Irrigation is an artificial application of water
to the soil. It is usually used to assist in growing crops in dry
areas and during periods of inadequate rainfall. Additionally,
irrigation also has a few other uses in crop production, which
include protecting plants against frost,suppressing weed growing in
rice fields and helping in preventing
soil consolidation.In contrast,
agriculture that relies only on direct
rainfall is referred to as rain-fed farming. Irrigation is often
studied together with
drainage, which is
the natural or artificial removal of surface and sub-surface water
from a given area.
Irrigation is also a term used in medical/dental fields to refer to
flushing and washing out anything with water or another
liquid.
Irrigation in a field in New Jersey,
United States.
History
Animal-powered irrigation, Upper
Egypt, ca. 1840
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.
Sophisticated irrigation and storage systems
were developed by the Indus
Valley Civilization in Pakistan
and North India, including the reservoirs at
Girnar in 3000 BCE and an early canal
irrigation system from circa 2600 BCE. Large scale
agriculture was practiced and an extensive network of canals was
used for the purpose of irrigation.
There is
evidence of the ancient Egyptian pharaoh
Amenemhet III in the twelfth dynasty (about 1800
BCE) using the natural lake of the
Faiyum
Oasis
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
noria, a water wheel with
clay pots around the rim powered by the flow of the stream (or by
animals where the water source was still), was first brought into
use at about this time, by
Roman
settlers in North Africa. By 150 BCE the pots were fitted with
valves to allow smoother filling as they were forced into the
water.
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. Due to their
engineering superiority in this sector, they were often called
'masters of irrigation'.
Most of these irrigation systems still exist
undamaged up to now, in Anuradhapura
and Polonnaruwa
, because of the advanced and precise
engineering. The system was extensively restored and further
extended during the reign of King
Parakrama Bahu (1153 – 1186
CE).
The oldest
known hydraulic engineers of China
were
Sunshu Ao (6th century BCE) of the
Spring and Autumn Period
and Ximen Bao (5th century BCE) of the
Warring States period, both of whom
worked on large irrigation projects. In the Szechwan
region belonging to the State of Qin of ancient China, the Dujiangyan
Irrigation System
was built in 256 BCE to irrigate an enormous area
of farmland that today still supplies water. By the 2nd
century AD, during the
Han Dynasty, the
Chinese also used
chain pumps that lifted
water from lower elevation to higher elevation. These were powered
by manual foot pedal, hydraulic
waterwheels, or rotating mechanical wheels pulled
by
oxen. The water was used for
public works of providing water for urban
residential quarters and palace gardens, but mostly for irrigation
of
farmland canals and channels in the
fields.
In
fifteenth century Korea
the world's
first water gauge, uryanggye (Korean:우량계), was
discovered in 1441 CE. The inventor was Jang Yeong-sil, a Korean engineer of the
Joseon
Dynasty
, under the active direction of the king, Sejong the Great. 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.
Present extent
In 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.
At the global scale 2,788,000 km² (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
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 moves over and across the land
by simple gravity flow in order to wet it and to infiltrate into
the soil. Surface irrigation can be subdivided into furrow,
borderstrip or basin irrigation. It is often called
flood
irrigation when the irrigation results in flooding or near
flooding of the cultivated land. Historically, this has been the
most common method of irrigating agricultural land.
Where water levels from the irrigation source permit, the levels
are controlled by dikes, usually plugged by soil. This is often
seen in terraced rice fields (rice paddies), where the method is
used to flood or control the level of water in each distinct field.
In some cases, the water is pumped, or lifted by human or animal
power to the level of the land.
Localized irrigation
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 Irrigation
Drip Irrigation - A dripper in
action
Drip irrigation, also known as trickle irrigation, functions as its
name suggests. Water is delivered at or near the
root zone of plants, drop by drop. This method 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 labor-intensive. Lower
water pressures are usually needed than for most other types of
systems, with the exception of low energy center 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. In the past one of the main disadvantages
of the subsurface drip irrigation (SDI) systems, when used for
turf, was the fact of having to install the plastic lines very
close to each other in the ground, therefore disrupting the
turfgrass area. Recent technology developments on drip installers
like the drip installer at New Mexico State University Arrow Head
Center, places the line underground and covers the slit leaving no
soil exposed.
