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INTRODUCTION
1.1 GENERAL
Irrigation may be defined as the process of supplying water to land by artificial means for the
purpose of cultivation.Ordinarily water is supplied to land by nature through rain but generally it is
not enough for the proper growth of plants.As such as the basic objective of irrigation is to
supplement the natural supply of water to land so as to obtain the an optimum yield from the crop
grown on the land.
In order to achieve this objective of irrigation, an irrigation system is required to developed, which
involves planning, designing, construction, operation and maintenance of various irrigation works
viz, a source of water supply, a distribution system for carrying water from the source to the
agricultural land and its application on the land, and various other associated works.The factors
which neccessitate irrigation are:
• Inadequate rainfall
• Uneven distribution of rainfall
• Growing a number of crops during a year
• Growing superior crop
Drip irrigation is sometimes called trickle irrigation and involves dripping water onto the soil at
very low rates (2-20 litres/hour) from a system of small diameter plastic pipes fitted with outlets
called emitters or drippers. Water is applied close to plants so that only part of the soil in which the
roots grow is wetted (Figure 60), unlike surface and sprinkler irrigation, which involves wetting the
whole soil profile. With drip irrigation water, applications are more frequent (usually every 1-3
days) than with other methods and this provides a very favourable high moisture level in the soil in
which plants can flourish.
METHODS OF IRRIGATION
Irrigation methods are commonly designated according to the manner in which water is applied
to the land to be irrigated.
1.2.1 Surface Irrigation Methods
The water is applied by spreading in it sheets or small streams on the land to be irrigated.These
methods are adopted for perennial irrigation system.
1.2.2 Sprinkler Irrigation Methods
The irrigation water is applied to the land in the form of spray, somewhat as in ordinary rain.It can
be used for all the crops except rice and jute and for almost all soils except very heavy soils with
very low filtration rates.
1.2.3 Sub-Surface Irrigation Methods
The water is applied below the ground surface so that it is supplied directly to the root zone of the
plants.The main advantages of these methods are that the evaporation losses are considerably
reduced and the hindrance caused to cultivation by the presence of borders, pipes and field channels
in the other methods of irrigation is eliminated.
1.3 DRIP OR TRICKLE IRRIGATION METHOD
Drip irrigation,also known as trickle irrigation or microirrigation is one of the sub-surface irrigation
method of applying water or frequent application of water to crops through small emitters in the
vicinity of the root zone, wetting a limited amount of surface area and depth of soil. The theory
behind drip irrigation is to apply sufficient moisture to the root of the crops to prevent water stress.
A major difference between drip system and most other systems is that the balance between crop
evapotranspiration and applied water is maintained over limited periods of 24 to 72 hours. The
conversion from sprinkler to drip irrigation can result in water use reduction of 50% and double
yield. This is a result of improved water use and fertility and reduced disease and weed pressure.
1.4 NEED OF DRIP IRRIGATION
Drip irrigation can help you use water efficiently.A well-designed drip irrigation system loses
practically no water to runoff, deep percolation, or evaporation. Drip irrigation reduces water
contact with crop leaves, stems, and fruit. Thus conditions may be less favorable for the onset of
diseases. Irrigation scheduling can be managed precisely to meet crop demands, holding the
promise of increased yield and quality.Growers and irrigation professionals often refer to
"subsurface drip irrigation,"or SDI.When a drip tape or tube is buried below the soil surface, it is
less vulnerable to damage during cultivation or weeding.
COMPONENTS AND WORKING
In drip irrigation, also known as trickle irrigation, water is applied in the form of drops directly near
the base of the plant. Water is conveyed through a system of flexible pipelines, operating at low
pressure, and is applied to the plants through drip nozzles. This technique is also known as „feeding
bottle‟ technique where by the soil is maintained in the most congenital form by keeping the soilwater-air
proportions in the optimum range. Drip irrigation limits the water supplied for
consumptive use of the plant by maintaining minimum soil moisture, equal to the field capacity,
thereby maximizing the saving. The system permits the fine control on the application of moisture
and nutrients at stated frequencies.
