Nitrogen application is critical to corn as it nears the knee high stage. Up to this point, the plant has consumed little N but will be taking up 2.5 lb/ac/day as it approaches tasselling.
Broadcasting granular fertilizer such as urea can cause leaf scorching from those granules that end up in the whorl. Likewise, dribble UAN application can cause substantial leaf burn since droplets either run either off the leaf or into the whorl. And corn may be too large or soil too wet to allow side-dress injection of ammonia or UAN into the ground.
A safe option is to dribble UAN (28-0-0) using drop pipes so it contacts the ground and avoids the leaves. This simply means plumbing the high clearance sprayer with nozzles every 30” (rather than the current 20” for pesticides) and attaching flexible hoses to direct liquid to the soil. In the USA, one brand of the off-the-shelf units called Y-Drop Applicators have been so popular they are sold out. If soils are moist and temperatures hot, you should consider adding Agrotain to minimize volatilization loss from the applied fertilizer.
Submitted by: John Heard, Crop Nutrition Specialist, MAFRD