Vol.4, No.9, 499-508 (2013) Agricultural Sciences
http://dx.doi.org/10.4236/as.2013.49067
Effects of N rates on N uptake and yield in erect
panicle rice
Guiyun Song1, Zhengjin Xu2*, Hengshan Yang1
1Agricultural College, Inner Mongolia University for the Nationalities, Tongliao, China
2Northern Japonica Rice Cultivation and Breeding Research Center, Shenyang Agricultural University, Shenyang, China;
*Corresponding Author:
Received 2 July 2013; revised 2 August 2013; accepted 20 August 2013
Copyright © 2013 Guiyun Song et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
The field experiment was conducted in 2005 and
2006 at Northern Japonica Rice Cultivation and
Breeding Research Center, Shenyang Agricul-
tural University, Shenyang, northeast China.
Shennong 265 (typical erect panicle rice cultivar),
and Liaojing 294 (traditional semi-erect panicle
rice cultivar) were grown under different N rates
to assess N uptake and N use efficiency. Nitrgen
(N) uptake of two rice cultivars increased in their
response to N improvement. Grain N of Liaojing
294 predominantly came from root absorption
on low N treatments, while grain N of Shen-
nong 265 mainly came from root absorption and
had less N re-transferring from vegetative or-
gans under high N rates. Shennong 265 pro-
duced less N uptake before heading and more N
uptake after heading than Liaojing 294. GY was
highly related with N fertilizer rate (r2 = 0.870** for
Shennong 265, r2 = 0.613* for Liaojing 294).
Shennong 265 was a N-unefficient genotype,
since it produced low yield at low N levels and
responded well to N application. Liaojing 294
was a N-efficient genotype producing high yield
at both low and high N rates. NNG and NFUE ex-
hibited positive correlation with N application
rates, but NUEPG showed negative correlation
with N application rates; GY as well as BIO and
N uses efficiency parameters (TN, NNG, NFUE)
which were all positively correlate, while the cor-
relation between GY as well as BIO and the other
N efficiency indicators expressed negative cor-
relation. The relationship between GY and TN as
well as BIO and TN was observed with signifi-
cant difference (r2 = 0.824**, r2 = −0.858**).
Keywords: N Use Efficiency Parameters; Erect
Panicle Rice; Biomass
1. INTRODUCTION
Donald first put forward “Ideotype” of wheat. Yin no-
ticed that erect spike of wheat was attributed to the pho-
tosynthesis of its spike and other vegetative organs, and
the increase of extinction coefficient of rice might be
owing to its curved spike in late grain-filling stage. In
addition, curved or half-curved spike rice (like Tiejing 4
and Liaojing 294) easily led to lodgeg and reduced yield
[1,2]. Therefore, erect panicle was one of important ag-
ronomic traits in designing “New Plant Type” of super
high yield rice [3,4]. In 1996, Shenyang Agricultural
University successfully developed a super-high-yield,
erect panicle, japonica rice, Shennong 265, and its grain
yield reached 12 t·ha−1. This cultivar has been grown
successfully through the northern China. Several other
super-high-yield japonica rice cultivars with the erect
panicle have also been successfully developed [5]. Many
studies have provided evidence that light diffusion in
different part (canopy, middle, and low part) of erect
panicle rice is reasonable especially in late grain-filling
stage. Erect panicle rice utilizes solar energy effectively,
accelerates CO2 diffusion, improves its growing eco-
logical conditions especially in its middle and low part of
rice, and increases population growth rate after heading,
which all contribute to higher biomass and yield [6,7].
Currently, the super rice of erect panicle is grown on
1,300,000 ha throughout China, in an area ranging from
the Yangzi River to the Songliao Plain [8,9].
N is usually the most yield-limiting nutrient in rice
cropping systems worldwide [10-12]. Chinese farmers
were likely to broadcast more N fertilizer than needed in
an attempt to increase the grain yield. China is currently
the world’s largest consumer of N fertilizer, and irrigated
rice accounts for nearly 7% of global N consumption.
