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Field Crops Research 144 (2013) 192–199

Contents lists available at SciVerse ScienceDirect

Field Crops Research

jou rna l h om epage: www.elsev ier .com/ locate / fc r

henological responses of maize to changes in environment when grown atifferent latitudes in China

uee Liua, Ruizhi Xiea, Peng Houa, Shaokun Lia,∗, Houbao Zhanga, Bo Minga, Haili Longa, Shumin Liangb

Institute of Crop Sciences, Chinese Academy of Agricultural Sciences/Key Laboratory of Crop Physiology and Ecology, Ministry of Agriculture, Beijing 100081, ChinaIndustrial Crop Research Institute of Yunnan Academy of Agricultural Sciences, Kunming 650205, China

r t i c l e i n f o

rticle history:eceived 28 December 2012ccepted 3 January 2013

eywords:aize

henological responsesDDhotoperiodatitudelimatic factororth spring maize region

a b s t r a c t

Environmental conditions greatly affect the growth of maize. To examine differences in phenologicalresponses of maize (Zea mays L.) to climatic factors under different environmental conditions as inducedby latitude, experiments were conducted from 2007 to 2010 at 34 sites in seven Chinese provinces locatedin the north spring maize region of China between latitudes 35◦11′ and 48◦08′N in the cultivation of hybridzhengdan958 (ZD958). Latitude is an important geographical factor which significantly affects tempera-ture, sunshine hours, and the duration of crop growth. The findings of this study indicate that for every1◦ increase in the latitude, northward, the growth durations of sowing to emergence and emergenceto silking were significantly increased by 0.7 d and 1.25 d, respectively as a consequence of loweringtemperatures (mean, maximum, and minimum temperatures). Reproductive growth duration (silkingto maturity), which was significantly correlated with the precipitation, decreased by 0.8 d with each 1◦

increase in latitude northward. At higher latitudes, the number of growing degree days (GDD) of maizevegetative growth duration (emergence to silking) was significantly higher, and the GDD of the reproduc-tive growth duration were significantly lower. The average photoperiod during the photoperiod-sensitivephase of maize development across all the experimental sites was 14.9 h with a range of 13.7–15.6 h. Totalleaf numbers increased from 18.7 to 23.7 with an average of 21.0 across all experimental sites. Significant

and positive linear relationships were found to occur between both latitude and photoperiods and lati-tude and total leaf number. In the north China spring maize region, the mean growth duration of ZD958was 143.73 d, which constituted 82.8% of the frost free period, the percentage increasing with higherlatitude. These findings strongly indicate that in order to ensure high and stable production of maize inthe north spring maize region of China, with its limited heat resources, especially in the high-latitude

cult

regions, there is a need to

. Introduction

The north spring maize region of China forms the largest maizeroducing area of the country and includes the provinces of Hei-

ongjiang, Jilin, Liaoning, inner Mongolia, and portions of Shanxi,ebei, Shaanxi, and Gansu, all of which are mainly located between

atitudes 33◦24′N (Wudu, Gansu province) and 50◦50′N (Heihe,eilongjiang province). The maize acreage of this region accounts

or 42.4% of that of China and 8.8% of that of the world which rep-esents about 46.4% and 8.6% of the total Chinese and global maizerain production, respectively (Li and Wang, 2010; FAO, 2011). Theegion thus plays a significant role in ensuring food security.

Because of the large latitudinal span of the north spring maizeegion, the climatic factors within this area vary significantlyLi and Wang, 2010). In this region, the annual accumulated

∗ Corresponding author. Tel.: +86 1082108891; fax: +86 10 82108891.E-mail address: lishaokun@caas.cn (S. Li).

378-4290/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.fcr.2013.01.003

ivate short-growth-duration cultivars.© 2013 Elsevier B.V. All rights reserved.

temperature above 10◦C, the sunshine hours, and precipitationrange from 2000 ◦C to 3600 ◦C, 2600 h to 2900 h, and 400–800 mm,respectively, These environmental ranges greatly influence maizedevelopment (Warrington and Kanemasu, 1983a). Because of this,the maize cultivars that are widely planted in the north springmaize region are diverse, and the phenomenon of “across-regionplanting” (planting cultivars in regions in which they can notgrow successfully) is a serious issue, especially in the high-latituderegion. The need to study phenological responses of maize tochanges in environment is therefore important.

