Managing Nitrogen for High-Protein Wheat
Alan Blaylock, Ph.D.
Dr. Alan Blaylock brings extensive North American and international experience in nutrient management to the agronomy team. University studies and service as a university extension soils specialist prepared him for a long career in the fertilizer industry. Having managed both domestic and global research and education programs, Dr. Blaylock has a wealth of experience in applying science-based nutrient management principles and products to solving practical questions. Dr. Blaylock earned Bachelor of Science and Master of Science degrees in agronomy and horticulture from Brigham Young University and a Ph.D. in soil science from Iowa State University. He has been in agriculture his entire life — from his childhood on an irrigated farm in eastern Oregon to teaching soil science at Iowa State University to his current role as an agronomist at Nutrien. These diverse experiences helped Dr. Blaylock develop the skills to excel in translating complex scientific principles into practical solutions. Although early in his university studies he explored computer science as a profession, deep family roots in agriculture brought him back to the people and values of his heritage. His career satisfaction comes from helping others improve the performance of nutrients and cropping systems.
Some wheat types are desired for their high protein content, a factor in good baking properties. Nitrogen (N) is needed for plant growth, grain development and protein storage in the grain. Increasing N supply may increase both yield and protein if water and other nutrients are sufficient. Nitrogen and other resources are used first to meet wheat’s yield requirements up to the limits of the growing environment. When yield reaches the maximum allowed by the growing environment, additional N is used primarily to produce additional grain protein. Wheat grown where yields are limited by drought or high-temperature stress frequently has higher grain protein, whereas wheat grown in high-yield environments with adequate rainfall or irrigation often has low protein.
Wheat N uptake is rapid during vegetative growth (Figure 1). Most of the N used for grain protein is taken up during this period of rapid vegetative growth and later remobilized to the grain during grain fill. If available in the soil in the presence of soil moisture sufficient for nutrient uptake, some N can still be taken up during and after heading. Nitrogen taken up during heading contributes primarily to grain protein, because yield potential has already been determined.
Achieving high-grain protein requires supplying sufficient N to meet the crop’s needs for vegetative growth and the yield allowed by the growing environment, plus additional N to achieve desired protein levels (Figure 2). Nitrogen taken up in excess of yield demand or after yield potential has been set contributes primarily to grain protein. Nitrogen fertilization practices can be managed to increase grain protein.
Through proper management, it is possible, in spite of challenges, to produce both high yields and high protein. Growers have little control over the growing environment in which the crop is grown, but they can control several important production variables that can greatly influence wheat grain protein.
- Variety. Select a variety that tends to produce greater grain protein. Wheat varieties vary in their grain-protein tendencies. High-yielding varieties tend to be lower in protein and may need special fertilizer management to meet protein goals.
- N rate. Supplying adequate N fertilizer may be the most influential management factor determining wheat grain protein. Base fertilizer rates on an appropriate yield goal for the environment. If N is applied for a 40 bu/acre yield goal, but actual yield turns out to be 60 bu/acre, protein is likely to be lower than desired. Montana State University recommends an average N rate of 3.3 lbs N/bu of spring wheat with a 40 bu/acre yield potential (Jones and Olsen-Rutz, 2012). Past cropping history can give an indication of N fertilizer adequacy. If protein in previous wheat crops was less than 12.5%, yield and grain protein were likely limited by insufficient N.
- Soil N. A soil nitrate test to a two-foot depth can help estimate residual N from the previous crop. Spring soil tests are often a better indicator of how much N will be available to the crop than fall tests.
- Other nutrients. Grain protein development requires adequate amounts of other nutrients, especially sulfur (S) and potassium (K). Soil test to determine if all nutrients are adequate and apply accordingly, but applying other nutrients to increase yield without also increasing N supply can decrease grain protein by dilution in more grain.
- Increase N efficiency. Use practices that minimize N losses and increase N-use efficiency. Nitrogen that is lost from the soil cannot contribute to either yield or grain protein. Pay attention to proper timing, placement and source to get the most from every pound of N applied.
- Late N supply. Use practices that extend N supply later into the growing season. Nitrogen in the subsoil has been shown to increase grain protein, as this N is taken up later in the season and, in dryland environments, may be in better soil moisture and more available than N in the dry surface soil (Bly et al., 1997; Brown et al., 2005; Jones and Olsen-Rutz, 2012). Late-season N applications can increase grain protein as yield potential is already set, and this N goes mainly to grain protein. The optimum timing for these applications is at flowering (Bly et al., 1997). However, surface applications that are not moved into the root zone by rainfall or irrigation may be stranded in dry soil or lost to volatilization, and may not be efficiently utilized. Irrigated systems have more options for late-season N applications and may respond better to late applications than dryland cropping systems. In high-yield years when yield potential exceeds expectations, late-season N applications have been reported to increase grain protein about 70% of the time (Jones and Rutz-Olsen, 2012). Nutrien’s ESN, a controlled-release N fertilizer has been shown to increase wheat grain protein by supplying N during late vegetative growth and heading.
- Test the crop. A flag-leaf N content less than 4.2% can be a good indicator of potential response to late N applications (Brown et al., 2005).
- Foliar N. Foliar N applications at heading may sometimes be used to increase grain protein. Rates must be low enough to prevent foliar burn. Damage to the flag leaf can reduce yields. Foliar applications have been shown to increase grain protein about 60-70% of the time (Woolfolk et al., 2002).
- Split application. In high-yielding irrigated systems and in environments where rainfall is available to move late N applications into the soil, split N applications are preferred over one single N application at planting. Applying all the N before planting can stimulate production of many tillers and excess vegetative growth that results in inefficient N use. In moisture-stressed environments, excessive pre-plant N and accompanying excessive early vegetative growth can exhaust soil moisture reserves and potentially decrease yield. Nutrien’s ESN is a good tool to replace split applications, control vegetative growth and still provide N during heading.
Best management practices are available to boost wheat grain protein without sacrificing yield. Select appropriate varieties, know your soil and crop N status, supply adequate pre-plant N, use fertilization practices that minimize N losses, and add N if flag-leaf N is lower than about 4 percent at flowering. When combined with other best-management practices, these practices ensure the best crop for your environment, efficient use of fertilizer nitrogen and greater crop value.
- Bly, A., H.J. Woodard, and D. Winther. 1997. Late-Season Foliar N Application Effects on Grain Parameters of Hard Red Winter Wheat Varieties (16797). South Dakota State University Plant Science Department TB 99, South Dakota Agricultural Experiment Station, 1997 Soil and Water Annual Report.
- Brown, B., M. Westcott, N. Christensen, B. Pan, and J. Stark. 2005. Nitrogen management for hard wheat protein enhancement. Pacific Northwest Extension publication, PNW578.
- Jones, C. and K. Olson-Rutz. 2012. Practices to Increase Wheat Grain Protein. Montana State University Extension Bulletin, EB0206.
- Woolfolk, C.W., W.R. Raun, G.V. Johnson, W.E. Thomason, R.W. Mullen, K.J. Wynn, and K.W. Freeman. 2002. Influence of Late-Season Foliar Nitrogen Applications on Yield and Grain Nitrogen in Winter Wheat. Agronomy Journal 94:429–434.