Effects of modified fertilization technology on the grain yield and nitrogen use efficiency of midseason rice

Field Crops Research 137 (2012) 203–212

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Effects of modified fertilization technology on the grain yield and nitrogen use efficiency of midseason rice Xiangming Zeng a , Baoji Han a , Fangsen Xu a , Jianliang Huang b , Hongmei Cai a , Lei Shi a,∗ a b

Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, Huazhong Agric. Univ., Wuhan 430070, China Crop Physiology and Production Center, Huazhong Agric. Univ., Wuhan 430070, China

a r t i c l e

i n f o

Article history: Received 29 May 2012 Received in revised form 8 August 2012 Accepted 9 August 2012 Keywords: Midseason rice Modified farmers’ fertilizer practice Modified super-high-yield fertilizer practice Grain yield Nitrogen use efficiency

a b s t r a c t Local popular midseason varieties of rice were used to study the effects of modified fertilization technology on the grain yield and nitrogen (N) use efficiency of midseason rice in central China. Field trials with five N treatments and four replications were conducted in Jingmen County (2008–2009), Honghu County (2009–2011), and Chibi County (2008–2011) in Hubei Province. The results showed that, relative to most farmers’ fertilizer practices (FFP), the grain yield of modified farmers’ fertilizer practices (MFP) in eight out of nine experiments showed an increase in ratio ranging from 0.3% to 16.6% and grain yield of super-high-yield fertilizer practice (SHY) in six of nine experiments showed an increase in ratio ranging from 2.4% to 20.9%. Relative to SHY, the grain yield of modified super-high-yield fertilizer practice (MSP) treatments in seven out of nine experiments showed an increase in ratio ranging from 0.2% to 20.4%. Relative to FFP, the nitrogen agronomic efficiency (NAE) and nitrogen physiological efficiency (NPE) values of MFP treatment in eight out of nine experiments showed an increase in ratio ranging from 26.0% to 110.3% and from 1.3% to 46.1%, respectively. Relative to SHY, the NAE and NPE values of MSP treatment in eight out of nine experiments showed an increase in ratio ranging from 5.2% to 151.7% and from 7.4% to 82.6%, respectively. Further analysis showed that the number of panicles in MFP, SHY, and MSP were greater than in FFP. This was attributable to the ability of the modified fertilizer technology to delay functional leaf senescence, maintain optimum leaf area index (LAI), an optimize shoot biomass, to a reasonable tiller number and to a healthy population structure with a high relative amount of productive tiller. This study may provide technical and theoretical support for simultaneously increasing rice grain yield and nutrient use efficiency, for optimization of the use of fertilizer by local farmers, and for facilitating sustainable increases in grain yield. © 2012 Elsevier B.V. All rights reserved.

1. Introduction China has 31% of the paddy fields in Asia and 19% of paddy fields on Earth, more than any individual country in the world. It also ranks among the world’s highest in terms of both total rice yield and unit area rice yield (Shen and Zhang, 2006). This gives China substantial influence on the stability of world grain production. In the past 60 years, food production has increased through the use of high-yield crop varieties and modern fertilizers, irrigation, and pesticides. It is estimated that the world population will reach 9 billion by 2050 (Godfray, 2010). The demand for food will continue to increase while agriculture fields decrease in size and the environment deteriorates. China and other rapidly developing countries face the dual challenge of substantially increasing grain yields while

∗ Corresponding author at: No. 1 Shizishan Street, Hongshan District, Wuhan 430070, China. Tel.: +86 27 87286871; fax: +86 27 87280016. E-mail addresses: [email protected], [email protected] (L. Shi). 0378-4290/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fcr.2012.08.012

at the same time reducing the environmental impact of intensive agriculture (Chen et al., 2011; Vitousek et al., 2009). A 2004 investigation of rice-planting practices in seven provinces (Jiangsu, Hunan, Zhejiang, Guangdong, Hubei, Hebei, and Heilongjiang) showed the use of nitrogen (N) in China’s rice fields to be significantly greater than the world average, with an average amount of 220 kg hm−2 used for midseason rice (Shen and Zhang, 2006). Among these provinces, the average amount of N-fertilizer used was the lowest in Heilongjiang Province at 150 kg hm−2 and the highest in Jiangsu Province at 314 kg hm−2 . It was 200 kg hm−2 in Hubei Province. According to Peng et al. (2002a), the average amount of nitrogen-based fertilizer applied to paddy fields in Jiangsu Province from 1995 to 2000 was 270.9 kg hm−2 . According to Tang and Rong (2009), in Hunan province from 1994 to 2003, more than 65% of the paddy fields were fertilized with more than 200 kg hm−2 of N-fertilizer. This indicated a significant increase in the amount of N fertilizer used in the recent years. It may continue to increase in the future. Over-fertilization is the main reason for the low N efficiency of fertilizers in China. Zhang et al. (2011) analyzed the results of

