By Douglas Beegle
With all of the rain we have had since June, there are a lot of questions about nitrogen (N) deficiency.
Two common scenarios are: it was too wet to sidedress, so the corn did not get the necessary N and the other problem was loss of applied N with the excessive rain. Both of these are potential serious limitations for corn this year. Up until tasseling, N application will be beneficial, especially if the crop did not receive adequate N because it was too wet to sidedress. It is more difficult to predict if the crop will respond to additional N if a normally adequate amount of N was applied but may have been lost. Especially if there is a significant amount of organic N in the system, the N level may rebound when the soil dries out.
However, if the crop is showing serious N deficiency symptoms (inverted yellow V, starting at the tip of leaf and going back the midrib on the lower leaves), a late application of N prior to tasseling may be beneficial. Unfortunately, after pollination, there are not a lot of good options. Corn uptake of N declines sharply after pollination. After pollination, corn is mainly redistributing N that it took up during the grand growth period. Therefore, even though applications to corn after tasseling with high clearance equipment are sometimes possible, generally they are not very effective. There have been reports from the Midwest of benefits from modest applications (30-60 lb N/A) within a couple of weeks after tasseling on severely deficient corn. This will probably not make up completely for the lack of N uptake by the corn earlier, but may provide some benefit. Application of a small amount of foliar N, will not likely provide any sustained benefit. This may green it up for a day or so, but the amount of N taken up by the crop will be so small from such an application, that it will have minimal overall impact.