Environmental conditions, especially climatic factors, such astemperature, photoperiod, sunshine hours, solar radiation andprecipitation, markedly influence maize growth and phenologi-cal response (Andrade et al., 1993; Andrade and Ferreiro, 1996;Otegui et al., 1996; Birch et al., 1998; Tollenaar, 1999; Stone et al.,

1999; Yang et al., 2004). Among these factors, temperature andphotoperiod are the two most important environmental variablesinfluencing the rate of maize development (Duncan, 1975; Hodges,1991; Birch et al., 1998; Tollenaar, 1999). There is evidence that

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Y. Liu et al. / Field Crops

ncreasing temperature during the vegetative stage of maize leadso a decrease in length of this stage in growth (Cooper and Law,978; Liu et al., 2010). Some studies from different agriculturalegions have also indicated that, as the temperature is increased, sooo is length of the growing season (Chen et al., 2011; De Jong et al.,001; Bootsma et al., 2004). On the other hand, maize is a short-daylant and photoperiod significantly affects maize growth by influ-ncing growth duration and leaf number. For example, Birch et al.1998) reported that a photoperiod extension (16.5 h) increased theime from emergence to tassel initiation and increased the num-er of leaves on five different cultivars differing in maturity anddaptation. Tollenaar (1999) also indicated that the time from sow-ng to silking increased when the photoperiod was increased from0 h–20 h during the photoperiod-sensitive phase in maize, but noifferences were found in the duration of the grain-filling period.ther workers, however, have reported that the grain-filling period

s reduced by an increase in photoperiod (Breuer et al., 1976; Allisonnd Daynard, 1979).

As important factors relating to crop phenology, heat unitequirements, such as growing degree days (GDD) and accumulatedemperature, influence crop growth and development (Stewartt al., 1998; Craufurd et al., 1998; Bartholomew and Williams,005). The heat unit required to complete a given growth phase ofaize is usually thought to be constant and dependent only upon

he cultivars (Wang, 1960; Sacks and Kucharik, 2011). However,everal studies have indicated that the heat units required for theompletion of a given growth phase of maize are not constant butay vary depending on other environmental conditions. For exam-

le, Tataryn (1974) found significant differences between locationsnd years in the accumulated temperature from emergence to theasseling and silking stages. In Manitoba, Canada, Major et al. (1983)ound that the maize heat unit requirements were dependent uponocation.

ZD958, which exhibits high yield, high quality, multi-resistance,nd extensive adaptability, has recently been one of the most com-only used maize (Zea mays L.) hybrids in China. It is the most

idely distributed cultivar across the north spring maize region

nd the Huanghuaihai summer maize region of China. In 2009,he planting area of ZD958 increased to 4,540,000 ha, accord-ng to the Chinese Agriculture Technology and Popularization

Fig. 1. The north spring maize region of China and the experimental sites d

ch 144 (2013) 192–199 193

Center. Because of global warming (IPCC, 2007), the planting areaof ZD958 has been enlarged and the planting region has beenextended northward; the north line for safe planting of ZD958 inthe Northeast has extended to 47◦N (You et al., 2008; Bai et al.,2010). Previous studies on phenological responses of maize havefocused mainly on different cultivars on a small scale (e.g. Birchet al., 1998; Tollenaar, 1999). On the other hand this most widelydistributed cultivar in China provided an opportunity to studyphenological responses of maize to environmental change andthe influencing factors on a large on-farm scale. Understandingthe effects of changing climatic resources of different latitudes onmaize phenological responses is also of importance in establishingsafe planting regions whereby the risk of across-region planting ofmaize using unsuitable cultivars is reduced. The objectives of thisstudy were thus to investigate (1) phenological changes of ZD958in relation to increasing latitude, and (2) the factors responsible forinfluencing growth duration with increasing latitude in the northChina spring maize region.

2. Materials and methods

2.1. Site description and experimental design

Experiments were conducted in 2007–2010 at 34 locationsin seven provinces (Heilongjiang, Jilin, Liaoning, Inner Mongolia,Hebei, Shanxi, Shaanxi) between 35◦11′N and 48◦08′N in the northspring maize region of China (Fig. 1 and Table 1). Details of thegeographical positions and environmental conditions are given inTable 1. This region is in temperate and cold temperate zones withhumid and semi-humid climates. The seasons are cold and dryin winter, and warm and short in summer. The annual accumu-lated temperature above 10 ◦C, sunshine hours, and precipitationare 2000–3600 ◦C, 2600–2900 h, and 400–800 mm, respectively.This climate together with good soil quality accounts for the northspring maize region as the main maize producing area in China.

