Efficient irrigation systems save money. However, many systems are not efficient resulting in wasted water,
increased power bills and reduced profits. The efficiency of the five common irrigation system types used in
Hawke’s Bay orchards were evaluated during the 2006/07 season. The Sustainable Farming Fund, NZPipfruit, Summerfruit NZ and Hawke’s Bay Regional Council funded the evaluations.
The five common irrigation system types evaluated were:
• Microsprinkler (continuous wetted strip)
• Microsprinkler (overlapping sprinklers)
• Drip tape
• Hand shift pipes
• Travelling under tree irrigators
Key Findings
System performance varied dramatically. Distribution Uniformity (how much water one tree receives in relation to another) is a key indicator of system performance. Table 1 shows the results of each of the evaluations. Table 2 shows interpretation ranges for these.
Table 1: Results of the evaluations
Table 2: Interpretation of Field Emission Uniformity results: Drip-micro irrigation
Note: A well-designed and maintained microsprinkler system should have a distribution/emitter uniformity
greater than 0.85. A figure of 0.80 is generally regarded as being the benchmark for adequate system
performance for all system types.
How Can System Performance Be Improved?
In most cases system performance can be greatly improved by undertaking simple, low cost measures:
Mobile Systems
(Hand Shift Pipes & Travelling Irrigators)
Standardise pipe length and nozzle size
Standard nozzle sizes and pipe lengths ensure you are able to apply the same amount of water to each tree.
It is impossible to obtain a uniform sprinkler pattern without doing this.
Determine ideal set spacings (distance between irrigation rows)
Both mobile systems tried to water too many rows at once. The far rows received only half as much irrigation
as the near ones. Reducing by one row would allow all rows to receive the same amount of water. The only
way to determine the correct spacing is to measure an irrigation event using a grid of catch cans.
Use alternate sets
Run the irrigation line in a different row each time to ensure that areas that receive the least water during one
event receive the most the next time and vice versa. Reducing the return time, so the drier areas don’t run of water
out before you get back, also needs to be considered.
Set pressure using pressure gauges
Estimating pressures of mobile pumps by the PTO/engine speed is not satisfactory. A pressure gauge needs
to be inserted just before the first sprinkler (at the end of the main line) to ensure you are applying the same
amount of water for each irrigation event. A permanent pressure test point is a cheap and practical means of
doing this. The PTO/engine speed can be adjusted accordingly to get the right pressure at the sprinkler.
Minimise canopy/weed interference
Good weed control and a canopy maintained above the irrigation zone are essential when using irrigation
systems that apply water over a number of rows (this is not always easy or practical with some varieties).
Interception/interference can have a major impact on the evenness of the application, especially if woody weeds
are present.
Under tree travelling irrigator
Hand shift pipes
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Microsprinkler and Drip Systems
Microsprinkler evaluation (continuous wetted strip)
Microsprinkler evaluation (overlapping)
Regularly flush/clean filters and laterals
Cleanliness is extremely important with microspinkler and drip systems. Sprinklers and drippers have small
orifices that block easily. Blockages affect the evenness of application (how much one tree receives in relation to another) and ultimately crop quality.
Check filters and flush laterals annually at least (if you have a river take without a gallery, weekly flushes/
checks are required). When flushing laterals, only open a few at a time to ensure there is enough pressure
and flow to flush any debris from the line.
Consider a total cleaning of your system (acid injection/chlorination) at least every five years (frequency is
dependent on irrigation water quality). This will remove precipitates (lime scale and iron) and bacteria/algae
growth, the main causes of blockages. You may prefer to get a professional service to do this for you.
Drip tape irreparably blocked after one seasons use
River take with no filters
Blocked filter
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Check block pressures are set as per system design.
Pressure has a major effect on the amount of water
applied. For example, one system had a block whose
pressure regulator was set at 150kPa instead of 200kPa
as per system design. This block was receiving 10mm
per irrigation event instead of 15mm. To the eye you
could not see any obvious difference between the block
outputs.
Checking block pressure is very easy; all you need is
a pressure gauge with a pressure test needle ($50). A
well-designed system should have pressure test points
installed after the valve so you can test block pressures
and adjust accordingly. If you have no pressure test
points at the valve, you can either install them ($10
each) or remove the sprinkler nearest to the valve and
test the pressure through this.
Pressure test point and pressure gauge
with test needle
What is an Irrigation Evaluation?
Irrigation evaluation is the practice of measuring and
analysing key aspects of irrigation system performance
and management. To effectively manage irrigation you
first have to measure it to determine actual performance. The second step is to identify which factors, if
any, are contributing to less than ideal performance.
Step three determines the relative impact of these
factors, and how they may be addressed.
Why Undertake an Irrigation Evaluation?
There are two areas where improvements in irrigation
efficiency can be made.
• System performance, i.e. is one plant receiving the
same amount of water as another?
• System management, i.e. are the taps turned on and
off at the right time?
Irrigation evaluations allow orchardists to check quality of
design, installation and long-term performance. They also
allow orchardists to demonstrate efficient resource use to
others: consumers, regulators and other resource users.
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Testing block pressure by removing the
sprinkler (the rubber around the needle
is taken from the inside of a pressure
test point)