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INTERNATIONAL JOURNAL OF AGRICULTURE & BIOLOGY
1560–8530/2002/04–4–517-520
http://www.ijab.org
Effect of Nitrogen on Grain Quality and Vigour in Wheat
(Triticum aestivum L.)
EJAZ AHMAD WARRAICH, S.M.A. BASRA, N. AHMAD, R. AHMED AND MUHAMMAD AFTAB†
Department of Crop Physiology, University of Agriculture, Faisalabad–38040, Pakistan
†Barani Research Institute, Chakwal, Pakistan
ABSTRACT
A field experiment was conducted to evaluate the effect of different levels of N on grain quality and vigor in wheat. Quality of
grains was determined by their protein and phosphorous percentage. Nitrogen application improved grain protein and reduced
phosphorous percentage. Seed vigor was determined by standard germination and electrical conductivity tests. Seeds obtained
from nitrogen fertilized plots showed increased final germination percentage, while time to 50% germination (T50) and mean
germination time (MGT) were significantly reduced with the nitrogen application. Seeds obtained from 120 kg N ha-1
treatment showed more vigor during electrical conductivity test as compare to 0, 60 and 180 kg N ha-1.
Key Words: Nitrogen; Grain quality; Vigor; Wheat
INTRODUCTION
In cereals, dry matter production depends upon source-
sink relationship, where the source being the potential
capacity for photosynthesis and the sink is the potential
capacity to utilize the photosynthetic products. Balanced
mineral nutrition is the most important for the best source-
sink regulation. An adequate supply of nitrogen to the crop
plants during their early growth period is very important for
the initiation of leaves and florets primordia (Tisdale &
Nelson, 1984). Grain yield of wheat per unit area depends
upon number of Kernels per unit area and kernel weight.
Grain weight is a genetically controlled trait which is greatly
influenced by environmental conditions during grain filling
(Kausar et al., 1993). Nitrogen application also increases the
rate of grain filling (Langer & Liew, 1973; Whingwiri &
Stern, 1982; Eichenaur et al., 1986). Differences in final
grain weight were primarily determined by the differences
in grain filling rates (Nass & Reiser, 1975) and grain filling
duration (Gebeyehou et al., 1982). The grain filling rate and
grain filling duration depends both on genetic (Wiigand &
Cuellar, 1981; Mashiringwani et al., 1994; Mou &
Kronstad, 1994) and environmental factors (Sofield et al.,
1977; Wiegand & Cuellar, 1981; Bauer et al., 1985;
Wheeler et al., 1996). Grain filling rate is dependent upon
the average temperature during grain filling (Zhaq, 1986).
High temperature accelerates assimilation rate and enhances
movement of Photosynthates from flag leaf to spike but
shorten the grain filling duration (Sofield et al., 1977;
Bruckner & Frohberg, 1987). Nitrogen plays a very vital
role in the process of grain filling (Green, 1984), increase
leaf area of the crop and may result in increased dry matter
production by intercepting more sun light (Wilhelm, 1998).
A good supply of nitrogen also results in higher net
assimilation rate (Sage & Pearcy, 1987), more productive
tillers (Wilhelm, 1998), more number of spikes per unit
area, number of grains per spike, biological yield and grains
yield (Al-Abdulsalam, 1997). Nitrogen fertilization increase
wheat protein contents (Robinson et al., 1979; Knowles et
al., 1991) which is a good indicator of grain quality and
vigour.
Among various constraints limiting, wheat
productivity in Pakistan such as delayed sowing, lower
fertilizer rate and water shortage, availability of good quality
seed is a major hindrance.
Low soil nitrogen contents result in low protein
content in wheat grain (Fowler et al., 1989). Nitrogen
fertilization increases wheat protein content (Ortiz-
Monasterio, 1997; Robinson et al., 1979; Knowles et al.,
1991) which increases grain quality and vigour. Application
of nitrogen later in the season is more effective than earlier
application in increasing grain protein content (Kelley,
1995). Application of nitrogen fertilizer near anthesis is
more efficient in increasing grain protein content than
earlier application (Wuest & Cassman, 1992).
The objective of this experiment was to explore the
role of nitrogen fertilizer application in wheat grain quality
and vigor.
