While southern parts of the country are seeing warming conditions on wheat, many others are still seeing snow pack. Ed Lentz, Ohio State University (OSU) crop scientist, says that when wheat fields are covered with snow, it is an easy decision to not apply nitrogen (N). How quickly that thought may change as the snow melts and time is available for field work, and driving across frozen ground does not leave ruts and spring is coming, he says. However, is applying N before greenup a good management decision?
To answer that question, a single broadcast N application was applied on frozen ground in late February or early March as urea, UAN (28%) or ammonium sulfate at the OARDC Northwest Research Station near Custar, OH, for three years. For two of the three years, yields from pre-greenup applications were as good as those made at greenup.
However, one year, yields were only slightly better than the zero check treatment, indicating significant N loss. In that loss year, all three N sources responded in the same manner – significant reductions in yield. Thus the 28% did not “burn” into the soil, ammonium sulfate did not “stabilize” into the soil and urea did not stay put until a rain. Basically, all three of the sources moved off the plots with water as the soil thawed out, much like losses from manure on frozen ground.
As a result of this study, OSU does not recommend N applications prior to greenup knowing that in many years, there will not be a yield loss from pre-greenup applications. This recommendation is also based on the time when wheat utilizes N. Wheat needs very little N until after Feekes 6 or stem elongation (after the end of April). After Feekes 6, N uptake increases rapidly until flowering. Results from the same study above also found that grain yields were not reduced delaying single nitrogen application until Feekes 6.
Thus, why take the risk from pre-greenup applications since the crop does not need large amounts of N until Feekes 6 and in some years much of the N may be lost from the pre-greenup application. In addition, the producer generally does not get N at a lower fertilizer cost in February or early March and the producer assumes all risk if the N is lost.
As a compromise between when the crop needs it and field conditions suitable for application, OSU recommends single application of N to Ohio wheat between greenup and Feekes 6. However, it would not surprise us when producers tell us that they applied it before greenup and had no yield loss, but then there will be those years of regret from that decision, says Lentz.