Currently, the general recommendation for winter wheat and winter rye is to apply the majority of the nitrogen fertilizer early in the spring. Residual nitrogen and starter fertilizer provide adequate nitrogen to allow the crops to grow and tiller in the fall and the early spring timing reduces the risk of leaching and demineralization, thereby increasing overall nitrogen use efficiency, and creating flexibility should the winter wheat completely winterkill.
Ideally, we like you to apply the balance of the nitrogen as soon as the crop breaks dormancy and resumes growth. Winter wheat, like spring wheat, has the greatest need and uptake of nitrogen between jointing and heading. Winter wheat will take up nearly 3/4 of the total amount of nitrogen it will use in a season in that period.
This spring has been cold and wet. Consequently, you may have been holding off, waiting for drier conditions. Unfortunately, time is not on your side, and the application needs to be made sooner rather than later, especially in the case of winter rye.
Winter rye is a very daylength sensitive crop, meaning that the crop uses, in this case, the increase in day length to trigger the transition from vegetative to reproductive growth after the crop met its vernalization need last fall and earlier this spring. The crop will start to joint and stem elongation will start based more on calendar date rather than accumulated heat units (or lack thereof).
While we currently lack the data to suggest that winter rye (hybrid rye or open-pollinated) needs a larger portion of its total nitrogen demand met prior to jointing (we have research underway to find out), we do know that the calendar day at which the crop starts to joint and stem elongation starts is rapidly approaching.
Bottom line: Apply your balance of nitrogen fertilizer sooner rather than later even if conditions are far from ideal as delaying the application will likely reduce the yield potential of the crop.
Source : umn.edu