Late Season Nitrogen Enhanced Wheat Protein as Affected by Late Season Moisture. B. D. Brown. University of Idaho

1
Late Season Nitrogen Enhanced Wheat Protein as
Affected by Late Season Moisture. B. D. Brown.
University of Idaho
Summary Late season N was more effective for
enhancing protein of non-stressed high yielding
wheat than moisture limited low yielding wheat,
despite the higher total protein involved in a
specific protein increase in more productive
wheat. Baking quality as defined by bake
volume was improved in each year as protein was
enhanced with LSN, ESN, or yield limited by
moisture during grain fill.
Introduction High protein premiums and
higher prices have increased traditional
irrigated soft white wheat grower interest in the
production of the hard red classes. Higher
returns from the hard red class are dependent on
avoiding discounted prices for low protein (lt
14). The importance of adequate nitrogen
(N) for yield and protein is generally
appreciated. Late season N (LSN), fertilizer
applied at heading (Feekes 10.1-5) has increased
wheat protein in several environments and the
practice is common in many hard wheat production
areas. But LSN rates appropriate for protein
enhancement in limited rainfall low yield
environments may not be appropriate for irrigated
high yield environments. Producers of irrigated
hard red wheat frequently fail to consistently
raise wheat protein to desirable levels (14)
with low to moderate LSN rates reported in
published studies (1,2). Yield is frequently
limited by moisture during grain fill. The
effect of moisture limited yield on the protein
and baking quality response to LSN has received
little attention. Higher wheat protein is
generally associated with improved baking
quality, thus the high protein premium and low
protein discounts in market prices. But there
are reports that LSN may not improve wheat baking
quality even if wheat protein is increased (3).
The objective of this study was to
determine the response of protein and baking
quality to LSN in wheat that varies in yield due
to late season available moisture..
Methods A hard red spring wheat field study
was conducted for four seasons (1995-98) at the
University of Idaho Parma Research and Extension
Center involving early season N (ESN) rates of 67
and 135 kg ha-1, LSN rates of 45 and 90 kg ha-1
applied at heading, and irrigation treatments
(IR) of 0, 0.5, and 1.0 times estimated ET from
the last uniform wetting. ESN and LSN were
topdressed urea incorporated with sprinkler
irrigation. Treatments were arranged as a split
plot randomized complete block design with four
replications. The ESN rate and IR treatments
were randomized among the main plots. Main plots
were 3 m wide and 27.4 m long and were divided
into three subplots each 9.1 m long The soil
was a Greenleaf-Owyhee silt loam (fine-silty,
mixed, mesic, Xerollic haplargids). Previous
crops were sudan grass (1995-97 seasons) and
potatoes (1998 season). Vandal hard red spring
wheat was seeded at 110 kg ha-1 with 17.8 cm row
spacing. The wheat received uniform rainfall or
sprinkler irrigation through the boot to heading
stage. The IR treatments during grain
filling were imposed using a drip irrigation
system. Four drip lines were spaced 0.6m apart
and parallel to the planted rows in the 3.0 m
wide main plots that received additional water
during grain fill. Different amounts of moisture
were applied during each drip irrigation set by
spacing emitters 30 cm (full irrigation) or 60 cm
(0.50 estimated ET) in the drip line. Bureau of
Reclamation (BOR) evapotranspiration estimates
from the Agrimet System were used to schedule
irrigations after heading. Grain yield was
measured with a small plot combine from 11.6 m2 .
The moisture corrected (12) protein was
determined using NIR and baking quality was
determined using AAcC method No. 10-10B at the
University of Idaho Aberdeen Wheat Quality
Laboratory. Bake volume was determined using
rape seed displacement. All data were
analyzed using analysis of variance procedures
available in SAS.
Results continued In contrast, protein in 95
increased as yield increased with added moisture
because the LSN topdressed by hand was not as
available for uptake in the non-irrigated
treatment due to dry soil conditions at the LSN
positioned depth. Protein increased
linearly in all years with each increment of LSN,
unless protein without LSN was above 17 (Figure
3). Except for 95, protein was highest when
yield was limited by moisture stress during grain
fill. Generally 45 kg ha-1 was needed to raise
protein from 13 to 14. Baking Quality
Bake volume increased each year with higher
protein regardless of whether the protein
increase was due to higher ESN, lower yields from
moisture stress during grain fill, or LSN (Figure
4). Bake volume improvement with LSN was limited
if wheat with no LSN was higher than 15 protein.
Bake volume was higher in 97 (1154 cm3) and 98
(1182 cm3) than in 95 (1026 cm3) and 96(1020
cm3). Bake volume was affected by IR treatments
in all years except 97. Improvement in bake
volume with LSN tended to be greatest with the
first LSN increment of 45 kg ha-1. Further
improvement in bake volume occurred with the
second LSN increment, but unlike the protein
improvement, the improvement in bake volume with
LSN was not linear. Either the protein
measurement reflects non-protein N that increases
with LSN or the protein resulting from high LSN
is poorer in quality for bread making.