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studies published in 2000 through 2005 covering different crops grown in different parts of China and found the N use efficiency of midseason rice to be 28.1% on average. This is much lower than that of midseason rice in the other parts of the world and also lower than that of midseason rice grown in China during the 1980s. Irrigated rice in China accounts for nearly 30% of global rice production and about 37% of global N consumption, but the average N recovery efficiency (NRE) is only 30% for this crop, nationwide. This means that nearly 70% of the N input is lost into the ecosystem. In Europe, South America and North America, more than 70% of N is taken up by crops (Liu et al., 2010; Peng et al., 2006). N fertilizer input is essential to high crop yield, but excessive use of N fertilizer causes eutrophication, soil degradation, loss of diversity, insect and fungal pathogen outbreaks, air pollution, water pollution, soil acidification, and emission of the greenhouse gas nitrous oxide (Chen et al., 2011; Liu et al., 2010; Vitousek et al., 2009; Godfray, 2010; Zhu and Chen, 2010; Guo et al., 2010; Tilman et al., 2001). In addition, inappropriate ratios of nitrogen, phosphorus, and potassium, incorrect timing of fertilization and inadequate use of compost add to the problems rice planting faced in China (Shen and Zhang, 2006; Wang et al., 2007). In recent years, the International Rice Research Institute (IRRI) has used a computerized decision support system, fast chlorophyll meter (SPAD), and leaf color chart (LCC) to develop site-specific N management (SSNM), real-time N management (RTNM), and fixedtime adjustable-dose N management (FTNM) techniques meant to increase the N use efficiency of irrigated rice systems (Dobermann and White, 1999; Dobermann et al., 2002; Peng et al., 1996, 2002b). They offer users an economical and efficient means of creating fertilization plans based on comprehensive analysis of such parameters as available soil nutrient supply, rice grain yield, nutrient absorption by the plants, and local rice prices. In the RTNM system, a limited amount of N is applied when the leaf N content drops below a critical value (Peng et al., 1996). The timing and frequency of N application and total N rates vary across seasons and locations, but N application is fixed at basal, mid-tillering (MT), panicle initiation (PI), and heading stages (HD). Leaf N content can be estimated non-destructively using SPAD or LCC (Cabangon et al., 2011; Peng et al., 1996; Singh et al., 2007). Evaluation of RTNM in Asia has generally shown that about 20–30% of N fertilizer could be eliminated without any significant decreases in yield (Hussain et al., 2000; Singh et al., 2002, 2007). In FTNM, the key components are an attainable target yield and the zero-N control grain yield, based on which the total N rate is estimated. The rates of N topdressing at the key growth stages are adjusted according to leaf N status measured with SPAD or LCC (Dobermann et al., 2002; Huang et al., 2008; Peng et al., 2010). Evaluation of FTNM in Asia has generally shown that average grain yield increases by 5–11% and average NRE increases by 31–40% relative to most farmers’ fertilizer practices (Dobermann et al., 2002; Peng et al., 2010; Xu et al., 2010). These optimum N fertilization values are associated with similar or better yields and N use efficiencies than with farmers’ fertilizer practices (FFP), but they greatly reduce the inputs of N fertilizer into the ecosystem, reducing environmental risk through integrated soil–crop system management (Chen et al., 2011; Ju et al., 2009; Yadvinder et al., 2007; Zhang et al., 2011). Hubei Province is one of China’s major areas of rice production. More than 50% of the cereal crop fields in Hubei Province are rice fields. They produce 70% of the total grains and 80% of the commercial grain supply of Hubei Province. This places Hubei third among rice-producing provinces in China, after Hunan and Jiangxi (Shen and Zhang, 2006). As the changes in land management shift from a household contract responsibility system to large-scale operations, it becomes essential to correct the belief that high input leads to high yield, which is still held by many farmers and to help them realize that modified fertilizer practices and efficient use of fertilizers

