Integrated Crop Management

Post-plant nitrogen applications on corn

Has the wet weather interrupted planned nitrogen (N) fertilizer applications? What are the options if corn has emerged? All is not lost. In fact, in wet springs sidedress N can be an advantage because delayed application avoids potential losses and increases use by the crop.

Some suggestions follow, in order of preference:

Row cultivation after surface application of urea and UAN is best to minimize volatile loss. Applications can begin immediately after corn planting as long as the rows are visible and application does not cover plants. Injection places N into the root zone, which is an advantage if surface soil dries or rainfall is inadequate to move surface-applied N into the soil. If corn becomes too tall for typical sidedress equipment, dribbling UAN can be accomplished with high-clearance equipment. Some precautions include the following:

In most situations, N applications delayed until approximately the V6 growth stage should not result in yield loss. The more fertilizer N or manure applied preplant or at planting, the greater the amount of residual soil N, or the larger the rotation effect for supplying available N (those fields with lowest expected response to applied N and least additional N need), the later applications can be delayed into the season with little crop N stress or yield loss. These fields should suffer the least if N application is delayed. If the soil N supply is low (fields with the greatest potential response to applied N and largest N need), and especially if little to no N was applied preplant or at planting, applications should be made before approximately V6 if possible and these fields should be targeted for priority applications.

Leaf injury from broadcast urea at 50 lb N/acre to V6 stage corn.

Leaf injury from broadcast ammonium nitrate at 50 lb N/acre to V6-stage corn.

This article originally appeared on page 72 of the IC-486 (9) -- May 14, 2001 issue.

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