Heavy early summer rains may cause growers to be concerned about the loss of nitrogen (N).
Fields in the Corn Belt that receive excessive rain early in the season (April and May) typically aren't in as much danger of losing nitrogen because it wasn't yet converted to the nitrate form. However, as the soil warms the potential for N loss increases. If heavy rain occurs in June, growers may want to consider applying additional N later to fields that have experienced ponding. Ponding reduces the oxygen in the soil which can cause the nitrate to be denitrified. Denitrifying bacteria in the soil will rob the oxygen from the nitrate and release the nitrogen gas into the atmosphere. A good indicator of a loss of N is when the corn starts to turn yellow with the lower leaves being most affected. These leaf tips of N deficient corn will have the classic V-to the midrib.
Research has shown that supplemental N applications can help maintain corn yield after such heavy rainfall events.
Common methods of remediating N deficits include banding UAN between the rows using a high-clearance applicator or broadcasting urea with a urease inhibitor, if the corn is still small enough to drive over. Aerial application of urea is another way to apply N to very tall corn. While corn can be responsive to late N applications up to tasselling time, it is also good to remember that sometimes extremely stunted, waterlogged areas in the field can be just too damaged to recover.