Review grain yield and nitrogen use efficiency in rice production regions in China

Journal of Integrative Agriculture 2015, 14(12): 2456–2466 Available online at www.sciencedirect.com

ScienceDirect

RESEARCH ARTICLE

Review grain yield and nitrogen use efficiency in rice production regions in China CHE Sheng-guo1, ZHAO Bing-qiang1, LI Yan-ting1, YUAN Liang1, LI Wei1, LIN Zhi-an1, HU Shu-wen2, SHEN Bing3 1

Key Laboratory of Plant Nutrition and Fertilizer, Ministry of Agriculture/Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R.China 2 College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, P.R.China 3 China Blue Chemical Ltd., Beijing 100029, P.R.China

Abstract As one of the staple food crops, rice (Oryza sativa L.) is widely cultivated across China, which plays a critical role in guaranteeing national food security. Most previous studies on grain yield or/and nitrogen use efficiency (NUE) of rice in China often involved site-specific field experiments, or small regions with insufficient data, which limited the representation for the current rice production regions. In this study, a database covering a wide range of climate conditions, soil types and field managements across China, was developed to estimate rice grain yield and NUE in various rice production regions in China and to evaluate the relationships between N rates and grain yield, NUE. According to the database for rice, the values of grain yield, plant N accumulation, N harvest index (HIN), indigenous N supply (INS), internal N efficiency (IEN), reciprocal internal N efficiency (RIEN), agronomic N use efficiency (AEN), partial N factor productivity (PEPN), physiological N efficiency (PEN), and recover efficiency of applied N (REN) averaged 7.69 t ha–1, 152 kg ha–1, 0.64 kg kg–1, 94.1 kg kg–1, 53.9 kg kg–1, 1.98 kg kg–1, 12.6 kg kg–1, 48.6 kg kg–1, 33.8 kg kg–1, and 39.3%, respectively. However, the corresponding values all varied tremendously with large variation. Rice planting regions and N rates had significant influence on grain yield, N uptake and NUE values. Considering all observations, N rates of 200 to 250 kg ha–1 commonly achieved higher rice grain yield compared to less than 200 kg N ha–1 and more than 250 kg N ha–1 at most rice planting regions. At N rates of 200 to 250 kg ha–1, significant positive linear relationships were observed between rice grain yield and AEN, PEN, REN, IEN, and PFPN, and 46.49, 24.64, 7.94, 17.84, and 88.24% of the variation in AEN, PEN, REN, IEN, and PFPN could be explained by grain yield, respectively. In conclusion, in a reasonable range of N application, an increase in grain yield can be achieved accompanying by an acceptable NUE. Keywords: rice, grain yield, nitrogen uptake, nitrogen use efficiency, China

Received 20 August, 2015 Accepted 5 November, 2015 CHE Sheng-guo, E-mail: [email protected]; Correspondence ZHAO Bing-qiang, Tel/Fax: +86-10-82108664, E-mail: [email protected] © 2015, CAAS. All rights reserved. Published by Elsevier Ltd. doi: 10.1016/S2095-3119(15)61228-X

1. Introduction Rice (Oryza sativa L.) yields have substantially increased in the past 64 years from only 48.6 million tons (Mt) in 1949 to 204 Mt in 2012 (National Bureau of Statistics 2013), which accounts for ca. 28.6% of global rice production (FAO 2012).

CHE Sheng-guo et al. Journal of Integrative Agriculture 2015, 14(12): 2456–2466

As population continuously increasing, projected to rise to 1.5 billion by 2030 (NPDSRG 2007; Zhao et al. 2010), an increase by 13.8% in rice production compared to in 2010 should be demanded to ensure food security (Cheng et al. 2007). However, the development of urbanization process and negative effects of climate limited the potential of available arable land for crops cultivated (Cheng et al. 2007; Peng et al. 2009), so rather than planting area expanding, increasing crop yield per unit area was required to meet population growth in the future. Part of the progress in rice production in the past attributed to a large amount of chemical fertilizer input, specially nitrogen (N) (Zhu and Chen 2002), consuming 38.3 Mt N in China in 2011, accounting for more than 30% of the world consumptions (FAO 2012). Simultaneous increase in the amounts of N fertilizer applied and rice production in the past led to farmers usually input luxurious N fertilizer to maximize crop yield (Lemaire and Gastal 1997; Peng et al. 2006; Gao et al. 2012). However, excessive application of chemical N can also lead to higher N surplus in soil and/or more losses by different pathways, such as emissions of gaseous, denitrification, surface runoff, and leaching. Low N use efficiency (NUE) and negative environmental impacts consequently occurred (Zhu and Chen 2002; Zhang et al. 2012). Many studies have been conducted to estimate NUE (Novoa and Loomis 1981; Dobermann 2005). According to Dobemann (2005), common NUE values for general crops ranged from 30 to 60 kg kg–1 for internal N efficiency (IEN), 40 to 70 kg kg–1 for partial N factor productivity (PFPN), 10 to 30 kg kg–1 for agronomic N use efficiency (AEN), and 30 to 50% for recover efficiency of applied N (REN), respectively, whilst at well managed systems or at low levels of N applied, NUE would break the upper thresholds. Cassman et al. (1996) indicated AEN of rice ranged from 15 to 18 kg kg–1 in farmers’ fields in Philippines. Ohnishi et al. (1999) reported REN of rice ranged from 35.4 to 55.5%, with the mean of 43.9% in northeast Thailand. Zhu et al. (1992) reported that REN of crops in China ranged from 28 to 41%, with an average of 35%. NUE of rice in China is considered low, even the lowest among the major rice-growing regions (Peng et al. 2006). Wang et al. (2001) confirmed that REN of rice in farmers’ N management practices was only 18%. Zhang et al. (2008) summarized 179 observations, finding that NUE of rice in China averaged 28.3% for REN, 10.4 kg kg–1 for AEN, 54.2 kg kg–1 for PFPN, and 36.7 kg kg–1 for PEN, respectively. In recent years, a decline trend in NUE was observed to some degree (Li et al. 2013). Lin (1989) reported that AEN of rice in China declined from 15–20 kg kg–1 within 1958–1962 to only 9.1 kg kg–1 within 1981–1983. Based on national statistics, Li et al. (2013) indicated that PFPN in China declined greatly from more than 1 000 kg kg–1

