Fall fertilizer is best applied as close to freeze up as possible to balance two objectives:
(1) allow soil to seal over the band and (2) reduce losses due to high microbial activity in warm soils.
Banding in wet soil conditions will increase ruts, and wet soils can also increase losses if the soil does not close well over the band.
Banding in dry soils can also increase gassing-off losses because soil does not provide a proper seal on the band.
Depth: Band urea at least 2” deep. For NH3 banding depth, Manitoba Agriculture soil fertility specialist John Heard recommends increasing the depth of the band if you are seeing a lot of gas or if you can still smell the gas strongly after applying it.
Adding phosphorus: If fields are short of phosphorus, consider a phosphate and urea blend in the fall. Work from Don Flaten at the University of Manitoba shows that phosphate and urea in a dual band applied in the fall can make phosphorus more readily available in the spring. With fall application of phosphate, save some to apply with the seed in the spring. In the spring, apply some with the seed to the point that does not reduce emergence and uniformity of emergence and place the rest of the P needed, based on soil testing, in a side or mid-row band with the rest of the nutrients.
Source : Albertacanola