Nitrogen applications for the 2012 corn crop
In fields with low nitrogen-supplying power (soils with low organic matter) or where no nitrogen has been applied, early application (before the V6 development stage) is recommended to avoid loss of yield potential. Another reason not to delay application, especially because of the dry conditions this year, is that the sooner nitrogen is applied, the greater chance it will have to be moved into the root zone by rain.
"In my opinion, the best options to sidedress nitrogen are to inject it into the soil or dribble it between rows," Fernandez said. If anhydrous ammonia is used, make sure the knife track gets properly sealed to avoid crop injury from free ammonia escaping to the atmosphere.
While most fields look very dry on the surface, adequate moisture is still present below the surface to retain the ammonia. According to Fernandez, "If the application is done at least 6 inches below the surface in fine-textured soils or at least 8 inches below the surface in coarse-textured soils, there should not be problems with ammonia volatilization." The advantage of dribbling nitrogen between crop rows over broadcast applications is that dribbling reduces the potential for volatilization of urea-containing fertilizers (urea and UAN) and reduces fertilizer contact with the foliage, thus reducing foliar damage.
If injection or dribbling options are not available, Fernandez recommends broadcast urea. This product has the least impact on leaf burn when compared to UAN, ammonium nitrate, or ammonium sulfate. If the canopy is wet, it is best to wait until it dries to minimize dry fertilizer adhesion to the leaves.
If there is not a high likelihood of rain, Fernandez suggests applying urea with a urease inhibitor (such as Agrotain) to minimize nitrogen volatilization. When urea is broadcast on the soil surface without a urease inhibitor, nitrogen losses start to increase 3 to 4 days after the application if there is no rain to incorporate it. After 10 days without rain, as much as 30 percent of the application can be lost. By contrast, ammonium sulfate and ammonium nitrate are not subject to volatilization losses if left on the soil surface.
The least desirable option is to broadcast a UAN solution because this application is most likely to injure the crop. If no other options are available, the application should be done as soon as possible because the smaller the plant, the less chance for fertilizer to make contact with it.
Some studies have shown that there is little damage if a UAN solution is broadcast when plants are about 6 inches tall. Similarly, for bigger plants (V4 stage), an application of up to 100 pounds of nitrogen per acre is unlikely to cause substantially reduced yield. This kind of application is best done a few hours before rain so the fertilizer can be washed off the leaves, although this is not advisable if a herbicide is combined with the UAN application (read the label to ensure this is allowable). Also, be aware that including a herbicide with UAN can intensify leaf burn damage.