Predicting the future key to irrigation efficiency for Vacy dairy farmer

As a volunteer rural firefighter, Peter Williams is used to checking weather forecasts often. As part of that role, it’s important to predict upcoming fire danger from wind, but it’s the predicted rainfall that he’s more concerned with on the Williams’ family dairy farm. 

Located in Vacy in the lower Hunter Valley, New South Wales, Peter has been active on the farm since leaving high school and milks between 300-350 jersey cows all year round.

Because of its location and soil, irrigation is essential to the productivity of the dairy farm.

“We irrigate between 150 to 200 hectares of our farm, and we wouldn’t survive without it. Most of the area we irrigate is undulating hills, and as we’re always saying, we’re about two weeks away from drought every time it stops raining,” Peter said. “If we couldn’t irrigate, we’d be out of feed very quickly.”

Forecasting ahead

Knowing when to irrigate is essential to getting the most out of your water, and Peter achieves this by utilising the weather forecasts provided by SWAN systems, delivered daily straight to his e-mail. 

He found out about the free service through his involvement as a reference group member of the Smarter Irrigation for Profit (SIP2) Dairy Optimisation Site at Tocal, NSW. 

“We start irrigating early, and don’t let the soil moisture get too low. Our light, shallow soils only hold a small amount of water, and you can’t hang off irrigating and hope for rain,” Peter said. “We signed up for the SWAN e-mail forecasts about twelve months ago. We’ve found it really useful.”

“Because of the way they structure the forecasts – they use a percentage to show the chance of moisture as well as the amount - it gives you a really accurate outlook for the week on what rainfall you’re expected to get.” 

“Another great thing about the forecasts is SWAN is quick to adapt. If the forecast changes, they’ll let you know, and not keep you in the dark. It allows you to adapt on a day-to-day basis,” Peter said.

Having trust in the forecasts is what gives Peter confidence in his irrigation scheduling. The soils across his farm are mostly a light loam soil, with a sandstone base. 
“Because of the texture of the soil, the structure we’ve got, and the climate we can lose our soil moisture in the middle of summer in three or four days.” Peter said. “The grass reacts very quickly to a moisture deficiency and that’s where the SWAN forecasts come in. The SWAN forecast provides us with a pretty accurate evapotranspiration (ETo) prediction for the coming seven days, along with rainfall. A quick calculation can determine what the moisture short-fall will be, and we schedule to at least fill that gap between ETo and rainfall with supplement irrigation.” 

Understanding Evapotranspiration and how it effects irrigation scheduling

While the SWAN forecasts feature predictions on chance of rain, range and estimated rainfall, it is the predicted ETo for the days ahead that has provided the most benefit
Understanding water inputs and losses from the soil is integral to knowing how much irrigation is needed to keep soils within the Readily Available Water (RAW) zone under irrigation. The RAW is the amount of water held in the soil profile that the plants can easily access and is determined by the depth of the pasture roots and the soil texture. It can be likened to the soil “bucket”.  ETo is a determination of how much moisture will be lost from the soil in millimetres per day, through plant use and evaporation- what can be lost from the soil “bucket” daily. 

“Now that we’ve installed centre pivots on our farm, we’re able to be really accurate with our irrigation coverage. By using the ETo forecasts, we’re able to better predict how much irrigation water is required to keep soil moisture within RAW and therefore keep our pastures growing at an optimal rate,” Peter said.
“Combined with the other parts of the forecast, it gives us confidence that our water budget is correct. The chance of rain, and how much, together with the ETo forecast tells us if we need to irrigate in the next seven days, how much water to irrigate with, and how long it’ll last,” he said.

Forecasting to save water, and money

“We’re on contract with our power company, and the network charges for essential energy are at a fixed, non-negotiable price. We pay quite a large fee every month we irrigate once we commence the season, whether we irrigate one day in the month or 15 days in the month, and that all adds up. This means we have been really cautious in the past to start-up irrigation too early in the season as once we start, our power costs go up across the farm.”

“With the SWAN forecasts it takes the tough decision of when to start up irrigation out of our hands. If we need to commence to ensure we keep growth rates up and production going, then the additional power costs are out-weighed by the results in the VAT and opportunities to conserve dry matter” Peter said. 

While knowing when irrigation is necessary for the drier months, it sometimes proves to be the opposite in the autumn for dairy irrigators of the Hunter and NSW north coast. Using weather predictions to refrain from irrigating to avoid saturation is also important. East Coast Lows are part and parcel of autumn in this dairy region of Australia. Allowing room in the soil “bucket” to capture moisture from predicted rainfall events is an integral management strategy and can also help to keep power costs down.    

“There’s nothing worse than starting to irrigate, and then it starts to rain right after.”

“Being able to accurately predict when it’ll be dry gives us confidence to know that the water, and the energy costs associated, won’t be wasted. It mitigates the risk involved, especially on our bottom line,” he said.

Getting the most out of your irrigation

SWAN systems provide e-mail forecasts direct to your inbox daily, but also have more in depth software available for water and nutrient management. Find out more at

The SWAN systems are part of a range of tools and resources being tested at Smarter Irrigation for Profit 2 (SIP2) sites across Australia, to optimise irrigation efficiency on dairy farms. 

SIP2 is supported by funding from the Australian Government Department of Agriculture Water and the Environment as part of its Rural R&D for Profit program, and Dairy Australia.

To find out more about the project, and find the tools and resources that will help you get more crop for your drop, visit Smarter Irrigation for Profit 2.



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