Definitions, history and development of trickle Irrigation

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CHAPTER ONE
INTRODUCTION
1.1 Definitions, history and development of trickle Irrigation
1.1.1 Definition
Drip irrigation is defined as the application of water through point or line sources
(Emitters) on or below the soil surface at a small operating pressure (20-200kPa) and at a low dis
charge rate (l-30l/h per emitter), resulting in partial wetting of the soil surface.
1.1.2 History and development of trickle irrigation system
Drip irrigation was used in ancient times by filling buried clay pots with water and allowing the
water to gradually seep into the soil. Modern drip irrigation began its development in Germany in
1860 when researchers began experimenting with subsurface irrigation using clay pipe to create
combination of irrigation and drainage systems. In 1913, E.B. House at Colorado State University
succeeded in applying water to the root zone of plants without raising the water table. Perforated
pipe was introduced in Germany in the 1920s. In 1934, O.E. Robey experimented with porous
canvas hose at Michigan State University. With the advent of modern plastics during and after
World War II, major improvements in drip irrigation became possible. Plastic micro-tubing and
various types of emitters began to be used in the greenhouses of Europe and the United States.
A new technology of drip irrigation was then introduced in Israel by Simcha Blass and his son
Yeshayahu. Instead of releasing water through tiny holes (blocked easily by tiny particles), water
was released through larger and longer passageways by using friction to slow water inside a plastic
emitter. The first experimental system of this type was established in 1959 in Israel by Blass, where
he developed and patented the first practical surface drip irrigation emitter. It is a common
misconception that drip irrigation was invented in Israel. There is no question that much of the
product innovation in this field occurred in Israel and that companies in Israel have contributed
significantly to the industry, but they cannot take all the credit for its development. The facts are
that drip irrigation system, with plastic pipes and the new plastic drippers, was invented and first
used and developed in Israel by Blass. It does not change the contributions made earlier and later.
This method subsequently spread to Australia, North America, and South America by the late
1960s.

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1.2 Advantages and Disadvantages of Drip Irrigation
1.2.1 Advantages
1. High degree control of water application because of this drip irrigation can achieve 90 percent
or more application efficiency, which can hardly be achieved by the other methods. For
sprinkler systems the field application efficiency usually ranges between 60 to 80% and 50 -
60% for surface methods.
The application efficiency for drip irrigation is based on the water desired in the root zone and
is not based on the whole area as sprinkler and surface methods. As opposed to the other methods
there is a possibility of exact timing and there is no limitation of irrigation time due to wind.
2. There is considerable water saving since the water could be applied almost precisely to the root
zone and there is no need to wet the entire area between crops. The total amount of water used
is less than the water requirement for the whole area. Substantial water saving can be achieved
especially for tree crop where plant spacing are large.
There are also some more advantages of partial wetting, viz:
 Weed control;
 Helps to have permanent travel between rows and farms because they are not totally
wetted;
 Insect, disease, and fungus problems are reduced, because of the minimized wetted
surface;
 Less soil crusting, reduced cultivation, and thus less soil compacting.
3. It is the most advantageous method for marginal soils like sandy and desert soils which cannot
be irrigated by other systems.
4. When compared to the sprinkler system, the drip method operates on much lower line pressure
thus providing a saving in energy requirement.
5. Enjoy advantage of dry foliage, i.e. maintaining dry foliage decrease incidence of plant
pathogens; chemicals applied will not be washed off from plant leaves and avoid leaf burn
from using poor quality water, for example saline water and waste water.
6. Maintain high soil water potential, i.e. the water content is always at reasonable potential, and
is available to plants, due to frequent applications.

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7. The method reduces salt concentration in the root zone, when irrigated with poor quality water.
I.e. there is a possibility to use poor quality water.
8. Like the sprinkler method, drip irrigation permits the application of fertilizers through the
system but here we have increased precision in application. We apply near to the plant. So
weeds do not get the fertilizer.
9. Advantageous for protected crops like flowers, pot vegetable and green house.
10. Elimination of the need for expensive drainage works.
1.2.2 Disadvantages of drip irrigation system
1. High initial cost of the system. The initial cost of the drip irrigation equipment is considered
to be its limitation for large-scale adoption. Economic considerations usually limit the use of
drip irrigation system to orchards and vegetables in water scarcity areas. The cost of the unit
per hectare depends mainly on the spacing of the crop. For widely spaced crops like fruits
trees the system may be even more economical than sprinklers. The main item of expenditure
is the cost of the lateral lines. As there is usually one lateral line for each crop row, the wider
the crop row spacing the lesser will be the initial cost on the drip system.
2. The requirement that the water, must be relatively clear. Emitters vary in size
between 0.5 to 1mm and they could easily be clogged. Clogging could be:
Physical clogging: due to sands, clay particles and debris.
Chemical clogging: due to carbonate or any other chemical precipitates and
encrustation formed due to applied chemical and/or use of hard water.
3. Salt concentration in soil. Salt will be accumulated in the periphery of the root zone where
there is no continual leaching. This will not be a problem if we change position of laterals/crop
rows year after year.
4. Do not change the microclimate like sprinklers.
5. Plastic laterals are liable to mechanical damage by rodents and human being.
6. Limited root development, with localized irrigation, roots will concentrate in the wetted zone.
If this zone is too small, the spread of roots will be inadequate. Hence yields may be affected
and trees might be blown over in strong winds. However, correct placements of drippers
overcome this danger.

