COLUMBUS – As soon as the snow melts, in many areas it will be time to apply nitrogen to wheat.
District agronomy specialist Ed Lentz recommends producers consider three management decisions for wheat production: nitrogen rate, application time, and nitrogen source.
Nitrogen rate. The Ohio State University considers yield goals, or yield potential, in their nitrogen recommendations. Thus, a realistic yield goal is needed to determine the optimum nitrogen rate.
Once the yield goal is determined, the recommendation may be based on the following equation for mineral soils, which have both 1 percent to 5 percent organic matter and adequate drainage:
40 + [1.75 x (yield potential – 50)]
If 20 pounds of nitrogen was applied per acre in the fall, the spring rate should be reduced by 20 pounds per acre.
Spring application. If the crop received fall N, spring nitrogen may be applied between late February and early April. Application should be made before early stem elongation. Lentz said OSU research has shown significant yield losses if the first spring application occurs after Feekes GS 7).
If no fall nitrogen has been applied, the application should be made at greenup.
In most years, yield gains from a split application have not been large enough to offset the cost of a second trip across a field, Lentz said.
A split spring application program may be a benefit in poorly drained fields that are prone to nitrogen loss, and also in years that the potential for nitrogen loss is great.
Years that have a potential for nitrogen loss generally have a warmer than normal winter followed by a warm and wet April.
This pattern has only occurred once in the past five years (2002).
For split programs, Lentz said research would recommend a small nitrogen rate at greenup with the largest rate applied at initial stem elongation.
Delayed application. Another approach in years of potential nitrogen loss is to delay the spring nitrogen application to Feekes GS 5 or early GS 6.
Over the past three years, Lentz said, Ohio State research has shown similar yields or slightly better yields for single applications at initial stem elongation (Feekes GS 6) compared to initial greenup.
The number of heads was not reduced by the application delay.
This option should only be considered when some nitrogen has been applied in the fall. A producer also runs the risk of not getting adequate nitrogen on timely if fields are unsuitable for application at the later stages.
Nitrogen sources. Most nitrogen sources are satisfactory for wheat, but price and availability may limit some products in a given year.
Urea, urea-ammonium nitrate solutions (UAN), and ammonium sulfate are often the most common.
Ohio State research has shown similar yields among these three sources except in years of nitrogen loss. Urea-ammonium nitrate solutions have the greatest potential for loss, then urea, and ammonium sulfate, the least.
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