Table 1 Monthly precipitation, hours of sunlight and mean temperature during rice growing season. Year

Precipitation (mm)

Hours of sunlight (h)

Mean temperature (◦ C)

Jingmen 2008 Jingmen 2009 Honghu 2009 Honghu 2010 Honghu 2011 Chibi 2008 Chibi 2009 Chibi 2010 Chibi 2011

132.5 109.8 144.7 239.5 135.8 173.1 161.9 255.1 178.6

117.2 125.0 193.4 170.5 200.8 147.3 157.2 131.2 167.9

23.2 23.2 25.0 24.2 24.4 25.3 25.4 24.5 24.8

are key to high yield. To understand the effects of modified fertilization practices on the grain yield and N efficiency of midseason rice in Hubei Province, we carried out three years field plot experiments using popular local rice cultivars in three representative rice-producing areas: Jingmen, Honghu, and Chibi. Yield components, N use efficiency, dynamic changes in the tillers, the number of panicles, SPAD value, and leaf area index (LAI) were assessed. 2. Materials and methods 2.1. Experimental sites and materials Field plot experiments were carried out in local farmers’ paddy fields at site 1 in Tuanlin, Jingmen (31.36◦ N and 113.29◦ E) from 2008 to 2009; at site 2 in Shakou, Honghu (29.48◦ N and 113.27◦ E) from 2009 to 2011; and at site 3 in Zhonghuopu, Chibi (29.76◦ N and 114.00◦ E) from 2008 to 2011. All of these sites are in Hubei Province. These experimental sites are major rice-producing areas, with sites 1 and 2 located on the Jianghan Plain in the center of Hubei Province and site 3 in a hilly area in southeastern Hubei Province, all in a subtropical climatic zone. Monthly precipitation, hours of sunlight, and mean temperature during rice growing season are given in Table 1. Soils in the paddy fields of this experiment included yellowbrown soil, hydromica clay, and red mudstone soil. Soil properties are listed in Table 2. The rice cultivars used in Jingmen in 2008 and 2009 were Guohaozayou 1 (GHZY1, hybrid cultivar) and Jufengyou 72 (JFY72), respectively; the rice cultivar used in Honghu from 2009 to 2011 was Fengliangyouxiang 1 (FLYX1); the rice cultivar used in Chibi was Luoyou 8 in 2008, 2010, and 2011 and Fengyou 22 (FY22) in 2009. All of the above rice cultivars are single midseason rice. Previous crops grown at these sites include oilseed rape, oilseed rape, and wheat, respectively. 2.2. Treatments and cultural practices Five treatments, each performed four times, were set up in the field plot experiments. The treatments were randomly distributed, and each plot was 30 m2 in size. Each plot was ridged and covered with a thin layer of fabric to prevent water and fertilizer from different treatments from mixing together. Each plot was independently irrigated and drained. The five treatments included treatment (1) no N fertilizer at any point during the growth period (control 1, CK); treatment (2) farmers’ fertilizer practice (FFP) (control 2); treatment (3) modified farmers’ fertilizer practice (MFP); treatment (4) super-high-yield fertilizer practice (SHY); and treatment (5) modified super-high-yield fertilizer practice (MSP). To improve the efficiency of fertilization, we used the FFP treatment as a control, and reduced the amount of N-fertilizer applied while balancing the application amount of P and K fertilizer. We also adjusted

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Table 2 Physical and chemical properties of experimental soils. Experimental site

pH (1:2.5 soil:water)

Organic matter (g kg−1 )

Alkali-N (mg kg−1 )

Olsen-P (mg kg−1 )

Available K (mg kg−1 )