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1.3 Adaptability of drip irrigation system
Crop types
Drip irrigation is most suitable for row crops (vegetables, soft fruit), tree and vine crops where one
or more emitters can be provided for each plant. Generally only high value crops are considered
because of the high capital costs of installing a drip system.
Slope
Drip irrigation is adaptable to any farmable slope. Normally the crop would be planted along
contour lines and the water supply pipes (laterals) would be laid along the contour also. This is
done to minimize changes in emitter discharge as a result of land elevation changes.
Soil type
Drip irrigation is suitable for most soils.
On clay soils water must be applied slowly to avoid surface water ponding and runoff.
On sandy soils higher emitter discharge rates will be needed to ensure adequate lateral wetting of
the soil.
1.4 Trickle System Components
The main components of the drip irrigation system (Figure 1.1) are:
1. The water source.
2. The pump and the energy unit.
3. Main Line (larger diameter Pipe and Pipe Fittings).
4. The filtration systems: Sand separator, screen filter, media filters & manifolds, backwash
controller.
5. Fertigation systems and chemigation equipment.
6. The controls in the automation of the system: Plastic Control Valves and Safety
Valves.
7. The water distribution system: Smaller diameter PE tubing (often referred to as “laterals”).
8. Emitting Devices at plants (Drippers).

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Figure 1.1: Components for a typical drip/trickle irrigation system.
The Water Source
The water source can be a treated water, well water, open channel, rivers, and lakes.
The clean water is essential for the drip irrigation. If water of poor quality is used, physical and
chemical or biological polluting agents can obstruct the emitters and drip laterals. The underground
well water is generally of good quality. In some cases, it can contain sand or chemical substances.
Although, superficial water from lakes, rivers, and open channels can be used, this water source
has the disadvantage of possible contamination by bacteria, algae, and other organisms. Almost all
water sources contain bacteria and elements that nourish it. A good filtration system is needed to
remove all the polluting agents that can obstruct or clog the drippers.
The Pump
The pumping and the power units represent a significant part of an initial installation cost of a drip
irrigation system. Therefore, for the selection of appropriate equipment, it is convenient to know
all the characteristics and operating conditions. It is necessary to acquire effective, reliable, and

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low cost pump and a power unit. A centrifugal pump is suitable for extracting water from
superficial sources or shallow wells.
It can also be used to increase the pressure in a main or submain line. The centrifugal pump is
relatively cheap and efficient. It is available for wide range of flows and pressures.
While selecting a pump, one should know total pressure in the system, operating pressure, total
volume of water for irrigation, and horsepower rating. A pump of a slightly greater capacity than
necessary can ensure sufficient water at a desired pressure.
The pump of a required size guarantees a good uniformity of water application.
On the contrary, an undersized pump and oversized drippers can cause non uniform emitter flow
throughout the field. Total pressure for the system generated by a pump depends on the following
factors:
1. The highest elevation: Elevation difference between a water source and an emitter located
at the highest elevation of the field.
2. The highest friction loss: The pressure required for the most distant emitter.
One should also consider discharge flow.
Energy or Power Units
In drip irrigation system, the electrical motors are preferable because of high overall efficiency,
ease of automation, quiet operation, and necessity of least maintenance.
The gasoline or diesel engines can also be used. However, these may cause variations in the
operational pressures and emitter flow. These have high maintenance cost and cause noise during
operation.
The Irrigation Controls
The volumetric valve
The volumetric valve measures volume of irrigation application and is necessary for proper
management.
The pressure gage
The pressure gage measures water pressure in the drip irrigation system. It is especially useful for
non-pressure compensating drippers. The pressure gages on the upstream and downstream side of
the filtering system indicates pressure loss that helps in programming the flushing process of