The main components of a typical drip irrigation system are:
• Water Source
• Pumping System
• Distribution System
• Drip Tape ( Drip Tube)
• Injectors
• Filtration System
2.1 DRIP TAPE (OR DRIP TUBE)
The drip-irrigation system delivers water to each plant through a thin polyethylene tape (or tube)
with regularly spaced small holes (called emitters). Selection of drip tape should be based on
emitter spacing and flow rate. The typical emitter spacing for vegetables is 12 inches, but 8 inches
or 4 inches may be acceptable. Dry sections of soil may develop between consecutive emitters when
a wider emitter spacing (18 inches) is used on sandy soils. Flow rates are classified into low flow
(<20gal/100ft/hr), medium flow (20 to 30 gal/100ft/hr) and high flow(>30 gal/100ft/hr). The risk of
emitter clogging is generally higher with the lower-flow drip tapes.
INJECTORS
Injectors allow the introduction of fertilizer, chemicals and maintenance products into the irrigation
system. Florida law requires the use of an anti-siphoning device (also called backflow-prevention
device) when fertilizer, chemicals or any other products are injected into a drip-irrigation
system.Backflow-prevention devices ensure the water always moves from the water source to the
field. The devices prevent chemicals in the water from polluting the water source.
FILTRATION SYSTEM
Because drip-irrigation water must pass through the emitters, the size of the particles in the water
must be smaller than the size of the emitter to prevent clogging. Nearly all manufacturers of dripirrigation
equipment recommend that filters be used. The filtration system removes "large" solid
particles in suspension in the water. Different types of filters are used based on the type of particles
in the water. Media filters (often containing angular sand) are used with surface water when large amounts of organic matter (live or dead) need to be filtered out.
Screen filters or disk filters may be used withgroundwater. A 200-mesh screen or equivalent is
considered adequate.
HOLTICULTURAL CONSIDERATIONS
The goal of drip irrigation is to bring water to the crop. The main parameters that determine crop
water use are the type of crop planted and row spacing. A drip irrigation system should be able to
supply 110% - 120% of crop water needs. In other words, the system should be slightly oversized.
In designing a drip-irrigation system, it is common to consider that vegetable crops ordinarily need
approximately 1.5 acre-inches of water for each week of growth or approximately 20 acre-inches of
water per crop. Actual crop water use will be more or less than this amount, depending on weather
and irrigation efficiency.
3.2 DESIGN CONSIDERATIONS
Start with what is already available, the water source or the field. If a water source is already
available (pond or well), the amount of water available may be used to calculate the maximum size
of each irrigation zone.
If no water source is available, the amount of water needed by the crop, based on the size of the
planted area, may be used to calculate the type of well or pond size needed.
3.3 LAY OUT OF BEDS AND ROWS
Because differences in altitudes affect water pressure, it is preferable to lay out beds perpendicular
to the slope. This arrangement of rows is called "contour farming”.
SYSTEM CONTROLS
System controls are devices that allow the user to monitor how the drip-irrigation system performs.
These controls help ensure the desired amount ofwater is applied to the crop throughout the
growing season.The different devices used for the control are:
• Pressure Regulators
• Water Meters
• Pressure Gauges
• Soil moisture Measuring Devices
• Electrical Timers
4.1 PRESSURE REGULATORS
Pressure regulators,installed in-line with the system, regulate water pressure at a given water flow
there by helping to protect system components against damaging surges in water pressure. Pressure
surges may occur when the water in the pipe has a velocity >5 feet /second ("water hammer") or
when water flowing in the pipe has no avenue for release due to a closed valve or a clog inthe pipe.
WATER METERS
Water meters monitor and record the amount of water moving through a pipe where the water meter
is installed. When a stopwatch is used together with a water meter, it is possible to determine the
water flow in the system in terms of gallons-per-minute.
