If we get conditions where temperatures drop far enough below freezing at night, the soil will support ground application equipment until mid morning.  That way nitrogen is getting on early before much growth occurs.  Waiting until soils have warmed up risk having conditions too wet to allow traffic.  Early nitrogen is very important to encourage tillering of winter injured wheat or poor stands.

Establishment of red clover cover crops is improved with this frost-seeding approach.  Co-application of clover seed with nitrogen has been a successful practice in Ontario and when moist weather follows wheat harvest and can produce considerable nitrogen credits.  Details at:  http://www.gov.mb.ca/agriculture/soilwater/nutrient/fnm02s02.html  

Answer supplied by John Heard, MAFRI Crop Nutrition Specialist