Topdressing dry ammonium sulfate is a more efficient alternative for several reasons:

• Given that it does not have the initial basic reaction of urea and urea-based products upon application, it is less prone to loss as ammonia gas
• Given that all of the nitrogen is in the ammonium form, it is less prone to leaching than nitrate on coarse soils, and less prone to denitrification on heavy soils
• Under conservation tillage, dry crystals are able to make it through the residue, making it less prone to immobilization