the high yield of irrigated rice in yunnan, china

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Field Crops Research 107 (2008) 1–11

The high yield of irrigated rice in Yunnan, China

‘A cross-location analysis’

Keisuke Katsura a,*, Shuhei Maeda b, Iskandar Lubis c, Takeshi Horie d,Weixing Cao e, Tatsuhiko Shiraiwa b

a Experimental Farm, Graduate School of Agriculture, Kyoto University, Takatsuki, Osaka 569-0096, Japanb Laboratory of Crop Science, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan

c Laboratory of Crop Production, Faculty of Agriculture, Bogor Agricultural University, Darmaga, Bogor 16680, Indonesiad National Agriculture and Food Research Organization, Tsukuba, Ibaraki 305-8517, Japan

e Key Laboratory of Crop Growth Regulation of Ministry of Agriculture, Hi-Tech Key Lab of Information Agriculture of Jiangsu Province,

Nanjing Agricultural University, Nanjing 210095, China

Received 18 September 2007; received in revised form 4 December 2007; accepted 12 December 2007

Abstract

A number of field trials on rice productivity have demonstrated very high yield, but reported limited information on environmental factors. The

objective of this study was to reveal the environmental factors associated with high rice productivity in the subtropical environment of Yunnan, China.

We conducted cross-locational field experiments using widely different ricevarieties in Yunnan and in temperate environments of Kyoto, Japan in 2002

and 2003. The average daily radiation throughout the growing season was greater at Yunnan (17.1 MJ m�2 day�1 average over 2 years) relative to

Kyoto (13.2 MJ m�2 day�1). The average daily temperature throughout the growing season was 24.7 8C at Yunnan, and 23.8 8C at Kyoto. The highest

yield (16.5 tonnes ha�1) was achieved by the F1 variety Liangyoupeijiu at Yunnan in 2003, and average yield of all varieties was 33% and 39% higher

at Yunnan relative to Kyoto in 2002 and 2003, respectively. There was a close correlation between grain yield and aboveground biomass at maturity,

while there was little variation in the harvest index among environments. Large biomass accumulation was mainly caused by intense incident radiation

at Yunnan, as there was little difference in crop radiation use efficiency (RUE) between locations. Large leaf area index (LAI) was also suggested to be

an important factor. Average nitrogen (N) accumulation over 2 years was 49% higher at Yunnan than at Kyoto, and also contributed to the large biomass

accumulation at Yunnan. The treatments of varied N application for Takanari revealed that the ratio of N accumulated at maturity to the amount of

fertilized N was significantly higher at Yunnan than at Kyoto, even though there was no great difference in soil fertility. The Takanari plot with high N

application showed a N saturation in plant growth at Kyoto, which might be related to low radiation and relatively high temperatures during the mid-

growth stage. These results indicate that the high potential yield of irrigated rice in Yunnan is achieved mainly by intense incident solar radiation, which

caused the large biomass and the N accumulation. The low nighttime temperature during the mid-growth stage was also suggested to be an important

factor for large biomass accumulation and high grain yield at Yunnan.

# 2007 Elsevier B.V. All rights reserved.

Keywords: Rice (Oryza sativa); Radiation use efficiency (RUE); Yield; Yunnan; Nitrogen; Leaf area index (LAI); Temperature

1. Introduction

Due to rising population numbers, Asian irrigated rice

production must increase by 43% over the next 30 years

(Cassman, 1999). However, further expansion of rice planted

area is difficult, because most arable land is already used for

rice production or converted into urban infrastructure (Horie

* Corresponding author. Tel.: +81 72 685 0134; fax: +81 72 683 1532.

E-mail address: [email protected] (K. Katsura).

0378-4290/$ – see front matter # 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.fcr.2007.12.007

et al., 2005). Many farmers are now obtaining yields close to

those produced at experimental stations (Conway and

Toenniessen, 1999), and yield potential of modern rice varieties

in irrigated rice fields has stagnated around 10 tonnes ha�1

since the first semidwarf tropical indica variety, IR8, was

released in 1966 (Peng et al., 1999). To break this yield barrier,

it is very important to clarify the environmental effects on rice

productivity, as well as the physiological traits causing high

productivity.

A number of field observations of grain yields over

13 tonnes ha�1 has been reported, for example in Yunnan,

mailto:[email protected]

http://dx.doi.org/10.1016/j.fcr.2007.12.007

K. Katsura et al. / Field Crops Research 107 (2008) 1–112

China (Amano et al., 1996a,b), Yanco, Australia (Williams,

1992), Tsaranoro, Madagascar (Rafaralahy, 2002), Nile Delta,

Egypt (Namba, 2003), Governorate, Egypt (Badawi, 2004), and

Maharashtra, India (Suetsugu, 1975). Only a little scientific

knowledge, however, is available to clarify the environmental

factors associated with a high record yield of rice. Ying et al.

(1998a) suggested that the high yield potential of irrigated rice

in Yunnan, China was brought about by long growth duration

and high crop growth rate (CGR). Horie et al. (1997) suggested

that high yield potential of irrigated rice in Yanco, Australia

was a result of intense solar radiation because of a similar

efficiency of dry matter production per unit of incident

radiation among all the experimental sites. In these experi-

ments, however, crop management techniques such as chemical

fertilizer application or planting densities were different

between the sites for which productivity was compared.

Additionally, the growth durations were largely different

between the experimental sites. For example, in a cross-

locational experiment between subtropical environments of

Yunnan, China and tropical environments of the International

Rice Research Institute (IRRI), Philippines (Ying et al., 1998a),

there was a near 40-day difference in growth duration between

the two sites. This makes it difficult to evaluate the effects of

environmental or physiological factors on high productivity.

