Research Update: Winter Wheat Grain Yield and Protein

 

For Nebraska dryland winter wheat producers, 2019 has been another challenging year. In many cases, grain harvested this summer had a protein level below 10%, except where producers applied fertilizer nitrogen (N) in hopes of getting a yield boost from wet spring weather experienced by much of Nebraska.

 

 

Figure 1. (Top) Bijesh Maharjan, Soil and Nutrient Management Specialist, pilots an unmanned aerial vehicle (UAV, or drone) equipped with sensors over a wheat test plot. (Bottom) An image captured from the drone, after processing, depicts the Normalized Difference Red Edge (NDRE) values for the plot. Maharjan’s team plans to use the sensor images to share algorithms with producers that they can use during the growing season to adjust N rates to increase grain yield and quality.

Reports of low protein levels came from some cooperative representatives and producers. The University of Nebraska-Lincoln wheat variety trials recorded protein level around 12% in most instances, with a few lines having below 10% in the Scotts Bluff County trial.

 

 

Wheat producers lose income as a discount kicks in at protein levels lower than 10%-11%. Low protein levels in wheat caused Nebraska producers to lose an estimated $2.3 million to $9.6 million dollars of the value of the 2016 wheat crop despite high yields. Similar low protein issues persisted in 2017.

 

So it is very timely that we continue generating data from a two-year study began in 2018 about how soil N levels affect protein levels in the grain from Nebraska wheat fields. The study is being conducted with the support from UNL Agricultural Research Division (ARD) and Nebraska Wheat Board. It also is intended to revise UNL fertility recommendations for the benefit of wheat producers.

 

The UNL research team hopes to evaluate how grain quality, yield and field stands are affected by N fertilizer rates and application timing. The trials are being conducted across the state and with variations in the amount of precipitation the plots receive. The study also is testing the effectiveness of crop sensors in monitoring crop conditions and whether inputs are needed during the growing season.

 

Among many potential factors, soil N is probably the most central factor affecting protein levels in wheat. With low grain market prices, producers are under pressure to lower their input costs, primarily N fertilizer. However, reducing or eliminating N applications to winter wheat will typically result in low protein when yields are high and/or residual soil N is low.

 

The interaction between N and available soil moisture is important for profitable winter wheat production. High levels of soil moisture and favorable growing conditions increase tillering and wheat yield. As wheat yield increases, the requirement for N increases.

 

In order to increase protein levels in wheat, N must be properly managed in the soil and be available for plant uptake during grain development.

 

Accurately predicting how much N wheat will need requires an extensive data set. The last predictive N algorithm for dryland winter wheat production in Nebraska was prepared in the 1970s. Considering the progress made in traits and management, and changing climatic conditions, there is a need for re-assessing the N recommendation in dryland wheat.

 

Working towards that goal, in 2018, a dryland winter wheat fertility trial was initiated at four locations:

Its goal is to understand effects of N application rate and timing on grain yield and quality. In 2019 the data from the four sites was affected by weather, disease and other factors.

 

Unfortunately, the trial at Scottsbluff was lost to hail damage. At Mead, increased N rates surprisingly did not result in gain in grain yield. This might be because of Fusarium Head Blight (FHB), among other factors. The severity of fusarium head blight is known to be higher in wheat fertilized with higher N rates. At Grant and Sidney, data suggests it is likely that grain yield can be improved with optimization of N rates and application timing. At Grant, precipitation was above-average from May through July, when the crop goes through tillering, booting, heading and flowering, increasing daily crop water use. This resulted in high yield across N treatments.

 

Grain quality analysis is yet to be conducted, but it is very likely that as in 2016 and 2017, grain quality would be affected by such a high yield, particularly at low N rate treatments. At Sidney as well, there was significant increase in grain yield with increasing N input. However, grain yield did not differ by application timing.

 

Selected grain subsamples from all four locations will be analyzed for selected end-use quality parameters on straight grade flour and whole-wheat flour, including protein (Leco), particle size distribution (whole wheat flour only), asparagine, and Mixograph at UNL Food Science lab in Nebraska Innovation Campus.

 

At all locations, post-harvest soil samples will be analyzed for residual mineral N, which will also shed some lights on yields observed in this experiment. It is likely that in years when there is abundant precipitation during fall and subsequent spring, soil N moves deeper into the soil profile, out of the root zone. That would suggest a potential benefit of split applications of N.

 

Data from this study also is suggesting that crop sensors can be effective in letting producers know whether additional inputs are needed during the growing season.

 

Data on vegetative indices obtained from hand-held and UAV (drone)-mounted sensors are being analyzed as well. The initial analysis results have shown significant differences in Normalized Difference Red Edge (NDRE) values among different N rates. Based on these results, the team will develop and share with producers crop-sensor-assisted, in-season N application algorithms to increase grain yield and quality.