Weekly Irrigation Requirements – Macalister Irrigation District
Macalister ETo Update
6 to 13 February 2019
- Flood irrigation interval for the last week was 10 days
- Spray irrigators needed to have applied on average 28 mm of irrigation water for the week
- The predicted weekly pasture water use for the MID in the next week is 35 mm
- Lake Glenmaggie is at 40%
* These figures are approximate and do not take into account rainfall on farm*
The Odd Spot
The next irrigation discussion group will be held on Thursday 21st February and there will be a change in the topics we plan to cover. It will still be at the AgVic Office in Maffra 11am-1pm, and will include a free BBQ lunch.
We plan to discuss where you all are at with water usage and how best to use what you have left, and good news/ideas that have been used in past dry seasons.
Everyone is very welcome to come along and please bring a friend! Please RSVP for catering purposes to Janice or Alexis on 5147 0800.
Permanent water auction next Tuesday 19th
This year’s permanent water share auction for the MID will be held on Tuesday 19th February at the SRW Maffra office. The following share volumes are available: 269 ML of High and Low Reliability Water Shares (bundled together). All shares will offered in 50ML parcels. To participate in the auction you need to complete a registration form and return it to SRW by 4pm Monday 18 February. Registration is free – www.srw.com.au.
ETo rates falling from January high
Thankfully the ETo rates on average over the last fortnight have been decreasing, with an average of 4 mm per day this week, and a forecast of 5 mm per day next week. Every little bit helps!
ETo – Last Week Totals
| Location | ETo mm | Effective rainfall mm (R) | Dairy pasture coefficient | Required irrigation mm (ETo – R) |
| Tinamba | 23.6 | 27.8 | 1 | 0 |
| East Sale | 33.9 | 18.8 | 1 | 15.1 |
| Boisdale | 27.3 | 23.4 | 1 | 3.9 |
Tip: To convert mm to megalitres/ha, divide by 100. Eg. 50mm = 0.5ML/ha.
Effective rainfall = daily rainfall minus 2mm.
ETₒ and the “crop coefficient” (conversion factor) of 1.0 applies to a healthy productive pasture 12 cm high.
MID average daily pasture water use over the last week was 4 mm/day.
The approximate MID flood irrigation interval based on last week’s daily pasture water use rate was 10 days.
(This figure assumes that 30 mm of readily available water is held in the pasture root zone divided by the 4 mm/day = 8 days and then add an extra two days to account for waterlogging). This does not take into account any rain your farm may have got during the week which will extend the interval.
Spray Irrigators in the MID needed to have applied on average 28 mm of irrigation water for the week to meet pasture water use (4 x 7).
This irrigation figure does not take into account any rainfall on your farm, which must be subtracted from the required irrigation figure, and assumes that the spray irrigation system is applying water at 100% uniformity.
This figure may be greater depending on specific spray irrigation system uniformity.
FORECAST ETo
For Thursday 14 January to Wednesday 20 Feburary.
The predicted weekly pasture water use for the Macalister Irrigation District is 35 mm per hectare (0.35 ML/ha), or a pasture water use rate of 5 mm/day.
The intention of this service is not for the information to be used in isolation when making decisions about irrigation scheduling.
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 particular circumstances. The State of Victoria as represented by its Department of Economic Development, Jobs, Transport and Resources accepts no duty of care and disclaims all liability in relation to use of this publication.
AgVic also provides weekly ET email updates for North East Victoria (contact dennis.watson@ecodev.vic.gov.au), Northern Victoria (robert.oconnor@ecodev.vic.gov.au) and the Mallee (maxine.schache@ecodev.vic.gov.au).
You can also follow on Twitter and Facebook.
Further information:
For more detail about using evapotranspiration data refer to this Agriculture Victoria fact sheet “What is evapotranspiration and how do I use it to schedule irrigations”or this scientific paper.
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