Thursday 18 April 2019

Weekly Irrigation Requirement$ Summary – Driving Water Productivity

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

IRRIGATION SCHEDULING TOOL

• The interactive scheduling tool helps you determine the most productive timing for the next irrigation for your unique circumstances. It uses the same ETo information in the tables below and operates with Microsoft Excel on mobile devices and desktop computers.
• It can be found HERE

 

IRRIGATION COMMENTARY

Keeping an eye on plant water requirements

• Total ETo for the past 7 days was 21mm, which is 4mm less than the previous week (25mm) and equal to the April weekly average (21mm), at Kyabram
• Based on cumulative ETo last week (21mm), the required surface irrigation interval for our reference crop of established pasture is 15 days, at Kyabram
• Forecast cumulative ETo for the next 7 days is 25mm, at Kyabram
• The temperature is forecast to reach 30oC again on Saturday, but Sunday is forecast to be the day with highest ET – over the next 7 days at Kyabram
• Unfortunately, no significant rain is forecast

 

This week’s 2019-20 water allocation announcements

South Australia

• The minimum opening water allocation for SA (“classes 3 & 8”) was announced to be 14%
• There is just under 60% likelihood that SA allocations will increase to 100% next season
• Private carryover in to next irrigation season will be made available to eligible SA irrigators (up to 20% of the volume of entitlement) because the opening allocation is below 50%
• Under the Murray Darling Basin agreement Vic and NSW are jointly responsible for providing 1850GL to SA, but under periods of low inflow (now) shared inflows are equally divided 3 ways
• Click here for more detail

NSW Murray

• The current NSW Murray allocation remains unchanged at 0% general security (GS) allocation
• 2019-20 NSW Murray GS entitlements are likely to open at 0%
• In the scenario of mean (“average”) inflows after 1 July, GS allocations could reach 23% by 1 Nov 2019
• It is estimated NSW Murray carryover will be much less than last year and is likely to be around 15% of GS entitlement. (The maximum permitted is 50%)
• Click here for more detail

 

Water in Focus – information sessions, 23^rd & 24^th April

• These sessions will provide information on how water management works in our region and will include the Murray Darling Basin Plan, allocations, outlooks, trade, pricing, on-farm management and tools
• The sessions will be run at Shepparton, Numurkah, Kyabram, Echuca and Cohuna
• Visit the Murray Dairy web site for more details

 

SOIL TEMPERATURE

• The soil temperature as measured by a capacitance probe at 9am this morning (Thursday 18 April) under irrigated pasture at 10cm depth at Lancaster was 16oC, 3oC warmer than last week (11 April)
• This time last year (18 Apr 2018), the soil temperature was 13oC

 

LAST WEEK’S REFERENCE EVAPOTRANSPIRATION⁺ – Pasture Irrigation Requirement$

Weekly Totals –  Thu 11 Apr to Wed 17 Apr, 2019

Location	ETo+ (mm)	Rainfall~ R (mm)	ETo – R (mm irrigation required)	Dairy x pasture crop coefficient	Average^ ETo  (mm /DAY)	Required@ Surface Irrigation Interval (days)	Spray> irrigators needed to apply (mm)
Deniliquin*	30	0	30	1	4.3	11	30
Kyabram*	21	0	21	1	3.1	15	21
Tatura*	25	0	25	1	3.5	13	25
Kerang#	25	0	25	1	3.6	12	25
Echuca#	24	0	24	1	3.5	13	24
Yarrawalla#	25	0	25	1	3.5	12	25
Numurkah#	25	0	25	1	3.5	12	25

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 calculated only using cumulative ETo, and needs to be considered in conjunction with rainfall on your farm.  For example, this time of the year (April) for each 3mm of effective rain on your property, typically an extra day can be added to the “required surface irrigation interval.”

 

NEXT WEEK’S FORECAST REFERENCE EVAPOTRANSPIRATION – Pasture Irrigation Requirement$^¥

Weekly Totals – Thu 18 Apr to Wed 24 Apr, 2019

Location	ETo (mm)	Rainfall R (mm)	ETo – R (mm irrigation required)	Average ETo (mm /DAY)	Required Surface Irrigation Interval (Days)	> Spray irrigators will need to apply (mm)
Deniliquin	30	0	30	4.3	11	30
Kyabram	25	0	25	3.6	13	25
Tatura	24	0	24	3.4	14	24
Kerang	29	0	29	4.2	12	29
Echuca	27	0	27	3.9	12	27
Yarrawalla	28	0	28	4.0	12	28
Numurkah	26	0	26	3.7	13	26

 

DAILY ETo and rainfall – last week & next week

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You can follow on Twitter and Facebook or to receive this weekly post as a weekly email contact  robert.oconnor@ecodev.vic.gov.au

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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.

The intention of this service is not for this information to be used in isolation when making decisions about irrigation timing.  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.

If you have any questions, comments or feedback related to this service please don’t hesitate to contact me, Rob O’Connor at robert.oconnor@ecodev.vic.gov.au. 

irriSAT (Ctrl click) is a free Australian web based irrigation scheduling tool that uses satellite ‘vision’ to tailor irrigation scheduling for your paddocks and crops.

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

* ETo and rainfall data sourced from the  Bureau of Meteorology

^# 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.

^~ “Rainfall R.”  Where a rainfall event is less than 2mm it is unlikely to be listed.  Any rain in excess of that which fills the soil profile (or reduces ‘cumulative ETo-R’ back below the estimated RAW) also needs to be disregarded in terms of plant available moisture.  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.”  For crops other than pasture refer to this fact sheet for discussion of an appropriate crop coefficient “What is evapotranspiration and how do I use it to schedule irrigations?”

^ 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.  Required surface interval =  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.)
^> “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.

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