If there’s a perfect recipe for success when it comes to variable-rate irrigation in potatoes, the researchers at the Canada-Manitoba Crop Diversification Centre (CMCDC) are still trying to find it.
The idea of variable-rate irrigation is hardly new. As early as 2012, news of field trials was coming out of Alberta, although one of the leads of that project, provincial researcher Ted Harms, later noted that his co-operating producers became frustrated with the technology and that more research was needed.
Nevertheless, by 2015 our sister publication Alberta Farmer reported that 50-60 variable-rate irrigation systems, otherwise known as VRI, were set up in the province as farmers chased more efficient water usage.
Researchers out of the CMCDC have been trying to get local numbers for those benefits, as well as a better footing on sensor technology that may or may not be appearing in future fields.
The Carberry station has played host to a list of AAFC variable-rate irrigation projects in recent years.
“It’s not an option that’s going to work for every producer,” Alison Nelson, AAFC researcher and one of the project leads at Carberry, said. “It depends on their field and the level of variability that they deal with, and it’s not going to be a one-size-fits-all solution in terms of how they manage it.”
Nelson’s team found that VRI did, in fact, provide an edge in 2016. The technology was put to the test at both the AAFC site in Carberry and a commercial field. Plots in the commercial field showed, “significantly higher tuber yields under VRI management,” although there was no difference to quality.
There was no similar yield bump at the AAFC site, but defects were cut in half with VRI. Hollow hearts, rot and green dropped from about 16.6 per cent in the regularly irrigated crop to 8.3 per cent with variable irrigation.
The results looked promising, the team noted in the CMCDC’s annual report that year.
Results told a different story in 2017. Variable-rate irrigation gave little benefit in either yield or quality, something Nelson suggests might be due to the dry weather.
“The irrigation was just running all the time to try and keep up,” she said. “There were very few times that we needed to vary the rate across the variable zones.”
The quality boost in 2016 may highlight one of the technology’s most prevalent selling points in Manitoba, given that the province was caught in a wet cycle for much of the preceding decade, according to Jarrett Powers, another Carberry AAFC potato project lead.
How to apply it?
Like other precision agriculture, Powers notes, VRI technology is still running ahead of the industry’s ability to use it. It’s no surprise to say that precision agriculture in general is as much about the farmer’s ability to gather and interpret data as it is the technological ability to turn a nozzle on or off via computer or deliver a specific product at a certain rate and soil depth.
The ability to turn nozzles on and off has been in place for some time, Nelson said, although the first implementations of the technology focused more around turning a pivot off when it crossed roads or uncultivated sections.
More detailed applications, managing the field according to zone, are a relatively recent avenue, she said.
“There’s still work to be done in terms of what’s the most useful decision support tools for producers,” she said. “What’s going to get the information into their hands on a regular basis to make those irrigation decisions on a daily basis? What’s most cost effective? What’s the most accurate and the most real-time information they can get?”
AAFC Carberry hopes that space-age technology might eventually give another option for field-level data.
One research project is putting passive microwave sensors to the test, similar to environmental soil moisture sensors used by NASA satellites.
“They don’t measure soil moisture, per se, but they measure the microwave energy that’s being emitted from the soil, and mostly from the surface, so the top 10 to possibly 20 to 30 centimetres, depending on the soil type and how wet or dry it is,” Powers said.
“That microwave energy is affected by soil moisture,” he added. “So they’re able to derive a soil moisture value based on the microwave energy value that the radiometers are measuring.”
The study hopes to validate soil moisture data from the radiometers and determine whether it can be used for irrigation scheduling.
This year’s data reflected the expected trends across their one test field, Powers said, with lower or less sandy spots indicating greater soil moisture, while sandier ridges indicated drier readings. There needs to be more work done on calibration to derive absolute soil moisture, he added.
AAFC has partnered with Skaha Remote Sensing for the project.
The AAFC team previously looked at mounting sensors on a UAV drone, but moved to mounting radiometers directly onto pivots this year.
Fertigation is the next logical step for VRI, Nelson said, something that early adopters in Alberta have been playing with, but has so far not been explored at the Carberry research station.