MATERIALS AND METHODS
The study was carried out at the Students Farm,
Department of Agronomy, University of Agriculture,
Faisalabad during the year 2000-2001. The treatments used
in the experiment were: T1: 0 kg N ha-1;T2: 60 kg N ha-1
applied at sowing; T3: 120 kg N ha-1 1/2 was applied at
sowing and ½ with first irrigation; T4: 180 kg N ha-1 1/3 was
applied at sowing, 1/3 with first irrigation and remaining 1/3
with third irrigation.
The experiment was laid out in randomized complete
block design with three replications and the net plot size was
1.5 x 6 m. Wheat variety, Auqab-2000, at a seed rate of 100
WARRAICH et al. / Int. J. Agri. Biol., Vol. 4, No. 4, 2002
518
kg ha-1 was sown in 6 rows spaced at 30 cm in each plot. All
Phosphorus in the form of Triple Supper Phosphate was also
applied at recommended rate at sowing. At maturity tillers
were counted a week before harvesting from a unit area (1
m2). Grain yield was recorded after harvesting the central
four rows from each plot. Grain quality and vigor was tested
in the laboratory by adopting the following procedure
Grain Quality
Determination of protein (%). Total nitrogen contents of
grains were estimated according to Ginning and Hibbards
method of sulphuric acid. Digestion and distillation was
made into saturated boric acid solution by Microkjeldahl’s
apparatus. The percentage of protein was calculated by
multiplying the grain N content with a constant factor of
6.25 (A.O.C.S., 1989).
Determination of phosphorous (%). One gram of seed
was digested in 20 mL of concentrated HNO3 and then 10
mL of 72% HClO4 was added to heat it to get colorless end
point. The digestion material was cooled and transferred to
100 mL volumetric flask, and to it 5 mL each of H2SO4,
ammonium vendate (0.25%) and ammonium molybadate
(5%) were added and allowed to stand for 3 min. Reading
was recorded on Backman Photometer 1211 using blue
filter paper. From standard curve actual reading was
calculated (Method 61, P-134.Agriculture Hand Book, US
Department of Agriculture.)
Grain Vigor
Standard germination test. Germination of control and
treated seeds was carried out between two layers of moist
filter paper in petridishes (Ashraf et al., 1999). Before
sowing, seeds were surface sterilized in 10 g L-1 sodium
hypo chlorite for 10 min, rinsed three times with distilled
water, soaked in 0.7 L L-1 ethanol for 1 min and again rinsed
three times with distilled water (Morris & Demacon, 1994).
There were 10 seeds sown per dish and experiment was
replicated thrice. The petridishes were covered with lids and
placed in an incubator at 25oC. Petridishes were monitored
daily and water was applied when needed.
Electrical conductivity of seed leachates. After washing
with deionized water, 5 g of wheat seeds was soaked in
beakers having 10 mL of deionized water. Electrical
conductivity of seed leachate was measured at room
temperature after 0.5, 1, 1.5, 2, 6, 12 and 24 h of the start of
the soaking (Ashraf et al., 1999).
The data were analysed according to the methods
described by Steel and Torrie (1984) at 1% probability
level.
RESULTS AND DISCUSSION
Grain Quality
Grain protein (%). Quality of cereal grains is determined
by their protein percentage. Nitrogen application to wheat
crop improves grain protein percentage. The results showed
that the protein percentage significantly increased with
increase in N fertilization rate (Table I). There was a
significant linear increase in protein percentage of grains
with increase in the nitrogen fertilizer rate. The highest
protein percentage was obtained from the seeds of the plots
fertilized @ 180 Kg N ha-1, while the lowest protein
percentage was found is the seeds that were obtained from
control plots.
Application of N late in the season is more effective
compared with earlier application in increasing grain protein
content (Kelley, 1995). Application of nitrogen near
anthesis is more efficient in increasing grain protein content
than earlier applications (Wuest & Cassman, 1992). The
increase in grain protein percentage with increasing levels of
nitrogen may be due to an increase in soluble proteins
(Krishchenko, 1984). Nitrogen application near anthesis
increased hard vitreous amber count (HVAC) which is
similar to grain protein contents (Robinson et al., 1979).
Grain phosphorous (%). The effect of different levels of
nitrogen on grain phosphorous percentage is shown in Table
I. Comparison of means for grain phosphorous percentage
revealed that increasing levels of nitrogen significantly
reduced grain phosphorous contents .The minimum value of
phosphorous percentage was observed in seeds that were
obtained from 180 kg N ha-1 fertilized plots while the
maximum phosphorous percentage was found in seeds
obtained from control plots.