Moreover, the rice varieties used in these experiments were

very limited. Therefore, cross-locational experiments using

widely different rice varieties with similar crop management at

both sites were needed, in order to better understand the major

factors affecting high yield records of rice.

The objective of this study was to clarify the environmental

factors promoting a high yield of irrigated rice in subtropical

environments of Yunnan, China by conducting a cross-

locational experiment in Yunnan and temperate environments

of Kyoto, Japan. Special attention was paid to light interception

and its utilization by crops, using on-site measurements of solar

radiation and leaf area dynamics. Attention was also paid to

nitrogen utilization by observing crops with varied amounts of

chemical nitrogen fertilizer application.

2. Materials and methods

Field experiments were conducted in 2002 and 2003 in the

subtropical environment of Taoyuan Village’s farm, Taoyuan

township, Yongsheng county, Yunnan province, China

(268120N, 1008340E, 1170 altitude) during the rice growing

season from mid March to mid September and in the temperate

environment of Kyoto University Farm, Kyoto, Japan (35810N,

135870E, 20 m altitude) during the rice growing season from

late April to early October. At Yunnan, about 30 tonnes ha�1

farmyard manure was applied in both years before beginning

irrigation (Technical officials in Taoyuan Agricultural Station,

personal communication, 2003).

Soil samples were taken at both sites from the plow layer

(0–15 cm) of five randomly chosen plots before beginning

irrigation in 2002. The samples were air-dried and passed

through a 2 mm sieve to remove the debris and stones. The

measurements included total carbon and nitrogen, cation

exchange capacity (CEC), organic carbon (SOC), mineralizable

N, and soil texture. Total carbon and nitrogen were analyzed with

the elemental analyzer (EA-1108, Fisons Instruments, Milano).

CEC was measured by the ammonium acetate extract method at

pH 5.0 and 7.0 (Soil and Plant Analysis Council, 1999). SOC

content was determined by Walkeley method (Walkeley, 1947).

Mineralizable N was determined by a 4-week anaerobic

incubation at 30 8C and by measuring the increase of NH4+–N

in soil water. Soil texture was examined by the sieving and

pipetting method (Gee and Bauder, 1986).

In 2002, seven common varieties, Nipponbare (japonica,

standard variety in Japan), Takenari (japonica, old variety in

Japan), Shanguichao (indica, high yielding variety in China),

Takanari (its parents are indica–japonica crossbred, high

yielding variety in Japan), IR72 (indica, standard variety in

IRRI), IR65564-44-2-2 (NPT), WAB450-I-B-P-38-HB (NER-

ICA, O. sativa � O. glaberrima) were grown at Yunnan and

Kyoto. These varieties were selected to test as diverse a

selection of varieties as possible. Twenty-eight-day-old

seedlings were transplanted on 5 May in Yunnan, and 22-

day-old seedlings were transplanted on 22 May in Kyoto.

Chemical fertilizers were applied 12 g P2O5, 12 g K2O and

4 g N m�2 as basal dressing, and 2 g N m�2 as top-dressing

every 20 days after transplanting until 10 days after heading.

In 2003, six common varieties, Nipponbare, Takenari,

Shanguichao, Takanari, Jinyou207 and Liangyoupeijiu were

grown in Kyoto and Yunnan. The latter two, which are recently

bred Chinese ‘‘super-hybrid’’ varieties (Li et al., 2001; Zou

et al., 2003), were added to anticipate the high rice yield.

Twenty-nine-day-old seedlings were transplanted on 16 April

in Yunnan, and 20-day-old seedlings were transplanted on 21

May at Kyoto. Fertilizer application rates were changed to

emphasize the later topdressing, in order to ensure the high rice

yield in 2003. Chemical fertilizers were applied as following:

14 g P2O5 and 7 g K2O m�2 as basal dressing, 3 g N m�2 at 7

days after transplanting, 7 g K2O and 4 g N m�2 at panicle

initiation, 4 g N m�2 at 2 weeks before heading and 3 g N m�2

at heading as top dressings. Heavy nitrogen plots (28 N), in

which N was applied twice as much as normal fertilized plots

(14 N) for basal and top-dressing, were prepared for Takanari

and Liangyoupeijiu. Total N application of 28 g m�2 was quite

high compared with conventional cultivation in Kyoto, but it is

relevant compared with conventional cultivation in Taoyuan

village, Yunnan. Additionally, no-nitrogen fertilized plots (0 N)

were prepared for Takanari to compare environmental N

availability between the two sites.

Except for the chemical fertilizer application shown above,

similar crop management and experimental methods were

adopted for both sites and years. Rice varieties were arranged in

a completely randomized block design with three replicates.

Plot sizes at Yunnan were 15.12 m2 (3.6 m � 4.2 m) and

19.44 m2 (2.7 m � 7.2 m) in 2002 and 2003, respectively and

at Kyoto were 21.87 m2 (2.7 m � 8.1 m) and 21.6 m2

(3.0 m � 7.2 m) in 2002 and 2003, respectively. Planting

density was 22.2 plants per m2 (0.3 m � 0.15 m) with two

seedlings per hill. Water, weeds, insects and disease were

controlled as required to avoid yield loss.

