An underperforming centre pivot or lateral move (CPLM) irrigation system can be costly. Poor performance can occur throughout the system including in the pump, motor, sprinklers, drive mechanism, and end gun. This can impact your system’s ability to operate at the expected capacity and can result in poor crop emergence, growth and yield; high water use; and high energy consumption.
This article provides a brief overview of what aspects of a CPLM to check, and the process for doing so. Further information can be found in the Agriculture Victoria Centre Pivot or Lateral Move Performance Check Factsheet.
System capacity is the maximum depth of water that can be applied to the entire irrigated area in one day, i.e., a system capacity of 12 mm/day means the machine cannot apply more than 12 mm in 24 hours over the entire irrigated area.
It is important to understand and design for the ‘managed system capacity’ for your system. This depends on the water requirement of your crop, the application efficiency and the operating hours of the system. These are discussed in detail in the Centre Pivot and Lateral Move System Capacity Fact Sheet.
Pump and Motor
Note the pump and motor specifications and ensure that they match those in the design. Many cases of poor CPLM performance are due to incorrect pump size. Look into the flow rate versus system head characteristic curves from the pump manufacturers and make sure that it is performing accordingly.
Measure the flow rate shown by the flow meter when the system is operating (where there is a flow meter fitted), with and without the end-gun operating, (if fitted). The flow rate measured should be consistent with the system design – if it is not, either the system is not operating as designed, or the flow meter is inaccurate. It is important to resolve which is the case, and why.
If your meter does not indicate the flow rate you can refer to the CPLM Performance Check Fact Sheet for instructions on how to calculate it manually.
The sprinklers and regulators should be those specified, with the nozzle sizes (or numbers) in the correct positions as designed. If a dry-wheel pack is fitted (recommended), ensure that the half-throw sprinklers are aligned correctly – pointing away from the towers or “behind” the towers if on boombacks.
The sprinkler package represents 7% of capital cost of a CPLM system but is responsible for 70% of irrigation performance, so it is worth ensuring it is working as designed.
Read the pressure shown on pressure gauges at the pump, at the Pivot centre and near the end of the pivot with the end-gun operating (if fitted). The pressures should be within 5% of the design pressure, after correcting for the elevation of the gauge (see CPLM Performance Check Fact Sheet).
If your pressure is less than designed it could be affecting the uniformity, particularly on higher ground or when the end gun is operating. If your pressure is higher than required, your pumping costs will be higher than necessary.
Application depth can be measured by placing catch cans or rain gauges at several points along the span-pipe for the duration of a pass. Make sure that the sprinkler distribution pattern passes completely over the cans.
From the catch can readings, compare the average depth applied to the depth indicated on the control panel. If the average depth differs by more than 5 % from the expected depth (according to the supplied chart), check that the speed of the outer tower is as specified for the required depth.
Measure the average speed of the outer tower by measuring the distance travelled in say 5 minutes.
For example, 8.7 m in 5 minutes = 1.74 m/minute.
Check this against your speed control dial or chart. If it is not within 5 %, you can use your measured speed to correct your speed and application rates or check with your supplier.
The distribution uniformity of a new pivot should be 90% or better and is measured by comparing the depth of water applied at various points in a field.
If you are concerned about your pivot’s distribution uniformity, check with your supplier or seek advice from Agriculture Victoria Irrigation Extension Officers.
End-guns typically exhibit poor uniformity as well as reduced pressure at the end of the boom. Therefore, it is recommended to not install an end-gun or remove it if installed. If an end-gun is fitted, it should have a booster pump, specified at the design stage.
Calculate the energy consumed by the system:
- For an electric machine, read the electricity and flow meter meters at the start and end of an irrigation. Calculate the electricity consumption (kWh) per ML pumped. This will should be in the order of 140 kWh/ML for a 35 m (50 psi) system, or 4 kWh/ML/m of head.
- For a diesel-powered system, measure the fuel used for a given volume of water pumped, and calculate the fuel consumption per ML pumped (l/ML). This should be in the order of 40 l/ML for a 35 m (50 psi) system, or 1.1 l/ML/m of head. A modern turbo-charged diesel may be 10% more efficient than this.
Content sources and further information
For more information on managed system capacity see the Centre Pivot and Lateral Move System Capacity Factsheet.pdf
For more information or for assistance checking your CPLM system, contact Agriculture Victoria irrigation extension officers:
Echuca: 03 5482 1922
Kerang: 03 5473 0180
Maffra: 03 5147 0800
Mildura/Irymple: 03 5051 4500
Tatura: 03 5833 5222
Rutherglen: 02 6030 4500