Precision irrigation has great potential, but it’s tricky

Understanding how moisture moves through parts of the field is one of the goals of the four-year study

Water has always been at a premium in the Irrigation Belt of southern Alberta.

“Our water system is closed,” said Willemijn Appels, an irrigation scientist with Lethbridge College. “There is no more extra water that can be withdrawn for agriculture. Our water licences are already allocated.

“We need to use water more wisely and make more out of what we have.”

That has been occurring. The recently announced $815-million expansion will bring another 200,000 acres in the south under irrigation, largely by replacing canals with underground piping and adding four new reservoirs. And a move to low-pressure centre pivots and drip is also producing ‘more crop per drop.’

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But the next frontier is precision irrigation, reducing water use by applying — based on soil moisture, topography and other factors — just the right amount in different parts of a field.

That’s the point of an ongoing four-year study led by Appels.

College researchers are monitoring both fields and existing management practices of area producers growing potatoes under irrigation. If successful, it may well mark the dawn of variable-rate irrigation (VRI) — a.k.a. ‘precision irrigation’ — in the province.

Appels does not expect to find comprehensive solutions that will revolutionize irrigation management. Even within a field, soil moisture is just too variable for that. Rather, the results of the project — which just completed its second growing season — will likely serve as a foundation for the development of tools to help growers understand if VRI would pay off for their farm, and what fields would offer the most bang for the buck.

“Ideally I would like to come up with a procedure,” said Appels. “When a farmer is considering upgrading their irrigation technology, we could offer a procedure that evaluates the potential impact of VRI as a function of the soil and topography variability of their field.

“It might say, ‘For this kind of field you should be looking at a useful application of VRI in, for instance, five out of 10 years or two out of five years. This may make a difference in X numbers of litres of water.’”

The project — a partnership between the college’s Centre for Applied Research, Innovation and Entrepreneurship and the Potato Growers of Alberta — is taking place on five volunteer farms chosen by the growers’ association.

The farm locations (comprised of five research areas each) are located across a wide swath of southern Alberta on irrigated farms near Vauxhall, Bow Island, Chin and Taber.

A key thing to know about precision irrigation is that it by and large doesn’t exist.

Precision practices today are mostly relegated to irrigation timing requiring diligent by-hand soil testing and rainfall monitoring, said Appels. Avoiding problem areas such as wetlands and salty patches can also be considered a precision practice.

The research team hopes to expand on that.

Basically, they are recording farmers’ irrigation water use and measuring how it corresponds to soil moisture levels and yield. Factors such as topography of the landscape (high- versus low-lying areas) are taken under consideration in the final analysis.

The value of VRI

The problem with variable-rate irrigation, and the reason why it’s rarely used, is that it’s both data and time intensive. Also, the necessary foundation — primarily soil moisture maps — does not exist on a mass scale.

“It’s quite complex because you need to be aware of how your field responds under certain circumstances, which means you have to either install a lot of sensors or sample a lot of different locations,” said Appels. “And lots of people don’t have time for that.”

Most producers currently adjust their irrigation to crop requirements, but that doesn’t account for potentially crucial factors such as topography and distribution of soil moisture. However, having access to representative field data — such as that being collected in this research — may help producers practise VRI to a greater extent.

“When you think about it, you grow this same crop throughout this highly variable field,” Appels said. “As long as you meet the water demand of that one crop you might be OK; you’re just providing what the crop needs whether or not that land happens to be on a hill or in a depression or on a slope.”

The problem with that approach is fields are rarely, if ever, uniform in terms of soil moisture. Actual moisture levels within a field can vary within a matter of metres, she said.

“If you think of the roots as a bucket, in one location the bucket may leak more than in another location,” she said. “You may have to change how much water you put in or what frequency you put it in.”

Potatoes were chosen for the project, which is funded by the Canadian Agricultural Partnership, for a couple of reasons. For one, it’s a high-value irrigation crop in the area, with processing infrastructure to match. Spuds are also very sensitive to the soil moisture around them, and can serve as a starting point for VRI on other irrigation crops such as canola, sugar beets, wheat and beans.

“Water is important to (those crops) and knowing the hydrology of a field can be beneficial for them.”

The research team is still in the process of analyzing the data from this year’s growing season, but what they do know is that variability within a field is highly dependent on the weather. Last year was dry (creating very little soil moisture variability) while this year’s rainfall has offered the researchers more to go on.

“This year, because of the June rainfall, soil moisture patterns were more complex and interesting for a while,” said Appels. “We’re running mode simulations to see if VRI at the various monitoring locations would have made a difference in yield or water use efficiency.”

Appels has high praise for the producers who have volunteered areas of their farms for the research.

“These are people who are interested in moving the irrigation industry forward. It’s been great to work with them.”

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