University of Illinois

No. 8/May 15, 1998

Sidedressed Nitrogen

Recent wet weather will force many growers, whether they planned to or not, to sidedress their nitrogen (N) on corn this year. There are several factors to consider.

What rate of N should I use? If corn was planted before May 1, use the normal rate of application. If it was planted after May 1, adjust the rate according to the expected reduction in yield. Reduce N rate by 1.2 pounds of N for each bushel of expected reduction in yield. Reduce yield expectation by 0.5 bushel for each day of delay in planting from May 1 toMay 10, an additional 1 bushel per day for each day of delay from May 10 to May 20, an additional 1.5 bushels per day from May 20 to May 30, and 2 bushels per day of delay after May 30.

Can I use any of the N fertilizers commonly available? The answer is yes, but some will work better than others. In priority order, our choices are as follows:

  • Injected urea-ammonium nitrate solutions (UAN) or anhydrous ammonia.

  • Broadcast ammonium nitrate or ammonium sulfate.

  • Broadcast urea.

  • Directed spray or dribble of UAN between the rows.

  • Broadcast spray of UAN.

Injection will eliminate the potential for foliar damage and the potential for volatilization losses of urea, but it will require a longer wait to allow the soils to dry for ensuring closure of the knife track. Such closure is important only for the application of ammonia. Start sidedressing as soon as you can see the row or tracks from the planter tractor and can matchthe applicator with the planter size. Be careful not to cover the row with loose soil.

Dry products such as urea or ammonium nitrate may be applied at any time after the corn is planted. If the corn is up, there may be some foliar damage associated with the granules that fall into the whorl of the plant, but this damage is unlikely to have a negative effect on yield. The damage will appear as small lesions on the leaf. If rain is not received within 3 to4 days after application, there is the potential that a portion of the broadcast urea might be lost through volatilization. Loss potential could be as high as 30 percent if rain is not received within 10 days after application. Directed spray or dribble of UAN between the rows will reduce the potential for foliar injury and may help reduce the potential for volatilization of the urea portion. Broadcast application of UAN over standing corn will result in foliar damage. If the corn is less than 6 inches tall, the effect on yield will be minimal.

How can I minimize damage from broadcast application of UAN? Apply as soon as possible. The larger the corn, the greater the foliar damage. Attempt to make broadcast application in advance of a rain. If there is rain within a few hours of application, the material will be washed off the leaves and give little problem. In addition, rain soon after application will greatly reduce the potential for volatilization loss.

Can I include a herbicide with my sidedress UAN? Minnesota research showed some yield depression associated with the addition of 2 pounds of atrazine (ai) per acre with 120 pounds of N per acre as UAN to corn in the three-leaf stage of growth. Combinations of UAN and 2 pounds of atrazine at rates of 90 pounds or less of N did not adversely affect yield.Researchers in Kansas evaluated the combination of 71 pounds of N as UAN with several different herbicides. They observed significant leaf burn on corn in the three- and six-leaf stage of growth, but yields were not affected. Be sure to check herbicide labels before applying them with UAN solutions.

Robert Hoeft (, Department of Crop Sciences, (217)333 -4424