the field. In general, the goal
   is to supply the entire field uniformly with water, so that each plant
   has the amount of water it needs, neither too much nor too little.

Surface irrigation

   In surface irrigation systems water is moving over the land by simple
   gravity flow in order to wet it and to infiltrate into the soil. They
   can be subdivided into furrow, borderstrip or basin irrigation.

Localized irrigation

   Spray Head
   Spray Head

   Localized irrigation is a system where water is distributed under low
   pressure through a piped network, in a pre-determined pattern, and
   applied as a small discharge to each plant or adjacent to it. Drip
   irrigation, spray or micro-sprinkler irrigation and bubbler irrigation
   belong to this category of irrigation methods.

Drip, or trickle irrigation

   Drip Irrigation - A dripper in action
   Drip Irrigation - A dripper in action
   Drip Irrigation Layout and its parts
   Drip Irrigation Layout and its parts

   Water is delivered at or near the root zone of plants, drop by drop.
   This type of system can be the most water-efficient method of
   irrigation, if managed properly, since evaporation and runoff are
   minimized. In modern agriculture, drip irrigation is often combined
   with plastic mulch, further reducing evaporation, and is also the means
   of delivery of fertilizer. The process is known as fertigation. Deep
   percolation, where water moves below the root zone, can occur if a drip
   system is operated for too long of a duration or if the delivery rate
   is too high. Drip irrigation methods range from very high-tech and
   computerized to low-tech and relatively labor-intensive. Lower water
   pressures are usually needed than for most other types of systems, with
   the exception of low energy centre pivot systems and surface irrigation
   systems, and the system can be designed for uniformity throughout a
   field or for precise water delivery to individual plants in a landscape
   containing a mix of plant species. Although it is difficult to regulate
   pressure on steep slopes, pressure compensating emitters are available,
   so the field does not have to be level. High-tech solutions involve
   precisely calibrated emitters located along lines of tubing that extend
   from a computerized set of valves. Both pressure regulation and
   filtration to remove particles are important. The tubes are usually
   black (or buried under soil or mulch) to prevent the growth of algae
   and to protect the polyethylene from degradation due to ultraviolet
   light. But drip irrigation can also be as low-tech as a porous clay
   vessel sunk into the soil and occasionally filled from a hose or
   bucket. Subsurface drip irrigation has been used successfully on lawns,
   but it is more expensive than a more traditional sprinkler system.
   Surface drip systems are not cost-effective (or aesthetically pleasing)
   for lawns and golf courses. Jain Irrigation Systems, Chapin
   Watermatics, Eurodrip, Plastro Irrigation Systems are major
   manufacturer of Drip Irrigation Systems.

Sprinkler irrigation

   Sprinkler irrigation of blueberries in Plainville, New York.
   Sprinkler irrigation of blueberries in Plainville, New York.

   In sprinkler or overhead irrigation, water is piped to one or more
   central locations within the field and distributed by overhead
   high-pressure sprinklers or guns. A system utilizing sprinklers,
   sprays, or guns mounted overhead on permanently installed risers is
   often referred to as a solid-set irrigation system. Higher pressure
   sprinklers that rotate are called rotors and are driven by a ball
   drive, gear drive, or impact mechanism. Rotors can be designed to
   rotate in a full or partial circle. Guns are similar to rotors, except
   that they generally operate at very high pressures of 40 to 130 lbf/in²
   (275 to 900 kPa) and flows of 50 to 1200 US gal/min (3 to 76 L/s),
   usually with nozzle diameters in the range of 0.5 to 1.9 inches (10 to
   50 mm). Guns are used not only for irrigation, but also for industrial
   applications such as dust suppression and logging.

   Sprinklers may also be mounted on moving platforms connected to the
   water source by a hose. Automatically moving wheeled systems known as
   traveling sprinklers may irrigate areas such as small farms, sports
   fields, parks, pastures, and cemeteries unattended. Most of these
   utilize a length of polyethylene tubing wound on a steel drum. As the
   tubing is wound on the drum powered by the irrigation water or a small
   gas engine, the sprinkler is pulled across the field. When the
   sprinkler arrives back at the reel the system shuts off. This type of
   system is known to most people as a "waterreel" traveling irrigation
   sprinkler and they are used extensively for dust suppression,
   irrigation, and land application of waste water. Other travelers use a
   flat rubber hose that is dragged along behind while the sprinkler
   platform is pulled by a cable. These cable-type travelers are
   definitely old technology and their use is limited in today's modern
   irrigation projects.

Centre pivot irrigation

   The hub of a center-pivot irrigation system.
   The hub of a centre-pivot irrigation system.

   Centre pivot irrigation is a form of sprinkler irrigation consisting of
   several segments of pipe (usually galvanized steel or aluminium) joined
   together and supported by trusses, mounted on wheeled towers with
   sprinklers positioned along its length. The system moves in a circular
   pattern and is fed with water from the pivot point at the centre of the
   arc. These systems are common in parts of the United States where
   terrain is flat.
   Center pivot with drop sprinklers. Photo by Gene Alexander, USDA
   Natural Resources Conservation Service.
   Centre pivot with drop sprinklers. Photo by Gene Alexander, USDA
   Natural Resources Conservation Service.