Average rate of N application for rice production in

G. Y. Song et al. / Agricultural Sciences 4 (2013) 499-508
500
China is high and N-use efficiency is low compared with
other major rice growing countries [13,14]. Low fertil-
izer-N use efficiency of irrigated rice increased environ-
mental pollution through rapid losses of applied N by
volatilization, denitrification and nutrient leaching from
farms [15-18]. The average apparent N losses with the
optimum N rates were less than 15 kg·N·ha−1, whereas
the farmers’ conventional N application rate resulted in
losses of more than 100 kg·N·ha−1. The study identified
genotypes which possess promising traits for improved N
uptake and use efficiency [19-21]. The remobilized N
was the largest contributor of N to the grain, and total N
accumulation during the grain filling period could be the
greater contributor to yield provement [22]. The yield of
rice can be improved by optimising the plant’s N uptake
through increased N recovery efficiency [23-25]. There-
fore, optimizing N use for crop considerably reduced N
losses to the environment without compromising crop
yields [26,27].
With increasing awareness regarding the need for en-
vironmental protection, it is important to improve N use
efficiency in the rice crop in the world and especially in
China. However, little effort has been made to explore
the potential panicle variability in N uptake and use effi-
ciency in northern China. The objective of this study was
to determine effects of different rates of N fertilizer on N
absorption and N use efficiency indicators of different
panicle rice cultivars grown under irrigated condition in
northeast China. The hypothesis tested was that Shen-
nong 265 had potential to produce high yield through
improving N use efficiency relative to Liaojing 294. This
study provides information needed for future studies on
breeding and cultivation of northern japonica rice in
China and the decrease of the N pollution.
2. MATERIAL AND MATHODS
2.1. Experimental Site
The study was conducted in 2005 and 2006 at the
Northern Japonica Rice Breeding and Cultivation Re-
search Center, Shenyang Agricultural University, Shen-
yang, Northeast China (123˚28′E, 42˚41′N, and elevation
40 m above sea level). The region is characterized by a
temperate sub-humid continental climate with average
temperature ranging from 6 to 11˚C, 2554 h of sun-shine,
61% - 65% of average relative humidity, 706 mm of an-
nual precipitation, 24 d of average rainy days, and 150 -
170 d of frost-free period. During growing season, air
temperature began to decrease gradually from late Au-
gust to October. Air temperature during growth season
was stable (Figure 1).
The study sites were located on clay loam, meadow
soil. The soil on the study sites had pH (1:5 soil/water)
5.7, organic matter content 21.6 g/kg, available N 84.5
mg· k g −1 (Table 1).
2.2. N Experiments
Cultivars Shennong 265 (typical erect panicle rice)
and Liaojing 294 (traditional semi-erect panicle rice)
were grown under irrigated condition with different N
rates in 2005 and 2006. These two cultivars had different
N characteristics and were selected from several years of
field experiment conducted before 2005. In 2005 and
2006, a field experiment was laid out as a randomized
complete block design with three replications. In 2005,
each plot was 5 m × 2.7 m. N treatments included 0 (N0),
100 (N1), 180 (N2), 260 (N3) kg·N·ha−1. In 2006, the
treatments consisted of two levels of N: 0 (N0), 180 (N1)
kg·N·ha−1 with three replications, each plot was 5.2 m ×
2.7 m. On each treatment, the N fertilizer (urea: 46% of
N by equivalent weight) was applied as four-time split.
In addition, 124 kg·ha−1 of K fertilizer (potassium chlo-
ride: 55% of K2O equivalent by weight) and 105 kg·ha−1
of P fertilizer (ordinary super phosphate: 14% of P2O5 by
equivalent weight) were also applied. 30% of the N and
100% of the P and K fertilizers were applied to the soil
before transplanting. The second 30% of the N fertilizer
was applied at tillering stage, 20% at panicle initaiation,
and the final 20% at heading stage. Also, 15 kg·ha−1 of
zinc sulfate (24% of Zn equivalent by weight) was ap-
plied before transplanting. The Polyethylene plastic
board was inserted into the underground to isolate be-
tween plots.
