Wednesday, 11 March 2026

Weekly Irrigation Requirements

Northern Victoria

This update provides reference evapotranspiration (ETo) information to assist with irrigation scheduling for improved yields and higher water productivity.

This information can also be viewed at ExtensionAUS Irrigating Agriculture where an interactive map provides live daily ETo data for any Victorian location.

In this update:

1. Summary
2. Water links
3. Last week’s irrigation requirement
4. Next week’s irrigation requirement
5. Daily ETo and rainfall
6. Soil temperature
7. Seven-day forecast – Cobram.

1.  Summary 

• Plant water requirement for the past 7 days was 33 mm.
  (for a reference crop of pasture at Kyabram).
• Forecast ETo for the next 7 days is 36 mm.
  (cumulative ETo at Kyabram).
• Current surface-irrigation interval is 11 days.
  (for Kyabram at 40mm refill point).‘Water requirement’ for our reference crop of pasture (ETo) at Kyabram*

Table 1: Water requirement for our reference crop of pasture (ETo) at Kyabram* * See the tables and graphs below for ETo (and rainfall) at more locations.

2. Water links 

Engage – 2026 Basin Plan Review: Have Your Say

Events – Irrigating Agriculture Events Page
Resources – Irrigation System Selection & Design Guidelines

3.  Last week’s reference evapotranspiration (ETo) 

Wednesday 4 March – Tuesday 10 March

Table 2: Total evapotranspiration values relating to Wednesday 4 March – Tuesday 10 March

4.  Next week’s forecast reference evapotranspiration (ETo)

Wednesday 11 March – Tuesday 17 March

Table 3: Total evapotranspiration values relating to Wednesday 11 March – Tuesday 17 March

5.  Daily evapotranspiration (ETo) and rainfall – last week and next week 

Figure 1: Total evapotranspiration and rainfall values relating to Wednesday 4 March to Tuesday 17 of March – Deniliquin

Figure 2: Total evapotranspiration and rainfall values relating to Wednesday 4 March to Tuesday 17 of March – Kyabram

Figure 3: Total evapotranspiration and rainfall values relating to Wednesday 4 March to Tuesday 17 of March – Tatura

Figure 4: Total evapotranspiration and rainfall values relating to Wednesday 4 March to Tuesday 17 of March – Kerang

Figure 5: Total evapotranspiration and rainfall values relating to Wednesday 4 March to Tuesday 17 of March – Echuca

Figure 6: Total evapotranspiration and rainfall values relating to Wednesday 4 March to Tuesday 17 of March – Yarrawalla

Figure 7: Total evapotranspiration and rainfall values relating Wednesday 4 March to Tuesday 17 of March – Numurkah

6.  Soil temperature 

Soil temperature measured at 9 am today (Wednesday):

• Wee Wee Rup (irrigated annual pasture): 24.38°C at 10cm.
• Wandella (irrigated lucerne): 23.6°C at 15cm.

7.  Seven-day forecast – Cobram

Figure 8: Weather forecast temperatures for Cobram from March 11 to March 17 – Source: Weatherzone.

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Disclaimer

The intention of this service is not for the information to be used in isolation when making decisions about irrigation. ETo data provides another handy tool in your irrigation ‘tool box’ and needs to be used in conjunction with other preferred scheduling methods and updated weather information.

This publication is provided solely for information purposes and no representation or warranty is made as to its quality, accuracy, completeness, suitability or fitness for any particular purpose.

You should make your own inquiries as to its appropriateness and suitability for your circumstances.

The State of Victoria as represented by the Department of Energy, Environment and Climate Action (DEECA) accepts no duty of care and disclaims all liability in relation to use of this publication.

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ETo data and associated irrigation information for the locations shown in these updates is updated daily and can be accessed on the Online ETo Tool.