   Most centre pivot systems now have drops hanging from a u-shaped pipe
   called a gooseneck attached at the top of the pipe with sprinkler heads
   that are positioned a few feet (at most) above the crop, thus limiting
   evaporative losses. Drops can also be used with drag hoses or bubbler's
   that deposit the water directly on the ground between crops. The crops
   are planted in a circle to conform to the centre pivot. This type of
   system is known as LEPA ( Low Energy Precision Application).
   Originally, most centre pivots were water powered. These were replaced
   by hydraulic systems ( T-L Irrigation) and electric motor driven
   systems (Lindsay, Reinke, Valley, Zimmatic). Most systems today are
   driven by an electric motor mounted low on each span. This drives a
   reduction gearbox and transverse driveshafts transmit power to another
   reduction gearbox mounted behind each wheel. Precision controls, some
   with GPS location and remote computer monitoring, are now available.
   Wheel line irrigation system in Idaho. 2001. Photo by Joel McNee, USDA
   Natural Resources Conservation Service.
   Wheel line irrigation system in Idaho. 2001. Photo by Joel McNee, USDA
   Natural Resources Conservation Service.

Lateral move (Side roll, Wheel line) irrigation

   A series of pipes, each with a wheel of about 1.5 m diameter
   permanently affixed to its midpoint and sprinklers along its length,
   are coupled together at one edge of a field. Water is supplied at one
   end using a large hose. After sufficient water has been applied, the
   hose is removed and the remaining assembly rotated either by hand or
   with a purpose-built mechanism, so that the sprinklers move 10m across
   the field. The hose is reconnected. The process is repeated until the
   opposite edge of the field is reached. This system is less expensive to
   install than a center pivot, but much more labor intensive to operate,
   and it is limited in the amount of water it can carry. Most systems
   utilize 4 or 5 inch diameter aluminium pipe. One feature of a lateral
   move system is that it consists of sections that can be easily
   disconnected. They are most often used for small or oddly-shaped
   fields, such as those found in hilly or mountainous regions, or in
   regions where labor is inexpensive.

Sub-irrigation

   Sub-irrigation also sometimes called seepage irrigation has been used
   for many years in field crops in areas with high water tables. It is a
   method of artificially raising the water table to allow the soil to be
   moistened from below the plants' root zone. Often those systems are
   located on permanent grasslands in lowlands or river valleys and
   combined with drainage infrastructure. A system of pumping stations,
   canals, weirs and gates allows it to increase or decrease the water
   level in a network of ditches and the control the water table thereby.

   Sub-irrigation is also used in commercial greenhouse production,
   usually for potted plants. Water is delivered from below, absorbed
   upwards, and the excess collected for recycling. Typically, a solution
   of water and nutrients floods a container or flows through a trough for
   a short period of time, 10-20 minutes, and is then pumped back into a
   holding tank for reuse. Sub-irrigation in greenhouses requires fairly
   sophisticated, expensive equipment and management. Advantages are water
   and nutrient conservation, and labor-saving through lowered system
   maintenance and automation. It is similar in principle and action to
   subsurface drip irrigation.

Manual irrigation using buckets or watering cans

   These systems have low requirements for infrastructure and technical
   equipment but need high labor inputs. Irrigation using watering cans is
   to be found for example in peri-urban agriculture around large cities
   in some African countries.

How an in-ground irrigation system works

   Most commercial and residential irrigation systems are " in ground"
   systems, which means that everything is buried in the ground. With the
   pipes, sprinklers, and irrigation valves being hidden, it makes for a
   cleaner, more presentable landscape without garden hoses or other items
   having to be moved around manually.

Controllers, zones, and valves

   Most Irrigation systems are divided into zones. A zone is a single
   Irrigation Valve and one or a group of sprinklers that are connected by
   pipes. Irrigation Systems are divided into zones because there is
   usually not enough pressure and available flow to run sprinklers for an
   entire yard or sports field at once. Each zone valve has a solenoid on
   it that is controlled via wire by an Irrigation Controller. The
   Irrigation Controller is either a mechanical or electrical device that
   signals a zone to turn on at a specific time and keeps it on for a
   specified amount of time. "Smart Controller" is a recent term used to
   describe a controller that is capable of adjusting the watering time by
   itself in response to current environmental conditions. The smart
   controller determines current conditions by means of historic weather
   data for the local area, a moisture sensor, weather station, or a
   combination of these.

Sprinklers

   When a zone comes on, the water flows through the lateral lines and
   ultimately ends up at the irrigation Sprinkler heads. Most sprinklers
   have pipe thread inlets on the bottom of them which allows a fitting
   and the pipe to be attached to them. The sprinklers are usually
   installed with the top of the head flush with the ground surface. When
   the water is pressurized, the head will pop up out of the ground and
   water the desired area until the valve closes and shuts off that zone.
   Once there is no more water pressure in the lateral line, the sprinkler
   head will retract back into the ground.

Problems in irrigation

     * Competition for surface water rights.
     * Depletion of underground aquifers.
     * Ground subsidence (e.g. New Orleans, Louisiana)
     * Buildup of toxic salts on soil surface in areas of high
       evaporation. This requires either leaching to remove these salts
       and a method of drainage to carry the salts away or use of mulch to
       minimize evaporation.
     * Overirrigation because of poor distribution uniformity or
       management wastes water, chemicals, and may lead to water
       pollution.

   Retrieved from " http://en.wikipedia.org/wiki/Irrigation"
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   with only minor checks and changes (see www.wikipedia.org for details
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