The dates of sowing and transplanting were summa-
rized in Tab le 2. There were 28 hills·m−2 (27 cm × 13.3
cm spacing in 2005) and 20 hills (30 cm × 16.5 cm
spacing in 2005), and two seedlings per hill. Weeds, in-
sects and diseases were controlled by applying herbicides,
insecticides, and fungicides according to commonly
management practices for rice crops in the northeast of
China.
2.3. Plant Sampling
Ten hills were randomly selected at each N treatment
plot to measure tiller number, leaf age, and plant height
every 7 days from June 10 to August 12.
Periodic harvesting (June 26, July26, August 6, Sep-
tember 8, October 4) of six hills from each plot were
done during growing season. After measuring leaf area,
the plant samples were separated into leaf, leaf sheath,
culm, panicle (stem panicle rachis, and grain), then each
fraction was placed into a drying oven at 105˚C and
dried for half an hour, which was followed by drying at
80˚C to a constant weight. After drying, all plant samples
were weighted and ground to pass through 2 mm sieve,
ground again to pass through 0.25 mm sieve, and stored
in sealed bottle until chemical analysis. Leaf, leaf sheath,
culm, stem panicle rachis, and grain (caryopsis hull)
were analyzed separately for total N by using the Kjelda-

G. Y. Song et al. / Agricultural Sciences 4 (2013) 499-508 501
(a)
0
10
20
30
40
50
7:00am 8:00am 9:00am
10:00am
11:00am
12:00
1:00pm
2:00pm
3: 00pm
4:00pm
5: 00pm
Radiation（mw.cm
-2
)
4-Jul6-Aug 18-Sep
(b)
0
10
20
30
40
50
7:00am 8:00am 9:00am
10: 00am 11:00am
12: 00
1:00pm 2: 00pm 3:00pm 4:00pm 5: 00pm
Temperature (ºC)
4-Jul 6-Aug18-Sep
(c)
0
10
20
30
40
50
7:00am
8:00am
9:00am
10:00am
11:00a m
12:00am
1: 00pm
2: 00pm
3:00pm
4:00pm 5:00pm
Radiation(mw.cm
-2
)
6-Aug 30-Aug 18-Sep
(d)
0
5
10
15
20
25
30
35
7:00am
8:00am
9:00am
10: 00am 11:0 0am 12:0 0am
1:00pm 2:00pm 3:00pm 4:00pm 5:00pm
Tem per atu re( ºC)
6-Aug 30-Aug 18-Sep
Figure 1. Temperature (a) and radiation (b) in 2005 and temperature (c) and radiation (d) in 2006 at different time of a day during
rice growing season.
Table 1. Soil physical and chemical properties of the 0 - 20 cm layer in experimental sites in April in 2005 and 2006.
Year Available N (mg·kg−1) Available P (mg·kg−1)Available K (mg·kg−1)Organic matter (g·kg−1) pH water (1:5)
2005 84.5 38.3 138.9 21.6 5.7
2006 82.5 35.3 131.6 20.5 5.7
Table 2. The key dates of the rice growth season in 2005 and 2006.
Transplanting
Year Sowing date
date density(hills·m−2)
Heading date Harvest date
2005 April 20 May 28 28 August 1 October 6
2006 April 15 May 20 20 August 2 October 4
hl method [28].
2.4. Soil Sampling and Analysis
Composite soil samples (five individual sample) from
0 to 20 cm depth were taken for analysis from each
treatment plot prior to transplanting in April. Separate
soil samples were also taken for soil pH. Available P was
determined by the Olsen method (0.5 M NaHCO3 extract
at pH 8.5)，total N was determined by Kjeldahl digestion,
distillation, and titration, available N was measured by
1.8 M NaOH hydrolysis, H3BO3 absorption, available K
(1 M NH4AC extract at pH 7) was determined by flame
spectrometry [29].
2.5. Note List about the Abbrevations
BIO is the abbrevation of biomass,
GY is the abbrevation of grain yield,
TN is the abbrevation of total N uptake,

G. Y. Song et al. / Agricultural Sciences 4 (2013) 499-508
502
TS is the abbrevation of tiller stage,
HS is the abbrevation of heading stage,
HT is the abbrevation of harvest time.