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in the 1950s to nearly 30 kg kg–1 in 2008. However, most previous studies on estimating NUE for rice in China often involved site-specific field experiments, or small regions with insufficient data (Dai et al. 2009; Fan et al. 2009), or summarized long ago or just used data within a few years (Zhu et al. 1992; Zhang et al. 2008). This concern is whether these values can best represent the current use efficiency of N applied into paddy soil. Therefore, in this study, we collect mass data for rice covering a wide range of water conditions, soil types, parent material, and field managements in China. The objectives of this study were to: (1) estimate grain yield and NUE at various rice production regions in China; (2) evaluate the relationships between N rates and grain yield, NUE; (3) elaborate the potential possibility of increase in NUE with rice yield increasing.

2. Results 2.1. Yield response Considering all 2 949 observations (Appendix A ), rice grain yield averaged 7.69 t ha–1, tremendously varying from 1.99 to 12.6 t ha–1 (Table 1). Northeast China (NE) had a significantly higher grain yield of 8.49 t ha–1 compared to the other regions, maybe due to a longer rice growth duration caused by the lower air temperature supposed to improve the yield potential. The grain yields in Southwest China (SW) and the middle and lower plain of the Yangtze River (MLYR) were slightly higher than those in south of the Yangtze River (SYR) and north central China (NC), but no significant difference was observed. While significantly lower grain yield in South China (SC) was detected than the other regions (Table 2). Li et al. (2009) also has found the region-variation in rice grain yield between Taoyuan and Nanjing in China. Under control treatments without fertilizer-N applied, the mean rice grain yield obtained was 5.83 t ha–1 over China. SW recorded the average yield of 6.75 t ha–1 for zero-N applied, which was significantly higher than those in NE, NC, MLYR, SYR, and SC (Table 2). As N applied, rice grain yield increased significantly by 42% across China. However, the increasing extent of grain yield as applied N increasing gradually reduced, even when exceeded 250 kg N ha–1, additional N fertilizer applied only obtained an increase in grain yield by 1.48%. This trend was further confirmed by the similar trend of stagnant or diminishing under most rice production regions, such as SYR, NC, NE, SW, and MLYR (Table 2). A parabolic model could significantly describe the response of rice grain yield to N rates applied (Fig. 1-A), and 41.6% of variation in N uptakes could be interpreted by applied N rates.

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Table 1 The variability analysis of all observed data and the average, minimum and maximum values of rice grain yield, plant N uptake in aboveground dry matter, N harvest index (HIN), indigenous nutrient supply (INS), internal N efficiency (IEN), reciprocal internal N efficiency (RIEN), agronomic N use efficiency (AEN), physiological N efficiency (PEN), partial N factor productivity (PEPN) and recovery efficiency of applied N (REN) in China Parameter Grain yield Plant N uptake HIN INS IEN RIEN AEN PEPN PEN REN Source of variation N rates Regions N rates × regions

Unit t ha–1 kg ha–1 kg kg–1 kg ha–1 kg kg–1 kg t–1 kg kg–1 kg kg–1 kg kg–1 % Grain yield

n1) 2 949 2 949 1 353 674 2 949 2 949 2 275 2 275 2 275 2 275 Plant N

Mean 7.69 152 0.64 94.1 53.9 1.98 12.6 48.6 33.8 39.3 HIN **

SD 1.75 51.3 0.09 28.0 13.9 0.50 6.46 22.8 19.1 14.3 IEN **

Minimum 1.99 24.2 0.28 24.2 20.7 0.74 –9.33 12.1 –61.4 –6.27 RIEN

25%Q2) 6.44 113 0.59 76.7 44.8 1.64 8.06 34.0 22.9 30.3 AEN

Median 7.77 152 0.66 90.8 51.8 1.93 12.3 43.0 32.4 38.4 PFPN

75%Q 9.01 189 0.71 108 61.2 2.23 16.4 55.7 41.6 46.1 PEN

Maximum 12.6 394 0.87 229 135 4.83 48.0 296 265 117 REN

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

**

1)

n, number of the observations. 2) Quartile. ** , significant at the 0.01 probability level.