The maize hybrid ZD958, is widely grown in the north springmaize region and the Huanghuaihai summer maize region, whichwas the reason for its choice in this study. At every experimentalsite, each plot was 15 m long and 6.5 m wide, consisted of 10 rows

istribution. The dots are the 34 experimental stations in this region.

194 Y. Liu et al. / Field Crops Research 144 (2013) 192–199

Table 1Locations and environmental conditions of the experimental sites.

Site Location Metro-ecological condition Irrigationcondition

Plantingyears

Northlatitude

Eastlongitude

Altitude(m)

≥10 ◦Caccumulatedtemperature (◦C)

Accumulatedsunshinehours (h)

Precipitation(mm)

Frost freeduration (d)

Wangkui, HLJ 46◦50′ 126◦29′ 180 3024 2720 502 162 Rainfed 2007–2008Qinggang, HLJ 46◦41′ 126◦06′ 151 2888 2571 499 158 Rainfed 2007–2008Zhaodong, HLJ 46◦03′ 125◦59′ 148 3223 2894 412 163 Rainfed 2007–2009Keshanxian, HLJ 48◦02′ 125◦52′ 276 2831 2638 488 157 Rainfed 2010Qiqihaer, HLJ 47◦21′ 123◦55′ 147 3187 2848 426 163 Rainfed 2009–2010Jiamusi, HLJ 46◦48′ 130◦19′ 98 3010 2438 532 158 Rainfed 2008–2009Mudanjiang, HLJ 44◦33′ 129◦38′ 306 3076 2319 536 158 Rainfed 2007–2010Hulan, HLJ 45◦52′ 126◦36′ 130 3283 2272 503 171 Rainfed 2008–2010Taonan, JL 45◦20′ 122◦48′ 147 3334 2814 295 157 Irrigated 2007–2008Qianguo, JL 45◦07′ 124◦50′ 138 3358 2663 403 172 Rainfed 2007–2009Nongan, JL 44◦25′ 125◦12′ 179 3410 2505 580 168 Rainfed 2007–2010Gongzhuling, JL 43◦30′ 124◦51′ 215 3559 2546 556 175 Rainfed 2007–2010Yitong, JL 43◦20′ 125◦19′ 265 3410 2505 580 168 Rainfed 2007–2008Siping, JL 43◦10′ 124◦21′ 170 3559 2546 556 175 Rainfed 2007Jilinshi, JL 43◦50′ 126◦33′ 221 3202 2308 697 158 Rainfed 2009–2010Tonghua, JL 41◦44′ 125◦57′ 457 3183 2380 709 166 Rainfed 2009–2010Kangping, LN 42◦45′ 123◦21′ 98 3598 2475 687 167 Rainfed 2007–2010Zhangwu, LN 42◦23′ 122◦33′ 102 3183 2380 709 166 Rainfed 2007–2010Shenyang, LN 41◦48′ 123◦26′ 53 3747 2313 717 182 Rainfed 2007–2008Haicheng, LN 40◦53′ 122◦41′ 25 4160 2554 730 205 Rainfed 2007–2010Jinzhou, LN 41◦06′ 121◦07′ 40 4010 2565 558 206 Rainfed 2009Dandong, LN 40◦08′ 124◦23′ 45 3605 2276 994 203 Rainfed 2009–2010Tieling, LN 42◦17′ 123◦51′ 65 3598 2475 687 167 Rainfed 2009–2010Tongliao, IM 43◦37′ 122◦16′ 178 3596 2910 316 178 Irrigated 2007–2010Chifeng, IM 42◦15′ 118◦53′ 682 3520 2917 336 165 Irrigated 2007–2010Arongqi, IM 48◦08′ 123◦29′ 230 2845 2758 436 151 Irrigated 2008Xinganmeng, IM 46◦05′ 122◦04′ 282 3287 2919 360 166 Irrigated 2008Dalateqi, IM 40◦24′ 110◦03′ 1422 3700 2876 303 164 Irrigated 2008Linhe, IM 40◦46′ 107◦26′ 1041 3466 3227 170 152 Irrigated 2009–2010Zunhua, HB 40◦12′ 117◦58′ 205 4367 2463 581 213 Rainfed 2008–2010Zhangjiakou, HB 40◦45′ 114◦55′ 1350 3737 2588 394 194 Rainfed 2009–2010Yulin, SAX 38◦17′ 109◦44′ 1217 3640 2602 419 182 Rainfed and