2.6. N Use Efficiency Indicators
1) N Needed by 100 kg Grain, NNG:
TN
N
NG 100
GY

2) N Physiological Efficiency, NPE: BIO NPE GY 
3) N Use Efficiency of Producing Grain, NUEPG:
GY
NUEPG TN 
4) N Fertilizer Use Efficiency, NFUE:
F0
F
GY GY
NFUE N


BIO is total aboveground dry weight on a dry-weight
basis (at 80˚C),
TN is total plant N uptake at harvest time,
GY0 is grain yield without N application,
GYF is grain yield with N application,
NF is N application rate,
All of the above quantities are expressed in kg·ha−1.
2.7. Statistical Analyses
Data was analyzed as a randomized compete block de-
sign with three replications using Excel 2003 [30] and
DPS-98 (Data Processing Software) [31]. Significance of
differences among treatments was determined by the
least significant difference (LSD) caculated at P < 0.05.
3. RESULTS
3.1. N Uptake Pattern
The N uptake by three rice cultivars increased signifi-
cantly with increase of N rate [Figure 2(a)]. N uptake in
the treatment without N application (N0) was lower than
that in treatment with N application. N uptake rate in-
creased sharply from tiller stage to heading stage, more
than half of N uptake accumulated from tiller stage to
heading stage. A limited change in N uptake at tiller
stage at different N treatments might be due to slower
growth after transplanting shock and low temperature in
May in northeast China. Shennong 265 showed a smaller
rate of N accumulation amount (11.61 - 21.43 g·m−2 in
2005 and 10.47 - 17.63 g·m−2 in 2006) and N accumula-
tion percent (8.91% - 29.34% in 2005 and 15.37 - 17.4%
in 2006) than those (12.29-24.31 g m-2 in 2005 and 11.66
- 18.06 g·m−2 in 2006) and (11.12% - 27.16% in 2005
and 16.52% - 17.36% in 2006) of Liaojing 294 at TS.
Liaojing 294 accumulated 61.64% - 80.12% in 2005
and 63.63% - 68.38% in 2006 of total N from TS to HS,
while Shennong 265 achieved 43.35% - 63.97% (in
2005）and 55.51% - 67.69%（in 2006）of total N from TS
to HS. Liaojing 294 built up 8.76% - 21.42% in 2005 and
14.6% - 21.16% in 2006 from HS to HT, while Shen-
nong 265 obtained 23.37-27.12%（in 2005）and 16.94%
- 27.09%（in 2006）from HS to HT. Shennong 265 was
1.61% - 16.70% higher of total N than that of Liaojing
294 from HS to HT Under different N treatments, and
Shennong 265 accumulated 0.69% - 18.18% less of total
N than that of Liaojing 294 [Figure 2(b)].
Total N uptake of Shennong 265 was more under high
N application (N2, N3 treatment in 2005 and N1 treatment
in 2006) at HT comparing with Liaojing 294. The rela-
tionship between GY as well as BIO and total N uptake
at HT of two rice cultivars were observed significant
difference (r2 = 0.824**, r2 = −0.858**, respectively).
Lower N uptake was taken up for Shennong 265 in 2006
compared with in 2005 (Figure 2). The remarkable dif-
ference of N uptake was observed between N3 and N1 as
well as N2 and N1 rate for Shennong 265 and Liaojing
294 at HS and HT in 2005, between N1 and N0 for Shen-
nong 265 at HS and at HT for Liaojing 294 in 2006 (P <
0.01). N uptake were also remarkable between N1 and N0
for Shennong 265 at TS and HT, and at TS and HS for
Liaojing 294 in 2006 (P < 0.05).