Historic daily ETo and rainfall data is sourced from BoM’s gridded Australian Water Outlook (AWO) service. These figures may change significantly over time, particularly in the first three days, because improvements are made to the dataset as more data is received by the BoM from different weather stations.
Forecast daily ETo and rainfall data is from BoM’s Gridded Evapotranspiration Products derived from the Australian Digital Forecast Database (ADFD), which AgVic receives on a ‘fee for service’ basis.

Reference evapotranspiration (‘ETo’). Refers to the evapotranspiration from an actively growing, well-watered, grass stand 120mm in height.

‘Rainfall R.’ Where a rainfall event is less than 2 mm it is usually not ‘effective’ in terms of adding to the soil moisture reserve (because it is unlikely to penetrate through the crop canopy) and is unlikely to be listed in the tables or graphs. Also be aware that any rain more than that which fills the soil root profile (run-off or deep percolation) is also not ‘effective’ from an irrigation perspective. Because rainfall can vary over short distances, you are encouraged to collect and use your own rainfall figures for your farm.

‘Crop coefficient.’ A crop coefficient refers to your crops relative water use potential. For crops other than pasture refer to Tech Note for discussion of an appropriate crop coefficient. Alternatively, you can use AgVic’s Online ETo Tool Interactive Spreadsheet which provides guidance on which crop coefficient to use for your crop and its stage of development.

The ‘Average (daily) ETo’ is calculated by dividing the total weekly cumulative ETo by 7 days.

To calculate the ‘Required surface irrigation interval’ it is assumed there is 40mm of ‘readily available water’ in the pasture root zone. e.g. Required surface irrigation interval = 40 mm ÷ average (daily) ETo, plus 1 day to allow for excess water to drain away following a surface irrigation event.
Important: The ‘required surface irrigation interval’ shown in these tables is an estimate calculated using cumulative ETo only over seven days and needs to be considered in conjunction with rainfall on your farm.

Rainfall is not included in these estimates. The figures presented are cumulative daily short crop reference evapotranspiration (ETo). Because rainfall can vary over short distances, please collect and use your own rainfall measurements. The rainfall figures in the tables are only a guide.

For more accurate irrigation scheduling particularly in spring and autumn, the cumulative deficit (‘ETo – R’) since the last irrigation usually needs to be calculated over a period longer than 7 days and the irrigation timed when the readily available water (40mm in this case) is depleted.

‘Spray irrigators need/ed to apply.’ This figure is based only on evapotranspiration minus rainfall (‘ETo – R’) for the given week and assumes excellent accuracy in terms of mm water applied, spray uniformity, and application efficiency.

Typically spray uniformity will not be 100% and extra water will need to be applied to best meet plant needs. The ‘spray irrigators need/ed to apply’ figure given in the table also assumes the rainfall is effective and contributes equivalently to the soil moisture reserve, which may not be the case.

In practice, the moisture deficit (or reserve) carried into the season also needs to be considered to ensure there is adequate soil moisture for maximum plant growth and to avoid a ‘green drought.’ It is best to use rainfall measurements collected on your property. Typically, with pressurised irrigation systems, irrigations occur more regularly than with surface irrigation to optimise plant growth.

Due to the cumulative error involved with using ETo data over a period, it is important that other scheduling methods are used in conjunction with ETo data for spray irrigation systems.

‘Next week’s forecast reference evapotranspiration – pasture irrigation requirement.’ Forecast ETo and rainfall data is sourced from AgVic’s online ETo tool, which uses forecast daily ETo data from BoM’s Gridded Evapotranspiration Products derived from the Australian Digital Forecast Database (ADFD). Forecast rainfall is also from BoM’s ADFD.

Tip: To convert mm to megalitres /ha, divide by 100. E.g. 50mm = 0.5ML /ha.

For more information about selecting an appropriate crop coefficient for your particular crop and its stage of development refer to this Tech Note What is evapotranspiration and how do I use it to schedule irrigations?, Ag Vic’s Online ETo Tool Interactive Spreadsheet, or the scientific booklet (FAO56) – Table 12, Chapter 6.