Table 2 Grain yield (t ha–1) for N rates at the field trials conducted at the six rice-growing regions, south of the Yangtze River (SYR), north central China (NC), Northeast China (NE), South China (SC), Southwest China (SW), and the middle and lower plain of the Yangtze River (MLYR) N rates 0 0–150 150–200 200–250 >250 Mean

SYR 5.56 BCd 7.37 Bc 7.95 Bb 8.31 Bab 8.40 Aa 7.25 BC

NC 5.98 Bb 5.37 Db 9.25 Aa 8.92 ABa 8.67 Aa 7.54 BC

NE 6.07 Bc 9.09 Aab 8.45 Bb 9.69 Aa 9.09 Aab 8.49 A

SC 4.92 Cc 6.05 Cb 6.94 Cb 6.74 Cb 8.65 Aa 6.23 D

SW 6.75 Ac 7.86 Bb 8.62 ABa 8.71 ABa 8.14 Aab 7.95 B

MLYR 5.85 Bd 7.73 Bc 7.94 Bb 8.96 ABa 9.02 Aa 7.86 B

China 5.83 d 7.57 c 8.01 b 8.80 a 8.93 a 7.69

Means followed by different capital letters within the row and by different small letters within the column mean significant difference among regions and N rates at the 0.05 probability level. The same as below.

2.2. Indigenous N supply (INS) and N uptake

was observed for HIN (Table 3 and Fig. 1-C).

INS across China varied widely from 24.2 to 229 kg ha–1, with an average of 94.1 kg ha–1. Considering rice production regions, NC has the highest N uptake of 144 kg ha–1, while SC has the lowest value of 75.6 kg ha–1. However, no significant difference in INS was observed among SW, MLYR, SYR, and SC (Table 3). Considering all data including zero-N applied, N uptake in aboveground plant averaged 152 kg ha–1, ranging from 24.2 to 394 kg ha–1 (Table 1), while the mean of N harvest index (HIN) was 0.64, varying from 0.28 to 0.82. For six rice production regions, plant N uptakes listed in descending sequence were NC, MLYR, NE, SYR, SW, and SC (Table 3). Compared to the zero-N treatments, N fertilizer could significantly improve N absorption. The response of plant N uptake to N rates was well fitted by a linear function (Fig. 1-B), and 54.8% of variation in N uptakes could be interpreted by applied N rates. The relatively inverse trend

2.3. N use efficiency IEN Across all of the field experiments, IEN wildly varied from 20.7 to 135 kg kg–1, with an average of 53.9 kg kg–1 (Table 1), indicating that kg–1 N absorbed by rice plant can produce more than 50 kg rice grain. IEN exponentially decreased as N rates increasing (Fig. 1-D), and 24.8% of variation in IEN could be interpreted by N rates. This decaying trend was also found in the six rice production regions. SW had the highest IEN, while NC had the lowest value (Table 4). RIEN The averaged value of reciprocal internal N efficiency (RIEN) was 1.98 kg, which means that 1.98 N kg should be needed to produce 100 kg rice grain yield. Whilst for various regions, RIEN listed in descending sequence were NC, MLYR, SYR, SC, NE, and SW (Table 4). RIEN was only 1.63 kg t–1 under zero-N, as N applied the values of RIEN increased significantly and the increasing trend could

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Y=–0.0212X2+0.016807X+5.8659 R2=0.4160 P<0.0001

Y=–0.0003X+0.6871 R2=0.1017 P<0.0001

0.9 0.6

200

4

40

Y=–0.0062X+146.0224 R2=0.7415 P<0.0001

AEN (kg kg–1)

300

H

200 100

0 6

0

100 200 300 400 500 600

0.0

Y=0.0522X+44.2924 R2=0.0474 P<0.0001

300 200

4

100

2

0 60

Y=–0.0290X+18.5049 R2=0.1308 P<0.0001

I

0

120

Y=–0.0470X+48.7024 R2=0.0703 P<0.0001

80

40 20 0

0

F

Y=0.0021X+1.6546 R2=0.2145 P<0.0001

PEN (kg kg–1)

0

RIEN (kg t–1)

IEN (kg kg–1) G

E

REN (%)

Y=–0.0634X+63.5757 R2=0.2484 P<0.0001

120 80

0.3

100

0

D

PFPN (kg kg–1)

400 300

8

C

Y=0.3471X+5.8659 R2=0.5475 P<0.0001

HIN

Yield (kg ha–1)

12

B 500 Plant N uptake (kg ha–1)

A 16

40 0

0

100 200 300 400 500 600

N rates (kg ha )

0

100 200 300 400 500 600

N rates (kg ha–1)

–1

N rates (kg ha–1)

Fig. 1 Relationships of N rates and rice grain yield (A), N uptake in above ground dry matter (B), N harvest index (HIN, C), internal N efficiency (IEN, D), reciprocal internal N efficiency (RIEN, E), physiological N use efficiency (PEN, F), partial factor productivity of applied N (PFPN, G), agronomic N use efficiency (AEN, H), and recovery efficiency of applied N (REN, I) in China. The solid line in this Fig. means the relationship. The same as in Fig. 3.

