Applying nitrogen fertilizer to wheat
The profitable production of winter wheat depends on an ample supply of fertilizer nitrogen.
Early spring conditions have provided few opportunities to apply nitrogen (N) fertilizer to wheat so far. Fortunately, wheat is still a couple weeks away from requiring a significant dose of the nutrient. The following outlines some considerations for growers as they develop their strategies for this year’s crop.
For wheat, Michigan State University Extension recommends approximately 1.1 pounds of N per bushel of potential yield for fields where the historical yields are relatively low. Where yield potentials are high, the ratio is closer to 1.2 pounds of N. According to MSU Extension bulletin E2904, “Nutrient Recommendations for Field Crops in Michigan,” the actual equation is:
Pounds of actual N = (1.33 x yield potential) – 13
So, for example, a field that normally yields 80 bushels per acre would need approximately 93 pounds of N; if 10 pounds were applied at planting, the remaining 83 pounds would be applied in the spring. The actual rate should be reduced where soil organic matter is high and, of course, where manure or other organic source has been applied. Also, growers who elect not to use a fungicide at heading would probably do well to limit their total spring time application to 80 to 90 pounds per acre.
On the other side of the range, some growers have had success in using 130 or more pounds of N where the crop demonstrates strong yield potential (120 bushels or more). Fungicides will be applied to sustain crop health and the risk of crop lodging is accepted.
N application timing
Single applications of N on wheat are often sufficient if applied a couple weeks following green-up, usually mid- to late April in many seasons. N should not be applied on frozen ground. Even when applied soon after the ice has thawed, there is a risk of N loss due to excessive rains in early April. This was clearly the case in 2013 in central Michigan as excessive rains during the second week of April led to significant N loss. Those that delayed all N application until late April achieved the highest N-use efficiency.
Split applications might be considered where growers feel that an early application of N is needed to encourage tiller development or they would like to try boosting rates on a particularly promising-looking crop. When splitting N applications, the first application could be made at green-up on frosted, but not frozen, ground and the remaining portion when wheat is at, or near, jointing (late April or early May). Again, there is some additional risk of N loss to the early-applied portion. If, in fact, N loss is suspected, there is an option of increasing the N rate in the second application.
Various types of N fertilizer can be used on wheat. The most common are granular urea or 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.