Irrigation is the replacement or supplementation of rainfall with water from another source in
order to grow crops or plants. In contrast, agriculture that relies only on direct rainfall is
referred to as dry land farming or rain fed agriculture. This document provides a review of
major technologies used in irrigation such as overhead irrigation, overhead pivot irrigation,
centre pivot irrigation, drip irrigation and subsurface drip (SDI) irrigation.
This Technical brief gives the description of the main irrigation systems in used and highlights
the major advantages & disadvantages regarding to installation cost, energy use, water
efficiency and uniformity, labour.
Since water remains the main issue in agriculture due to increasing water scarcity, one of the
central objectives of the SAI Platform is to promote a better management of water use in
farming activities. The SAI Platform therefore encourages the adoption of drip irrigation system
(surface & subsurface) due to its higher water efficiency and crop productivity compared to
Obviously, the principal obstacle for farmers to adopt drip systems is currently the important
initial investment. However, it is essential to keep in mind that the system will quickly be
profitable according to higher crop yield, less pumping cost and less water use.
Although drip irrigation suits to almost all type of vegetables and fruits, the method is generally
use for cash crop. Despite this, this technology is currently used to produce cereal (maize, corn).
Although there are many definitions of irrigation efficiency, they can be grouped into
three main categories: irrigation efficiency, application efficiency and distribution
efficiency (or uniformity).
In general, irrigation efficiency is related to the percentage of water delivered to the field
that is used beneficially. These definitions are more relevant when considering seasonal
water allocation or seasonal water use.
Where the focus is on the performance of a single event, application efficiency (AE) is
most commonly used. In broad terms, application efficiency is the percentage of water
delivered to the field that is used by the crop.
Distribution uniformity (DU) is an expression that describes the evenness of irrigation
water application to a crop over a specified area.
Cost -Variable depending on the system.
Description - Sprinkler irrigation is a method of applying irrigation water which is similar to natural
rainfall. Water is distributed through a system of pipes by pumping and is sprayed above
the crop by an impact sprinkler.
pressure & flow
Impact sprinklers (guns) operate at:
- pressures of about 5 to 9 bar (70 to 130 psi).
- flows of 3 to 76 l/s (10.8 to 273.6 m3
/h ; 39.6 to 1003 gmp).
- nozzle diameter of 10 to 50mm (0.39 to 1.96 inch).
Remarks & Recommendations
- The nozzle is that part of a sprinkler which actually distributes the water. The discharge opening or
orifice used on a sprinkler to control the volume of discharge, distribution pattern, diameter and droplet
size. The volume of discharge from the sprinkler is primarily a function of nozzle size and pressure.
Wetted diameter is a function of nozzle size and pressure, but it is also greatly affected by the type of
- Guns also have relatively low initial costs as compared to permanent or portable solid set irrigation
systems, and they require less labor than portable multi-sprinkler systems because they must be
manually moved between sets.
- Hand-moved (portable) guns are most adaptable to relatively small acreages.
- More water is lost during high evaporative demand periods (hot, dry days) than during low demand
periods (cool, cloudy, humid days). Thus, sprinkler irrigation systems usually apply water more efficiently at night (and early mornings and late evenings) than during the day.
- More water is lost by sprinklers that discharge water at high angles, over great distances, and at great
heights above the ground surface because of greater opportunity time for evaporation. In addition,
greater water losses occur from systems which discharge a greater proportion of small droplet sizes
because small droplets are more readily carried by wind and they expose more surface area to the
atmosphere for evaporation.
- Application efficiencies will be reduced if water falls between widely spaced plants or outside the crop
root zone, as in the cases when irrigating young crops.
- Sprinkler irrigation application efficiencies are reduced by non uniform water application. Non uniform
application causes some areas to be over-irrigated (and lose water and nutrients to deep percolation)
while other areas are under-irrigated (reducing crop yields). Thus, system design affects application
efficiency. Non uniform water application occurs when sprinklers are not properly selected nor properly
matched to the sprinkler spacing and operating pressure used.
- Non uniformity also occurs if pressure losses within the irrigation system are excessive (due either to
friction losses or elevation changes).
- Other causes of non uniformity such as clogged nozzles or enlarged nozzles from abrasion by pumping
sand also reduce application efficiencies.
- Sprinkler water application patterns must overlap sufficiently (typically about 50%) to apply water
uniformly. Because of this need for overlap, non uniformity occurs at the edges of fields where overlap
is not possible.
- Part-circle sprinklers can be used at the edges of fields to improve uniformity, but they are more
mechanically complicated and more expensive than full-circle sprinklers.
- Low labour and maintenance with fixed irrigation sprinklers.
- Guns irrigation system are flexible, they allow irrigation of oddly-shaped fields (but
wheel sprinkler can be used with a maximum of 15o
- Can be used for frost control.
- Relatively high pumping costs
- Incorrect operating pressure, and component wear or failure can still distort application
patterns and reduce uniformity and application efficiency leading to important water
and chemicals loses.
- Gun irrigation systems require large energy inputs per unit of water delivered because of
their high operating pressures.
- Relatively high labor requirements, both to move the portable guns between sets and to
set up the self-propelled (travelling) guns.
- During water applications, sprinkler irrigation systems lose water due to evaporation
and wind drift. More water is lost during windy conditions than calm conditions.
- Wet leaves from irrigation favours foliar diseases.
- Apparition of white leaves spot if irrigation water contains bicarbonate.
