The key to a successful spring broadcast N application is to apply early when soil conditions are still cool. A healthy winter wheat crop will resume growth early in the spring. Cereal crops use 70 per cent of their N by late tillering, and late applications of N will hinder the plant’s ability to convert this into yield. As a rule of thumb, spring N applications should be made as soon as it is dry enough to operate equipment without making too many ruts. Some growers will even apply very early when they can still travel on the frost; however, it is not a good idea to apply N on frozen soils.
Liquid UAN (28-0-0) and ammonium sulfate (including sulfur fines) are less susceptible to volatilization losses then urea (46-0-0), but under ideal conditions, spring topdressing can occur on cool soils and/or just before a significant precipitation event. Under these circumstances, any of these products will perform equally well. However, if warm and humid conditions persist for a period of time, some N losses will likely occur. To minimize volatilization losses associated with these products, the use of commercial urease inhibitors, such as Agrotain, can be considered. The amount of trash on the soil surface may affect liquid N efficiency by immobilizing applied N.