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filters. The intervals and range of pressure gage must match with the operating pressure of the
system for good management.
The pressure regulator or pressure relief valve
The pressure regulator or pressure relief valve can be fixed or adjustable. When installed in the
principal or secondary lines, it can compensate the changes in elevation or frictional losses of lines.
The manual valves, the automatic metering valves, the semiautomatic valves, and timers are
recommended for the drip irrigation system. The automatic flow valves provide desired amount of
irrigation in a specified time. These also reduce pressure variations among the lateral lines in an
uneven land. The combinations of pressure regulator and flow control valve are also available.
Air relief valve or vacuum breaker
This valve removes air from the drip irrigation system. The suction or vacuum is developed when
the irrigation system is shut off. This vacuum can obstruct the drippers if the dirty water or dust is
suctioned into the system. Vacuum breaker or air relief valve of “one inch for each 25 gpm of
flow” is recommended.
Flushing valve
The flushing valve at the end of each lateral helps in the flushing of the system.
Emitters/drippers
An emitter (dripper) is a device which applies water to the soil from the distribution system. The
two major categories of emitters are point source and line source. Both categories have been
successfully used in various cropping situations. Point source emitters are applied on widely
spaced crops such as orchards and vineyards, and line source systems are placed on more closely
spaced row crops. The emitter should be available in small increments of discharge, i.e., in the
order of 1 L/h.
Types of emitters
Emitters are classified based on some characterizing features, viz:
1. Emitter discharge and its variation
A given emitter has average discharge, i.e. nominal discharge expressed at a pressure of 1 atm
and 20Oc water temperature and this varies with a variation in pressure. There are also variations
resulting from manufacturing processes this variation is measured using coefficient of variation
(cvf) and it varies between 0.02 and 0.5 of the nominal discharge.

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2. Form of pressure dissipation
All pressure at the inlet should be dissipated to a level nearly equal to the atmospheric pressure, at
the outlet. To effect this different pressure dissipating mechanisms are used, viz.
* Long narrow flexible PVC or PE tubes (Micro tubes/capillary tubes)
* Nozzles or orifices of small size, varying between 0.4 to 0.6mm.
* Smaller perforations on the trickle line.
* Spiral water paths (Coiled Microtubes or Screw threads)
3. How they are connected to the trickle line
Based on this feature emitters could be:
In - line drippers: where you cut the lateral tube and built the dripper in between.
On - line dripper or side - fitted dripper: where you make an accommodating hole and insert the
emitter.
Internally built in: manufacturers built in the emitters in the drip line
4. Flow regime
This classification is based on whether the flow is laminar, sub laminar, or turbulent. Different
emitters will have different flow regimes.
Generally, emitters are classified as:
- Laminar flow,
- Turbulent,

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- Orifice,
- Vortex,
- Partially pressure compensating, or
- Pressure compensating.
Laminar flow emitters (long path)
- Are long, narrow tubes, and energy is dissipated in the tube.
- The emitter exponent, x, is 1.0, which indicates that flow is directly proportional to
pressure.
- The drawback is that tube diameter is narrow and prone to plugging.
- The tube geometry may be straight (spaghetti tubing) or follow a spiral flow path around
a cylindrical core.
Turbulent flow emitters
- Dissipate energy in turbulent eddies that form in tortuous paths within the emitter.
- The emitter exponent, x, is 0.57
- Are designed so that vortices are set up in the flow path.
- One advantage of turbulent flow emitters is that they have a larger diameter flow path
because energy is dissipated in turbulent eddies rather than in small diameter tubes or
orifices. Thus, they are less likely to plug than laminar flow or orifice emitters.
- Pressure compensating emitters with a diaphragm that retracts until pressurization are even
less likely to have plugging than normal turbulent emitters.
Orifice emitters
- Dissipate energy in a single orifice;
- The diameter is extremely small (less than laminar) and
- These emitters are prone to plugging.
- The flow varies with the square root of pressure so x = 0.5.
Vortex emitters
- Are similar to orifice emitters except that the water passes through one turbulent eddy
before exiting the orifice;
- The turbulent eddy decreases the emitter exponent x to 0.4.
- As with orifice emitters, vortex emitters have a narrow orifice and are prone to plugging.

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Pressure compensating emitters
- Have virtually no change in flow rate over a range of pressures.
- These are emitters with diaphragm closing as pressure increases and vice versa.
Pipelines
Most of the plastic pipelines used in irrigation are composed of the following four kinds of
materials.
- Polyvinyl chloride (PVC)
- Polyethylene, low density (PEb) and high density ( PEh)
- Polypropylene (PP)
- Acrylonitrile - Butadiene - Styrene (ABS)
Of these four, PVC, PEb and PEh are by far the most widely used in trickle irrigation. Because of
its higher hydrostatic design stress, PVC is more economical in large sizes whereas the PE’S (with
much lower design stress) are used mainly for small diameter pipes where flexibility is desired
such as for laterals and sometimes sub mains.
1.5 Economics of trickle system
The cost of the drip irrigation system can vary widely, depending on the crop characteristics and
the type of drip laterals (disposable or permanent tubes). The cost of drip irrigation is about
$2200/ha per hectare for vegetable crops with wider row spacing. For vineyards with narrow row
spacing, the costs can be go up to $3400/ha. For vegetables crops with narrow row spacing (tomato,
pepper, etc.) the cost can vary from $2900 to $4900/ha. For vegetable crops with disposable drip
lines, the cost of replacing the disposable lateral lines can vary from $340 to $450/ha during the
year.
These estimations are for a system of high quality and include pumps, filters, controls, the network
of main lines and emitters. In situations where there is more than one basic pump, sufficient
equipment for filtration and control, costs vary from 20 to 25% less of the calculated expenses.
The typical expenses for operation and maintenance of a drip irrigation system vary widely
depending on the local conditions and the irrigation efficiency.