Table 3 Total N uptake in aboveground dry biomass (kg ha–1) and N harvest index (kg N in grain kg–1 total N in plant) for N rates at the field trials conducted at the six rice-growing regions, SYR, NC, NE, SC, SW, and the MLYR N rates Plant N 0 0–150 150–200 200–250 >250 Mean HIN 0 0–150 150–200 200–250 >250 Mean

SYR 87.9 BCe 145 Bd 158 BCc 189 Bb 213 Ba 145 CD 0.70 Ba 0.66 BCb 0.62 Ab 0.63 Ab 0.62 ABb 0.65 BC

NC

NE

144 Ac 171 Abc 210 Ab 273 Aa 288 Aa 201 A

91.1 Be 131 BCd 159 BCc 181 BCb 206 Ba 151 BC

0.58 Ca 0.55 Da 0.40 Bb 0.43 Bb 0.45 Bc 0.52 D

0.69 Bab 0.72 ABa 0.65 Ab 0.66 Aab 0.56 Bc 0.65 BC

SC 75.6 Cc 107 Db 141 Ca 158 Ca 145 Ca 1168 E 0.78 Aa 0.74 Aab 0.74 Aab 0.63 Ab 0.67 Aab 0.73 A

SW

MLYR

97.6 Bd 125 Cc 151 Cb 164 BCab 170 Ca 136 D

96.3 Be 147 Bd 173 Bc 186 BCb 202 Ba 159 B

0.69 Ba 0.71 ABCa 0.68 Aa 0.63 Ab 0.62 ABb 0.67 B

0.67 Ba 0.65 Ca 0.63 Ab 0.62 Ab 0.59 ABc 0.63 C

China 94.1 e 142 d 166 c 184 b 202 a 152 0.68 a 0.66 b 0.63 c 0.63 c 0.60 d 0.64

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be described by a significant linear function (Fig. 1-E), and 21.5% of the variation in RIEN was explained by N rates. PEN Significant difference among six rice-growing regions in physiological N efficiency (PEN) was only observed between NE and the others (Table 5). NE has the highest PEN value of 48.6 kg kg–1. Considering all observations across China, the average PEN was 33.8 kg kg–1. Negative values of PEN were also observed, mainly because that there were no increases in grain yield and/or plant N uptake as fertilizer-N applied. As N rates increasing, PEN usually obviously decreased, although R2 of the declining relationship between PEN and N rates was below 5% (Fig. 1-F). PFPN PFPN across China averaged 48.6 kg kg–1, ranging from 12.1 to 296 kg kg–1 (Tables 1 and 5). Difference in PEPN among six rice-growing regions was observed. NE had a highest PFPN of 58.1 kg kg–1, while MLYR has a lowest value of 44.9 kg kg–1. PFPN decreased with fertilizer-N increasing and this decreasing trend could be described by

a significant exponential function (Fig. 1-G). AEN Considering all observations, AEN tremendously varied from –9.33 to 48.0 kg kg–1, with an average of 12.6 kg kg–1. The negative value of AEN was detected, mainly because than no increase in grain yield occurred as applied N compared to zero-N plots. The relationship between AEN and N rates could be fitted by a decay exponential function (Fig. 1-H). NE has the highest AEN of 18.2 kg kg–1, which indicated that compared to other regions, the N effectiveness of increase in grain yield for N addition was most manifest at NE. REN Large differences in REN were observed among rice producing regions or N rates (Table 6). NC had the highest REN of 46.2%, while SW had the lowest value of 30.8%. Considering all observations across China, REN averaged 39.3%, ranging from –6.27 to 117%. The values of greater than 100% and less than 0% could be supposed as abnormal observations. There was a declined trend occurred as

Table 4 Internal N efficiency (IEN, kg grain kg–1 N in aboveground dry matter) and reciprocal internal N efficiency (RIEN, kg N in aboveground plant t–1 grain ) for N rates at the field trials conducted at the six rice-growing regions, SYR, NC, NE, SC, SW, and MLYR N rates IEN 0 0–150 150–200 200–250 >250 Mean RIEN 0 0–150 150–200 200–250 >250 Mean

SYR

NC

NE

67.7 ABa 52.8 Cb 52.5 Bb 45.3 Bc 40.7 Cd 54.4 C

43.9 Cab 32.7 Dbc 45.1 Ca 37.3 Cabc 30.6 Dc 39.3 D

68.6 ABa 71.1 Aa 54.6 ABb 54.5 Ab 45.0 BCc 59.7 AB

1.57 Bd 1.99 Bc 2.00 BCDc 2.29 Bb 2.53 Ba 1.97 BC

2.05 Abc 2.30 Ab 2.26 Ac 3.00 Aa 3.31 Aa 2.47 A

1.54 Bc 1.45 Cc 1.90 CDb 1.94 Cb 2.28 BCa 1.79 DE

SC 70.0 ABa 58.8 Bab 51.9 Bbc 43.0 BCc 61.2 Aab 58.1 B 1.58 Bc 1.80 Bbc 2.09 ABCab 2.40 Ba 1.73 Dbc 1.88 CD