Table 1

Daily average solar radiation and average, minimum and maximum tempera-

tures in Yunnan and Kyoto in 2002 and 2003

Growth stage 2002 2003

Yunnan Kyoto Yunnan Kyoto

Daily average radiation (MJ m�2 day�1)

Earlya 18.7 16.3 19.1 11.6

Midb 15.5 14.6 16.3 11.5

Latec 16.3 12.6 16.5 12.0

Whole 16.9 14.8 17.4 11.6

Daily average temperature (8C)

Early 24.3 22.6 25.4 21.8

Mid 24.3 27.4 25.2 25.3

Late 23.2 23.8 25.5 22.3

Whole 24.0 24.7 25.3 23.0

Daily minimum temperature (8C)

Early 21.4 18.3 18.7 18.2

Mid 21.2 23.7 20.9 21.7

Late 18.6 19.6 21.5 18.0

Whole 20.5 20.7 20.2 19.1

Daily maximum temperature (8C)

Early 29.7 27.1 31.4 26.0

Mid 29.0 31.4 29.7 29.7

Late 30.1 28.3 30.8 27.8

Whole 29.6 29.0 30.6 27.7

Each value shows the averaged value for each day during the period.a From transplanting to 50 days after transplanting.b From 51 to 100 days after transplanting.c After 101 days after transplanting.

K. Katsura et al. / Field Crops Research 107 (2008) 1–11 3

Plant materials were initially harvested from 20 plants at

transplanting and later from eight hills 20 days after

transplanting, at panicle initiation, 2 weeks before heading,

at full heading, 2 weeks after heading, and finally at maturity to

measure green leaf area and dry weight of green leaf, stem

(culm and leaf sheath), panicle and dead foliage. Twenty-four

hills were harvested from each replicate to measure the yield

and yield components at maturity. The grain yield was adjusted

to moisture content of 14%.

The stratified clipping method was employed in 2003 to

measure the light extinction coefficient (K) for the varieties used

in the present study at Kyoto in 2003. After the measurement

of relative light intensity for each layer (20 cm interval) by

photosynthetically active radiation ceptometer (AccuPAR,

Decagon, USA), leaf area for each layer was measured 2 weeks

before and after heading using nine plants from each variety. The

values of K for the varieties used in 2002 were quoted from Lubis

(2003), who measured K for all the seven varieties used in the

present study in 2002. Lubis (2003) used similar crop manage-

ment at Kyoto and the same experimental method as shown

above for two plants with three replications.

RUE (g MJ�1) is defined as aboveground biomass accumula-

tion per total solar radiation intercepted by the crop (Monteith,

1977). RUE is calculated in this study using K, leaf area index

(LAI), and CGR (g m�2 day�1) by the following equation:

RUE ¼ CGR

S0½1� expð�K � LAIÞ� (1)

where S0 is incident solar radiation (MJ m�2 day�1). The values

of K measured 2 weeks before heading were used to calculate

RUE from transplanting to heading, and those measured around

2 weeks after heading were used for RUE from heading to

maturity for each variety. Daily LAI and CGR were interpo-

lated from periodic sampling data.

Tissue nitrogen concentration was determined by the near

infrared spectroscopic analysis method (BRAN + LUEBBE,

Infra Alyzer 500) equipped with IDAS software, calibrated

with the Kjeldahl method. A data logger (2100A, Thermic, Eto

Denki Co., Japan) was used to record radiation and temperature

each minute with a pyranometer sensor (2103A, Thermic) and

temperature sensor (2119A, Thermic) at the experimental fields

of both sites and years.

As the main experiments, the effects of location and variety

were analyzed for each of 2002 and 2003 results, using the split

plot design with location as the main and variety as the subplots,

respectively. The effect of different N application was analyzed

as a side-experiment with three N levels by the two sites and

three replications. Thus the 0 N and 28 N treatments were

excluded for statistical analysis for the main experiment.

Statistical analysis of variance was made by IRRISTAT

(International Rice Research Institute, 2006).

3. Results

Seasonal changes in daily temperature and solar radiation are

shown in Table 1. The average daily radiation from transplanting

to maturity was larger at Yunnan (16.9 and 17.4 MJ m�2 day�1 in

2002 and 2003, respectively) relative to Kyoto (14.8 and

11.6 MJ m�2 day�1 in 2002 and 2003, respectively). Solar

radiation at Kyoto in 2003 was extremely low compared with

normal years. The average daily temperature throughout the

growing season was 24.0 8C and 25.3 8C in 2002 and 2003,

respectively, at Yunnan, and 24.7 8C and 23.0 8C, in 2002 and

2003, respectively, at Kyoto. Daily average, minimum and

maximum temperatures at Yunnan tended to be higher in the

early growth stage, slightly lower in the mid-growth stage, and

higher again in the late-growth stage, as compared to Kyoto in

both years. Soil characteristics at both sites were shown in

Table 2. Soil characteristics measured in this study were similar

to those measured in the previous reports at a farmer’s field in

Taoyuan village, Yunnan (Ying et al., 1998a) and Kyoto

University Farm (Hasegawa and Horie, 1994).

The effects of location and variety on yield were highly

significant in both years (Tables 3 and 4). In 2002, the average

yield of seven varieties was 33% higher at Yunnan

(10.6 tonnes ha�1) than at Kyoto (8.0 tonnes ha�1). The

highest yield of 12.1 tonnes ha�1 was produced by Takanari

at Yunnan, while at Kyoto it was 10.6 tonnes ha�1 by Takanari.

In 2003, the average yield of six varieties was 39% higher at

Yunnan (11.8 tonnes ha�1) than at Kyoto (8.5 tonnes ha�1).

The highest yield of 16.5 tonnes ha�1 was produced by

Liangyoupeijiu (heavy N application plot) at Yunnan, while

the highest yield at Kyoto was 9.9 tonnes ha�1 produced by

Liangyoupeijiu.

