The Weekly Irrigation Requirements for Northern Victoria have now finished and will recommence at the start of the next irrigation season.

Friday 4 May 2018

Weekly Irrigation Requirement$ Summary – Driving Water Productivity

This update provides ‘reference evapotranspiration’ (ETo) data to assist with improved irrigation scheduling for top growth rates and yields.

This interactive Irrigation Scheduling Tool helps you determine the most productive timing for the next irrigation for your unique circumstances.

Irrigation commentary

Recent plant water requirements

• With shorter day-lengths, less ‘kick’ in the sun and cooler temperatures, plant water requirements are ‘winding down,’ but have not yet reached annual minimums
• Cumulative ETo over the last 7 days at Kyabram was 17mm (or 2.4 mm /day)
• This compares with an April average over the last 7 years of 19mm /week (2.7 mm /day) at Kyabram
• Looking ahead, the ETo average for May and June is 11 mm /week and 8 mm /week (1.6 mm /day and 1.1 mm /day) respectively at Kyabram
• These are much lower than average ETo rates back in January 2018 of 48 mm /week (6.8 mm /day) at Ky

Todays rain

• BoM stations recorded rainfall of 8mm to 12mm on the irrigated plains and up to 70mm in the hills in the last 24 hours (so far)
• Rain in the last 24 hours: Upper Murray – Lake Hume 12mm, Albury 13mm, Thredbo 66mm, Biggara 26mm, Hunters Hill 30mm, Corryong 16mm, Tumbarumba 28mm, Falls Creek 30mm, Mt Buller 40mm.   Goulburn:   Lake Eildon 19mm, Mt Buller 40mm,  Dohertys 33mm, Tonga Bridge 20mm, Jamieson 36mm.   http://www.bom.gov.au/vic/flood/rain_river.shtml

 Centre Pivot /Lateral Move Course

• Irrigators in the Shepparton Irrigation Region have the opportunity to attend a Centre Pivot /Lateral Move Irrigation course at Tatura on 22nd and 23rd May, 2018
• The course is designed for both those who are considering a centre pivot or lateral move system and those who already have one
• To find out if you are eligible for subsidised course costs, please contact Rebecca Pike (AgVic) by Friday 11 May on 03 5482 0426 or email pike@ecodev.vic.gov.au

 Soil temp

• The soil temperature (as measured by a capacitance probe) at 9am this morning under irrigated pasture at Lancaster at 10cm depth was 14oC, the same as last week

Last Week’s Reference Evapotranspiration – Pasture Irrigation Requirement$

 Weekly Totals –  Fri 27 April to Thu 3 May, 2018

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

The “required surface irrigation interval” shown in these tables is based only on cumulative ETo and needs to be considered in conjunction with rainfall on your farm.  For example, this time of the year (Mayil) for each 2mm of effective rain that falls on your property, typically an extra day needs to be added to the “required surface irrigation interval.”

ETo during May at Kyabram over the previous 7 years has averaged 11mm /week or 1.6 mm /day (BoM ETo).  Average ETo for the previous month of April  (for the previous 7 years) is 19 mm /week or 2.7 mm /day.

Next Weeks Forecast Reference Evapotranspiration – Pasture Irrigation Requirement$^¥

Weekly Totals –  Fri 4 May to Thu 10 May, 2018

Daily ETo & rainfall – last week & next week

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* ETo and rainfall data sourced from Bureau of Meteorology http://www.bom.gov.au/watl/eto/

^# ETo and rainfall data sourced from the Queensland government’s SILO web site based on climate data provided by the Bureau of Meteorology.  This is “triangulated” data – based on calculations and measurements from the closest weather stations which are not on-site.  Comment: SILO ETo data generally appears to be slightly lower than BOM ETo data. http://www.longpaddock.qld.gov.au/silo/index.html

⁺ Reference evapotranspiration (“ETo”).  Refer to the ‘Important Background Information’ section above.

^~ “Rainfall R.”  Where a rainfall event is less than 2mm it is unlikely to be listed.  In practice it is not always be the case that all rain contributes to plant available moisture reserves and is available for plant growth.  Any rain in excess of that which fills the soil profile (or reduces ‘cumulative ETo-R’ back below the estimated RAW) needs to be disregarded.  Because rainfall can vary over short distances, irrigators are encouraged to collect and use their own rainfall figures for their farm.

^x  “Dairy pasture crop coefficient.”  Refer to the section above “Crops Other Than Pasture”, for more information.

^ The “Average (daily) ETo” is simply 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.  eg.  40mm  ÷  average (daily) ETo, plus 2 days to allow for excess water to drain away following a surface irrigation event.  (Where SILO ETo data is used – Kerang, Echuca, Yarrawalla and Numurkah, 1day is added rather than 2 days because SILO ETo figures are appearing to be slightly lower than BOM ETo figures.)  The “required surface irrigation interval” is based only on cumulative ETo and needs to be considered in conjunction with past and forecast rainfall for your farm.
^> “Spray irrigators need/ed to apply.”  This figure is based only on evapotranspiration minus rainfall (“ETo – R”) and assumes a good spray uniformity and application efficiency.  If a spray irrigation system has compromised spray uniformity or application efficiency, then more water will need to be applied to best meet plant needs.   Typically with pressurised irrigation systems, irrigations will be applied more regularly than once per week in summer to optimise plant growth.

¥ “Next weeks forecast reference evapotranspiration – pasture irrigation requirement.”  These figures are sourced from the BOM.  Unfortunately this is a ‘fee for service’ arrangement and the forecast ETo figures are not publically available.