SW

MLYR

73.4 Aa 67.0 Aa 59.2 Ab 54.2 Abc 49.0 Bc 62.6 A

62.5 Ba 54.0 BCb 46.6 Cd 48.7 ABc 45.4 BCd 52.0 C

1.46 Bd 1.60 Ccd 1.77 Dbc 1.92 Cb 2.12 Ca 1.72 E

1.67 Bd 1.92 Bc 2.23 ABa 2.10 BCb 2.27 Bca 2.02 B

China 64.8 a 55.7 b 49.9 c 48.8 c 45.2 d 53.9 1.63 d 1.90 c 2.11 b 2.12 b 2.29 a 1.98

Table 5 Physiological N use efficiency (PEN, kg increase in grain yield kg–1 N uptake from N applied) and partial factor productivity of applied N (PFPN, kg grain kg–1 N applied) for N rates at the field trials conducted at the six rice-growing regions, SYR, NC, NE, SC, SW, and MLYR N rates PEN 0 0–150 150–200 200–250 >250 Mean PFPN 0 0–150 150–200 200–250 >250 Mean

SYR

NC

NE

SC

　 35.7 Ba 36.6 Ba 26.6 Bb 16.7 Cc 32.8 B 　

65.7 Aa 33.1 Bab 26.6 Bb 19.4 BCc 34.0 B 　

64.3 Aa 46.3 Ab 47.5 Ab 30.3 ABc 48.6 A 　

36.7 Ba 30.5 Ba 27.0 Ba 34.6 Aa 33.3 B 　

66.9 BCa 45.3 BCb 37.6 Bc 28.1 ABd 53.5 AB

58.5 Ca 56.3 Aab 42.2 ABb 26.6 Bc 51.2 BC

60.1 BCa 41.2 Db 30.5 Cb 32.4 Ab 48.0 BC

101 BCa 48.7 Db 42.9 Cb 28.0 Ab 58.1 BC

SW

MLYR

China

45.9 Ba 36.0 Bab 30.0 Bb 24.2 ABCb 37.1 B 　

36.6 Ba 29.0 Bc 33.5 Bb 30.0 ABc 32.5 B 　

38.6 a 32.9 b 32.4 b 28.7 c 33.8

71.2 Ba 49.2 Bb 39.0 ABc 26.3 Bd 53.2 AB

68.3 BCa 44.0 CDb 39.8 ABc 29.4 ABd 44.9 C

69.0 a 45.3 b 39.3 c 29.1 d 48.6

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Table 6 Agronomic N use efficiency (AEN, kg increase in grain yield kg–1 N fertilizer applied) and apparent recovery efficiency of N applied (REN, the percentage of fertilizer N recovered in aboveground biomass at the maturity) for N rates at the field trials conducted at the six rice-growing regions, SYR, NC, NE, SC, SW, and MLYR N rates AEN 0 0–150 150–200 200–250 >250 Mean REN 0 0–150 150–200 200–250 >250 Mean

SYR

NC

NE

SC

SW

MLYR

China

　 15.8 Ba 12.9 Cb 10.2 BCc 5.9 Bd 13.4 B 　

　 15.3 Ba 15.7 Ba 9.8 BCb 7.7 ABb 13.4 B 　

　 23.0 Ba 18.8 Cab 18.1 Cab 10.7 Ab 18.2 CD

　 13.0 Ba 10.8 Cab 7.8 Cab 9.5 Ab 11.3 CD

　 12.1 Ba 11.0 Cab 8.9 Cb 5.4 Bc 10.2 D 　

　 15.1 Ba 11.5 Cb 12.9 Bc 10.2 Ad 12.4 C

15.0 a 12.5 b 12.1 b 9.6 c 12.6

48.1 Aa 37.7 BCb 39.9 Bb 35.6 Ab 43.2 A

50.6 Aa 50.8 Aa 49.1 Aa 40.6 Ab 46.2 B

36.8 BCa 40.9 Ba 39.4 Ba 35.3 Aa 38.1 B

39.1 BCa 36.6 BCa 30.0 Ca 27.5 Ba 36.1 B

32.4 Ca 33.4 Ca 30.9 Ca 21.8 Bb 30.8 C

44.1 ABa 40.3 Bb 39.2 Bb 34.6 Ac 39.3 B

43.3 a 39.3 b 38.3 b 34.1 c 39.3

N rates increasing, and could be described by a linear or exponential function with small adjusted R2 of 7.09% (Fig. 1-I).