Table 2

Soil characteristics at Yunnan and Kyoto in 2002

Total N (%) Total C (%) C/N CEC

(meq/100 g)

SOC (%) NH4+–Na

(mg/100 g)

Sand (%) Silt (%) Clay (%) Soil texture

Yunnan 0.13 2.90 23.2 16.3 1.86 3.28 63.5 26.9 9.1 Loam

Kyoto 0.28 4.49 16.2 14.2 4.06 7.65 52.1 40.4 7.6 Loam

a NH4+–N content after 4-week anaerobic incubation at 30 8C.

Table 3

Grain yield and yield components of rice varieties grown at Yunnan and Kyoto in 2002

Rough grain

yielda (tonnes ha�1)

Panicle number

per m2

Spikelet number

per m2 (�103)

Spikelet number

per panicle

Ripening

ratio (%)

Grain

weight (mg)

Yunnan

Nipponbare 10.5 463 46.3 100 78 22.7

Takenari 11.2 439 55.9 127 81 19.2

Shanguichao 11.9 399 71.5 179 77 17.0

Takanari 12.1 321 59.9 187 62 23.8

IR72 11.4 467 54.4 117 67 22.6

IR65564-44-2-2 9.9 282 47.8 169 61 24.8

WAB450-I-B-P-38-HB 7.4 242 31.5 130 76 24.1

Average 10.6 373 52.5 144 72 22.0

Kyoto

Nipponbare 6.6 384 27.5 72 76 24.0

Takenari 7.1 325 32.2 99 80 21.3

Shanguichao 8.5 360 44.4 123 90 17.4

Takanari 10.6 278 41.0 147 87 23.5

IR72 9.8 415 42.1 102 83 22.3

IR65564-44-2-2 7.6 214 30.0 140 75 25.4

WAB450-I-B-P-38-HB 5.5 220 22.4 102 75 25.3

Average 8.0 314 34.2 112 81 22.7

Analysis of variance

Site 240*** 48*** 336*** 125*** 41*** 27***

Variety 50*** 54*** 59*** 60*** 6*** 239***

Site � variety 6** 2 NS 5** 3* 8*** 6**

LSD (0.05)

LSD site 0.4 22 2.1 6 3 0.3

LSD variety 0.7 33 3.8 11 6 0.5

LSD site � variety 0.9 47 5.4 16 8 0.7

*,**,*** F value significant at the 0.05, 0.01 and 0.001 probability levels, respectively. NS means non-significant at P = 0.05.a The values or grain yields were adjusted to 14% water content.


All the yield components, excluding the ripening ratio in

2003, were significantly different between the two sites

(Tables 3 and 4). Panicle number per m2, spikelet number

per m2 and spikelet number per panicle were significantly

greater at Yunnan than at Kyoto, while grain weight was

significantly smaller at Yunnan relative to Kyoto. The

correlation coefficients between grain yield and yield

components were highest for spikelet number per m2 for both

years (r = 0.928*** in 2002 and r = 0.890*** in 2003). The

maximum spikelet number per m2 at Yunnan was 71,500 by

Shanguichao in 2002, while that at Kyoto was 44,400, also by

Shanguichao in 2002. The second highest correlation with grain

yield was observed in spikelet number per panicle.

The average total growth duration from sowing to maturity

at Yunnan was 144 and 141 days in 2002 and 2003, respectively,

while that at Kyoto was 140 and 149 days in 2002 and 2003,

respectively (Tables 5 and 6). Growth durations of Nipponbare

and Takenari at Yunnan were shorter than those at Kyoto by 28

and 17 days, respectively in 2003. For the other varieties,

however, there were small differences in growth duration

between the two sites.

Aboveground biomass at maturity was significantly larger

at Yunnan than at Kyoto in both years (Tables 5 and 6). The

average aboveground biomass was 34% and 30% larger at

Yunnan than at Kyoto in 2002 and 2003, respectively. Above-

ground biomass at maturity was significantly correlated with

grain yield (r = 0.899*** in 2002 and r = 0.919*** in 2003).

Harvest index (HI) was higher in 2003 than in 2002, but there was

little difference in HI between the two sites (Tables 5 and 6).

Mean CGR from transplanting to maturity was significantly

larger at Yunnan than at Kyoto in both years (Tables 5 and 6),

and significantly correlated with aboveground biomass

(r = 0.938*** in 2002 and r = 0.888*** in 2003). The average

CGR from transplanting to maturity was 37% and 48% larger at

Table 4

Grain yield and yield components of rice varieties grown at Yunnan and Kyoto in 2003

Rough grain

yielda (tonnes ha�1)

Panicle number

per m2

Spikelet number

per m2 (�103)

Spikelet number

per panicle

Ripening

ratio (%)

Grain

weight (mg)

Yunnan

Nipponbare 8.6 635 35.7 56 80 23.4

Takenari 6.3 382 41.8 109 56 18.0

Shanguichao 13.0 385 67.3 175 94 17.4

Takanari(14 N) 13.6 326 61.8 189 68 24.9

Jinyou207 13.9 323 56.7 176 81 24.2

Liangyoupeijiu (14 N) 15.4 310 63.5 205 77 25.2

Takanari (0 N) 10.6 282 44.4 158 82 23.4

Takanari (28 N) 15.1 369 69.7 189 75 22.8


Averageb 11.8 394 54.5 152 76 22.2

Kyoto

Nipponbare 7.6 326 30.0 92 81 22.8

Takenari 7.0 289 31.2 108 80 20.6

Shanguichao 8.0 292 42.2 144 84 17.6

Takanari (14 N) 9.6 239 41.0 172 70 23.6

Jinyou207 8.8 205 36.2 177 71 24.9


Takanari (0 N) 7.3 172 28.8 168 85 23.1

Takanari (28 N) 9.8 256 41.3 161 69 23.3


Averageb 8.5 262 36.4 144 77 22.6

Analysis of varianceb

Site 542*** 400*** 603*** 15** 1 NS 6*

Variety 171*** 103*** 96*** 336*** 28*** 332***

Site � variety 53*** 30*** 20** 27*** 18*** 14***

LSD (0.05)b

LSD site 0.3 14 1.5 4 2 0.3

LSD variety 0.5 24 2.7 7 4 0.5

LSD site � variety 0.7 34 3.8 10 6 0.7

*,**,*** F values significant at the 0.05, 0.01, and 0.001 probability levels, respectively. NS means non-significant at P = 0.05.a The values of grain yields were adjusted to 14% water content.b Takanari (0 N), Takanari (28 N) and Liangyoupeijiu (28 N) were excluded from the variety average and analysis of variance because of different N application.