PRESSURE GAUGES
Pressure gauges monitor water pressure in the system and ensure operating pressure remains close
to the recommended or benchmark values. Based on where the pressure gauge is installed, it will
measure water pressure in a various ranges, from 0-100 psi near the pump to 0-20 psi at the end of
drip tape.Pressure gauges may be installed at set points (near the pump, before and after the filter,
near the Field.They can also be mounted as portable devices and installed temporarily at the end.
4.4 SOIL MOISTURE MEASURING DEVICES
Soil-moisture-measuring devices (such as tensiometers, capacitance probes or Time Domain
Reflectometry probes) are used to measure soil moisture in the root zone of the crop.
4.5 ELECTRICAL TIMERS
Electrical timers connected to solenoid valves may be used to automatically operate a drip-irrigation
system at pre-set starting and ending operating times of day.
SYSTEM MAINTENENCE
The goal of drip-irrigation maintenance is to preserve the high uniformity of water application
allowed by drip irrigation. A successful program of maintenance for a drip-irrigation system is
based on the prevention-is-the-best-medicine approach. It is easier to prevent a drip tape from
clogging than to"unclog" it or replace it.
5.1 WATER SAMPLING
An essential part of drip-irrigation management is determining water quality through water testing.
Water testing will help determine water chemical composition, pH, and hardness.These parameters
have direct implications on chlorination, acidification and filtration needs for irrigation water.
Table 5.1 Water quality parameter levels for emitter plugging potential of
Drip irrigation systems
WATCH FOR LEAKS
Leaks can occur unexpectedly as a result of damage by insects, animals, or farming tools.
Systematically monitor the lines for physical damage. It is important to fix holes as soon as
possible to preventuneven irrigation.
5.4 CHLORINE CLEARS CLOGGED EMITTERS
If the rate of water flow progressively declines during the season, the tubes or tape may be slowly
plugging, resulting in severe damage to the crop. In addition to maintaining the filtering stations,
regular flushing of the drip tube and application of chlorine through the drip tube will help
minimize clogs. Once a month, flush the drip lines by opening the far ends of a portion of the tubes
at a time and allowing the higher velocity water to rush out the sediment.Because algae growth and
biological activity in the tube or tape are especially high during warmer months,chlorine usually is
applied at 2-week intervals during these months.
5.4 CHEMIGATION
Manage irrigation and fertilization together to optimize efficiency. Chemigation through drip
systems efficiently delivers chemicals in the root zone of the receiving plants. Because of the
precision of application, chemigation can be safer and use less material.
5.5 FERTILIZATION
Soil microorganisms convert nitrogen (N) fertilizers to nitrate. Nitrate is water soluble, available to
plants, and subject to leaching loss.Fertilizer can be injected through the drip system. Fertilizer
usually is introduced into the irrigation system in front of the filter station so the filters can remove
any precipitates that occur in the solution Fertilizers containing sulfate, phosphate, calcium, or
anhydrous or aqua ammonium can lead to solid chemical.
PLACEMENT OF TAPE
The drip tape must be close enough to the surface to germinate the seed if necessary, or a portable
sprinkler system should be available. For example, a tape tube 4 to 5 inches deep has successfully
germinated onion seeds in silt loam soil.Tape at 12 inches failed to uniformly germinate onions.
5.7 TIMING AND RATES
The total irrigation water requirements for crops grown with a drip system is greatly reduced
compared to a surface flood system because water can be applied much more efficiently with drip
irrigation. For example, with furrow irrigation, typically at least 4 acre-feet/acre/year of water is
applied to onion fields in the Treasure Valley of eastern Oregon and southwestern Idaho. Depending
on the year, summer rainfall, and the soil, 14 to 32 acre-inches/acre of water has been needed to
raise onions under drip irrigation in the Treasure Valley.
5.8 STANDARD MAINTENANCE
Add chlorine or other chemicals to the drip line periodically to kill bacteria and algae. Acid might
also be needed to dissolve calcium carbonates. Filters must be managed and changed as
needed.Even with filtration, however, drip tape must be flushed regularly. The frequency of flushing
depends on the amount and kinds of sedimentation in the tape