Economic, environmental and social benefits are prompting a growing number of Australasian and US farmers to adopt precision variable rate irrigation systems.
New Zealand, a country generally known for its ample annual rainfall and phenomenal natural crop growth, is an unlikely origin for a precision irrigation development that’s gaining traction globally. However, light soils and sporadic precipitation in some regions, plus readily available water for irrigation, mean close to 800,000 ha or 6.5% of the country’s farmland is artificially watered.
Originally, much of that was with flood irrigation using border-dykes but, in the drive for water use efficiency and environmental protection, spray irrigation has become the norm, mostly with centre-pivots.
An increasing number of centre-pivots are being fitted with controllers on every sprinkler that tailor the amount of irrigation applied on the move according to crop type, growth stage, soil hydrology, topography, weather and environmental risk. Farmers using it report improved yields and returns with reduced run-off and other benefits.
They include Peter and Sandra Mitchell, cropping farmers from near Oamaru, in New Zealand’s South Island, who fitted VRI (Variable Rate Irrigation) on a 500 m pivot covering 85 ha in 2013. “We were growing all sorts of crops under it, with different soil-types, north and south facing slopes and flats and a spring-fed waterway: there was so much variability it was perfect for it,” recalls Peter Mitchell.
As members of a new irrigation scheme, their water supply was also relatively expensive at NZ$ 612/ha/year (€ 358) before on-farm pumping and scheme share capital costs, so any water savings would be worth more to them than to farms with cheaper water supplies. Participating in a research project to evaluate the installation, also reduced set-up costs and provided expert monitoring and advice in the first couple of years. “We bought all the hardware and they did all the soil tests etc.” Those soil tests revealed available water holding capacity to 1m deep ranged from 116mm to 217 mm.
Over the first two seasons, VRI reduced water use 27% which, based on an all-inclusive water cost of NZ$ 800/ha (€ 468) saved NZ$ 216/ha (€ 126), or NZ$ 18,000/year (€ 10,536) across the 85 ha pivot area. “So it was just over a four year payback on water savings alone,” Mitchell says reflecting on the $ 70,000 (€ 40,971) cost to put VRI on the 500 m pivot. The water saving meant they could either reduce their shareholding in the scheme, releasing capital, or use the water elsewhere.
They chose the latter, as they did when they put VRI on another pivot two years later. That was a 750 m machine covering a semi-circle of 85 ha. The water saved was redeployed with a gun on 12 ha of previously dryland, lifting cereal yields from 7t/ha to 10.5t/ha and making high value seed crops an option. “You don’t get offered seed contracts here without irrigation.”
Wheat yields under the pivot also increased by an estimated 5%, thanks to better matching application to demand. At NZ$ 400/t (€ 234) and 11t/ha of wheat, that equates to another NZ$ 220/ha (€ 129). “And when we put high value seed crops in, the gain is probably more,” he points out.
Add it all together, and Mitchell says it was “absolutely” the right decision to invest in VRI and they’ve since put it on a linear irrigator as well. All areas have been EM (electro-magnetically) scanned, costing about NZ$ 40/ha (€ 23) and they’re investing in 60cm AquaCheck probes at about NZ$ 3,000 (€ 1,756) each plus running costs to check soil moisture readings.
However, he wonders if such spot checks on soil moisture will one day be superseded, or augmented by an on-the-move laser, EM or possibly sonar scans from the pivot measuring soil moisture content continuously and fine-tuning water applications accordingly in real-time.
Grower points on VRI
World record holders for wheat yield, Eric and Maxine Watson, from Ashburton, were also in the vanguard of New Zealand growers to adopt the technology, though the world record crop was grown under one of two irrigators they have yet to fit with VRI. “We’ve done seven out of nine,” Maxine told Future Farmer magazine. She says they’re using 20% less water as a result, with associated power savings and yield increases, particularly on areas where overlaps or different crops under one irrigator caused over- and/or under-watering.
‘It’s the shoulder seasons or a wet summer when it’s most value. In a hot dry summer everything’s flat out’
Hew Dalrymple, a North Island cereal and veg grower, echoes those water savings. He installed his first VRI-equipped pivot in 2009 and now has it on 13 of his 31 irrigators covering 2,000 ha near Bulls. “Mechanically they seem very reliable but the software’s where they vary most,” he comments, pointing out Valley Irrigation, as well as Lindsay Corporation and a couple of other companies now offer VRI systems in New Zealand. “It’s the shoulder seasons or a wet summer when it’s most value. In a hot dry summer everything’s flat out.”
The video underneath shows the Zimmatic by Lindsay
Andrew Curtis, chief executive of Irrigation New Zealand (INZ), a voluntary, farmer-funded representative body for water users, says there’s no recent data on areas under VRI, but he estimates between one in five and one in six (17-20%) of all new pivots in New Zealand are fitted with it. That’s likely to continue to grow, provided a current “crossroads” for the technology can be negotiated. “There’s got to be better industry support for it after initial set-up. We’ve found about a third of the systems are not being used.”
Frequently that’s because management of the farm has changed and the newcomer hasn’t got to grips with the system. INZ is working to rectify that because it estimates half of the area likely to end up under pivot irrigation in New Zealand has sufficient variability in soil, topography and/or crop for VRI to be commercially and environmentally beneficial.
Currently just over 45% of New Zealand’s 780,000 ha that’s irrigated is under pivots but that’s predicted to grow to 60% of what will likely be 850,000 ha watered by 2023, suggesting several hundreds of thousands of hectares could be under VRI there before too long. “Development of better software and decision support tools for precision VRI will be key,” says Carolyn Hedley, of New Zealand’s Landcare Research institute, who has led much of the independent analysis of VRI instalments in New Zealand to date.
That includes monitoring the first use of Lindsay’s FieldNET Advisor software in New Zealand’s 2017/18 summer to see how well the model predicts actual soil moisture and crop canopy temperature measurements. “To date it is performing well,” says Hedley. The aim is also to determine what type of sensors will best inform such model-based VRI scheduling software, she adds.