Yunnan than at Kyoto in 2002 and 2003, respectively. Intercepted

radiation from transplanting to maturity was also significantly

larger at Yunnan than at Kyoto in both years (Tables 5 and 6), and

significantly correlated with CGR from transplanting to maturity

(r = 0.844*** in 2002 and r = 0.831*** in 2003). There was no

significant difference in RUE from transplanting to maturity

between the two sites (Tables 5 and 6). The values of K calculated

from the stratified clipping method are shown in Table 7. The

values of K ranged from 0.34 to 0.47 before heading and from

0.53 to 1.02 after heading. Generally, the values of K were larger

in 2003 than in 2002.

The average N accumulation at maturity for all varieties was

62% and 36% larger at Yunnan than at Kyoto in 2002 and 2003,

respectively (Tables 5 and 6), and significantly correlated with

aboveground biomass at maturity (r = 0.868*** in 2002 and

r = 0.888*** in 2003). According to the results of the N fertilizer

experiment for Takanari in 2003, Takanari (0 N) at Yunnan

absorbed a significantly larger amount of N than did Takanari (0

N) at Kyoto (Table 8). Takanari (0 N) at Yunnan had absorbed

12.0 g N m�2 by maturity, while Takanari (0 N) at Kyoto had

absorbed 9.0 g N m�2. As the amount of fertilized N increased, N

accumulation at maturity increased. The ratio N harvested

(defined as the ratio of the difference of N accumulation between

Takanari (14 N or 28 N) and Takanari (0 N) at maturity to the

amount of total fertilized N) was significantly higher at Yunnan

than at Kyoto (Table 8). As the amount of fertilized N increased,

aboveground biomass at maturity increased at Yunnan, but did

not increase at Kyoto (Table 8).

4. Discussion

Grain yield over 16.5 tonnes ha�1 was achieved at Yunnan in

the present study. This value is among the highest recorded in

the replicated experimental plots. Even though the harvested

area was small (3.24 m2 total for yield determination), this yield

level is comparable to the previous reports at Yunnan (Amano

et al., 1996a,b; Ying et al., 1998a,b). This indicates that the rice

productivity at Yunnan is currently almost the highest in the

world compared with previous reports (Williams, 1992; Horie

et al., 1997). Aboveground biomass at maturity was sig-

nificantly larger at Yunnan than at Kyoto, while there was little

difference in HI between the two sites. Our results indicated

Table 5

Growth duration, aboveground biomass at maturity, harvest index, CGR, incident radiation and intercepted radiation from transplanting to maturity, radiation

interception ratio, RUE, LAI at heading, and N accumulation at maturity of rice varieties grown at Yunnan and Kyoto in 2002

Growth

durationa

Aboveground

biomass

at maturity

(tonnes ha�1)

Harvest

Index

CGRb

(g m�2 day�1)

Incident

radiation

(�103 MJ m�2)

Intercepted

radiation

(�103 MJ m�2)

Radiation

interception

ratio

RUEb

(gMJ�1)

LAI at

heading

(m2 m�2)

N accumulation

at maturity

(g m�2)

Yunnan

Nipponbare 140 19.5 0.47 17.4 1.91 1.22 0.64 1.59 8.0 22.7

Takenari 161 21.8 0.44 16.4 2.28 1.55 0.68 1.35 8.2 17.3

Shanguichao 143 20.1 0.51 17.7 1.95 1.31 0.68 1.53 8.8 19.9

Takanari 139 20.4 0.52 18.7 1.85 1.19 0.65 1.72 7.4 22.2

IR72 146 19.4 0.50 16.6 2.01 1.36 0.68 1.43 7.2 16.8

IR65564-44-2-2 147 19.1 0.45 16.4 1.98 1.28 0.65 1.49 6.4 20.6

WAB450-I-B-

P-38-HB

134 13.1 0.48 12.4 1.80 0.97 0.54 1.35 4.7 13.8

Average 144 19.1 0.48 16.5 1.97 1.27 0.64 1.49 7.2 19.0

Kyoto

Nipponbare 134 14.6 0.39 13.1 1.72 0.95 0.55 1.54 5.5 12.9

Takenari 147 15.0 0.41 12.0 1.87 1.00 0.53 1.51 4.8 11.9

Shanguichao 132 14.6 0.50 13.2 1.69 0.89 0.53 1.65 5.1 12.0

Takanari 148 15.4 0.59 12.2 1.88 1.04 0.55 1.48 4.4 12.1

IR72 149 17.0 0.50 13.4 1.89 1.09 0.58 1.56 4.9 13.8

IR65564-44-2-2 141 13.2 0.50 11.1 1.78 0.93 0.52 1.42 4.2 10.9

WAB450-I-B-

P-38-HB

126 10.0 0.48 9.6 1.62 0.78 0.48 1.29 3.5 8.6

Average 140 14.3 0.48 12.1 1.78 0.95 0.54 1.49 4.6 11.8


Site 144*** 0 NS 164*** 455*** 195*** 0 NS 97*** 150***

Variety 20*** 6** 12*** 41*** 13*** 4* 8*** 7***

Site�variety 2 NS 2 NS 2 NS 12*** 3* 2 NS 2 NS 3*

LSD (0.05)