3. Discussion In our study, rice grain yield collected from field experiments averaged 7.69 t ha–1, which is 14.1 and 73.2% as high as the national and world’s average rice yield in 2012 (FAO 2012). This discrepancy may largely attribute to more advantageous geographical position, natural conditions and field management practices for trial plots compared to farmer’s paddies. In the 1980s, the highest production for rice recorded in field experiments was only 6.06 t ha–1 observed by Lin (1989), obviously lower than our observations. This improvement may be mostly due to the development of high-yielding cultivars (including hybrid varieties), improved agricultural practice and regulation, and increasing fertilizer applied (Zhu and Chen 2002; Peng et al. 2009; Yu et al. 2012). Considering rice production regions, NE had the greatest rice grain production of ca. 8.49 t ha–1 in China. Meanwhile, NC and MLYR had higher rice yields than SYR and SC. These patterns are consistent with the findings from national statistic data (National Bureau of Statistics 2013). The difference may be a comprehensive result from climate factors, cropping systems and farmer’s practices. NE has a sub-temperate, continental monsoon climate with lower air temperature, and has only mono-cropping systems with longer rice growth duration from late April or early May to late September or early October. At NC and MLYR, single rice is usually rotated with winter wheat, barley, oil rape, or other crops, while for SC and MLYR, double-, even triple-cropping rice is planted (Table 7). INS for rice in China averaged 94.1 kg ha–1, which is higher than the values of 54 kg ha–1 in five Asian countries esti-

mated by Dobermann et al. (2003b) and 39 kg ha–1 in West Africa reported by Haefele et al. (2003). The discrepancy may also reflect the difference in the rice yield in N-omitted plots. An average yield of 5.83 t ha–1 was obtained in China, while only 3.9 t ha–1 recorded by Dobermann et al. (2003b). INS also estimated using other crops in China, such as 121 kg ha–1 for winter wheat (Yue et al. 2012) and 130 kg ha–1 for corn (Xu et al. 2013). Soil, as a huge nutrient pool, can supply most of the nutrient requirements by plant growing. In general, more than half amount of N in plant is taken up from soil internal N (Lea and Azevedo 2006; Zhang et al. 2012). However, external N inputs are essential for meeting N requirements and improving rice productivity, particularly for the high-yielding intensive systems (Ohnishi et al. 1999; Hossain et al. 2005). In this study, the rice grain yield increased and plant N uptake significantly increased as N applied (Tables 2 and 3). However, when N rates exceeded 250 kg ha–1, additional N fertilizer applied only resulted in an slight increase in grain yield by 1.48% compared to that at 200–250 kg N ha–1, even a decline occurred at some rice production regions, such as NC, NE and SW (Table 2); Whilst N uptake increased significantly by 9.77%. These results illustrate that N absorbed by plant when fertilizer-N applied in excess was not converted to grain efficiently, which is further confirmed by the tendencies of declining in HI and increasing in RIEN with increasing N rates (Table 1 and Fig. 3-C). This phenomenon of luxury absorption by crops has also been reported by Cui et al. (2009). Therefore, just considering rice grain yield and N uptake, a rational N fertilizer applied in soil for achieving high rice grain yield in most rice-planting regions may situate in the range of 200 to 250 kg N ha–1. The stagnation even decreasing in grain yield with exces-

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Table 7 Characters of experimental sites for rice production in six regions in China Region

Province

NC

Tianjin, Beijing, Shandong, Henan, Hebei

NE

Heilongjiang, Liaoning, Jilin

SC

Gungdong, Guangxi, Hainan

SW

Guizhou, Sichuan, Yunnan, Chongqiang

SYR

Anhui, Jiangsu, Hubei, Shanghai

MLYR

Hunan, Fujian, Jiangxi, Zhejiang

Cro.

Pre. (mm)

Tem. (°C)

390–1063 (661) Single 374–978 (584) Double 1 033–2 234 (1 672) Single and 818–1 338 (1 107) double Single and 829–1 451 (1 102) double Double 630–2 145 (1 342)

–6.8–29.1 (13.6) –24.2–25.7 (5.6) 7.7–29.9 (23.0) –4.0–22.6 (13.6) –0.8–29.3 (15.7) 1.8–30.7 (17.8)

Single

Sum

Planting area Mh % 0.87 2.90

Grain yield Mt % 6.58 3.22

No. 47

4.43

14.7

32.1

15.7

142

4.33

14.4

24.2

11.9

101

4.45

14.8

30.8

15.1

253

6.59

21.9

50.3

24.7

1 700

9.08

30.1

57.2

28.0

706

98.6

2 949

29.8

98.8

201

Cro., cropping system; Pre., precipitation, values in parentheses present the averages; Tem., temperature, values in parentheses present the averages; planting area and grain yield, data about rice planting areas and grain yield was collected from National Bureau of Statistics of China; no., number of the observations.