3.2. Grain N
N absorbed by rice during the vegetative growth stage
contributes to reproductive growth and grain filling
through N re-transferring [32]. Shennong 265 contained
3.18 - 4.66 g·m−2 N (Figure 3) in the grain which came
from N re-transferring from vegetative organs, and 4.32 -
8.04 g·m−2 N received from root absorption in reproduc-
tive stage under different N rates, which accounted for
28.33% - 50.48% and 49.52% - 71.67% of total N in
grain, respectively. Liaojing 294 had 4.08 - 8.53 g·m−2 N
from N re-transferring and 2.09 - 3.35 g·m−2 N from root
absorption in the grain in 2005. The N amounts taken up
by root of Shennong 265 were consistently lower in 2006
than in 2005, there was 3.84 - 6.21 g·m−2 N from root
taken up, which accounted for 49.45% - 59.42% of total
N in grain, and the rest was from N re-transferring from
vegetative organs in 2006. Liaojing 294 got 3.37 - 7.21
g·m−2 N from re-transferring, and 3.64 - 3.75 g·m−2 N
from root taken up in 2006. Liaojing 294 had less differ-
ence in N between root taken up and re-transferring from
vegetative organ under low N level, but less root uptake
and more N re-transferring from vegetative organs under
high N rates.
There was remarkable in the N re-transferring amount
between N3 and N1 treatment for Liaojing 294 in 2005,
and in the root uptake amount between N3 and N2 rate in
2005 and N1 and N0 treatment in 2006 for Shennong 265
in grain filling stage (Figure 3) (P < 0.01). High N rates

G. Y. Song et al. / Agricultural Sciences 4 (2013) 499-508 503
N treatments and cultivars.
Figure 2. Total N uptake determined at three different stages by Shennong 265 and Liaojing 294.
led to an increase of N re-transferring from vegetative
organs, while low N levels improved N uptake by root.
The only exception was Shennong 265 at N3 treatment in
2005 where N uptake amount and percent by root of
Shennong 265 were significantly greater relative to the
Liaojing 294. This indicates that Shennong 265 might
has an advantage since no lodging occurred at harvest,
and root could absorb more nutrients than that of Liao-
jing 294 during grain-filling stage.
3.3. Effects of N Fertilizer on Yield and HI
GY and BIO of two rice cultivars were highly corre-
lated with N fertilizer rate (except of the correlation be-
tween BIO and N rate for Liaojing 294) (Tab le 3). GY
and BIO of Shennong 265 and Liaojing 294 in 2006 in-
creased significantly with the rise of N rate application.
The maximum GY and BIO of Shennong 265 was ob-
tained at N3 treatment in 2005 and N1 rate in 2006. Liao-
jing 294 reached the highest BIO and GY at N1 rate in
2006. The greatest GY and BIO of Liaojing 294 was ob-
served at N2 treatment in 2005, and this cultivar did not
respond well to additional N fertilizer. Liaojing 294 cul-
tivar exhibited a significant decrease in GY from N2 to
N3 treatment, and 2/3 of plants lodged before harvest
under N3 treatment. The GY and BIO of Shennong 265
between N3 and N2 level in 2005, N1 and N0 treatment in
2006 reached significant different. Notable difference
was also observed between N2 and N1 treatment for
Liaojing 294 in 2005, and N1 and N0 rate for Liaojing
294 in 2006. Singh [33] grouped rice genotypes in
N-efficient and N-inefficient types based on GY response
to N supply. N-efficient genotypes that produced high
yield at both high and low N rates was Liaojing 294, and
lack of response to N application might be due to lodging.
N-inefficient genotype that produced low yield at low N
levels but responded well to N application was Shen-
nong 265.
GY of rice could also be expressed as product of BIO
and HI. The HI for Shennong 265 was consistently
higher than that of Liaojing 294, with the only exception
of N0 treatment in 2006 (Ta bl e 3). The highest BIO al-
ways resulted in consistently lower HI. The highest HI of
two rice varieties appeared at low N rates (N0 or N1
treatment), while the lowest HI showed at the highest N
rate might be attributed to longer vegetative phase with
excessive N. HI of Liaojing 294 at all N rates ranged
from 46% - 52%, while Shennong 265 ranged from 48%
- 56% (Table 3).
