Early spring is the time wheat growers implement nitrogen (N) fertilization strategies. This means estimating the amount of N needed and estimating how much of the N might be lost due to excessive rainfall and saturated soils.
Michigan State University Extension recommends approximately 1.1 pounds per acre of fertilizer N per bushel of potential yield where the historical yields are relatively low. Where yield potentials are high, the ratio is closer to 1.2 pounds of N.
The actual equation is: Pounds of actual N = (1.33 x yield potential) – 13, according to MSU Extension Bulletin E2904, “Nutrient Recommendations for Field Crops in Michigan.” So, for example, for a field that normally yields 80 bushels per acre, you would apply approximately 93 pounds of N; if 10 pounds were applied at planting, the remaining 83 pounds would be applied in the spring.
Of course, the actual rate should be adjusted based on the grower’s experience on their farm and where there are organic sources of N, such as high organic matter soil or manure applications.
Another consideration is whether a grower intends to use a fungicide soon after heading to protect against foliar and head diseases. Where the crop is protected from diseases, the profitable response elevated rates of N is much more likely. Conversely, if a fungicide is not part of a grower’s program, the spring-time N rate should probably be limited to 80 or 90 pounds per acre.
Beyond this, the grower’s challenge is to minimize the loss of fertilizer N due to excessive early spring rainfall. The answer, in part, might be to delay N application until mid- to late April or splitting the N application between green-up and full tillering (approximately May 1). For those that apply their entire N at green-up, some N loss can be avoided by blending in some ammonium sulfate or a delayed release formulation with their granular urea as opposed to relying solely on urea.
Another consideration this spring is an inordinate amount of acreage was planted exceptionally late last fall. These acreages would likely benefit from some N as early as possible; that is, at green-up or on frosted ground. Fertilization should not be made to frozen ground, however.
Various types of N fertilizer can be used on wheat. The most common are granular urea and ammonium sulfate, and liquid 28 percent UAN (urea/ammonium nitrate blend). Which material is used is less important than how evenly it can be distributed across the field. Because liquid materials are more likely to be spread evenly, UAN through streamer nozzles has gained popularity.