Evaluating
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3 min read
Irrigation systems require suitable application depth, rate, and return periods to meet soil, plant, and climate needs. This page encourages evaluating your system against its design specifications to find potential improvements. A detailed evaluation can be completed independently using farmer-focused guidelines, or by an irrigation consultant. The 'bucket test' is a highly recommended annual evaluation method for checking the application depth, rate, and uniformity of your irrigation system. Various tools, like the 'Check-it bucket test' app from IrrigationNZ or the 'DIY irrigation evaluation guide', are available to help with this process.
An irrigation system that has an appropriate application depth, rate and return period to match the soil characteristics, plant demands and climate needs will be more able to maintain soil moisture levels.
An evaluation requires knowing what the system is specified or designed to do, and checking it is performing to that level. It will also identify areas for improvement.
A detailed system evaluation can be completed by an irrigation consultant or a farmer can carry out their own, using instructions and guidelines developed for farmers.
The table below identifies areas where water losses occur in an irrigation system, and typical amounts. The best ways to improve water use efficiency are to improve how evenly the water is applied, and to optimise the application rate and depth of your system.
Expected water losses on spray irrigation systems
| Where water loss occurs | Range | Typical |
|
Uneven application (non-uniform distribution) |
5-30% | 15% |
| Excessive application depth | 0-50% | 10% |
| Losses from open races | 0-30% | 10% |
| Blown away by wind | 0-20% | <5% |
| Surface run-off | 0-10% | <5% |
| Leaking pipes | 0-10% | <1% |
| Evaporation in the air | 0-10% | <3% |
| Water non-target areas | 0-5% | <2% |
| Interception by plants | 0-3% | <2% |
Bucket test
A bucket test is a great way to evaluate your system. It should be done at least once a year to ensure that the system is in top shape.
Carrying out a ‘bucket test’ will help determine the application depth, rate and how uniformly water is being applied during an irrigation event. The ‘bucket test’ method is based on collecting irrigation water strategically placed buckets and measuring water is collected over a certain period of time.
How to do a bucket test
There are a number of different ways that you can complete a bucket test on your irrigation system.
- Download the Check-it bucket test app from IrrigationNZ. The app steps you through the bucket test process and calculates your results.
- IrrigationNZ also has a number of other e-learning resources to help you evaluate your irrigation system.
- Alternatively, download and print the DIY irrigation evaluation guide to work through the bucket test process and calculations for your irrigation system.
- DairyNZ also has an Irrigation bucket test calculator which enables farmers to undertake the ‘bucket test’ and enter their data and have results calculated for them.
Reviewing the results
The most common signs of poor performance are:
- pump is operating under-pressure or under-flow
- irrigator is operating under-pressure or under-flow
- incorrect depth applied
- off-target irrigation
- ponding or runoff
- brown grass or dry ground.
The most common reasons for under-performance are:
- incorrect sprinkler nozzle selection
- maintenance has fallen behind e.g. broken sprinklers, blocked screens or worn pumps
- pushing the system too hard. For example, adding new sprinklers without upgrading mainline or pumps
- long return interval. Irrigators that take too long to come back around, resulting in stressed plants
- poor sprinkler spacing. Too little overlap between sprinklers leaves dry areas in between
- application depth is too high and some of the applied water is lost to drainage
- wear and tear due to normal system operation. Equipment just wears out overtime, especially pumps
- the system simply isn’t designed to do what it needs to do (or what it was designed to do).
What can I do about it?
Options for making improvement range from adding to the existing system (e.g. including another rotary boom) in order to reduce the return period and/or the application depth per run, through to a total change in irrigation type e.g. border dyke to spray irrigation.
It is important to remember that changing or improving irrigation system capability should not be done in isolation, but incorporated with soil moisture monitoring and continual performance evaluation to achieve maximum improvements in irrigation efficiency.
Firstly, it is important to:
- keep up-to-speed with system maintenance
- check the system regularly
- keep records so that you can compare new readings to past readings
- consult your system supplier before making any changes to the system.
If simple problems are encountered, you can fix them yourself. However, the system supplier should be the usual first port of call for anything more complex.
Call the irrigation system supplier when:
- the design information has not been supplied
- instructions for operating or maintaining the system have not been provided
- the performance measure does not match what the supplier said the system would do
- specific components are not working or are worn out
Sometimes you need to call in a third-party irrigation expert.
Ask for outside advice when:
- the cause of the problem cannot be found using the basic steps or by the system supplier
- you and the system supplier cannot agree on who is responsible for a problem with the system
- the system is very complex or has multiple suppliers
- the basic checks show good performance, but you want more detailed checks to maximise efficiency.