3.4. N Use Efficiency Parameters
The NPE, NFUE, NNG, and NUEPG showed that two
rice cultivars exhibited a significant difference with

G. Y. Song et al. / Agricultural Sciences 4 (2013) 499-508
504
N treatments and cultivars
Figure 3. N uptake and re-transferring amount and percent by Shennong 265 and Liaojing 294 cultivars in grain-
filling stage; (a), (b) in 2005 and (c), (d) in 2006.
Note: NUR = N uptake amount by root; NTV = N re-transferring from vegetative organ. N re-transferring from vegetative organ = total N
uptake at heading stage in vegetative organs—total N uptake at maturity in vegetative organs; N uptake by root at grain-filling stage = to-
tal N in grain—N re-transferring amount from vegetative organs—total N in grain at heading stage.
Table 3. Yield indicators of Shennong 265 and Liaojing 294 cultivars at four rates of N fertilizer.
Year Cultivars N level GY (t·ha−1) BIO (t·ha−1) HI (%)
2005 Shennong 265 N0 8.01 ± 0.44 cB 15.10 ± 1.56 cC 53.6 ± 3.4 abA
N
1 8.43 ± 0.49 bcB 15.29 ± 0.11 cC 55.1 ± 3.4 aA
N
2 8.96 ± 0.21 bB 18.26 ± 0.96 bB 49.1 ± 1.5 bcA
N
3 10.22 ± 0.60 aA 21.12 ± 0.91 aA 48.4 ± 1.0 cA
Liaojing 294 N0 8.17 ± 0.53 cB 16.99 ± 0.35 cB 49.4 ± 2.2 aAB
N
1 8.85 ± 0.73 bcB 17.22 ± 1.31 cB 50.8 ± 0.5 aA
N
2 10.31 ± 0.10 aA 20.63 ± 0.21 aA 50.1 ± 0.2 aAB
N
3 9.03 ± 0.24 bAB 18.84 ± 0.10 bAB 46.9 ± 0.8 bB
2006 Shennong 265 N0 6.96 ± 0.73 bB 13.52 ± 0.90 bB 51.5 ± 2.0 aA
N
1 9.47 ± 0.47 aA 19.35 ± 0.60 aA 49.9 ± 0.5 bA
Liaojing 294 N0 6.82 ± 0.17 bB 13.17 ± 0.62 bB 51.8 ± 1.3 aA
N
1 8.59 ± 0.53 aA 17.21 ± 0.93 aA 48.9 ± 1.0 bA
Note: HI = GY (t·ha−1) / BIO (t·ha−1); “A, B, C, D” significant at 1% level, “a, b, c, d” significant at 5% level, the same as the below.
varying N application rates (Table 5). For example,
NUEPG of two rice cultivars decreased with the increase
of N application rate. Significant correlations were ob-
served between NUEPG and N rates for Shennong 265
(r2 = −0.661*) and for Liaojing 294 (r2 = −0.844*). The
highest and lowest NUEPG of two rice cultivars were
observed at the lowest and the highest N rate, respec-
tively. The Liaojing 294 had higher NUEPG at different
N rates in contrast to Shennong 265. This also might
show that NUEPG might be useful parameters (in addi-
tion to GY) in identifying N-efficient genotypes. The
NUEPG ranged from 33.56 to 63.18 kg·kg−1 for Shenn-

G. Y. Song et al. / Agricultural Sciences 4 (2013) 499-508 505
nong 265, from 32.13 to 55.12 kg·kg−1 for Liaojing 294.
There was remarkable in NUEPG between N0 and N2
level as well as N2 and N3 treatment for Shennong 265,
and between N0 and N3 treatment for Liaojing 294 in
2005 (P < 0.01).