irrigated2009–2010

Chengcheng, SAX 35◦11′ 109◦56′ 715 3649 2647 620 197 Rainfed 2009–2010Xinzhou, SX 38◦25′ 112◦44′ 847 3785 2115 412 194 Rainfed and

irrigated2009–2010

10-Year (2001–2010) mean values of meteorological annual variables were obtained from the nearest meteorological stations of different provinces in China (HLJ, Heilongjiang;J

wptwbtwsNpKNgap

2

iwwps

L, Jilin; LN, Liaoning; IM, Inner Mongolia; HB, Hebei; SX: Shanxi; SAX: Shaanxi).

ith a row spacing of 0.65 m, and was replicated four times. Maizelant density was 6.0 × 104 plants ha−1. The crop was cultivatedaking one harvest per year as continuous maize. At all sites, seedsere sown by hand and planted from the end of April to the

eginning of May and harvested from the end of September tohe beginning of October. All experiments were well managed andeeds, diseases and insect pests were well controlled. The data

et contained many different nutrient management treatments.itrogen applications ranged from 138 to 380 kg N ha−1, Phos-horus (P) applications ranged from 0 to 177 kg P2O5 ha−1, and

applications ranged from 0 to 112 kg K2O ha−1. These rates of, P and K applications were based on soil chemical analysis touarantee non-limiting conditions of nutrient supply. To ensurebsence of water stress, irrigation was applied at sites with lowrecipitation (Table 1).

.2. Database

Throughout the period from 2007 to 2010 at each of the exper-mental sites dates of sowing, emergence, silking and maturity

ere recorded. Additionally from 2008 to 2010 total leaf numberas also reported. An emergence date was taken when 60% of thelants had emerged, a silking date when 60% of the ears showedilk emergence and a physiological maturity date when the black

layer appeared in the placental region of the kernel (Ritchie et al.,1992; Shi et al., 2006).

Weather data (maximum temperature, mean temperature,minimum temperature, sunshine hours, solar radiation and precip-itation) from the maize growing seasons of 2007 through 2010 atthe experiment locations and the annual weather data from 2001to 2010 were obtained from the Chinese Meteorological Admin-istration (CMA Archives, 2010). Different growth durations arerepresented by numbers of days (sowing to emergence, emergenceto silking, silking to maturity and sowing to maturity).

The growing degree days (GDD) were defined by the followingequation where Tmax, Tmin and Tbase are the maximum, minimumtemperature and 10 ◦C respectively (McMaster and Wilhelm, 1997;Yang et al., 2004). Because GDD for maize are normally calculatedusing an upper threshold temperature, we set this equal to 30 ◦C inthis study (McMaster and Wilhelm, 1997).

GDD =n∑0

[Tmax + Tmin

2

]− Tbase

The photoperiods during the photoperiod-sensitive phase ofmaize development at two weeks after seedling emergence, includ-ing civil twilight were calculated using the method outlined in Jonesand Kiniry (1986).

Research 144 (2013) 192–199 195

2

pbdsarammt

3

3

3

stgnttstsdvsg

3a

s

Latitu de (°N )

y = 0.97 87x + 15 .595

R 2 = 0.284 **40

50

60

70

35 40 45 50

2007

2008

2009

2010

V/W

(%

)

in different years was 9.13%, which was the highest, and thesecond was emergence to silking, for which it was 5.46%. Thecoefficients of variation in the periods of silking to maturity and

Table 2Maize growth durations in different locations during 2007–2010.

Growth duration (d) Mean Maximum Minimum Coefficient ofvariation (%)

F

Y. Liu et al. / Field Crops

.3. Statistical analysis

Calculations were performed and tables and figures were pre-ared using Microsoft Excel 2003. The regression relationshipsetween latitudes and the growth durations (days), GDD duringifferent growth durations (sowing to emergence, emergence toilking, silking to maturity and sowing to maturity), photoperiods,nd leaf numbers were calculated. Multiple regressions and cor-elations between the calendar days of different growth durationsnd climatic factors [temperatures (mean, maximum, and mini-um), sunshine hours, solar radiation and precipitation] over theaize growth period were performed with Statistical Analysis Sys-

em (SAS).