Baking volumes were not consistently related to
specific protein concentrations. For example, 96
bake volumes associated with protein above 17
were smaller than in 97 or 98 wheat testing less
than 14 protein. Baking quality is clearly
dependent on more than crude protein.
Nevertheless, baking quality was invariably
improved when protein was enhanced with LSN at
heading.
Results continued were delayed in 97 and 98 since
rainfall or soil moisture was believed adequate.
By the end of the season, wettest and driest IR
treatments differed by 16.5, 32.6, 12.7, and 17.4
cm water received for the 95, 96, 97, and 98
seasons, respectively. IR treatments differed
more in 96 because they were started earlier and
there was little rainfall during the rest of the
season. Grain Yield Grain yield was
higher with the 135 kg ha-1 ESN rate in 1996
(4.27 vs 3.97 Mg ha-1) and 1998 (6.10 vs 5.88 mg
ha-1) but did not differ significantly in other
years. Grain yield increased significantly
with late season N only in 1997, increasing from
6.20 to 6.66 Mg ha-1. There were no significant
yield interactions involving LSN. Water
added at the 0.5ET rate during grain fill
increased yield in all seasons but the full
irrigation treatment was necessary for maximum
production in only 96 and 97 (Figure. 2). Yield
increased from as little as 28 to as much as
286 with additional water during grain fill.
The full irrigation treatments provided less
than the predicted ET by the end of the season in
all years. But yields were not affected by end
of season ET deficits of 25 cm in 95 and 17 cm in
98. Soil moisture was no doubt used in part to
make up part of the deficit. It is also likely
that BOR predicted ET was greater than actual ET,
particularly late in the grain filling
period. Protein Protein increased in all
years with the highest ESN rate with increases
ranging from 0.3 to 0.9 for the extra 67 kg
ha-1 N added. Except for the 95 season,
protein declined as yield increased from the
first increment of added water (Figure 2). This
was especially evident in 1996 when yield
increased almost threefold with the wettest
treatment and protein decreased from 17.5 to 13.
Discussion We anticipated that LSN for
enhancing protein would be more effective when
yield was limited since more N was available per
unit of grain produced and the total protein N
associated with a change in protein concentration
would be less in lower than higher yielding
wheat. On the contrary , we found the
protein increase with LSN was greatest in years
with the highest yields, as in 97. Within years,
the protein increase with LSN was either no
different or considerably higher in the most
productive wheat as compared to the yield limited
by reduced moisture. The greater
efficiency of LSN under higher yields and well
watered conditions may be attributed in part to
greater root access to LSN as periodic wetting
maintained root activity at LSN positioned
depths. The results may not be relevant for
foliar LSN applied at rates that would avoid leaf
burn. Also, more efficient utilization of N
taken up by wheat can not be ruled out. Few
studies have employed top-dressed LSN rates for
protein enhancement as high as the 90 kg ha-1
used in our study. The results suggest that the
efficiency of protein enhancement under well
watered conditions does not differ for moderate
and high LSN rates, provided protein is not high
to begin with.
Figure 2. Mean yield (dark symbols) and protein
(open symbols) as affected each year by late
season water (IR treatments).
Figure 3. Mean protein as affected by late
season N at heading and moisture provided during
grain fill. Bars within figures are the LSD.05
for the LSN effect..
Figure 1. Cumulative ET and water (irrigation
and rainfall) received each season after May 14
for IR treatments.
References 1. Stark, J. C., and T. A. Tindall.
1992. Timing split applications of nitrogen for
irrigated hard red spring wheat. J. Prod. Agric.
5221-226. 2. Christensen, N. W. , and R. J.
Killorn. 1981. Wheat and barley growth and N
fertilization under sprinkler irrigation. Agron.
J. 73307-312. 3. Sylvester-Bradley, R. 1990.
Does extra nitrogen applied to breadmaking wheat
benefit the baker. In Cereal Quality II
Aspects of Applied Biology No. 25, Association of
Applied Biologists pp. 217-228.
Results Moisture Received Cumulative ET
(CumET) and cumulative water received from
irrigation and rainfall (Cumwat) after May 15 or
jointing (Feekes 6) are indicated in Figure 1 for
each year and IR treatment. Water received
uniformly as rain or irrigation after May 15 (UW)
was 5.1 cm in 95, only 1.5 cm in 96, 7.8 cm in
97, and 5.3 cm in 98. IR treatments
Acknowledgement This field study was
accomplished with the technical support of Dr.
Roger Gibson, Scientific Aide, and seasonal
employees Janet Murakami and Vernon Booth. The
baking quality determinations were obtained with
the cooperation of Kathryn OBrien and the
University of Idaho Aberdeen Wheat Quality
Laboratory.
Figure 4. Mean bake volume as affected by late
season N at heading and moisture provided during
grain fill. Bars within figures are the LSD.05
for the LSN effect