Nutrient applications for wheat
Relatively early harvest in most of Illinois this year should allow enough time to get wheat planted and well established before it gets cold. If a wheat crop is in your plans this fall, consider a few pointers to ensure adequate nutrient availability and successful establishment of the crop.
Nitrogen (N) is important for vegetative growth, but the amount taken up by roots and vegetative tissues does not exceed 30 to 40 lb N per acre before it gets too cold. Nearly all modern varieties of wheat have been selected for improved standability. While concern about lodging under high N rates has decreased considerably, to minimize any lodging risks it is best not to apply too much nitrogen in the fall. Also, because N applications will promote excessive vegetative growth, the crop may come across disease problems later.
If the soil has large potential to supply N, fall applications before planting may not be necessary. Also, this year's cornfields should have some leftover N in the soil, as the crop probably did not use it all during dry conditions in July and August. Normally, in any given year an application of 20 to 30 lb N per acre in the fall is all that is needed to get wheat established. This amount can be supplied in the form of di-ammonium phosphate (DAP), which should also supply what is needed for phosphorus fertility (see the later discussion).
The total N required for a wheat crop depends on the capacity of the soil to supply it. Dark soils high in organic matter require less N than light-colored soils with low organic matter. For soils with organic matter higher than 4%, 70 to 90 lb N per acre is typically sufficient; soils with organic matter between 2% and 4% often maximize yields with a rate of 100 to 120 lb N per acre; soils with organic matter of less than 2% require 150 lb N per acre.
While the full amount of N can be applied with anhydrous ammonia and a nitrification inhibitor in the fall, the preferred method is to apply most of what is needed by top-dressing in the spring, right before the crop greens up and starts to take N. Application at this later time minimizes the potential for loss and provides needed N that might not be available from the soil due to slow mineralization of soil N by bacteria during cool springs. The top-dressing can be accomplished with dry or liquid N solutions as long as they don't contain free ammonia. If you use urea, it is important to apply it when leaves are free of dew or moisture and the soil surface is not excessively dry.