. Results

.1. Analysis of variations in maize growth durations

.1.1. Relationships between the growth durations and latitudesMaize growth durations of sowing to emergence, emergence to

ilking, and silking to maturity were significantly correlated withhe latitudes, but no significant correlation was found betweenrowth duration from sowing to maturity and the latitude in theorth spring maize region during 2007–2010 (Fig. 2). According tohe linear regression between the growth durations and latitudes,he sowing to emergence duration (Fig. 2A) and the emergence toilking duration (Fig. 2B) increased by 0.7 d and 1.25 d, respec-ively, with a 1◦ increase in the north latitude. By contrast, with theame latitude increase the growth duration of silking to maturityecreased by 0.8 d (Fig. 2C). With increased latitudes, the ratio ofegetative growth duration to the entire growth duration increasedignificantly (Fig. 3). This is because of the increasing vegetativerowth duration and the relatively constant total growth duration.

.1.2. Changes in maize growth duration in different locationsnd different years

The average durations of sowing to emergence, emergence toilking, silking to maturity, and sowing to maturity were 14.61,

A

C

Gro

wth

du

rati

on

(d

)

Latitu de (°N )

y = 0.70 24x - 15.543

R 2 = 0.17 1**

0

10

20

30

40

35 40 45 50

2007

2008

2009

2010

y = -0.797 1x + 95 .498

R 2 = 0.089 *

40

60

80

100

35 40 45 50

2007

2008

2009

2010

Sowing to emergence

Silking to maturity

ig. 2. Relationships between maize growth durations [sowing to emergence (A), emerge

Fig. 3. Relationship between V/W and latitude. Note: V represents days of vegetativegrowth duration and W represents days of the entire growth duration.

68.70, 61.13, and 143.73 d, respectively (Table 2). The coefficient ofvariation of sowing to emergence in different locations was 28.73%,which was the highest among the periods, with silking to maturitybeing second, for which the coefficient of variation was 11.03%. Thecoefficient of variation of 6.67% for sowing to maturity was lowest.

The coefficients of variation for different years are presentedin Table 3. The coefficients of variation varied in different growthdurations. The coefficient of variation of sowing to emergence

Sowing to emergence 14.61 28 6 28.73Emergence to silking 68.70 88 51 10.27Silking to maturity 61.13 80 43 11.03Sowing to maturity 143.73 159 108 6.67

B

D

Latitu de (°N )

y = 1.245 8x + 14.88

R 2 = 0.208 **40

60

80

100

35 40 45 50

2007

2008

2009

2010

100

120

140

160

180

35 40 45 50

2007

2008

2009

2010

Emergence to silking

Sowing to maturity

nce to silking (B), silking to maturity (C) and sowing to maturity (D)] and latitudes.

196 Y. Liu et al. / Field Crops Research 144 (2013) 192–199

Table 3Maize growth durations in 2007–2010 across different locations.

Growth duration (d) 2007 2008 2009 2010 Coefficient of variation (%)

Sowing to emergence 15.69a 16.17a 13.39a 13.9a 9.13Emergence to silking 70.43a 71.24a 70.52a 63.24b 5.46Silking to maturity 61.73ab 58.76b 60.62ab 63.70a 3.37Sowing to maturity 147.08a 144.83ab 144.43ab 139.63b 2.18

Note: Values followed by the same lowercase letter in the same row are not significantly different at p ≤ 0.05 according to LSD test.

Latitu de (°N ) Lat itu de (°N )

A B

C D

y = -1.07x 2 + 92 .08 1x - 1869 .8

R 2 = 0.109*0

50

100

150

200

250

35 40 45 50

2007

2008

2009

2010

y = 7.823 4x + 478.83

R 2 = 0.057*500

700

900

1100

35 40 45 50

2007

2008

2009

2010

y = -32 .425x + 2105 .3

R2 = 0.360**200

400

600

800

1000

1200

35 40 45 50

2007

2008

2009

2010

y = -25 .595x + 270 0

R2 = 0.19 9**

1200

1400

1600

1800

2000

2200

35 40 45 50

2007

2008

2009

2010

Sowing to emergence Emergence to silking

Silking to maturity Sowing to maturity

GD

D

F emer(

swtw

3a

tw2biw

ig. 4. Relationships between GDD of different maize growth durations [sowing toD)] and latitudes.

owing to maturity were 3.37% and 2.18%, respectively. Thereas no significant difference for the growth duration of sowing

o emergence between different years, and significant differencesere found in the other growth durations between years.