Sprinkler irrigation
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.
Center pivot irrigation
Center pivot irrigation is a
form of sprinkler irrigation consisting of several segments of pipe
(usually galvanized steel or aluminum) 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 center of the arc. These systems are common in parts
of the United States where terrain is flat. Newer irrigations have
drops as shown in the image that follows.
Most center 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
bubblers that deposit the water directly on the ground between
crops. The crops are planted in a circle to conform to the center
pivot. This type of system is known as LEPA (
Low Energy Precision
Application). Originally, most center pivots were water
powered. These were replaced by hydraulic systems (
T-L Irrigation) and electric motor
driven systems (
T-L, Reinke, Valley, Zimmatic). Most
sprinklers features
GPS devices. Reinkes usually
have strobe lights and are red. Valleys have a blue label, while
Zimmatics' lights are high with either a red or white Zimmatic
label.
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 10 m 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
diameter aluminum 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
Subirrigation 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
moisten
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 thereby
control the water table.
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.
Automatic, non-electric irrigation using buckets and ropes
Besides the common manual watering by bucket, an automated, natural
version of this also exist. Using plain polyester ropes combined
with a prepared ground mixture can be used to water plants from a
vessel filled with water.The ground mixture would need to be made
depending on the plant itself, yet would mostly consist of black
potting soil, vermiculite and perlite. This system would (with
certain crops) allow you to save expenses as it does not consume
any electricity and only little water (unlike sprinklers, water
timers, ...). However, it may only be used with certain crops
(probably mostly larger crops that do not need a humid environment;
perhaps e.g. paprika's).
Irrigation using stones to catch water from humid air
In countries where at night, humid air sweeps the countryside,
stones are used to catch water from the humid air by
condensation.
This is for example practiced in the
vineyards at Lanzarote
.
Dry terraces for irrigation and water distribution
In
subtropical countries as Mali
and Senegal
, a special type of terracing (without flood
irrigation or intent to flatten farming ground) is used.
Here, a 'stairs' is made through the use of ground level
differences which helps to decrease water
evaporation and also distributes the water to
all patches (sort of irrigation).
Sources of irrigation water
Sources of irrigation water can be groundwater extracted from
springs or by using
wells, surface water withdrawn from
rivers,
lakes or
reservoirs or non-conventional sources like
treated
wastewater,
desalinated water or
drainage water. A special form of irrigation
using surface water is
spate
irrigation, also called
floodwater harvesting. In case of a
flood (spate) water is diverted to normally dry river beds (wadi’s)
using a network of dams, gates and channels and spread over large
areas. The moisture stored in the soil will be used thereafter to
grow crops. Spate irrigation areas are in particular located in
semi-arid or arid, mountainous regions. While floodwater harvesting
belongs to the accepted irrigation methods,
rainwater harvesting is usually not
considered as a form of irrigation. Rainwater harvesting is the
collection of runoff water from roofs or unused land and the
concentration of this
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
pipe,
sprinklers,
and irrigation
valves being hidden, it makes
for a cleaner, more presentable landscape without garden
hose or other items having to be moved around
manually. This does, however, create some drawbacks in the
maintenance of a completely buried system.
Water source and piping
The beginning of a sprinkler system is the
water source. This is usually a tap into an existing
(city) water line or a
pump that pulls water
out of a well or a pond. The water travels through pipes from the
water source through the valves to the sprinklers. The pipes from
the water source up to the irrigation valves are called
"mainlines", and the lines from the valves to the sprinklers are
called "lateral lines". Most piping used in irrigation systems
today are
HDPE and
MDPE or
PVC or
PEX
plastic pressure pipes due to
their ease of installation and resistance to corrosion. After the
water source, the water usually travels
through a
check valve. This prevents
water in the irrigation lines from being pulled back into and
contaminating the clean water supply.
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 has a
solenoid
valve 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
soil moisture
sensors (water potential or
water
content), 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
Academic resources
Irrigation by country
See also
References
External links
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