Jingmen Honghu Chibi

5.9 6.8 5.1

37.0 33.9 31.2

176.9 170.6 129.8

12.6 11.2 8.9

67.6 114.3 78.6

the ratio between basal fertilizer, fertilizer used during the tillering stage, and fertilizer used during the heading stage to achieve grain yield and N use efficiency (MFP) similar to or better than that of FFP treatment. The SHY treatment was designed specifically to exceed the grain yield per unit area produced using FFP treatment. SHY treatment involved more N fertilizer than FFP, generous use of compost and Zn fertilizer, and increased transplanting density. The MSP treatment was designed in an attempt to determine the lowest amount of N fertilizer that could be used without dropping grain yield and N use efficiency below that produced using the SHY treatment. We used urea with 46% N, super phosphate with 12% P2 O5 , and potassium chloride with 60% K2 O as fertilizers. Fertilization and cultural practice of FFP was based on the common practice of the local farmers. The CK plots received a full dose of P and K, “full” here defined as the amount present in FFP. These doses were administered within 1 day of transplantation (DAT). For experiments during the first year (Jingmen 2008, Chibi 2008, and Honghu 2009) the N, P, and K levels for MFP, SHY, and MSP were determined based on the investigation of N, P, and K levels of FFP-treated fields, alkali-N, Olsen-P, and available K content of soil samples and on our field trial experience. Experiments during subsequent years, the N, P, and K levels for these treatments were mainly determined based on the grain yield responses to the treatments administered during the preceding years, and in SHY and MSP plots in Honghu and Chibi in 2010 and 2011, fertilizer N was top-dressed during different development stages during a cropping season based on crop needs as determined by a chlorophyll meter (SPAD meter, Soil and Plant Analysis Division, Minolta Co.). For N topdressing at midtillering and panicle initiation, if the SPAD reading was greater than 40, plan topdressing N was decreased by 5%; if the SPAD reading was less than 36, plan topdressing N was increased by 5%; if the reading was between 36 and 40, plan topdressing N was kept the same. The first half of N topdressing was applied during the first stage of panicle initiation, and the remaining half was applied 7 days after the first stage of panicle initiation, as described previously (Huang et al., 2008). Fertilizer P was applied only once before 1 DAT and fertilizer K was applied twice, the first half before 1 DAT and the second half at early panicle initiation. Zinc sulfate with 23% Zn and rape seed cakes with 5.2% N, 0.8% P2 O5 , and 1.0% K2 O were applied at 15 kg hm−2 and 1500 kg hm−2 , respectively, in treatments 4 and 5. The fields were dry-ploughed, irrigated, and harrowed 1 week before transplantation. Detailed information regarding the amounts of fertilizer and the times of fertilization are given in Table 3. The seedlings were transplanted at a density of 19.8 cm × 23.1 cm in CK and FFP and 16.5 cm × 26.4 cm in MFP, SHY, and MSP plots. Then 33-day-old seedlings were transplanted on 21 May 2008 and 27 May 2009 at site 1; 29-day-old, 31day-old, and 40-day-old seedlings were transplanted on 14 June 2009, 24 May 2010, and 1 June 2011, respectively, at site 2; and 32-day-old, 32-day-old, 39-day-old, and 35-day-old seedlings were transplanted on 22 May 2008, 1 June 2009, 2 June 2010, and 3 June 2011, respectively, at site 3. The water levels in the paddy fields were kept deep for five days so that growth would resume after transplantation. They were kept shallow for tillering

from the 6th to the 25th days after transplantation. After the seedlings reached 80% productive panicles, the fields were drained and they remained dry for 5–7 days. They were then irrigated to keep the water level low until heading. After heading, the paddy fields were irrigated and then completely drained before the next irrigation. This water-then-dry cycle was repeated until 7 days before harvesting, when the fields were drained. Measures were taken to control disease, pests, and weeds. 2.3. Measurements 2.3.1. Dynamics of tillering We counted the tiller number of ten rice plants each plot every seven days, starting one week after rice transplantation and continuing through the heading stage. The values of every ten plants were averaged. 2.3.2. Leaf SPAD SPAD readings were measured based on ten randomly assigned topmost fully expanded leaves according to the procedures described by Peng et al. (1996). We assessed the SPAD of completely unfolded leaves at the tops the plants (if the flag leaf was completely unfolded then the flag leaf was measured; otherwise, another leaf was chosen) using a chlorophyll meter (SPAD-502) every seven days starting one week after rice transplantation. We continued to measure these values until heading. Ten leaves were randomly selected from each plot, and three points (top, middle, and bottom) were measured on each leaf. Average values were calculated. 2.3.3. LAI During the mid-tillering (MT), panicle initiation (PI), and heading (HD) stages, the leaf area of 10 representative individual plants from each plot were measured using a LAI meter (LI-3100, LI-COR, Lincoln, NE, U.S.) and the leaf area index (LAI) was calculated using the following formula: LAI = average leaf size × number of leaves per shoot × number of shoots per hill × number of hills per unit of ground area