LSD site 0.8 0.03 0.7 0.03 0.02 0.08 0.7 1.2

LSD variety 1.6 0.05 1.3 0.06 0.03 0.16 1.0 2.3

LSD site � variety 2.2 0.08 1.9 0.08 0.04 0.22 1.4 3.3

*,**,*** F value significant at the 0.05, 0.01 and 0.001 probability levels, respectively. NS means non-significant at P = 0.05.a Growth duration from sowing to maturity.b Averaged value from transplanting to maturity.


that the high grain yield at Yunnan likely resulted from larger

biomass accumulation.

In the present study, HIs of high yielding varieties were over

0.55 in 2003, even though many researchers believe that HI is

already close to its practical maximum value around 0.50

(Mann, 1999). Recent studies, however, have achieved an HI of

around 0.55 under high yielding conditions (Amano et al.,

1996a; Horie et al., 1997; Peng et al., 2000; Yang et al., 2002,

2007). Considering that a hypothetical uppermost limit of HI

for cereals would be 0.6 or less (Austin, 1994), the HIs of high

yielding varieties in the present study are near the ceiling of HI

for high yields. An additional increase in rice grain yield,

therefore, would be achieved with an improvement in biomass

production with maintenance of high HI.

Ying et al. (1998a) suggested the importance of growth

duration for the high grain yield of rice from cross-locational

experiments between Yunnan and IRRI. In the present study,

there was not a big difference in growth duration from sowing to

maturity between the two sites (except for Nipponbare and

Takenari in 2003). However, it could be said that growth

duration over 140 days from sowing to maturity was long

relative to tropical environments, such as IRRI, where growth

duration is about 110–130 days (Peng and Khush, 2003; Yang

et al., 2007). Thus, growth duration is likely to be a necessary,

but not a sufficient factor for high rice yields. A growth duration

of 150 days from sowing to maturity is likely to be enough to

achieve a high yield of around 15 tonnes ha�1. Nipponbare and

Takenari have relatively strong photosensitivity. Because of

this, the earlier sowing date in 2003 (compared to 2002)

hastened the heading date at Yunnan in that year and caused a

large reduction of biomass production in Yunnan. This resulted

in a strong interaction between variety and location (G � E

interaction) in 2003 on yield and related characteristics. In

2002, however, these two japonica varieties performed even

better at Yunnan than at Kyoto, but in a different direction from

that in 2003, which also caused a G � E interaction on many

characteristics. Therefore, it is difficult to reach a general

conclusion for G � E interaction on yield, because the results

were not consistent between years.

The present study showed that daily average incident solar

radiation at Yunnan was higher than at Kyoto in both years. A

number of field trials achieved a high yield of rice in intense

Table 6

Growth duration, aboveground biomass at maturity, harvest index, CGR, incident radiation and intercepted radiation from transplanting to maturity, radiation

interception ratio, RUE, LAI at heading, and N accumulation at maturity of rice varieties grown at Yunnan and Kyoto in 2003

Growth

durationa

Aboveground

biomass at

maturity

(tonnes ha�1)

Harvest

index

CGRb

(g m�2 day�1)

Incident

radiation

(�103 MJ m�2)

Intercepted

radiation

(�103 MJ m�2)

Radiation

interception

ratio

RUEb

(gMJ�1)

LAI at

heading

(m2 m�2)

N accumulation

at maturity

(g m�2)

Yunnan

Nipponbare 122 13.2 0.56 14.2 1.69 0.96 0.57 1.37 3.9 16.5

Takenari 137 15.6 0.35 14.4 1.92 1.18 0.61 1.32 3.8 18.4

Shanguichao 150 19.7 0.57 17.9 2.16 1.43 0.66 1.37 5.9 20.7

Takanari (14 N) 147 19.5 0.60 16.5 2.11 1.33 0.63 1.46 5.2 18.7

Jinyou207 133 19.7 0.61 17.9 1.96 1.31 0.67 1.50 6.2 22.8

Liangyoupeijiu

(14 N)

157 23.0 0.58 17.9 2.24 1.58 0.70 1.45 5.9 22.7

Takanari (0 N) 145 15.5 0.59 13.4 2.07 1.19 0.58 1.31 3.7 12.0

Takanari (28 N) 149 22.0 0.59 18.4 2.12 1.40 0.66 1.56 7.3 26.6

Liangyoupeijiu

(28 N)

157 24.4 0.58 19.2 2.22 1.59 0.71 1.54 7.6 31.1

Averagec 141 18.4 0.54 16.5 2.01 1.30 0.64 1.41 5.1 20.0

Kyoto

Nipponbare 150 13.3 0.49 10.3 1.50 0.93 0.62 1.43 5.3 15.3

Takenari 154 14.2 0.43 10.6 1.56 1.02 0.65 1.39 5.2 15.8

Shanguichao 143 13.3 0.52 10.9 1.43 0.93 0.65 1.43 5.2 12.9

Takanari (14 N) 149 14.9 0.56 11.6 1.48 0.93 0.63 1.60 5.9 14.2

Jinyou207 142 13.9 0.54 11.5 1.43 0.93 0.66 1.49 5.8 14.6

Liangyoupeijiu

(14 N)

