For this article we thought it would be useful to share some insights from the irrigator performance tests we have undertaken this season.
All the pivots we’ve tested were potentially very efficient irrigation systems, however, for a number of older machines (+15,000 hours) we are starting to see performance impacts from worn nozzles and regulators (particularly for surface water takes), alongside maintenance issues such as broken rotators and hooked up or split droppers. Remember 70% of a pivot’s performance is directly due to how its sprinkler pack is performing, so you need to check and test these at least annually.
The other issue we are finding is sprinklers and regulators not being replaced correctly. Each regulator has a pressure rating on it and each nozzle a number, so make sure you replace like with like. We have also come across a couple of pivots where the sprinkler pack has been installed incorrectly (one along the length the other on three individual spans). Spending an hour walking along your pivot checking each regulator and nozzle with the sprinkler chart is likely one of the most productive investments you will make on your farm each season!
Rotorainers can be very efficient irrigation systems providing they are well maintained and operated at the correct pressure and flow rate. The key information you need to know for a Rotorainer is its design pressure and flow rate. Typically, both M125 and M250 are designed to operate at 275 kPa (400 psi). All Rotorainers come with a pressure gauge on them, however, as pressure gauges typically do not survive the Canterbury winter, we suggest replacing them with an 8mm tap and keeping a quality 600 kPa pressure gauge in your ute instead. This lets you regularly check the pressure at the cart with confidence, without the annual cost of replacing pressure gauges.
The flow rate required for your Rotorainer will depend upon how it has been nozzled, but typically anything less than 18 l/s for an M125 and 25 l/s for an M250 means you will have insufficient flow to drive them, and therefore excessive application depths and poor uniformity. The other common finding through our Rotorainer assessments is the depth being applied is greater than the soils Readily Available Water. In many instances the machine was running at 4 or 5 cams instead of at 8 cams (full speed) so it was an operational issue – staff that were unaware of the importance of the cam setting.
Turbo Rains also have the potential to be efficient, however we find their main challenge is the high instantaneous application rate (IAR). At 40l/s (how most were setup) the IAR is around 95 mm per hour. For most Canterbury soils this is way to high and results in much of the water applied running-off into low spots or preferential flow through the soil. To resolve this, you can install a new drive turbine with a speed controller, and nozzle the Turbo Rain back (preferably replacing the flood jet nozzle with sprinklers).