.2. Relationships between the GDD of different growth durationsnd latitudes

The GDD of sowing to emergence, emergence to silking, silkingo maturity, and sowing to maturity were significantly correlatedith the latitudes in the north spring maize region from 2007 to

010 (Fig. 4). According to the non-linear negative relationshipetween the GDD of sowing to emergence and latitudes (Fig. 4A),

n the regions south of 43◦02′N, the GDD for emergence increased,hereas those in the regions north of 43◦02′N decreased with

y = 0.1069x + 10.247

R 2 = 0.596**

13

14

15

16

35 40 45 50

2007200820092010

Latitude (°N)

Photo

per

iod (

h)

A

Fig. 5. Relationships between photoperiod (

gence (A), emergence to silking (B), silking to maturity (C) and sowing to maturity

increasing north latitude. With increasing latitudes, the GDD of thevegetative growth duration increased by 7.82 ◦C as a result of anincrease in latitude of 1◦ (Fig. 4B). By contrast, the GDD of the repro-ductive growth duration and the entire growth duration decreasedby 32.43 ◦C (Fig. 4C) and 25.6 ◦C (Fig. 4D), respectively, as a resultof an increase of 1◦ in the north latitude.

3.3. Relationships between the photoperiods and latitudes, andleaf number and latitudes

The average photoperiod across all the experimental sites was

14.9 h with a range of 13.7–15.6 h. A significant and positive linearrelationship occurred between the photoperiods and latitudes witha correlation coefficient of 0.596 (Fig. 5A). This showed that thephotoperiods increased significantly with increasing latitudes in

Latitude (°N)

Tota

l le

af n

um

ber

y = 0.1446 x + 14.756

R 2 = 0.164**

18

20

22

24

35 40 45 50

2008

2009

2010

B

A), total leaf number (B) and latitudes.

Y. Liu et al. / Field Crops Research 144 (2013) 192–199 197

Table 4Correlation coefficients between different growth durations and climatic factors in the corresponding growth stages.

Days of growth duration (d) T̄ (◦C) TM (◦C) Tm (◦C) R̄ (mm) S̄ (h) Ra (MJ m−2)

Sowing to emergence −0.3906** −0.3358** −0.4177** 0.0354 −0.0268 −0.0431Emergence to silking −0.4921** −0.4554** −0.5026** −0.1514 −0.0547 −0.1339Silking to maturity 0.0620 0.0383 0.1022 0.2910* −0.1063 −0.0490Sowing to maturity −0.5446** −0.4555** −0.5513** −0.3124** 0.2108 0.1013

Note: T̄ is daily mean temperature; TM is daily maximum temperature; Tm is daily minimum temperature; R̄ is daily mean precipitation; S̄ is daily mean sunshine hours; Ra

is daily solar radiation.* Correlation coefficients significant at p < 0.05.

** Correlation coefficients significant at p < 0.01

Table 5Multivariate linear regression model between different growth durations and climatic factors in the corresponding growth stages.

Growth duration (d) Regression model Multiple correlation coefficient Significant level

Sowing to emergence Y1 = 21.6835 − 0.7308X13 0.1579 0.01Emergence to silking Y2 = 119.5934 − 2.3115X21 0.2304 0.01Silking to maturity Y3 = 57.6201 + 1.1976X34 0.08 0.05Sowing to maturity Y4 = 151.9230 − 1.8366X13 + 1.4409X35 0.3339 0.01

Note: Y is days of growth duration of sowing to emergence (Y1), emergence to silking (Y2), silking to maturity (Y3) and sowing to maturity (Y4); Xij is the j weather factor att ce, em3 , dailyh

tin

apatcawl

3

tsaathd

msgtsp(mdttmfTicmt

he i growth duration, i = 1, 2, 3, 4 represent growth durations of sowing to emergen, 4, 5, 6 represent daily mean temperature (◦C), daily maximum temperature (◦C)ours (h) and daily mean solar radiation (MJ m−2) respectively.

he north spring maize region from 2007 to 2010. The photoperiodncreased by 0.11 h as a result of an increase of 1◦ latitude to theorth.

