Farm Progress

Slideshow: Research uses variable-rate irrigation to create yield response curves for crops.

Tyler Harris, Editor

December 27, 2017

5 Slides

One of the fields at the West Central Water Resources Field Laboratory south of Brule, Neb., could be a poster child for in-field variability.

"It's got about every soil type you can imagine. It's close to the Platte River. There was at one time a tributary that went right through the field. So there are low-lying areas toward the middle and high-lying areas around the outside," says Tim Shaver, University of Nebraska Extension nutrient management specialist. "Generally, we would expect low lying areas to be higher-yielding. But this field is the opposite, because topsoil was moved away by the river at some point. It's left only 6 to 8 inches of topsoil in the middle of the field, and the outer lying areas have good, deep soils. From a research standpoint, it's the greatest amount of soil variability I've dealt with."

That's why this field and three others like it are the perfect place to research variable-rate irrigation. VRI systems were installed on these four center pivot-irrigated fields near Brule in 2011, where Shaver has spent the last six years studying VRI. However, Shaver isn't just interested in variable rate for irrigation — he's studying how variable-rate irrigation can be used in conjunction with variable-rate nitrogen applications.

Responding to plant needs
Most VRI research has traditionally relied on soil moisture sensors to measure and address in-field variability. And while Shaver is using neutron probes and capacitance probes to measure soil moisture content, he's also taking a different approach to account for deficiencies in the plants themselves — using crop canopy sensors just like those used in Project SENSE (Sensors for Efficient Nitrogen Use and Stewardship of the Environment) to measure reflectance.

"Soil moisture sensors will be fixed in place,” he says. “All these sensors are expensive, so figuring out how many we need and using them can be a challenge. Depending on the variability in the field we may need to use a lot of sensors. We're using the crop as a way to express soil variability that's out there. It doesn't always work, but quite often it does."

However, unlike Project SENSE, which uses reflectance sensors mounted on a high-clearance machine, nitrogen rates aren't calculated automatically. At the Brule lab, researchers have to plug measurements into an algorithm to manually calculate a nitrogen rate.

"Up until the last few years there hasn't been a lot of work integrating these two, because the relationship is quite complicated and it is difficult to vary water and nitrogen together. We had to do some basic research to ask, 'if we're in a location where we can put less or more water, does the amount of nitrogen needed correlate with that?'" Shaver says. "The interesting finding is that it does react the way we expect. Areas where we need more water, we need more nitrogen. What's exciting is we can actually do that — we can put less water and N in areas with less yields, and move that resource to part of the field with a high yield potential."

Yield response for different crops
About 130 miles away, at the Panhandle Research and Extension Center near Scottsbluff, Neb., Xin Qiao is also delving into site-specific VRI research. For Qiao, who started his role as Extension water and irrigation management specialist at the Panhandle REC in May 2017, VRI not only serves as a way to address variability, but opens up possibilities for different irrigation treatments on different crops. He hopes to create a yield response curve from different irrigation treatments.

While a VRI-capable lateral irrigation system was installed in 2016, Qiao notes he won't start researching the system until the spring of 2017.

The lateral, a four-span system, covers 16 acres with about four aces under each span. Under each span will be eight separate treatments, replicated ten times for a total of 80 plots under each span. The Nebraska Panhandle is known for a wide range of crop diversity, and Qiao hopes to establish a yield curve for the dominant crops in the region, like corn, sugar beets and dry edible beans, as well as specialty crops.

"Before, when we calculated water use efficiencies for different irrigation management scenarios, it was based on frequency,” Qiao says. “Treatment 1 might be one irrigation application per week, treatment 2 would be two applications per week. With VRI, you're able to not only test the frequency, but you're changing the irrigation rate at different plots. I'm hoping we can achieve a more detailed water use efficiency curve for those crops. Hopefully, in our water-limited environment we can demonstrate to irrigators that even if you reduce your applications by a certain amount, you can still expect a certain amount of yield."

 

About the Author(s)

Tyler Harris

Editor, Wallaces Farmer

Tyler Harris is the editor for Wallaces Farmer. He started at Farm Progress as a field editor, covering Missouri, Kansas and Iowa. Before joining Farm Progress, Tyler got his feet wet covering agriculture and rural issues while attending the University of Iowa, taking any chance he could to get outside the city limits and get on to the farm. This included working for Kalona News, south of Iowa City in the town of Kalona, followed by an internship at Wallaces Farmer in Des Moines after graduation.

Coming from a farm family in southwest Iowa, Tyler is largely interested in how issues impact people at the producer level. True to the reason he started reporting, he loves getting out of town and meeting with producers on the farm, which also gives him a firsthand look at how agriculture and urban interact.

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