- Can damage fruit close to harvest.
CENTRE PIVOT IRRIGATION
The centre pivot irrigation is a form of overhead sprinkler that apply small amount of
water at frequent intervals to a unit area of crop. It consists of a span of pipe which is
supported on wheeled frame towers and is self propelled around a central pivot point.
Water is usually delivered to the pivot point through a buried mainline pipe.
Centre pivot irrigation operate at:
- pressures 0.7 to 5.5 bar (10 to 80 psi).
- center pivot systems are either electric or oil-drive.
- the system may vary in length from approximatively 60m to 790m and is capable
to irrigate a circular area up to 200 ha (500 acres).
It exists 3 main types of centre pivot irrigation system:
- high pressure sprinklers
- low spray sprinklers
- LEPA system (Low Energy Precision Application)
(For more informations on their specific performances, see paper: Optimal
performances from center pivot sprinklers systems).
Drip irrigation is sometimes called trickle irrigation and involves dripping water onto the
soil at very low rates (2-20 liters/hour) from a system of small diameter plastic pipes
fitted with outlets called emitters or drippers. Water is applied at frequent intervals near
the root zone of plant over a long period, so that only part of the soil in which the roots
grow is wetted.
Drip irrigation system operate at:
- Pressures typically range from 0.2 to 2 bars.
Emitter discharges are in the form of small streams or individual drops, with flow rates
ranging from 1 l/h to 7 l/h, but most commonly being 3.5 l/h (0.013 gmp)
Conventional drip irrigation systems cost between $1,200 and $3,000 per hectare
+High water application efficiency ~ 85% - prevent losses due to evaporation or run-off,
and if the flow rates are set correctly, water losses due to deep percolation ( i.e. water
penetrating the soil below the root system and flowing into the water table) can be
+ Highly uniform distribution of water.
Usually operated at lower pressure than other types of pressurized irrigation => reduce
Improved fertilizer and pesticide management – Precise and more timely application of
fertilizer and pesticide result in a higher efficacy, and may also reduce their use.
Less water quality hazards - runoff into stream is reduced or eliminate and there is less
nutrient and chemical leaching due to deep percolation.
Smaller and more frequent irrigation application may reduce salinity hazards and
minimize soil erosion.
+ Drip irrigation can be use on hilly land.
+ Water efficiency not affected by windy conditions, hot and dry days.+ Foliage remains dry thus reducing the risk of diseases.
+ Programmable system – Automatisation possible.
Drip irrigation also allows the grower to customize an irrigation program most
beneficial to each crop.
Drip can provides an ideal moist environment for the roots which optimize growth and
thus can increase crop yield.
Drip allow to control where the water is applied which help minimizing weed growth.
- High initial investment.
- Timely and consistent maintenance and repairs are a requirement.
Filtrations issues - Clogging of water emitters if water is not properly filtered and the
equipment not properly maintained.
- Longevity of the system is variable. The PVC lines are often damage by roots.
- Application efficiencies of drip systems are primarily dependent on the design of the
systems and on their maintenance and management.
- Need to be trained to the system.
Remarks & Recommendation
- Length of lateral lines should not exceed the manufacturer's recommendations for the specific tape
used. Excessive length of laterals will result in poor uniformity and uneven water application. As a result,
the amount of water applied by the emitters in the last section of the lateral will be significantly reduced
when compared with the amount of water applied by the emitters close to the lateral entrance.
- All delivery lines (mains and submains) should be sized to avoid excessive pressure losses and
velocities. Since the flow rate of the emitters is usually a function of the pressure, the water application
at the beginning of the line may be very different from the water application at the end of the line which
results in poor application uniformity.
- The maximum size of the zones depends on the flow rate from the well. The water flow rate from an
existing water pump limits the maximum size of the irrigation zone.
- Zones should be approximately the same size. Variation in crop zone sizes will reduce the efficiency of
pumpoperation. When all zones are of the same size, pipe sizes and system cost will normally be
- Pressure regulators may be required if the pressure produced by the pump is too large or if zones vary
greatly in size.
- Drip irrigation systems require filtration. Selection of filters depends on water source and water quality.
Surface water normally requires sand media filters to trap organic materials such as algae, bacteria, and
other organic debris. Screen or disk filters are usually sufficient for well water.
- An irrigation system should include an injection port to allow for injection of fertilizer and also of
chlorine or other chemicals to clean the pipes (to avoid clogging).
- Any irrigation system that will be injecting fertilizers or toxic chemicals is required to be equipped
with proper backflow and anti-siphon equipment to prevent the chemicals from contaminating the
- When preparing chemicals to clean the pipes, DO NOT MIX ACIDE AND CHLORINE IN THE SAME
- Flowmeters and pressure gauges should be used to help manage the system. Sudden changes in water
flow rates or pressures indicate system problems. These problems usually require immediate attention.
For example, an increase in flow rate may be a sign of a broken pipeline, whereas, a gradual decrease
may indicate plugging problems. Flowmeters are also a necessary tool for proper irrigation scheduling. It is important to know how much water is applied to each zone with every irrigation cycle. The duration
of the cycle may not be sufficient, especially if the flow rate is gradually decreasing due to plugging of
- Air release valve installed at the highest point on the mainline is necessary to avoid suction of soil into
the emitters when the system is shut off.
- Flush the drip line once a month by opening a portion of the tape at a time and allowing the higer
velocity water to wash out the sediment.
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