Now that we are tasseling the next question is how late can we correct an N deficiency? It is best to get the N on as early as possible. However, yield responses that return income greater than the costs for application and fertilizer materials have been observed for N applied up to and slightly beyond the tassel stage. The magnitude of yield increase is dependent upon the severity of N deficiency and the ability of the crop to recover and respond to applied N (the growth and yield potential left after water damage and early season N deficiency). Any surface application is dependent upon rainfall to move applied N into the root zone, otherwise it cannot benefit the corn crop.
In the Lebanon area some contest fields in the past had recieved 100 lb of N at tassel only to gain a net yield increase of about 5 bu/acre so do not plan on increasing yields all that much. There are alot of factors that play a role. If the field has obvious yellowing from bottom to mid plant then perhaps and N application will increase yields up to normal versus none at all. Penn State chlorophyll meter guidelines do not go over about 80 lbs of N in season so I am not sure going extremely high on N applications farther above 50-80 will make much difference in the end.