Download - Wheat Life

WGC REPORTS WL
The three hard wheat “briefs” published in 2005 by the Washington Grain Commission.
to re-evaluate spring wheat yield potentials before the
remainder of the N is applied at or near planting.
The timing of fall fertilization for DNS and hard white
spring is critical. Early fall application is desirable in low
rainfall areas to ensure adequate time for some of the
N to convert from the ammonium form, which is not
mobile in soil, to nitrate (mobile form) and move down
the profile with over-winter precipitation. In high rainfall
zones, late fall application after soil temperatures have
dropped below 50º F is recommended. This not only limits
the conversion process, it also helps to prevent excessive
movement within the soil profile and the potential
loss of nitrates through leaching out of the root zone.
Monitoring. When yield potentials increase due
to favorable weather conditions, grain protein potential
will decrease unless additional N is supplied to compensate
for the higher yield. Hard wheat growers should
periodically evaluate whether the yield potential of the
crop has increased and ask themselves whether the N
supply (Table 1) is still adequate given the higher yield
potential. If not, supplemental N should be applied as
early as possible to adjust for the higher yield potential.
Tissue sampling can be used as a guide to determine
whether a crop contains adequate nutrients at various
growth stages. Whole-plant samples can be tested for N
and S content and compared to established critical values
to determine sufficiency. Many commercial agronomic
labs in Washington are capable of performing tissue testing
services. For DNS, a flag leaf N concentration of 4.5
percent at flowering is associated with 14 percent grain
protein.
Adjusting. In situations where an adjustment in
the N program is necessary to respond to a higher yield
potential, an in-season application may be warranted.
Late winter/early spring applications of N can effectively
supplement pre-plant applications and help achieve yield
and protein goals. Research shows the earlier in-season
applications can be made on dryland winter wheat the
better. Positive yield and protein response diminishes
with later in-season applications and may lower test
weights in low rainfall areas. Some consultants also recommend
a small amount of S be applied with in-season
WASHINGTON GRAIN COMMISSION
WHEAT LIFE JANUARY 2012 57