From a plant-growth viewpoint, sidedressing is the ideal time for N application. However, if not done correctly, it can cause seedling injury. If the corn has emerged and is still small enough that you can use conventional equipment, the choices in rank order are:|
· Inject anhydrous ammonia or UAN solutions
· Broadcast ammonium nitrate or ammonium sulfate
· Broadcast urea
· Dribble UAN solutions between the row
· Broadcast UAN solutions
The first two will clearly be the most effective and safest techniques to use. Broadcast urea and dribble UAN (assuming that the dribble hoses do not go over the top of the row) will not damage the crop, but as with any nonincorporated urea treatment, they have the risk of N loss from volatilization. Broadcast UAN solutions have the dual risk of volatilization as well as plant injury.
Minnesota research reported slight to moderate leaf burn and stunting of early-season growth from the broadcast application of UAN at the V3 stage of growth at rates of 60 and 90 lb N/acre and severe burn with 120 lb N/acre. In this research, the early-season stunting did not translate into a yield reduction at harvest. However, one always needs to keep in mind that other environmental stresses, such as cold temperature, excessive precipitation, dry soils, and so on, in combination with the fertilizer injury could cause yield reduction.
Inclusion of atrazine at the rate of 2 lb/acre with the UAN treatments enhanced the leaf burn and stunting and resulted in significant yield reduction when the N rate exceeded 90 lb N/acre with the atrazine.
If fertilizer and herbicide need to be applied to corn that has emerged, the choices in rank order are:
· Apply a herbicide that is labeled for postemergence application, using water as the carrier, and then wait 5 to 7 days (check the label for the herbicide to see how soon tillage can be done after application) before injecting UAN or ammonia.
· Apply a herbicide that is labeled for postemergence application, using water as the carrier, and then broadcast ammonium nitrate or dry ammonium sulfate.
· Apply a herbicide that is labeled for postemergence application, using water as the carrier, and then broadcast urea.
Do not use a fluid fertilizer (including UAN solution) as the carrier when applying herbicides after corn emergence.Robert Hoeft