April 6, 2012

One potential problem with spring application of N solution (UAN) in drier stress years is plant injury and possible yield loss. Many farmers apply herbicide and N solution to save a trip over the field. For dryland wheat, the N should be applied early (late March) to allow distribution into the root zone with spring precipitation; however,  this timing may be too early for effective weed control. Later applications are optimum for weed control but may cause problems with plant injury because of the herbicide-fertilizer combination. Visual damage to the wheat is usually apparent and some yield reduction may occur. (See Figure 1.)

Research at the UNL West Central Research and Extension Center at North Platte showed the extent of plant injury and effects on yield have not been predictable, but caution is advised. Yield losses ranged from 2-7 bu/ac and occurred about 40% of the time, especially for sprayings that caused 5-20% visual damage after Zadok stage 29 (before jointing). In this research, 40 lb/ac N was used so injury may be greater or less depending upon your N rate. Wheat under stress was damaged more than vigorously growing wheat and damage was greater on more developed wheat.

Gary Hergert
Extension Soils Specialist, Panhandle REC