It's generally understood that several factors affect wheat protein content. Chief among them are variety, environment and, perhaps most importantly, nitrogen.
In recent years, growers have been docked at the elevator for lower protein content, and sometimes earning a premium for higher protein content, raising the question: How can growers influence factors in their control to improve protein?
Over the past two years, Bijesh Maharjan, Nebraska Extension soil and nutrient management specialist at the University of Nebraska-Lincoln's Panhandle Research and Extension Center, and graduate student Deepak Ghimire have been working to get a better handle on how nitrogen, among these other components, influences wheat protein content.
"When I came to western Nebraska, I learned right away that during our wet spring season, wheat does really well in terms of producing yield," Maharjan says. "The problem is that protein then takes a hit. That's what prompted me to start this project in the first place. As I dug a little deeper, I realized our wheat fertility recommendations in Nebraska are based on old datasets. That requires we do some updating on our data, so we can revise recommendations for wheat."
The study includes four sites throughout the state: Scottsbluff, Grant, Sidney, and one near Mead in eastern Nebraska. Treatments include different nitrogen rates and application timings, with rates ranging from no nitrogen to 75 pounds per acre in three locations in Scottsbluff, Sidney and Grant. At the eastern Nebraska plot, Maharjan used rates as high as 100 pounds. However, Maharjan notes, they ran into a few hurdles in 2019.
"In Scottsbluff, we lost our trial to a hailstorm. In Mead, there was pretty severe fusarium head blight," he says. "Because of that, we didn't see an effect from our treatments at those two sites. At Grant and Sidney, we saw a good response of N rates, and what really amazed me was yield response to N rate in addition to protein. After putting on more than typical 100% recommendation, you would assume the yield increase would level out, but that didn't happen."
"In Grant, where we had good moisture early in spring, with our highest rate of 75 pounds, the yield hit close to 100 bushels, which is really good," Maharjan adds. "At Sidney, it's drier, and our highest yield was about 60 bushels per acre."
While yield almost always improved with higher nitrogen rates, there wasn't always a direct correlation to higher protein, Maharjan says.
"What we saw is at a low rate of nitrogen, from 15 to 30 pounds even up to 45 pounds in some cases, the protein stayed below 11%," he says. "In both Grant and Sidney, the protein content was below 12%. Depending on the elevator you take your grain to, that protein discount can kick in at 10%, and some may want above 11%."
At the Mead site, they were able to reach higher protein levels, but at the expense of yield and various grain quality components because of fusarium head blight.
"In Mead where we had fusarium, we had protein a little over 13%, but then we had a hit on yield. So yield and protein are kind of inversely related," Maharjan says. "As you get more bushels, just by mere dilution, protein is lowered. So in Mead, where we have a lot of moisture and rain, our yield was under 70 bushels, and with a higher nitrogen rate, we did hit 13% protein."
"This is the first year of data, and in our nitrogen timing treatment we might look into later applications," he adds. "Timing may have an effect. We put down our last topdress application before jointing. Our recommendation has traditionally been not to go beyond jointing, but some research now is showing protein gains with later applications. So, in the third year, we're adding a higher rate, and a late application beyond what we've been doing."
In 2020 and 2021, Maharjan hopes to reach higher protein levels of at least 12%, and once a trend line is established correlating higher nitrogen rates with higher protein levels, he hopes to add an economics layer based on nitrogen costs, wheat prices and premiums, yields and protein levels to determine an economically optimum rate.
As part of the project, Maharjan also is measuring crop reflectance with sensors, calculating vegetative indices, and correlating those indices with nitrogen rates and crop yields. The goal is to calibrate the sensors while establishing a correlation between vegetative indices, nitrogen and yield. This includes crop canopy sensors from Holland Scientific, as well as Trimble's GreenSeeker.
"Even in the first year, we learned quite a bit," he says. "There's a good scope of adding nitrogen to boost yield, although protein is still elusive. We've got some good data from crop sensors showing values correlating nitrogen rates and grain yield."