The NPE and NNG of two rice cultivars expressed a
reversed trend in comparison to NUEPG (Tab l e 5 ). The
NPE and NNG improved with increasing N rates. Liao-
jing 294 cultivar had higher NNG than Shennong 265 at
same N rate in 2005, while Shennong 265 had higher
NNG than Liaojing 294 in 2006. The highest NNG and
NPE of two rice crops were observed at the highest N
application rate. The NNG was significantly correlated to
the N application rate for Shennong 265 (r2 = 0.701**)
and for Liaojing 294 (r2 = 0.797*) (Ta b l e 4 ). The NFUE
observed for these two rice cultivars varied substantially
among the N rates (Table 5). NFUE of Shennong 265
improved with the increase of N application, but Liaojing
294 exhibited a reversed trend in 2005. Shennong 265
needed high N levels, while Liaojing 294 need low N
levels to reach an ideal NFUE. NFUE of Shennong 265
differed between years, and it was consistently lower in
2005 than in 2006. The correlation coefficient between
NFUE and N application rate for Shennong 265 and
Liaojing 294 in 2006 was significant (r2 = 0.715**, r2 =
0.996**). Remarkable difference were observed in NPE
between N0 and N1 treatment for Liaojing 294, and in
NNG between N3 and N1 level as well as N1 and N0
treatment for Shennong 265, and between N3 and N1
treatment for Liaojing 294 in 2005 (P < 0.01).
Differences in N use efficiency among the genotypes
were best characterized by correlating yield and the
amount of N fertilizer to N use efficiency parameters.
The relationships between GY and N use efficiency pa-
rameters (TN, NNG, NFUE) were all positive, while the
correlation between GY as well as BIO and the other N
efficiency indicators were negative. Significant differ-
ence were also observed between GY and TN as well as
BIO and TN (r2 = 0.824**, r2 = 0.858**) (Table 4).
4. DISCUSSION
4.1. N Fertilizer Requirement for Maximum
Yield and HI
The result of this study showed that the yield of Liao-
jing 294 was observed to be suppressed with increasing
N fertilizer, while the yield of Shennong 265 increased
with the increasing of N application rate in 2005. This
indicates that excess N fertilizer had a detrimental effect
on the yield of Liaojing 294. This is in conformity with
an experiment by Tirol et al. and Ohnishi et al. [19,23],
who grouped rice genotypes in N-efficient and N-ineffi-
cient types based on GY response to N supply. Cultivars
that did not respond to increasing N-application rates and
obtained relatively low grain yield with low N supply
were considered inferior types. Efficient genotypes might
be described as those which produce high GY at subop-
timal N levels through increased N uptake/or a more ef-
ficient utilization of the N taken up for GY.
From the results in this experiment we might conclude
that Liaojing 294 was N-efficient genotypes because it
produced high yield at both high and low N rates, and
lack of response to N application might be due to lodging.
Shennong 265 was N-inefficient genotype that produced
low yield at low N levels but responded well to N appli-
cation.
Based on the overall results of this experiment, it was
revealed that application of appropriate N fertilizer pro-
duced higher values for yield of different panicle rice
cultivars. N2 treatment will be appropriate for Liaojing
294 in enhancing GY and BIO. While N3 rate will be
suitable for Shennong 265 in improving GY and BIO.
Therefore, application of N fertilizer beyond 180 kg·ha−1
will not be economical for half-erect panicle rice, while
180 - 270 will be appropriate in enhancing the yield of
erect-panicle rice, Shennong 265.
GY and BIO for two rice cultivars basically increased
and the HI decreased with the improving of N fertilizer
rate. Increased HI largely accounted for enhanced GY
potential of high yielding rice cultivars. The present ex-
periment suggested that the HI declined significantly
with increasing N rate indicating that if we wanted to fur-
ther improve the yield, we should increase BIO or op-
timize combination of BIO and HI. This is in conformity
with the experiment reported by Chen et al. [34].
4.2. N Use Efficiency Indicators of Rice
Cultivars
Responses of N use efficiency indicators differed
largely among two rice cultivars studied. NUEPG de-
creased with the increase of N rates. Lower N uptake and
higher N use efficiency indicators (except NFUE, NPE,
and NNG) were attained at low N application rate. This
means that to achieve high N efficiency, low N fertilizer
and straw N concentration are needed. NNG and NPE in-
creased with the increase of N rates, therefore, the in-
crease of NNG and NPE could be at the expense of N
application. These results indicated that excessive N ap-
plication in China might be inconsistent with the physio-
logical requirement of the rice, thereby leading to low N
use efficiency indexes (NUEPG) and high NNG and
NPE.
