Nitrogen management for late planted wheat
Because of the wet fall and delayed planting wheat has had little time to tiller and grow this season. In some situations, producers were unable to apply starter N to the crop before planting. The general recommendation is to apply N one time between greenup and early stem elongation. However, producers have asked would applying N earlier offset the low fall tiller numbers (increase spring tiller numbers) and would tiller number and growth benefit from a split application?
Some points to remember as we determine a management plan:
1) Wheat requires very little N until early stem elongation. Seldom is N the limiting factor for fall growth and tillering. Even if N was not applied this fall, in most years organic matter in the soil is adequate to release enough N for early spring growth. We general recommend 20 – 30 pounds of N in the fall as insurance since we are planting no-till. However, where we have included fall treatments in N studies we have not seen a yield benefit. Another factor to consider this year, available soil N is more abundant with moderate winter temperatures, such as those we have experienced this winter.
2) Tillers that appear in the fall are responsible for most of the yield in the crop. Spring emerging tillers that develop into a spike generally are much smaller than fall tillers. From my observations, deficient levels of N for the growing season affect number of spikelets per head more than spikes per plant. However, vegetative tiller numbers may be increased with earlier N (we have not taken this measurement) but it has not affected yield.
With these points in mind, there is no reason to change management strategies. Spring N should be applied between greenup and early stem elongation. However, applying N before greenup should be avoided. Research data has shown that N applied prior to greenup, regardless of form may be lost and yields greatly reduced. Urea, urea-ammonium nitrate (28%) and ammonium sulfate were included in these studies. In most years, greenup does not occur until March 10 – 15 and in some years as late as April 1. I have not seen it occur in February anywhere in the state.
Split application of N would be an acceptable management system and may have larger yields compared to a single topdress at initial greenup, depending on the weather. Also a split would be a hedge if weather prevented N to be applied prior to stem elongation. However, research data has shown that a single topdress of N applied at early stem elongation yielded as well or better than a split application and unless large N losses occurred at early greenup, yields were similar between early greenup and split applications. Also keep in mind that if N losses were great at early greenup, N would also be lost from the first part of a split program. Thus a producer selecting the right time and N source should expect yields similar to a split application -- saving the cost and potential damage of a second trip across the field.