Boosting Protein with MidSeason N Application: It Has Risks, But it Seems to Work

Have you ever noticed that some "agronomy" issues and questions are perennial, just like the coming of snow in the fall, the migration of geese, or teenagers asking for cash. The perennial issue I was just reminded of was this: Can I boost my wheat protein by topdressing or foliar applying nitrogen in the middle of the growing season?

On the local level, Mel Westcott, working over at Corvallis, has shown a modest degree of success with mid-season applications of nitrogen to wheat to boost protein. A study by Anthony Bly and Howard Woodard examined the timing influence of application of foliar N on grain yield and protein in hard red winter and spring wheat. Between 1995 and 2000 they evaluated the effect of applying 30 pounds per acre of N as UAN (a 1:1 solution of UAN and water) at Feekes scale 10.0 (boot stage) or Feekes scale 10.8 (post pollination). The 30 pounds per acre of N was in addition to their normal nitrogen application to achieve their intended yield goal of 50 bu/acre. They reported the following:

1. Timing of foliar application of N did affect the protein response.
2. The variety of wheat didn't make a difference.
3. A foliar application of N at post pollination did increase protein percentage, but yield decreased.
4. A foliar application of N at the boot stage also increased protein percentage, but not as much as an application later in the season.
5. Generally, where yield goal was exceeded, grain protein level was depressed.

What this translates into is the frequently-repeated admonition that you need to satisfy the yield requirements for nitrogen before you can boost or enhance protein. If the yield goal exceeds the nitrogen available, most of the nitrogen will go into grain production. The general rule is "Yield First, Protein Second."

Bly and Woodard proposed that a majority of the grain protein responses occurred when the targeted yield goal is exceeded (70% of the time). The increased grain protein response only occurred 23% of the time when the yield goal was not achieved. The way Bly and Woodard addressed this was: "From this, farmers should be aware of their yield potential, and if they feel the crop will exceed the initially expected or targeted yield goal, a post pollination application of 30 pounds foliar N would have a good chance (70%) of increasing grain protein."The bottom line is this: it looks like another study showing that mid to late-season foliar N applications can increase wheat protein in hard red wheats under the right conditions. Now, the question that wheat growers need to assess is whether a ½ % increase in protein in a 40 bushel/acre hard red spring wheat crop or a 0.8% increase in protein in a 70 bushel/acre winter wheat crop offsets the cost of applying 30 pounds of UAN at boot or post-pollination. Does the added value of the improved quality offset the cost of the treatment?

As a final note, Bly and Woodard offered a word of caution about a potentially negative impact of the foliar N application on grain yield. Grain yield was slightly decreased with foliar application. The foliar application did cause burn of plant material and could have caused the yield reductions. All foliar applications were made in the afternoon on days when temperatures were 70 oF or above. Some researchers suggest that the time of day when foliar application was made caused a difference in burn as well as protein response. Bly and Woodard tried to apply the foliar treatments at a time within the application window when they thought they would cause the most burn, which were sunny, warm afternoons. Farmers would be applying N at all times during the day. Therefore, the warmest temperatures of the afternoon probably resulted in the maximum burn.