Genotypes with superior NUEPG and consistent GY at
suboptimal N levels have been identified. Among all
these N use efficiency indicators, NUEPG appeared to be
a more promising indicator for quantifying and ranking
N-efficient genotypes, and NFUE seemed to be the least
suitable indicator because these two rice cultivars both

G. Y. Song et al. / Agricultural Sciences 4 (2013) 499-508
506
Table 4. Correlation coefficients between yield parameters and N use efficiency indicators as well as between N application rates and
N use efficiency indicators for rice cultivars used in this study.
Yield parameters N application amount (kg·ha−1)
N use efficiency indicators
BIO GY HI Shennong 265 Liaojing 294
TN 0.858** 0.824** −0.633* 0.868** 0.901**
NNG 0.561 0.485 −0.600* 0.701** 0.797*
NPE −0.457 −0.348 0.673* 0.146 −0.387
NUEPG −0.518 −0.452 0.575 −0.661** −0.844**
NFUE 0.396 0.372 −0.239 0.715** 0.548
Note: **significant at 1% level, *significant at 5% level.
Table 5. Nitrogen efficiencies of different panicle rice cultivars at four rates of N fertilizer.
Year Cultivar N levels NPE (kg·kg−1) NUEPG (kg·kg−1) NNG (100 kg·kg−1) NFUE (kg·kg−1)
2005 Shennong 265 N0 96.16 ± 2.87 aA 50.62 ± 1.22 aA 1.98 ± 0.05 cB
N
1 83.76 ± 2.86 bB 46.12 ± 1.29 bA 2.17 ± 0.06 cB 64.85 ± 3.74 aA
N
2 76.68 ± 0.43 cBC 37.62 ± 1.32 cB 2.66 ± 0.09 bA 45.94 ± 1.07 bB
N
3 71.65 ± 4.99 cC 34.75 ± 1.65 cB 2.88 ± 0.13 aA 39.29 ± 2.28 cC
Liaojing 294 N0 109.27 ± 2.22 aA 52.96 ± 1.92 aA 1.90 ± 0.18 cB
N
1 92.03 ± 2.37 bB 47.39 ± 1.70 bB 2.11 ± 0.07 bcB 68.06 ± 5.61 aA
N
2 86.89 ± 1.72 bB 43.94 ± 0.89 cB 2.30 ± 0.30 bB 52.85 ± 0.54 bB
N
3 69.28 ± 1.44 cC 33.20 ± 0.51 dC 3.01 ± 0.05 aA 34.72 ± 0.93 cC
2006 Shennong 265 N0 90.44 ± 2.33 aA 46.17 ± 2.50 aA 2.17 ± 0.21 aA
N
1 87.93 ± 2.987 bA 43.88 ± 1.59 aA 2.28 ± 0.26 aA 39.83 ± 2.96
Liaojing 294 N0 90.77 ± 2.17 aA 47.02 ± 1.92 aA 2.13 ± 0.28 aA
N
1 86.41 ± 2.64 aA 42.26 ± 2.85 aA 2.27 ± 0.43 aA 40.78 ± 3.84
had the highest NFUE when they got maximum GY.
Shennong 265 exhibited significantly higher NPE, and
NFUE as well as lower NNG comparing with Liaojing
294 under the highest N level, and the reverse trend ex-
pressed at low N rates. This indicates that Shennong 265
might have some advantages in contrast to Liaojing 294
only at high N rates.
5. ACKNOWLEDGEMENTS
This research project was financed by The National Natural Science
Foundation of China (30871468), National Science & Technology
Support Project (2011BAD35B02), Inner Mongolia National Science
Foudation(2012MSO312), and The Scientific Research Foundation for
the Returned Overseas Chinese Scholars, State Education Ministry. Liu
Wan, He Mei and Zhang Xijuan assisted in the field experiment;
Salmon Zhao helped with data analysis. The author thanked Dr. Krzic
for her assistance during preparation of this manuscript.
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