Making confident irrigation decisions

When Tom Middlebrook of Bowman Farm and Adam Forbes of Kywong Flat both raised hands at local irrigators meeting to become the long-term 'Scheduling Decision' sites of the project, they were optimistic that it would help to increase their efficient and effective use of available water and help to return greater profits from irrigation.

Whilst neighbours, the management of different water allocation entitlements has delivered two individual stories throughout the project's duration.

There is, however, aligned agreement in the benefits both have gained by maximising their use of available data and weather forecast predictions to better inform the irrigation schedules of their centre pivots.

The project, funded by funding from the Australian Government's National Landcare Program (NLP), supported the installation of capacitance soil moisture probes with real-time logger and telemetry capabilities that can be viewed from a smartphone.

These have played a pivotal role in providing the primary source of data on when to irrigate and the effectiveness of irrigation and rainfall events.

"It's boosted my confidence in decisions around irrigation," Mr Middlebrook said.

"Being able to understand what is happening below the surface, especially on this farm where water is limited most times of the year, and knowing when to turn the irrigator on and make the accurate decisions needed to drive production when we have water."

The Bowman Farm site is 15 hectares and irrigated from the Bowman River on a restricted entitlement, heavily reliant upon seasonal flows within the small catchment area.

This means that water access ceases during dry spells.

During summer, the usual plan is to grow a summer crop of maize or sorghum followed by an autumn sown, mixed pasture of barley or wheat/ Italian rye/ brassica as part of the milking platform.

"In year one of the project we managed to finish the summer maize brilliantly with water available," Mr Middlebrook said.

"Our usual practise was to stop irrigation earlier but the sensors down to 1 metre were telling us to irrigate, so we did.

"The next summer of 2018 we commenced crop irrigations about four weeks earlier than previous years, with water available it made sense to keep moisture levels within the optimal zone.

"We thought we were in for a record yield, but rainfall of any kind stopped and so did flow in Bowman River.

"Whilst this was a hit to production, there is no doubt we benefited from commencing irrigation early and the end result was a yield equal to the previous year."

In contrast, the scenario for Kywong Flat is a water source coming from the more reliable Barrington River, supplying the 50 hectare, seven-span centre pivot of the project sites.

Historically, water limitations have not been an issue and scheduling for irrigation has been determined to manage wet paddocks and off-peak power usage.

The two soil moisture monitors on the farm were installed on two varying soil types; a heavy, shallow soil usually managed as a winter rye and summer lucerne/chicory system, and a lighter, deeper soil managed as a winter Italian rye/white clover and summer kikuyu/paspalum system.

"The first two years of the project saw us refine the way we were irrigating," Mr Forbes said.

"Although managing these two contrasting soil and plant types under the one pivot, I used the soil moisture monitoring data to irrigate areas of the pivot a little differently.

"We have stuck with off-peak timing, but small amounts more frequently certainly suit the heavier soil, and larger amounts less often suit the deeper soil.

"The equipment not only allows me to determine when I need to irrigate, but certainly allows me to monitor how far down the soil profile the water is being effective for both irrigations and rainfall."

Early in the project both farmers also adopted the IrriPasture weather-based water balance tool and more recently registered to receive a free daily water requirement notification from SWAN Systems.

"IrriPasture provided a pretty accurate forecast on when irrigation was going to be needed again and how much, and helped to keep a good diary of irrigation applications, but now that I have more confidence on using real-time data, the daily notifications from SWAN allow me to keep an eye on the seven-day rainfall and evapotranspiration without too much effort," Mr Middlebrook said.

"Knowing where soil moisture levels sit, in or out of the optimal zone, combined with knowledge of the coming wetting and drying conditions, I can make informed timing and rate decisions that pay-off more often than not."

The autumn rains of 2019 did not eventuate in the Gloucester region of NSW.

This saw the Bowman Farm site removed from both the milking and cropping platform from May 2019 until February 2020, with no access to water over this period.

Remarkably, for the first time in 20 years, Kywong Flat also went without irrigation for a two-month period.

"In early January there were a couple of opportunities granted to water, so the irrigators went on," Mr Forbes said.

"We were able to monitor soil moisture closely to ensure the profile was wetted right-up and we made the decision to use peak power to see this through.

"The production gains versus power costs staked-up in this case."

Significant late January to mid-February 2020 rainfall, totalling more than 400 millimetres, saw flows return to both river systems and soil moisture lifted back into optical zones.

The response at Kywong Flat was swift, but with ETo still high early Oats were sown on the heavy, shallow soil site rather than waiting for cooler conditions for the usual ryegrass.

"The decision to plant early oats on the milking platform proved to be a valuable feed source in the autumn gap," Mr Forbes said.

"Usually the gap is supplied by homegrown summer maize and spring ryegrass silage which was impossible due to the drought conditions."

"On the other site we prepared early and went in with the Italian rye/ white clover, but we were careful to monitor temperature and ETo for the ideal sowing conditions."

At Bowman Farm a late February sowing of a barley/Italian rye/ brassica saw good soil moisture deliver a 32-day turn-around and first grazing four days earlier than 2019.

Whilst the 2020 autumn/ winter pastures on both farms were kick-started with good soil moisture, March through to July delivered lower than average rainfall.

With ETo remaining relatively high, and plant growth active, in April soil moisture began to decline and irrigation was needed to maintain levels within the optimal readily available water (RAW) zone.

While there was a risk that irrigating could be followed by heavy rain, especially during the prime east coast low season, and cause a wet winter, there were three compelling factors that pointed to irrigating:

There would be an immediate loss of valuable growth in the autumn/winter feed gap with moisture stress in April.

Moisture stress early in the growth of cereals can produce lasting setbacks by reducing tiller numbers; and

While rain had ceased, there was still flow in the river systems and it was important to access that benefit.

"Looking at the soil moisture data reinforced that to continue to drive active growth, provide every opportunity to apply nitrogen, and increase the nutritional value of grazed feed with options to potentially conserve silage, irrigation was needed," Mr Middlebrook said.

"This is where the project has really come into its own.

"After all our hard work to recover from the drought, if we had followed our historical way of irrigating, we would not have irrigated and the result would have been lost production."

Learning from this period, it is critical to commence irrigation early after soil moisture commences its trend downwards.

It also highlights the need to buck traditional practices, using available data to respond accordingly and being ready to irrigate in times when historically rainfall was more reliable.

"We are irrigators most of the year-round now," Mr Forbes said.

"When ETo outstrips rainfall, soil moisture begins to decline and plant growth is active, we always need to be ready to irrigate.

"The more we strategically irrigate, the more control we have on the water and energy inputs we use to drive our production."

For further information on the Hunter Smarter Farming: Irrigating for Profit project, contact Marguerite White on 0447 500 415 or mwhite@icdprojectservices.com.au.

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