The total leaf numbers increased from 18.7 to 23.7 with anverage of 21.0 across all the experimental sites. A significant andositive linear relationship occurred between total leaf numbernd latitudes with a correlation coefficient of 0.164 which showedhat with latitudes northward total leaf number increased signifi-antly (Fig. 5B). Total leaf number increased by 0.14 as a result ofn increase of 1◦ latitude northward. This total leaf number trendith latitudes was probably because of photoperiod change with

atitude.

.4. Relationships between growth durations and climatic factors

In order to identify the main climatic factors associated withhe growth durations (sowing to emergence, emergence to silking,ilking to maturity, and sowing to maturity), a Pearson correlationnalysis was carried out between the different growth durationsnd the mean temperature, maximum temperature, minimumemperature, daily mean precipitation, and daily mean sunshineours and daily mean solar radiation over the different growthurations (Table 4).

No significant correlations were found between any of theaize growth durations and the corresponding daily mean sun-

hine hours and daily mean solar radiation (Table 4). In the maizerowth durations of sowing to emergence and emergence to silking,he effect of the daily mean precipitation of each duration were notignificant and negative correlations were found between the tem-eratures (mean, maximum, and minimum) and growth durationsTable 4). This means that temperatures (mean, maximum, and

inimum) were the major climatic factors for the maize growthurations of sowing to emergence and emergence to silking. Inhe growth duration of silking to maturity, no significant correla-ions were found between the temperatures (mean, maximum, and

inimum) and the growth duration, but a positive correlation wasound between daily mean precipitation and the growth duration.he major climatic factor for the maize growth duration of silk-

ng to maturity was the daily mean precipitation. As for the majorlimatic factors that affected the length of time from sowing toaturity, negative correlations were found between the tempera-

ures (mean, maximum, and minimum), daily precipitation and the

ergence to silking, silking to maturity and sowing to maturity respectively, j = 1, 2, minimum temperature (◦C), daily mean precipitation (mm), daily mean sunshine

growth duration. Temperature (mean, maximum, and minimum)and daily precipitation were found to be the main climatic factorsfor the growth duration of sowing to maturity (Table 4).

Multiple linear regression analysis equations with correla-tion coefficients between the growth durations and climaticfactors for the stages of sowing to emergence, emergence to silk-ing, silking to maturity, and sowing to maturity are shown inTable 5. Although the R2 (multiple correlation coefficient) valueswere low, the positive correlations were significant and showedthat growth durations were influenced by different climaticfactors.

4. Discussion

4.1. The growth duration change with latitudes

Latitude is an important geographical factor, affecting the dis-tribution of temperature, photoperiod, sunshine, solar radiationand precipitation, and thus significantly influencing the durationof crop growth (Sprague and Dudley, 1988; Yan et al., 2009, 2010,2011). Historically, as crop plants were taken to higher latitudesor to places with greater seasonal fluctuations in climatic factors,they were often unwittingly selected for better adaptation to theirnew environments (Evans, 1996). In many cases, the adaptation ofcrops to harsher environments depended more on changes in thelengths and timing of their life cycle, allowing them to escape themost adverse conditions, than on changes in the ability to toleratesuch environments (Evans, 1996).

In this study, significant correlations were found between maizegrowth durations of sowing to emergence, emergence to silking,and silking to maturity, and latitude. With the latitude northward,the vegetative growth duration increased significantly and thereproductive growth duration decreased significantly. The reasonsfor vegetative growth duration increasing were mainly focused onthe two aspects as follows. Firstly, negative correlations were foundbetween the temperatures (mean, maximum, and minimum) andthe vegetative growth durations (Table 4). With latitudes north-ward, the temperature decreased significantly which resulted in

an increase of vegetative growth duration (Liu et al., 2010). Sec-ondly, as maize is a short-day plant, it is significantly influencedby long photoperiods. A critical photoperiod of 12.5 h for maizehas been reported in many studies with photoperiod sensitivity

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inear at photoperiods in excess of this critical value (Aitken, 1980;arrington and Kanemasu, 1983a; Kiniry et al., 1983; Birch et al.,

998). In our study photoperiods increased from 13.7 h to 15.6 hhich exceeded the critical photoperiod of 12.5 h and increased

ignificantly with latitudes northward (Fig. 5A). This increasinghotoperiod and total leaf number with latitudes northward coulde responsible for delaying tassel initiation and silking, as a resultf the increasing duration of vegetative growth (Aitken, 1980;arrington and Kanemasu, 1983b; Kiniry et al., 1983; Ellis et al.,

992; Tollenaar, 1999).The significant decrease in reproductive growth duration with

orthward latitude is probably the consequence of increasedhotoperiod decreasing the duration of the grain filling periodBreuer et al., 1976; Allison and Daynard, 1979). Another probableeason for the shorter reproductive period with latitudes north-ard may be due to the adaption of maize to the environment

Evans, 1996). The lower temperature, especially cold tempera-ure in higher latitudes region, might result in the prematurity of

aize and thus the shorter reproductive period (Afuakwa et al.,983).