2.3.4. Panicle rate The panicle rate is here defined as the ratio of the number of panicles to the maximum tiller number. It is an important index of the quality of the rice population and plays a major role in the assessment of grain yield (Ling, 2000). 2.3.5. N content During the mid-tillering, panicle initiation, heading, and maturity stages, plants grew in a 0.48 m2 area containing 12 hills in each plot were harvested and sampled. They were divided into leaves, stem-sheaths, and panicles (at full heading stage). They were then dried and weighed to determine total aboveground biomass per unit area per each plot during different growing stages. We selected

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Table 3 Amount and timing of fertilizer applied. Year

Treatment

Total application (kg hm−2 )

Basal fertilizer (kg hm−2 )

N

P2 O5

N

K2 O

Top dressing (kg hm−2 )

P2 O5

K2 O

45 45 45 63 31.5

MT

PI

HD

N

N

K2 O

N

0 50 40.5 36 20.3

0 0 0 36 20.3

0 0 0 27 13.5

0 0 0 18 13.5

Jingmen 2008

CK FFP MFP SHY MSP

0 165 135 180 135

90 90 90 90 90

45 45 45 90 45

0 115 94.5 90 81

90 90 90 90 90

Jingmen 2009

CK FFP MFP SHY MSP

0 165 135 225 165

90 90 90 120 90

45 45 75 120 75

0 115 67.5 135 82.5

90 90 90 120 90

45 45 45 60 45

0 50 33.8 45 33

0 0 33.8 33.8 33

0 0 30 60 30

0 0 0 11.2 16.5

Honghu 2009

CK FFP MFP SHY MSP

0 165 160.5 240 180

48 48 90 105 90

40.5 40.5 75 150 90

0 112.4 99 144 108

48 48 90 105 90

40.5 40.5 45 52.5 45

0 48.2 41.3 48 36

0 0 24.8 36 27

0 0 30 52.5 45

0 0 0 12 9

Honghu 2010

CK FFP MFP SHY MSP

0 165 135 240 180

60 60 90 105 90

45 45 75 195 120

0 115.5 81 96 108

60 60 90 105 90

45 45 37.5 97.5 60

0 49.5 33.8 72 45

0 0 13.5 60 18

0 0 37.5 97.5 60

0 0 6.75 12 9

Honghu 2011

CK FFP MFP SHY MSP

0 180 150 255.3 199.6

60 60 60 105 90

45 45 45 150 120

0 126 75 120 90

60 60 60 105 90

45 45 22.5 75 60

0 54 37.5 60 45

0 0 37.5 97.7 77.3

0 0 22.5 75 60

0 0 0 97.7 77.3

Chibi 2008

CK FFP MFP SHY MSP

0 165 135 195 135

90 90 90 90 90

45 45 45 90 45

0 115 94.5 97.5 81

90 90 90 90 90

45 45 45 63 31.5

0 50 40.5 39 20.3

0 0 0 39 20.3

0 0 0 27 13.5

0 0 0 19.5 13.5

Chibi 2009

CK FFP MFP SHY MSP

0 180 135 225 180

90 90 90 105 90

45 45 75 150 90

0 126 67.5 101.2 81

90 90 90 105 90

45 45 45 75 45

0 54 33.8 33.8 27

0 0 33.8 67.5 54

0 0 30 75 45

0 0 0 22.5 18

Chibi 2010

CK FFP MFP SHY MSP

0 165 135 240 180

90 90 90 105 90

45 45 90 195 120

0 115.5 54 96 72

90 90 90 105 90

45 45 45 97.5 60

0 49.5 40.5 72 54

0 0 33.8 60 45

0 0 45 97.5 60

0 0 6.8 12 9

Chibi 2011

CK FFP MFP SHY MSP

0 165 165 215.4 192

90 90 90 105 90

45 45 45 135 120

0 115.5 82.5 105 90

90 90 90 105 90

45 45 22.5 67.5 60

0 49.5 33 52.5 45

0 0 33 29.0 67.5

0 0 22.5 67.5 60

0 0 0 29.0 67.5

MT: mid-tillering stage; PI: panicle initiation stage; HD: heading stage.

mature individuals and divided them into straws, full grains, and empty grains and then dried them at 80 ◦ C in bags until weight remained constant. The dried tissues were weighed, ground to powder, and sieved. Plant and grain samples were digested with H2 SO4 –H2 O2 , filtered, and separated into samples of constant volume. Then N content was measured using a flow injection analyzer (FIAstar5000, Sweden).

