It started with a suspicion that the linear move variable rate irrigation system had several nozzles functioning erratically. They would appear to be plugged and then function fine. The sprinkler system ran north-south over a 12-acre field used in Colorado State University’s Testing Ag Performance Solutions 2024 corn grain farming competition, located at the CSU Agricultural Research, Development, and Education facility in Fort Collins, Colorado. The TAPS competition format itself compounded the difficulty in isolating and confirming the problem, because of its plot-level variability.
For example, in TAPS, one field is divided into multiple plots randomly assigned to teams. Each team has access to direct and remote sensing data about field conditions to make management decisions for their plots, such as fertilization and irrigation, which are implemented on site by university field staff. The goal of the competition is to be the most profitable or input-use efficient. (For more on TAPS, read the Fall 2021 issue of Irrigation Today.)
In 2024, CSU-TAPS’ 12-acre competition field was divided into 90 plots of approximately 60 feet by 82 feet each, with three noncontiguous plots assigned to each team to manage. Differences in team decisions on irrigation amounts alone made for a lot of variability in the field, and that made pinpointing erratic nozzles even more difficult.
“The first indication we had a problem was stunted growth and uneven plant development,” says Wub Yilma, precision irrigation manager for CSU-TAPS.
At this point, the CSU-TAPS team turned to using drone imagery of the entire field, stepping back to help pinpoint the problem. Normalized Difference Vegetation Index data, which correlates reflectance values with vegetation density, allowed the team to confirm the stressed plants in line with the track of the irrigation system.
To root out the cause, ARDEC staff climbed onto the linear to investigate the system and discovered some bad wiring connections causing intermittent electrical shorts when the system was operating. They were able to make repairs, solving an unusual and complex system problem thanks to the combination of field observations with drone imagery.
“The small plots and the variability in management decisions [in TAPS] makes each nozzle particularly important,” says Omer Izrael, CSU-TAPS program manager. “We are maximizing the resolution the linear irrigation system is capable of applying. It is very important that each plot receives the irrigation amounts participants prescribe for them.”
“For the competition, we harvested only the middle sixth rows [of each plot],” Izrael adds. “Luckily, for the competition, because we could avoid [the affected plants] in the harvest, it didn’t matter.”
NDVI images can also be used in harvest planning to avoid stressed rows, Yilma pointed out.
“For a farmer, [the problem] would have mattered a great deal,” Izrael says. “Even one sprinkler nozzle can impact the amount of water that plants receive, and in a big field, this could translate significantly in terms of reduced yield.”
Once the 2024 competition irrigation was complete, the CSU-TAPS team set out to get a baseline assessment of the irrigation system’s overall distribution uniformity with a catch can test.
In a neighboring field, the team distributed 200 32-ounce graduated cylinders, or “catch cans,” in two rows every five feet. Running the irrigation system over the field on a wind-free day, they measured the irrigation water caught in each can, checking for even application. (Catch can testing can be done on a planted field when the plant height does not interfere with the ability of the cans to catch water.)
Entering measurements from each can into a standard irrigation uniformity spreadsheet, Yilma was able to calculate the coefficient of uniformity for the system.
“We found the CU to be 85.91%, which is high,” Yilma explains. “The higher CU meant more consistent water application rates, where every part of the field received the same amount of water.”
Knowing that information is crucial for the TAPS competition format, Izrael says, because a key aspect of the competition is input efficiency — exploring what farm management decisions result in the highest yields with the least input costs, including irrigation water.
“The teams’ irrigation decisions really make a difference on the ground,” Izrael says. “Applying sufficient irrigation at the right time for the plants’ growth stage is very important. By timing the irrigation properly, you can save several inches of water throughout the season.
“We want to make sure each [team] has equal opportunity in the competition — that participants’ irrigation decisions are actually implemented consistently and precisely,” he adds. “We want to make sure the system applies the right amount for the plot.”
This spring, the CSU-TAPS and ARDEC crews plan to dewinterize and assess the irrigation system as normal, checking for nozzle clogs, leaks, and wear. They also plan to run another catch can test on the system prior to the 2025 competition, Yilma says, for “peace of mind.”
