Centre Pivot is the most popular method of irrigation in the South East, being used for approximately half the total irrigated area. The popularity of centre pivot systems is justified by their capacity to provide efficient and uniform application of irrigation water across a wide range of crop types and field conditions. Lower labour requirement in comparison to other irrigation systems is of further benefit.
BUT CONSIDER
- Does the centre pivot meet the water requirements of the crop?
- Is the centre pivot designed according to your site characteristics?
- Has the centre pivot been installed correctly?
- Is the centre pivot performing to specification?
- Has an irrigation schedule or water budget been prepared for the centre pivot and
target crop?
- Is a maintenance program in place?
Regular System Checks
Several aspects of the centre pivot irrigation system should be checked regularly to ensure correct operation. Performing these tasks regularly, say every 100 irrigation hours, allows the operator to identify, locate and rectify any problems across the irrigation system. Things to look at include:
- Flow rate (from meter readings)
- Supply pressure
- End pressure
- Checks for damaged or blocked sprinklers
- Machine maintains alignment and tower drives engage and operate smoothly
- Signs of uneven crop development due to poor irrigation uniformity (donut patterns)
Centre Pivot Performance Evaluation
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| centre pivot approaching line of catch cans - source M Zerk |
- Pump efficiency
- Emitter pressure
- Speed of rotation/travel
- Depth of irrigation per pass
- Average Application Rate (AAR)
- Distribution Uniformity (%)
These can be divided into three parts:
1. System Capacity and Managed System Capacity (mm/day). Calculate flow rate (L/s) and effective irrigated area (ha) to determine system capacity. Then determine Pump Utilisation Ratio (PUR) and application efficiency (Ea %) to determine managed system capacity and see if the system can match the daily crop water requirements.
2. Average Application Rate (AAR mm/h). Calculate AAR of the pivot and compare to the soil infiltration rate. Problems with ponding and runoff can occur if AAR is far in excess of the soil infiltration rate.
3. Distribution Uniformity (DU %). Calculate DU from irrigation water collected in catch cans and compare to industry standards (i.e. DU of at least 85 %). Ensure that sprinkler performance is suitable to promote uniform crop growth.
The correct procedure for taking measurements and recording an accurate assessment of sprinkler performance can be found in the international standard ISO 11545:2001.
Services are available to help determine centre pivot performance.
For more information on the services available, contact:
Michael Zerk
Irrigation Consultant
Rural Solutions SA
Struan Research Centre
p: 08 8762 9176 m: 0428 101 539