2.3.6. Field observations and yield measurements Once the rice had matured, a 5 m2 subplot was marked out in the middle of each plot. Plants within the subplots were harvested to measure the grain yield (GY). Twelve individual plants along the diagonal of each harvested subplot were selected and their panicles (PN) and spikelets per panicle (SPP) were counted. Relative number of filled grains (filled-grain percentage, FP) and 1000-grain weight (GW) were assessed. Aboveground total biomass (ATB) was also measured and harvest index (HI) was calculated. 2.3.7. Calculations and analysis

Agronomic efficiency (AE) =

grain yield in the plot received N fertilizer (GN ) − grain yield in the zero-N control (G0 ) ; amount of N fertilizer applied (FN )

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Table 4 Grain yield and its components in different fertilizer treatments. Year

GY (kg hm−2 )

Treatment

b

PN (×104 panicle hm−2 ) b

SPP

GW (g) b

a

FP (%) ab

HI (%) a

ATB (kg hm−2 )

Jingmen 2008

CK FFP MFP SHY MSP

7145.2 8731.8a 8393.2a 8559.5a 8574.6a

222.8 267.8ab 278.6ab 281.3ab 297.0a

120.3 126.5b 126.0b 141.3a 125.9b

31.0 30.6a 31.4a 29.5a 30.3a

85.6 85.3ab 87.6a 81.9ab 81.0b

54.5 53.1ab 51.2b 51.2b 50.9b

13,112.2b 16,441.2a 16,390.6a 16,729.7a 16,847.4a

Jingmen 2009

CK FFP MFP SHY MSP

6705.0b 7429.5ab 7581.0ab 7926.0a 7558.5ab

184.7d 196.4c 224.4b 210.4bc 243.1a

184.8c 225.7ab 204.2b 235.5a 205.8b

24.6b 25.3a 25.5a 24.5b 25.2a

71.6a 64.8a 69.9a 68.9a 68.3a

45.2a 40.9ab 39.8b 39.4b 38.5c

14,850.0c 18,150.0b 19,050.0ab 20,100.0a 19,650.0a

Honghu 2009

CK FFP MFP SHY MSP

7855.0c 8770.0b 9000.0b 9505.0a 9580.0a

179.2d 227.4c 336.4b 328.5b 377.4a

153.5b 152.1b 150.9b 173.3a 157.0b

26.8a 27.0a 27.1a 27.2a 27.0a

84.7a 84.2a 81.0b 79.9b 79.4b

57.2a 50.8ab 43.1b 44.4b 44.6b

13,737.1c 17,273.1b 20,885.2a 21,427.1a 21,755.5a

Honghu 2010

CK FFP MFP SHY MSP

7013.5b 7893.9a 7921.5a 7783.9a 8214.1a

185.6b 246.3a 252.5a 260.0a 275.0a

155.0b 156.4b 160.5ab 162.6a 159.5ab

26.7a 26.2a 25.9ab 25.6b 26.2a

87.2a 82.7ab 81.0ab 76.9b 85.1a

55.6a 50.3b 41.1c 42.1c 42.2c

12,606.0c 15,708.0b 19,283.4a 18,506.3ab 19,450.0a

Honghu 2011

CK FFP MFP SHY MSP

7252.0b 8350.0a 9476.7a 10,096.1a 9632.9a

186.5b 225.5ab 251.6ab 267.2a 250.0ab

165.2b 236.5ab 258.2a 228.9ab 253.9a

27.5a 26.6ab 26.3ab 25.1b 25.6b

88.3a 86.7a 85.3a 80.0a 80.7a

55.1a 52.5a 47.9b 49.9a 49.1a

131,64.5c 15,912.5b 19,789.2a 20,252.4a 19,632.9a

Chibi 2008

CK FFP MFP SHY MSP

5967.8c 7993.5b 8844.3b 8184.0b 9855.0a

172.0b 241.6a 274.5a 261.9a 254.3a

167.2b 168.4b 166.9b 186.3a 186.4a

