Proper timing of spring N application can significantly increase winter wheat yield. Figure 1 shows the yield obtained at the economic optimum N rate (EONR, N rate where profitability was maximized) when N was applied in spring at green-up or at growth stage 30 (GS30, hollow stem – just prior to first node). At all sites except Lamartine-15, yield was greater when N was applied at green-up compared to GS30. Averaged over all sites, there was a 10 bu/a advantage to applying N at green-up. Applying additional N can not compensate for the yield loss caused by applying N at the later timing as demonstrated by the data in Figure 2.
To maximize yields, growers should try to apply N as soon as possible in the spring, taking into consideration soil physical conditions. Applying N when the ground is barely traffickable will likely result in rutting, compaction, and possibly yield loss if plants are damaged. One tactic to accomplish early N application might be to apply N in the morning before the top few inches of soil have re-thawed. Care should be taken to insure that N does not runoff the field before it has a chance to move into the soil.