New Zealand irrigation
Irrigation uniformity and bucket testing in New Zealand
Every irrigator puts more water in some places than others. A bucket test measures how much, so you can fix the cause, save water and power, and show your council or scheme the system is working.
How a bucket test works
- Lay out catch cans in a line or grid under the irrigator, clear of crop and obstacles.
- Run the irrigator past at its normal settings and note the panel setting, wind and pressure.
- Measure the depth in every can and enter the readings.
- Work out the average depth applied and how evenly it was spread.
Full method: how to bucket test a centre pivot, step by step.
DU and CU, in plain terms
Distribution uniformity (DU, low quarter) is the average of the driest quarter of your readings divided by the average of all of them. If the driest quarter got 8 mm and the average was 10 mm, DU is 80%.
Christiansen's uniformity coefficient (CU) looks at how far every reading sits from the average, not just the driest quarter. Both are in common use in New Zealand.
IrrigationNZ design standards say spray systems, including pivots, should be designed for a minimum DUlq of 80% or CUc of 85% (higher for shallow-rooted crops and frost fighting). Treat these as design targets, not a pass mark for an older machine — the trend across seasons matters most.
Council and scheme compliance
Requirements vary by region, consent, farm plan and scheme. In Canterbury, Environment Canterbury recommends a bucket test once a year and expects a commissioning test on new systems. If a Farm Environment Plan is part of your consent, your audit may look for evidence your irrigation equipment operates efficiently. Some schemes require a test every year. If you're unsure, check your consent conditions or ask your council or scheme.
A paper sheet can't show where or when a test was done. UniformAg Pro records GPS-located cans, photos, the panel setting and an edit history, and produces a PDF report you can hand to an auditor or scheme.
Common questions
- What is a bucket test?
- Catch cans or buckets are laid out under an irrigator, it runs past at normal settings, and the depth caught in each can is measured. The readings show how much water was applied and how evenly.
- What is a good DU for a centre pivot?
- IrrigationNZ design standards say spray systems, including pivots, should be designed for a minimum DUlq of 80% or CUc of 85%. These are design targets for new systems, not a pass or fail mark for an existing machine.
- Do I have to bucket test for my consent?
- It depends on your region, consent conditions, farm plan and scheme. In Canterbury, Environment Canterbury recommends a test once a year, and your Farm Environment Plan audit may look for evidence your irrigation operates efficiently. Check your conditions or ask your council or scheme.
Related guides
- How to bucket test a centre pivot, step by step
- What distribution uniformity means for your water and your yield
- Bucket testing and irrigation compliance in New Zealand
- Reading your bucket test results and deciding what to fix
Sources: IrrigationNZ design standards; Environment Canterbury, “More reasons than ever to be a smart irrigator” and Farm Environment Plans guidance. General information only — check your own consent conditions.