24.8b 26.0ab 25.5ab 25.4ab 26.2a

86.4a 82.2a 82.1a 73.5b 79.5ab

56.1a 50.8b 52.9b 51.2b 57.1a

10,634.5c 15,720.4b 16,726.4a 15,985.9b 17,254.1a

Chibi 2009

CK FFP MFP SHY MSP

5059.5d 6990.0c 8152.5ab 7815.0b 8571.0a

163.9c 190.3bc 227.0b 225.7b 260.1a

150.5c 184.2ab 198.0a 197.3a 178.9b

26.1a 26.8a 27.0a 26.3a 26.7a

80.4a 79.7a 76.4a 77.9a 78.0a

47.5a 44.8ab 40.9c 41.3c 42.6b

10,650.0c 15,600.0b 19,950.0a 18,900.0a 20,100.0a

Chibi 2010

CK FFP MFP SHY MSP

5479.4c 6996.8ab 7173.6ab 6668.3b 7373.2a

156.4d 188.4c 209.9ab 199.5bc 227.7a

175.2b 177.8ab 186.8ab 193.0a 182.7ab

26.7a 26.3a 25.9a 25.9a 26.6a

89.8a 82.6a 85.9a 81.1a 85.3a

48.2a 46.3a 48.6a 41.6b 42.5b

11,357.5c 15,106.6b 17,250.0ab 17,288.3ab 17,365.0a

Chibi 2011

CK FFP MFP SHY MSP

6106.3c 8196.1bc 8526.6b 8437.3b 9182.0a

163.9b 169.4b 217.5a 223.8a 253.8a

138.2b 159.5ab 171.7a 177.6a 176.0a

27.1a 26.8a 26.5a 26.1a 26.7a

89.6a 85.7a 83.0a 82.0a 84.5a

56.6a 59.8a 55.4a 52.5a 60.0a

10,787.4c 13,696.1b 15,401.9ab 16,062.2a 15,307.7ab

GY: grain yield; PN: panicle number; SPP: spikelet number per panicle: GW: 1000-grain weight; FP: filled-grain percentage; HI: harvest index; ATB: aboveground total biomass. ANOVA analysis was conducted among different treatments in the same year and values suffixed with different letters indicate the significance at the 0.05 level.

Recovery efficiency (RE) =

total aboveground plant N accumulation in the plot received N fertilizer (TN ) − total aboveground plant N accumulation in the zero-N control (T0 ) ; FN

Physiological efficiency (PE) =

GN − G0 ; TN − T0

Partial factor productivity (PFPN ) =

GN . FN

3. Results 3.1. Effects of modified fertilizer practices on grain yield and its component factors

2.4. Statistical analysis We used Microsoft Excel 2003 and SPSS 13.0 to analyze the data. The analysis of variance and mean comparison were based on the least significant difference (LSD) test at the 0.05 probability level for each variety and year. Figures were made using Origin 7.5.

The grain yields of FFP, MFP, SHY, and MSP treatments were dramatically higher than those of the corresponding CK treatment in all three locations during all four years across all nine experiments (Table 4). Relative to FFP, the grain yield of MFP treatment in eight out of nine experiments (except for Jingmen 2008) showed

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Table 5 The nitrogen use efficiency of different fertilizer treatments. Year

Treatment

NA (kg hm−2 )

NHI a

NRE (%)

NAE (kg grain kg−1 )

NPE (kg grain kg−1 )

PFPN (kg grain kg−1 )