240 Indigenous N supply (kg ha–1)

sive application of N fertilizer would cause higher N surplus in soil or loss by emissions of gaseous, denitrification, surface runoff, or leaching, consequently low NUE occurred (Zhu et al. 2002; Zhang et al. 2012). Five parameters for NUE, such as IEN, AEN, PEN, PFPN, and REN, all declined with increasing N rates considering a national scale and most rice production regions (Tables 3–6 and Fig. 2). Most previously studies have reported this phenomenon (Peng and Cassman 1998; Ohnishi et al. 1999; Wang et al. 2001; Zhang et al. 2012; Andrews and Lea 2013; Sui et al. 2013). Currently, considering all observations from field trials, the average values of IEN, remained within the ranges for general crops summarized by Dobemann (2005), from 30 to 60 kg kg–1 for IEN, 40 to 70 kg kg–1 for PFPN, 10 to 30 kg kg–1 for AEN, and 30 to 50% for REN, respectively. However, more N input generally occurred compared with other areas of the world, which resulted in relatively lower NUE in China (Ladha et al. 2005; Li et al. 2013). Many strategies had been used to increase rice grain yield and improve crop NUE. Peng et al. (2006) reported that compared to farmers’ fertilizer practice, real-time N management could improve NUE by 35.9% in IEN, 37.5% in REN, 303% in AEN, and 251% in PEPN, whilst grain yield increased by 2.8%; for fix-time adjustable-dose N management, the corresponding values of increasing were 21.2, 37.5, 228, 106, and 6.9%, respectively. Pan et al. (2012) stated that splitting and delaying N application would result an increase in grain yield by 8.4% and REN by 10.1% at 150 kg N ha–1, whilst there would be more profitable for the N rate of 240 kg ha–1. Meanwhile, Zhang et al. (2012), Pan et al. (2012) and Sui et al. (2013) also had presented field-experiment evidences that at a reasonable N applied, NUE was usually improved with increasing grain yield.

180

120

60

0

SYR NC NE SC SW MLYR China Rice-growing regions

Fig. 2 Indigenous N supply at south of the Yangtze River (SYR), north central (NC), Northeast (NE), South (SC), Southwest (SW), and the middle and lower plain of the Yangtze River (MLYR) in China. Solid and dashed lines in this box figure indicate median and mean values, respectively. The box boundaries indicate the upper quartiles and lower quartiles, the whisker caps indicate the 90th and 10th percentiles, and the circles represent the 95th and 5th percentiles.

Therefore, to further clarify the potential possibility of grain yield-NUE relationship, correlation analysis was conducted using the data under a relatively reasonable N rate of 200 to 250 kg ha–1 on the basic of above analysis and evaluation. The relationships between grain yield and AEN, PEN, REN, IEN, and PFPN were all could be obviously described by a positive linear function, and 46.49, 24.64, 7.94, 17.84, and 88.24% of the variation in AEN, PEN, REN, IEN, and PFPN were explained by grain yield (Fig. 3). At the same N input, rice grain yield and NUE can be simultaneously improved by improvement of other crop-soil management techniques, including N application methods.

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60 40

60 30

10

40

20 Y=2.6612X–11.3158 R2=0.0794 P<0.0001

90

F

60

30

6

8

10

12

14

0

4

5

Y=–1.1516Ln(X)+4.6115 R2=0.1858 P<0.0001

4

0 4

Y=4.2278X+2.0991 R2=0.8824 P<0.0001

60

RIEN (kg kg–1)

AEN (kg kg–1)

20

E

Y=2.6612X–11.3158 R2=0.4644 P<0.0001

REN (%)

30

C

0

20 D

Y=5.1753X–13.1452 R2=0.2464 P<0.0001

90 PEN (kg kg–1)

80 IEN (kg kg–1)

B 120

Y=2.6998X+25.0646 R2=0.1787 P<0.0001

PFPN (kg kg–1)

A 100

6 8 10 12 14 Grian yield at 200–250 kg N ha–1

3 2 1

4

6

8

10

12

14

Fig. 3 Relationships of rice grain yield and internal N efficiency (IEN, A), physiological N use efficiency (PEN, B), partial factor productivity of applied N (PFPN, C), agronomic N use efficiency (AEN, D), recovery efficiency of applied N (REN, E), and reciprocal internal N efficiency (RIEN, F), in China.

4. Conclusion Understanding the current situations of NUE in various rice-growing regions and relationships between grain yield and NUE significantly affected the development of an optimal N management. According to the data base for rice across China, the rice grain yield averaged 7.69 t ha–1. N fertilizer significantly improved plant N uptake and increased the rice grain yield. However, when N rates exceeded 250 kg ha–1, the phenomenon of luxury absorption occurred, mainly because that grain yield increased slightly increase, even decreased, but N uptake increased significantly. Considering all observations obtained from published papers, N rates of 200 to 250 kg ha–1 applied commonly achieved higher rice grain yield compared to less than 200 kg N ha–1 and more than 250 kg N ha–1. At N rates of 200–250 kg ha–1, AEN, PEN, REN, IEN, and PFPN had a significantly positive linear function with rice grain yield, and most of the variation in AEN, PEN, REN, IEN, and PFPN could be explained by grain yield.

5. Materials and methods 5.1. Site characteristics The major rice planting region in China could be divided into six areas, namely: north central China (NC), Northeast China

(NE), Southwest China (SW), south region of the Yangtze River (SYR), middle and lower alluvial plain of Yangtze River (MLYR), and South China (SC), respectively (Table 7 and Fig. 4). Provinces, the rice cropping system, precipitation, temperature, planting area and grain yield under all rice production regions are detailed in Table 7. SC, SYR, MLYR, and SW regions have more precipitation with the great potentiality of maintaining and expanding the paddy field for irrigated lowland rice, while in NC and NE China, because of the scarcity of precipitation, the cropping system of aerobic rice becomes more and more attractive, specially, for SC regions increasing serious shortage of freshwater resource (Tong et al. 2003; Dai et al. 2009).