.2. The GDD change with latitudes

Heat unit requirements such as accumulated temperature androwing degree days (GDD) and are important factors that influ-nce crop growth and development (Stewart et al., 1998; Craufurdt al., 1998; Bartholomew and Williams, 2005). In our study, signif-cant correlations were found between the GDD of different maizerowth periods and latitude. With increased latitude, GDD of theegetative growth duration increased, and GDD of the reproduc-ive growth duration decreased. The reasons for the increasingnd decreasing GDD of vegetative and reproductive growth dura-ions were mainly due to the vegetative growth duration increasend reproductive growth duration decrease. Many studies con-rmed these results which indicated that the accumulated heatnits required for the completion of a given growth phase mightary with locations and other environmental conditions (Tataryn,974; Major et al., 1983). However, this conclusion differed fromhe conclusions of some studies reporting that the accumulatedemperature required by maize was constant and only dependedpon the crop cultivars (Wang, 1960; Bunting, 1976; Sacks anducharik, 2011).

.3. Comparison of maize growth durations in China and the U.S.

In the field experiments conducted at 74 sites from 2007 to010 between 35◦11′N and 48◦08′N, the average growth duration ofD958 was 143.73 d, which was 82.8% of the frost free period in theorth spring maize region of China, and the percentage was higher

n the higher-latitude regions. For example, in 2009, at the site iniamusi of Heilongjiang province, the growth duration of ZD958ccupied 95.71% of the frost free period in this region, indicating

risk to achievement of crop maturity. In comparison the Cornelt in the U.S. is mainly distributed from 38◦ to 43◦N with envi-onmental conditions similar to those of the north spring maizeegion of China. In the U.S., the growing duration of 72.68% of maizeultivars is 97 to 116 d, with an average of 102.77 d, the shortesturation of 72 d and the longest duration of 119 d (n = 216, Syngentagronomy Research Bulletin, 2011). Compared with the cultivars

n the U.S., the cultivars in China had thus longer growth dura-ions. These observations indicate that in order to ensure a high

nd stable production of maize in the north spring maize region ofhina, some short-growth-duration cultivars should be cultivatedo adapt to the limited heat resources especially in the high-latitudeegions.

ch 144 (2013) 192–199

5. Conclusions

Environmental conditions, especially climatic factors such astemperature, photoperiod, sunshine hours, solar radiation and pre-cipitation, greatly affect maize growth. Maize adapted to regionswith different ecological resources by changing its growth dura-tions. Growth durations from sowing to emergence and fromemergence to silking were significantly affected by the tempera-tures (mean, maximum, and minimum), increasing by 0.7 d and1.25 d as a result of an increase of 1◦ in the north latituderespectively. Compared with the vegetative growth duration, thereproductive growth duration, which was significantly correlatedwith the precipitation, decreased by 0.8 d with 1◦ northward in lati-tude. With increasing latitudes in China, the GDD of vegetative andreproductive growth varied significantly. Whereas with increas-ing latitude the GDD of vegetative growth duration increasedsignificantly, that of reproductive growth duration decreased sig-nificantly. The average photoperiod was 14.9 h and the total leafnumber averaged 21.0 across all the experimental sites. Significantand positive linear relationships were found between the photo-periods, total leaf number and latitudes. In the spring maize regionof northern China, the mean growth duration of ZD958 was 143.73d, which made up 82.8% of the frost free period and this value waseven greater in the high-latitude regions. In order to ensure a highand stable production of maize, some short-growth-duration cul-tivars should be utilized that are compatible with the limited heatresources in this region of China, especially at high-latitudes.

Acknowledgments

We thank the National Basic Research Program of China(973,Program: 2009CB118601), the National Maize Industry TechnologyRD Center, Ministry of Agriculture and the National Maize Produc-tion System in China for their financial support. The authors are alsograteful to Dr. Ernest Kirkby of the Faculty of Biological Sciences ofthe University of Leeds, UK for useful discussion and correction ofthe English text.

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