Farm Journal Test Plot evaluates irrigation technology
For more than a decade, the Farm Journal Test Plots has varied corn populations and nitrogen rates to respond to natural management zones in the field. In 2012, the crew added variable-rate irrigation to its site-specific farming portfolio.
In partnership with Valmont Industries, Inc., who provided the system, software and supporting in-field technologies, the Valley Variable Rate Irrigation (VRI) system was installed on a pivot owned by farmer Dan Meeker in Mason County, Ill., for a multi-year test plot. In addition to an upgraded control panel, valves were installed at each sprinkler head.
"This has been a customer-driven product," says Jake LaRue, director of research and development for Valley Irrigation. "Farmers are already using and realize the benefits of variable-rate planting, fertilizer application and spraying."
The chosen 80-acre field has two sandhills that have shown noticeable decreases in yield every year.
"Our goal was to increase the water enough on the sandhills to bring those areas up to the production levels of the rest of the field," explains Isaac Ferrie, who oversaw this Farm Journal Test Plot.
The pivot used in our testing was outfitted for Zone Control, which allows for prescriptions to vary by management zone in addition to sector. The crew divided the pivot into six control sections.
"Since this was our first full year with the technology, we wanted to understand how the soils respond to irrigation. For example, what impact would applying ½" of water have on soil moisture levels?" Ferrie explains. "For the first half of the growing season, we applied a uniform rate; then, starting in July, we used the VRI technology in two of the six control sections."
In the field, Irrometer soil moisture sensors were placed at three depths—6", 18" and 24"—in a representative zone for each of the four main soil types. These sensors are networked to a modem in the field that wirelessly transmits the data to the test plot crew.
A series of thermal images from Aerial Crop Reconnaissance Experts as well as NDVI maps provided by GeoVantage provided another way to monitor how the crop responded to irrigation.
"The thermal images show us crop temperature and the NDVI maps are a measure of crop biomass," Ferrie says. "We found that cooler crop temperatures and higher biomass levels correlated to higher yields."
Just enough water. The thermal images were used by Ferrie to make changes in the prescription maps from month to month. For this first year of collecting data, the frequency of the water was programmed on the farmer’s normal watering practices, and the test plot crew created the prescription rate maps.
"The standard rate was 0.8", and the variable-rate prescriptions ranged from 1.16" to 0.58"," Ferrie says. "The summer of 2012 was extreme—and even at the highest watering rate, some areas didn’t receive enough water. The pivots couldn’t run fast enough to apply adequate water to some areas."
Despite the difficult conditions, the test plot team and farmer continued the study, which paid off in valuable baseline information.
"In a drought, there is still only so much water you can apply in a day," says Farm Journal Field Agronomist Ken Ferrie. "When it got too hot, we had corn abort ears, and if an area is lost to the drought, no matter how much water we apply, we might not bring it back."
Ferrie says that using this technology in conjunction with in-field scouting could help prioritize water schedules in extreme weather conditions. "Just like with other variablerate technologies, you have to learn it to know it," he says.
Our study with Valley will be a multiple-year effort. "We look forward to working with this technology and with multiple years of yield data to see if we can predict how much water it takes to maintain yields on certain soil types," Ken Ferrie says. "Right now, this field isn’t in an area with water restrictions. However, with increasing environmental restrictions, water limits could be an issue some day."
Irrometer soil moisture sensors were placed at three depths in each main soil type. Data was wirelessly transmitted to the Farm Journal Test Plots office.
Water control. LaRue, who manages variable-rate irrigation studies across the country, says farmers are investing in this technology for multiple reasons but primarily to have greater control of where and how much water they apply.
"Some are looking at this tool for conservation, some are looking at it as a way to increase yields in lower-producing areas," he explains. "In our studies, we’re learning there are nuances to the technology, and farmers are making changes to how they manage their pivots—for example, cutting back on application rates but making more rotations."
That adjustment is one that the test plot crew is considering in 2013. They suspect there are higher rates of runoff from the sandhills, which is limiting how much water is reaching the soil profile. Moving forward, plans include to learn more about the infiltration rate on the sandhills and apply that to more effectively use variable-rate irrigation.
In the meantime, Valmont is making changes for spring 2013 so the technology will be easier for the farmer to use. The Valley Speed Control package allows farmers to adjust water by each sector of the pivot’s path.
"We now offer pivots set up for the Speed Control application to be outfitted with a quick-start prescription from the factory," LaRue says. "These maps are built from our three years of experience with VRI and use Natural Resources Conservation Service soil maps as a baseline."
You can e-mail Margy Fischer at firstname.lastname@example.org.