5.2. Data sources The database analyzed in this paper, involving grain yield, N uptakes in grain and straw, and plant N in aboveground dry matter, was derived from scientific journals and degree theses published during 2000 and 2013 in China. N concentration, or/and N uptake with rice grain yield should be required in the literatures, meaning that those just containing grain yield dates without N uptake information were not considered in this paper. The experimental sites derived for the database were widely distributed across a wide range of water conditions, soil type, parent material and field managements (Fig. 4, Table 7, Appendixes A and

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N

Experimental sites North central China North China South China South of the Yangtze River Southwest China The middle and lower alluvil plain of the Yangtze River 0

420 840

1 680

2 520

3 360 km

Fig. 4 Geographical distribution of field experimental sites for rice in south of the Yangtze River, north central China, Northeast China, South China, Southwest China, and the middle and lower plain of the Yangtze River in China.

B). The rice varieties were all commonly planted by local farmers for high-yielding production and well adapted to local conditions, highly representing the variation in rice production at present. The site-specific experiments, selected from literatures for this analysis, were only concluded under field conditions with well field management controlling weeds, pests and diseases in time. The studies under laboratory simulation or greenhouse culture for rice were excluded. The layout of each experiment was a randomized complete block design with at least three replications. Plant samples were collected at physiological maturity of rice for determining components of yield, harvest index, nutrient (N, P or K) concentration or other parameters at all experimental sites. Grain yields were obtained at harvestable maturity with standard moisture content of 0.135 g H2O g–1 fresh weight, while stay yield and aboveground dry matter were determined by drying to constant weight at 70°C.

5.3. Data analysis Indigenous N supply (INS), defined as the total N uptake un-

der N omitted treatments but with P and K fertilizers applied, reflected the soil inherent fertility conditions and could be developed to estimate fertilizer recommendations (Dobermann et al. 2003a). The nutrient harvest index (HIN) means the nutrient uptake in gain as a proportion of total nutrient accumulation in aboveground dry biomass. The reciprocal internal efficiency of nutrient (RIEN) is defined as the nutrient accumulation in aboveground dry matter to produce per ton grain yield. The internal efficiency (IEN) means the amount of grain yield produced by per kg plant nutrient accumulation in aboveground dry matter (Witt et al. 1999). Physiological efficiency of applied N (PEN) is defined as kg yield increase per kg increase in N uptake from fertilizer-N. Partial factor productivity of applied N (PFPN) represents kg grain yield per N applied. Agronomic efficiency of applied N (AEN) is used to express kg increase in grain yield per N applied. Recovery efficiency of applied N is explained as the percentage of N applied recovered in above ground biomass. Other indices include reciprocal internal N efficiency (IEN, kg grain kg–1 N in plant) and internal N efficiency (RIEN, kg N in plant t–1 grain) (Novoa and Loomis 1981; Dobermann 2005). The parameters involved in above were calculated ac-

CHE Sheng-guo et al. Journal of Integrative Agriculture 2015, 14(12): 2456–2466

cording to the following formulas: N accumulation in grain HIN (kg kg–1)= Plant N uptake IEN (kg kg–1)=

Grain yield Plant N uptake

RIEN (kg kg–1)=

Plant N uptake Grain yield

References (1) (2) (3)

AEN (kg kg–1)= Grain yield of N applied–Grain yield of N omission (4) N applied to soil PEPN (kg kg–1)=

Grain yield of N applied N applied

(5)

PEN (kg kg–1)=

(6) Grain yield of N applied–Grain yield of N omission N upake of N applied-N uptake of N omission

REN (kg kg–1)= N uptake of N applied–N uptake of N omission N applied to soil

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(7)

The collected data sets were grouped and summarized based on the regions of rice productions and N rates. According to the findings by Zhang et al. (2008), N applied in to fields could been classified into three groups, reasonable for 150 to 250 kg N ha–1 applied, insufficient for less than 150 kg N ha–1, and excessive for more than 250 kg N ha–1, respectively. To further clarify N rates added, 150–250 kg ha–1 was further separated into two ranges, 150–200 and 200–250 kg ha–1. Means of grain yield, N uptake and NUE components among various rice-planted regions and N regions were compared based on Tukey’s multiple comparison tests at the 0.05 probability level using the general linear model (GLM) of SAS software (SAS Institute 1990). The relationships between N rates and grain yield, N uptake and NUE, or between grain yield and NUE, were fitted as quadratic, linear or power models using SigmaPlot 10 for Windows. According to the determined coefficients (R2), the best model functions were conducted to fit the relationships.

Acknowledgements This research was supported by the Key Technologies R&D Program of China during the 12th Fvie-Year Plan period (2011BAD11B05). We are also grateful to all the scientists who work at the fertilization of rice because this paper was completed based on the database covered national wide. Appendix associated with this paper can be available on http://www.ChinaAgriSci.com/V2/En/appendix.htm

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