155 15.6 0.55 11.6 1.57 1.07 0.68 1.46 5.6 15.0

Takanari (0 N) 147 11.1 0.57 8.8 1.46 0.71 0.48 1.44 2.9 9.0

Takanari (28 N) 152 14.9 0.57 11.3 1.53 1.01 0.66 1.47 7.0 18.2

Liangyoupeijiu

(28 N)

159 17.2 0.49 12.4 1.61 1.18 0.73 1.46 6.1 19.8

Averagec 149 14.2 0.51 11.1 1.49 0.97 0.65 1.47 5.5 14.6

Analysis of variancec

Site 231*** 7* 490*** 3121*** 6* 3 NS 5* 291***

Variety 36*** 25*** 15*** 292*** 72*** 6** 9*** 10***

Site�variety 19*** 4* 4* 202*** 23*** 1 NS 5** 15***

LSD (0.05)c

LSD site 0.6 0.02 0.48 0.01 0.00 0.02 0.3 0.7

LSD variety 1.0 0.04 0.83 0.02 0.01 0.08 0.6 1.1

LSD site � variety 1.4 0.06 1.18 0.03 0.02 0.12 0.9 1.6

*,**,*** F value significant at the 0.05, 0.01 and 0.001 probability levels, respectively. NS means non-significant at P = 0.05.a Growth duration from sowing to maturity.b Averaged value from transplanting to maturity.c Takanari (0 N), Takanari (28 N) and Liangyoupeijiu (28 N) were excluded from the variety average and analysis of variance because of different N application.


solar radiation environments (Horie et al., 1997; Ying et al.,

1998a; Namba, 2003), which suggests the importance of solar

radiation to limit rice yields (Murata, 1965; Monteith, 1977;

Horie and Sakuratani, 1985). Biomass production can be

expressed by a product of intercepted radiation and RUE, and

intercepted radiation was affected by incident solar radiation and

leaf area. There was no significant difference in RUE between the

experimental sites in both years. In the present study, the value of

K was measured only twice during the growth period as shown in

our previous report (Katsura et al., 2007) and only at Kyoto.

However, since rice leaves generally look droopier in early

growth stage than in later stages before heading, the value of K

might be higher in the early growth stage, than at 2 weeks before

heading. To examine the possible influence of changing K values

on RUE estimates, the RUE was recalculated, with K 50% larger

than the measured value, for the case of Shanguichao in 2002 at

Yunnan from its initial transplanting to panicle initiation. The

resultant decrease of RUE from transplanting to maturity was

only 5% from the original estimate. In addition, there was a big

difference in the value of K between years, even in the same

variety. For example, therewas a 32% and a 56% difference in the

value of K between years in Shanguichao, before and after

heading, respectively (Table 7). The reason for the difference is

unclear, but might have been caused in part by measurement

conditions. If the value of K was interchanged between years

after panicle initiation stage, there was less than 3% difference in

RUE in Shanguichao. The effect of K on RUE might be relatively

small. However, the continuous measurement of K or radiation

interception ratio to reveal the seasonal and locational variation

in K must be needed for further detail analysis.

Table 7

The values of the light extinction coefficient (K) for each variety and year

calculated from stratified clipping method

Before heading After heading

2002

Nipponbare 0.36 0.58

Takenari 0.34 0.70

Shanguichao 0.35 0.63

Takanari 0.40 0.57

IR72 0.40 0.64

IR65564-44-2-2 0.40 0.56

WAB450-I-B-P-38-HB 0.43 0.61

2003

Nipponbare 0.45 1.02

Takenari 0.44 0.90

Shanguichao 0.46 0.99

Takanari 0.41 0.75

Jinyou207 0.47 0.66

Liangyoupeijiu 0.47 0.92

Takanari (0 N) Not measured 0.79

Takanari (28 N) Not measured 0.72

Liangyoupeijiu (28 N) Not measured 0.79


In 2002, LAI at heading was significantly larger at Yunnan,

which caused significantly larger radiation interception ratio

(Table 5). Incident solar radiation at Yunnan was only 11%

larger than at Kyoto, which is not enough to explain the 33%

difference in grain yield between the two sites in 2002. The

large LAI, as well as intense radiation in 2002, was also an

important factor for high grain yield in Yunnan. The lower leaf

area expansion at Kyoto in 2002 might be attributable to slower

initial biomass growth and lower leaf N content per unit leaf

area (LNC) than those at Yunnan in 2002 (Yoshida et al., 2007).

However, the reason for low LNC at Kyoto in 2002 was not

revealed in this study and further studies are necessary. On the

other hand, there was not a big difference in LAI at heading and

Table 8

N accumulation at maturity, ratio N harvested and aboveground biomass at matur

Amount of total

N fertilization (g m�2)

N accum

maturity

Yunnan

Takanari (0 N) 0 12.0

Takanari (14 N) 14 18.7

Takanari (28 N) 28 26.6

Kyoto

Takanari (0 N) 0 9.0

Takanari (14 N) 14 14.2

Takanari (28 N) 28 18.2


Site 68***

Treatment 114***

Site � treatment 6*

LSD (0.05)

LSD site 1.5

LSD treatment 1.8

LSD site � treatment 2.6

*,**,*** F values significant at the 0.05, 0.01, and probability levels. NS means na (Accumulated N by 14 or 28 N � accumulated N by 0 N)/fertilized N.

radiation interception ratio between the two sites in 2003. It

could be said that intense solar radiation was a major factor for

high rice yield at Yunnan in 2003. The average daily incident

radiation from transplanting to maturity at Yunnan (around

17 MJ m�2 day�1), was lower than that in the other environ-

ments that achieved high rice yields, such as Yanco, Australia

(around 23 MJ m�2 day�1; Ohnishi et al., 1993) and Nile Delta,

Egypt (around 26 MJ m�2 day�1; Namba, 2003). An incident

radiation of around 17 MJ m�2 day�1 is enough to achieve high

rice yields of around 16 tonnes ha�1.