Nitrogen application to wheat crop reduced grain
phosphorous percentage (House & Welch, 1984). Cereal
grains are major source of protein, and ideal wheat cultivar
should be high in grain nitrogen content but low in grain
phosphorous. High grain phosphorous levels may have
adverse effects on human health, because of anti-nutrient
phytate which is the major storage form of phosphorous in
wheat (House & Welch, 1984; Raboy et al., 1991). These
results are in good agreement with the findings of Dikeman
et al. (1982), Peterson et al. (1983), Raboy et al. (1991) and
Schulthess et al. (1997).
Table I. Effect of nitrogen on grain quality in wheat
Treatments Grain nitrogen (%) Grain phosphorous (%)
T1 1.49c 0.84a
T2 1.84b 0.79a
T3 1.92b 0.61b
T4 2.27a 0..57b
LSD(at p=0.01) 0.09 0.09
Table II. Effect of nitrogen on grain vigor in wheat
Treatments Standard germination tests
Final
germination (%) T50
(days) Mean
germination
time(days)
T1 80c 3.00a 2.5a
T2 90b 2.00b 2.00b
T3 100a 2.00b 2.00b
T4 100a 2.00b 2.00b
LSD(at p=.01) 2.11 0.06 0.06
N EFFECT ON WHEAT GRAIN QUALITY / Int. J. Agri. Biol., Vol. 4, No. 4, 2002
519
Grain Vigor
Final germination percentage. The most important vigor
evaluation test is germination percentage of seeds as it helps
to achieve target plant population. Individual comparison of
treatment means (Table II) shows the significant effect of
different nitrogen levels on final germination percentage of
wheat seeds in standard germination test. The germination
percentage of seeds of those plots, which were fertilized
with 60, 120, and 180 kg N ha-1 were statistically higher to
that of control. The maximum final germination percentage
(100%) was obtained from seeds of the plots that were
fertilized with 120, and 180 kg N ha-1.
The increase in final germination percentage may be
due to nitrogen application that increased grain protein
contents, grain protein yield, Hard Viterous Amber Count(
HVAC), grain volume, weight and kernel size (Ottman et
al., 2000).
Time to 50% germination (T50 days). The seeds which
showed less T50 were vigorous and able to germinate in less
time. The individual comparison of treatment means (Table
II) shows significant effect of different nitrogen treatments
on the t50 of wheat seeds in standard germination tests. The
time to 50% germination of seeds of those plots, which were
fertilized with 60, 120, and 180 kg N ha-1 was statistically
less to that of control. Seeds from the plots that were
fertilized with nitrogen showed less t50, because nitrogen
application near anthesis are more efficient at increasing
grain protein content (Wuest & Cassman, 1992), which may
help in reducing the time to 50% germination
Mean germination time (MGT) (days). It is an important
indicator of seed vigor. The seeds which show less mean
germination time (MGT) are designed as more vigorous
seeds and are able to germinate with less period of time. The
comparison of treatment means (Table II) show significant
effect of different nitrogen treatments on the mean
germination time of wheat seeds in standard germination
tests. The MGT of seeds of
those plots, which were
fertilized with 60, 120, and
180 kg N ha-1 was
statistically less to that of
control. The reduction in
mean germination time with
nitrogen application may be
due to that nitrogen
fertilization increase wheat
grain protein contents.
(Robinson et al., 1979;
Knowles et al., 1991; Ortiz-
Monasterio, 1997), which in
turn increased the grain vigor
and reduces the mean
germination time.
Electrical conductivity of
seed leachets (μs/cm2). The
rate of solute leakage
measured by conductivity test has been widely used as vigor
test. Non-viable and deteriorated seeds have been reported
to leak more solute when placed in water than viable or
vigorous seeds. The Fig. 1 shows the effect of different
nitrogen treatments on the solute leakage of wheat seeds.
The leachates of the seeds obtained from the crop fertilized
@ with 120 kg N ha-1 had the minimum electrical
conductivity than the all other treatments. Maximum EC
value was recorded in control. Overall results of electrical
conductivity test show that EC of the seed leachates was
decreased with increase in nitrogen level upto 120 kg N ha-1,
after that it increased with increase in nitrogen level but less
than control.
CONCLUSION
The conclusion of this experiment is that nitrogen
application improves the grain quality and vigor in wheat by
improving the grain protein contents. The improved protein
contents increase the final germination percentage and
reduced the T50 and Mean Germination time.
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