Instructions:  1) Enter your “target refill point.” (The hover text will guide your choice.)  2) Choose your “Crop coefficient.” (The hover text will guide your choice.)  3) Click on the appropriate box in the left-hand-column to indicate the date of your last irrigation.  4) Enter your own rainfall if different to the “BoM rain (mm)”.

Next irrigation:  The due-date for your next irrigation is then shown in the graph where the green line (“cumulative deficit”) intersects the red line (“target irrigation refill point”), or in the “Cumulative deficit (mm)” column on the date where the colour coding turns red.

Allowing for drainage:  For practical reasons, the calculation of the irrigation deficit (cumulative ‘ETc – R’) commences the day immediately after irrigation.  If irrigation water is slow to drain from your bays (eg. longer than 1 day), you may need to increase the suggested target irrigation refill point to allow for this.

Data source:  All evapotranspiration and rainfall data used on this page is provided by the Bureau of Meteorology.  Historic daily ETo and rainfall data is sourced from BoM’s Australian Water Outlook, which is a free service.  Historical daily ETo and rainfall 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 data is from BoM’s Gridded Evapotranspiration Products derived from the Australian Digital Forecast Database (ADFD).  Forecast rainfall is also from the ADFD.  The ADFD data is acquired by AgVic on a fee for service basis.  Because rainfall can vary over a short distance, it is preferable to collect and use your own rainfall data for irrigation scheduling purposes.

Use with care:  This tool only provides a guide and needs to be used in conjunction with other preferred irrigation scheduling methods.  You should make your own enquires as to the appropriateness and suitability of this tool for your particular circumstances.

Incomplete data displayed?:  There may be interruptions to the supply of historic data (“past week”) to this ETo Tool due to an upgrade being carried out by our data provider, the Bureau of Meteorology, to their weather data generating system during September, October and November 2024.  Thanks for your patience, and apologies for any inconvenience.  The Bureau is working hard to minimise these interruptions.  We look forward to an  improved data service when the upgrade is complete.  In the meantime, if there are data interruptions, alternative ETo data can be sourced from BoM watl and /or SILO.  Currently this Tool only provides complete data sets for Victorian locations.    

Pilot:  This tool is currently being piloted and is only in draft form.