Variable rate irrigation can boost water use efficiency and may bump yield. But there are wrinkles to iron out before the technology is widely adopted.
Variable rate systems include an electronic control panel, a pivot positioning system (usually GPS), and sprinkler control valves. Farmers upload prescriptions to the control panel, which then applies water accordingly.
Each major sprinkler manufacturer has a variable rate option, says Dale Tomasiewicz, irrigation agronomist with Canada-Saskatchewan Irrigation Diversification Centre. Tomasiewicz and his colleagues use the technology for their research plots.
Irrigators can also control lateral speed as a simplified version of variable rate, Tomasiewicz says. By varying speed, farmers can vary water application. Management zones will be the full length of the pivot, from the edge to the centre.
“That can be helpful, to some extent, depending on how the variability within your field lays out,” says Tomasiewicz.
Why try VRI?
Tomasiewicz says there are a couple of situations where variable rate irrigation is useful. Horticulturists with several fields under one pivot could avoid pie-shaped management zones. Variable rate technology also avoids overwatering from overlapping pivots.
The technology also addresses field variability. For example, potato growers could avoid overwatering draws and low spots, cutting disease.
“So if you could adjust your watering in those different areas, overall you would probably save water. But also improve yield and reduce diseases,” says Tomasiewicz.
The system could be adjusted after a heavy rain to drop water application in low-lying areas. “Or you may have poor crop growth areas that don’t need as much water,” says Tomasiewicz.
There may be more benefits to variable rate irrigation with high-value crops such as potatoes. Farmers with high water costs might save money by switching to the new technology.
Before ponying up for a system, farmers should look at the variable on each field and do the math, Tomasiewicz says. “And see if the cost of the system, which is still fairly high, is going to be more than covered by the benefits in each field.”
Few farmers have adopted the technology at this stage. “And I think that’s probably good because all the i’s have not been dotted in terms of telling growers how to use them and developing those prescriptions… for how much water should go on each part of the field,” Tomasiewicz says.
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Barriers to variable rate
Ted Harms is a soil and water specialist with Alberta Agriculture and Rural Development in Brooks. In 2012 and 2013 he ran projects studying variable rate irrigation instruments and water prescriptions.
Before variable rate irrigation can be a game changer, “I would have to think that if I’m going to spend $40,000, it better be not just avoiding puddles in my field, but it has to start paying for itself,” says Harms.
“So if you could start using water as a driver to start bringing up some of those poorer spots, well then it starts making sense,” Harms adds.
Variable rate system costs aren’t the only hurdle irrigators need to jump. Farmers also need information to use the system to its full potential, Harms says. This includes soil water status and how much water has been applied to different field areas.
Tomasiewicz compares variable rate irrigation to variable rate fertilization. But farmers must decide how much water to apply each time they irrigate. And ideally they’d use a custom prescription every time.
And while applying variable water rates seems obvious, developing prescriptions isn’t easy.
“You look out in the field, the low areas are wet. The high areas are dry. Well, put more water on the higher areas,” says Tomasiewicz.
“But after you do that a couple times, that’s not the situation anymore. So you need information. And the best information, of course, is real time soil moisture information. But to get that very frequently at many locations within a field is challenging.”
In 2012, Harms tested equipment that required him to manually download information from each sensor. “And then it quickly became apparent that, well this was nuts. And it really was in a form that I couldn’t use.” Harms says it took three days to gather and process the data.
Last summer Harms used six CWS655 soil-water probes and six tipping bucket rain gauges that sent information to a data logger at the pivot point. The data logger then forwarded data to the Brooks office.
“Every day I was getting what the status in that field was,” Harms says. The consultant could then use the data to prescribe water applications.
The catch? The extra software and hardware cost $12,000 in addition to the basic variable rate irrigation system. Farmers would also need a computer guru to make the system work, says Harms.
Along with the in-field sensors, farmers will need to shell out for maintenance, upgrades, field-mapping, and consultant costs. The more management zones under one pivot, the higher the costs.
Harms says he can’t see the technology going very far until the dealers spend as much time on the management aspect as they have on the equipment development aspects.
“I can sit here on my smart phone and see what my pivots are doing at any time of the day… Now you have to start incorporating that management aspect of the VRI systems into that,” says Harms.
Though the technology hasn’t been widely adopted yet, Tomasiewicz says there is keen interest in the irrigation industry.
“I think it’s something that people see as something that’s going to happen with time. It’s just a matter of how quick.” †