Increase of nitrogen absorption is essential for increased

biomass and grain yield (Greenwood et al., 1990; Sheehy et al.,

1998). In the present study, the amount of N accumulation at

maturity (averaged over varieties) was 62% and 36% higher at

Yunnan than at Kyoto in 2002 and 2003, respectively, and

significantly correlated with grain yield. The earlier study (Ying

et al., 1998b) also found a large N accumulation in the crop at

Yunnan. According to the N fertilizer experiment for Takanari

in 2003, Takanari (0 N) absorbed 12.0 g N m�2 by maturity at

Yunnan, while 9.0 g N m�2 was absorbed at Kyoto. A major

part of this difference occurred in early growth stage, before the

panicle initiation stage (Fig. 1). In general, the amount of

mineralized N in paddy soil increases as the accumulated

effective temperature increases (Stanford et al., 1973;

Hasegawa and Horie, 1994). N accumulation by plants is

accelerated by higher temperature and/or intense radiation

(Takahashi et al., 1976; Mengel and Viro, 1978; Ta and Ohira,

1982; Shoji and Mae, 1984; Hirokawa et al., 1993). The large N

accumulation by Takanari (0 N) in the early growth stage at

Yunnan might have come from higher air temperature and

intense solar radiation in the early growth stage. On the other

hand, there was not a big difference in N accumulation by

Takanari (0 N) between the two sites after the panicle initiation

stage. This means that there was no great difference in soil

fertility between the two sites, because N accumulation rates by

ity of Takanari grown at Yunnan and Kyoto in 2003

ulaltion at

(g m�2)

Ratio N harvesteda Aboveground biomass

at maturity (g m�2)

1552

0.47 1948

0.52 2196

1106

0.37 1486

0.33 1487

10* 78***

0 NS 26***

1 NS 2 NS

0.13 141

0.13 172

0.18 243

on-significant.

Fig. 2. Seasonal change in the aboveground biomass in Takanari with different

N application in 2003.

Fig. 3. Seasonal change in LAI in Takanari with different N application in

2003.

Fig. 1. Seasonal change in the N accumulation in Takanari with different N

application in 2003.


plants without N application during mid- and late-growth stages

were affected by soil fertility (Wada et al., 1989).

One of the reasons for large N accumulation at Yunnan was

the high ratio of N accumulated at maturity to the amount of

fertilized N (ratio N harvested; Table 8). The ratio N harvested

of over 0.50 at Yunnan is similar to high values reported in

previous studies (Cassman et al., 1993, referred to as recovery

efficiency). There was not a big difference in N accumulation

by Takanari (14 N and 28 N) in the early growth stage between

the two sites, but the difference became large after the panicle

initiation stage (Fig. 1). Besides, Takanari (14 N and 28 N) at

Yunnan kept absorbing N until the maturity, while there was

little N accumulation in Takanari (14 N and 28 N) at Kyoto

during the grain filling stage (Fig. 1). This contributed to the

large biomass production during the grain filling at Yunnan

(Fig. 2).

On the other hand, there was no significant difference in

aboveground biomass and grain yield between Takanari (14 N)

and (28 N) at Kyoto, even though Takanari (28 N) absorbed

more N and had a larger LAI (Fig. 3) than Takanari (14 N).

Similar phenomena, N saturation in plant growth, were

observed by many researchers (Murayama, 1982; Roberts

et al., 1993; Singh et al., 1998; Swain et al., 2006), and were

partly due to increased respiration/photosynthesis ratio (Osada

and Murata, 1962a,b; Shi and Akita, 1988). Respiration rate of

rice reached its maximum value around heading stage (Sakai

et al., 2001; Saito et al., 2005; Xu et al., 2006), and affected by

air temperature (McCree, 1974; Amthor, 1989) and nitrogen

concentration (Sakai et al., 2001; Xu et al., 2006). Around the

heading stage at Kyoto, high air temperature (which increased

the rice respiration loss, especially in organs with high N

concentration) and low radiation (which reduced the gross

photosynthesis) around heading stage increased the respiration/

photosynthesis ratio and might have induced a N saturation in

plant growth in Takanari (28 N). Many researchers have

suggested the importance of lower night temperatures or larger

diurnal temperature ranges for high rice yields (Yamamoto,

1954a,b; Kawashima et al., 1998; Lee and Akita, 2000; Peng

et al., 2004; Sheehy et al., 2006). The minimum temperature

during the mid-growth stage at Yunnan was lower than at

Kyoto. Consequently, coupled with the intense radiation, which

enhanced the photosynthesis, Takanari (28 N) produced large

biomass and grain yield without causing over-growth at

Yunnan.

In conclusion, the yield of tested varieties was, on average,

33–39% greater in Yunnan than in Kyoto. The high yield in

Yunnan was attributable primarily to the intense incident solar

radiation, which caused the large biomass accumulation and the

great absorption of N. The low temperature during the mid-

growth stage, coupled with the intense solar radiation, might

support the large biomass accumulation. In addition, a faster

LAI development was suggested to be an important factor for

high yields in Yunnan.


Acknowledgements

We thank the staff of Key Laboratory of Crop Growth

Regulation of Ministry of Agriculture, Hi-Tech Key Lab of

Information Agriculture of Jiangsu Province, Nanjing Agri-

cultural University for their advice and support during my stay

in China. We also thank the staff of the Laboratory of Crop

Science, Graduate School of Agriculture, Kyoto University for

their experimental support.

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