DRIP IRRIGATION
Drip irrigation, also known as trickle irrigation or
micro irrigation is an irrigation method which
minimizes the use of water and fertilizer by allowing water to drip slowly to
the roots of plants, either onto the
soil surface or directly onto the root zone, through a network of valves,
pipes, tubing, and emitters.
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It is becoming popular for row crop irrigation. This
system is used in place of water scarcity as
it minimizes conventional losses such as deep percolation, evaporation and
run-off or recycled water is
used for irrigation.
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Small diameter plastic pipes fitted with emitters or
drippers at selected spacing to deliver the
required quantity of water are used. Drip irrigation may also use
devices called micro-spray heads, which spray water in a small area, instead of dripping
emitters.
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Subsurface drip irrigation (SDI) uses permanently or
temporarily buried drip per line or drip tape located at or below the plant roots.
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Pump and valves may be manually or automatically
operated by controller Drip irrigation is
the slow, frequent application of water to the soil though emitters placed
along a water delivery line.
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The term
drip irrigation is general, and includes several more specific methods. Drip irrigation applies the water through small
emitters to the soil surface, usually at or near the plant to be irrigated.
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Subsurface irrigation is the application of water below the soil surface. Emitter
discharge rates for drip and subsurface irrigation are generally less than 12 liters per hour.
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Components of Drip Irrigation System
(Listed in Order
from Water Source)
(a) Pump or pressurised water source.
(b)
Water Filter(s) - Filtration Systems
: Sand Separator, Cyclone, Screen
Filter, Media Filters.
(c) Fertigation Systems
(Venturi injector).
(d) Backwash Controller.
(e) Main Line (larger diameter
Pipe and Pipe Fittings).
(f) Hand-operated, electronic, or hydraulic Contvl
Valves and Safety
Valves.
(g) Smaller diameter
polytube (often referred
to as "laterals").
(h) Poly fittings and Accessories (to make connections).
(i)
Emitting Devices at plants (Example
: Emitter or Drippers, micro
spray heads, inline
drippers, trickle rings).
Suitabi1ity:and
Limitation
(a) From stand
point of crops, soil, and topography, drip irrigation is best suited for tree,
vine, and row crops. A lot of
research work has been conducted to establish the suitability of drip
irrigation for different vegetable
crops. Drip irrigation has been found suitable both for field vegetable crops and also under covered cultivation practices.
(b) With
respect to water quantity and quality, drip irrigation uses a slower rate of
water application over a longer period
of time than other irrigation methods. The most economical design
would have water
flowing into the farm area throughout most of
the day, every day, during peak use periods. If water is not
available on a continuous basis,
on-farm water storage may be necessary.
(c)
Though a form of pressurized irrigation, drip is a low
pressure, low flow rate method. These conditions require
small flow channel
openings in the emission devices,
which are prone to plugging.
(d)
High efficiencies are USP of drip irrigation system.
Properly designed and maintained drip systems are capable of high efficiencies. Design efficiencies should
be on the order of 90 to 95%.
(e)
Labour and energy considerations are very important
consideration in drip irrigation system. Due
to their low flow characteristics, drip irrigation systems usually have few
sub-units, and are designed for long
irrigation times.
(f)
Drip irrigation systems generally use less energy than
other forms of pressurized irrigation systems.
The emission devices usually operate at pressures ranging from 5 to 25 PSI.
Additional pressure is required to
compensate for pressure losses through the control head (filters and control valves)
and the pipe network.
(g)
Economic factors need special attention in case drip irrigation system
as initial cost and operational cost is reasonably high. Drip
systems costs can vary greatly. Depending on crop (plant. and therefore. emitter and hose spacings)
and type of hose employed (permanent or "disposable" thin-walled tubing).
Advantages
The advantages of drip irrigation are :
1. Minimized fertilizer nutrient loss due to localized application and reduced leaching,
allows safe use of recycled water.
2. High water distribution efficiency. Moisture within the root zone can be maintained at field capacity.
3. Leveling of the field not necessary. Soil type plays
less important role in frequency
of irrigation, minimised soil erosion.
4.
Highly uniform distribution of water, i.e. controlled by output of each nozzle.
5.
Lower labour cost.
6.
Early maturity and good harvest.
7.
Foliage remains dry thus reducing
the risk of disease.
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Performance Indicator
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Conventional Irrigation Methods
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Drip Irrigation
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Water saving
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Waste lot of water.
Losses occur due to percolation, runoff and
evaporation
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40-70% of water can be saved over conventional irrigation methods. Runoff and
deep percolation losses
are nil or
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negligible.
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Water use efficiency
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30-50%, because losses
are very high
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80-95%
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Saving in labour
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Labour engaged
per irrigation is higher than
drip
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Labour required only
for operation and
periodic maintenance of the system
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Weed infestation
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Weed infestation is very high
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Less wetting of soil, weed
infestation is very less or almost nil.
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Use of saline water
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Concentration of salts increases and adversely affects
the plant growth. Saline water cannot
be used for
irrigation
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Frequent irrigation keeps the salt concentration within
root zone below
harmful level
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Diseases and pest
problems
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High
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Relatively less because of less atmospheric humidity
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Suitability in different soil Type
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Deep percolation is more
in light soil and with limited soil
depths. Runoff loss is more
in heavy soils
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Suitable for all soil types as flow rate can be controlled
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Water control
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Inadequate
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Very precise and easy
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Efficiency
of fertilizer use
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Efficiency
is low because
of heavy losses due to leaching and runoff
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Very high
due to reduced loss of
nutrients through leaching and
runoff water
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Soil erosion
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Soil erosion is high because
of large stream sizes used for irrigation.
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Partial wetting of soil
surface and slow application rates eliminate
any possibility of soil
erosion
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Increase in crop yield
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Non-uniformity in available moisture reducing
the crop yield
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Frequent watering eliminates moisture stress
and yield can be increased up to 15- 150%
as compared to conventional methods of irrigation.
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