In season N applications to wheat
Much of the winter wheat in central South Dakota has finished the tillering phase of growth and begun to elongate. If the weather continues to provide us with adequate moisture, producers may find they would like to add some additional nitrogen to their crop to ensure nitrogen does not limit yield or protein.
If excellent growing conditions exist, producers can add nitrogen in a stream bar to wheat prior to flag leaf. If the nitrogen is added prior to a rain it should move into the root zone and be available to the plant relatively quickly.
Nitrogen that is added to wheat after tillering will not affect the head size of the plant since that yield component has already been set by the plant. However it can increase the seed set, kernel size and protein in the plants. These can also affect yield.
If the yield potential of a crop is higher than the yield goal, research has shown that there is a 70% chance of increasing protein in the grain by applying additional nitrogen. If the goal is to increase protein in grain, research has shown the nitrogen can be added as late as post flowering in wheat. Producers making this decision should consider cost of application and nitrogen product and should also know or have an idea of potential protein discounts or premiums.
Some caution must be taken when foliar N applications are made at flag leaf or later to avoid leaf burn. The nitrogen should not be applied when the plant is flowering but either pre or post anthesis to avoid affecting pollination. The N source should be UAN or preferably a 20% low biurite liquefied urea product. The liquid N should be diluted 1:1 (UAN: water) to reduce leaf burn. If possible the nitrogen should be applied on a cool cloudy day or in the early evening when the plants are not under stress or entering a stressful period. The plants should be dry when application takes place. It is not recommended to apply more than 30 lbs N/acre at this time. Nitrogen applied to wheat post flag leaf has been shown to increase protein in the grain, however, this protein gain does not necessarily improve baking quality of the wheat flour.