Excess precipitation leads to nitrogen loss
Early fall applied N, such as liquid manure, would have significant conversion to nitrate last fall. The nitrate component of UAN solution (28 or 32 percent N) is immediately subject to loss, and the nitrification rate of urea and ammonium in UAN will be more rapid than anhydrous ammonia. Therefore, loss potential is greater with such applications.
An aspect of this spring that is somewhat different from past wet springs is the late corn planting and slow growth. From my observations in north central Iowa, the corn crop at this time is the smallest I remember in the 2000s. Corn N demand has been very low so far, and for late planted fields, season-long demand may be less due to lower productivity.
When warm, wet soils provide a good environment for microbial mineralization, the conversion of organic N to ammonium. Ammonium will accumulate under anaerobic conditions. While corn may die in ponded field areas, if replanted, the accumulated ammonium will supply crop-available N and perhaps an amount adequate to meet crop needs.
For corn fields with intended sidedress or split/sidedress N application, major loss conditions this spring have been avoided. For fields that had fall or early spring N applied, a visual way to check if corn will respond to additional N is to apply sidedress N fertilizer strips as soon as possible across several fields and watch the corn response. This can give a visual clue to potential for more N need and provide reference areas for mid-vegetative stage crop greenness measurement or canopy sensing.