Jingmen 2008

CK FFP MFP SHY MSP

0 165 135 258 213

0.66 0.64ab 0.61b 0.59b 0.61b

– 23.4a 21.4ab 19.9b 25.2a

– 9.6a 9.2a 5.4b 6.7b

– 37.1a 37.6a 28.2b 35.8a

– 52.9b 62.2a 33.2d 40.2c

Jingmen 2009

CK FFP MFP SHY MSP

0 165 135 303 243

0.61a 0.55bc 0.56bc 0.52c 0.57b

– 16.7b 21.2a 13.1c 15.5b

– 4.4b 6.5a 4.0bc 3.5c

– 23.2c 25.6b 26.3b 29.2a

– 45.0b 56.2a 26.1d 31.1c

Honghu 2009

CK FFP MFP SHY MSP

0 161 135 319 257

0.76a 0.70b 0.64c 0.61c 0.62c

– 35.9c 59.8a 29.5d 46.5b

– 5.8c 12.2a 5.4c 7.7b

– 21.2b 25.8a 23.0ab 21.6b

– 54.5b 70.4a 30.1d 38.0c

Honghu 2010

CK FFP MFP SHY MSP

0 165 135 318 258

0.61a 0.56b 0.55b 0.55b 0.54b

– 57.7a 58.9a 35.7c 40.8b

– 5.0b 6.3a 2.5c 4.5b

– 8.9b 11.1a 7.7c 11.1a

– 47.8b 58.7a 24.5d 31.8c

Honghu 2011

CK FFP MFP SHY MSP

0 180 150 333.3 277.6

0.59a 0.66a 0.59b 0.53c 0.56bc

– 44.3b 61.2a 36.0c 35.7c

– 13.7b 25.1a 13.5b 14.2b

– 17.8d 26.0c 34.7b 42.0a

– 53.9b 61.8a 35.2d 40.3c

Chibi 2008

CK FFP MFP SHY MSP

0 165 135 273 213

0.67a 0.62b 0.62b 0.62b 0.65ab

– 34.9b 42.5a 23.4c 25.9c

– 12.3c 21.3a 8.1d 18.3b

– 41.8b 53.2a 36.2c 52.9a

– 48.4b 65.5a 30.0c 46.3b

Chibi 2009

CK FFP MFP SHY MSP

0 180 135 303 258

0.63a 0.59b 0.58b 0.54c 0.53c

– 23.3d 48.5a 27.1c 34.8b

– 10.7c 22.9a 9.1c 13.6b

– 43.2a 45.1a 31.0b 33.3b

– 38.8b 60.4a 25.8d 33.2c

Chibi 2010

CK FFP MFP SHY MSP

0 165 135 318 258

0.58a 0.54ab 0.52b 0.51b 0.56a

– 34.4b 54.5a 28.7c 33.0b

– 9.5b 12.6a 2.9d 7.3c

– 21.3a 22.5a 13.9b 23.4a

– 42.4b 53.2a 20.5d 28.6c

Chibi 2011

CK FFP MFP SHY MSP

0 165 165 293.4 270

0.76a 0.72b 0.70b 0.58c 0.71b

– 27.3d 41.4a 35.9b 32.5c

– 23.0ab 20.0b 13.2c 24.1a

– 49.7a 51.7a 28.8c 34.0b

– 6.6b 8.6a 4.6c 7.7ab

NA: amount of nitrogen applied (in the SHY and MSP treatments, the nitrogen from rape seed cakes (78 kg hm−2 ) was included in the NA figure); NHI: nitrogen harvest index= N in grains/total N absorption in plant; NRE: nitrogen recovery efficiency = [total aboveground plant N accumulation in the plot received N fertilizer (TN ) − total aboveground plant N accumulation in the zero-N control (T0 )]/NA; NAE: nitrogen agronomic efficiency = [grain yield in the plot received N fertilizer (GN ) − grain yield in the zero-N control (G0 )]/NA; NPE: nitrogen physiological efficiency = (GN − G0 )/(TN − T0 ); PFPN : nitrogen partial factor productivity = GN /NA.

an increase in ratio ranging from 0.3% to 16.6%; grain yield of SHY treatments of six out of nine experiments (excluding Jingmen 2008, Honghu 2010, Chibi 2010) showed an increase ratio ranged from 2.4% to 20.9%. Relative to SHY, grain yield of MSP treatment of seven out of nine experiments (excluding Jingmen 2008, Honghu 2011) showed an increase in ratio ranging from 0.2% to 20.4% (Table 4). Among the paddy fields in Honghu (2009, 2010) and Chibi (2008, 2009, 2010, 2011), the greatest rate of increase occurred with MSP treatment; in Jingmen 2009 and Honghu 2011, the greatest rate of increase occurred with the SHY treatment; and in six of the nine fields, the lowest rate of increase occurred with FFP treatment (Table 4). The GY of MFP, SHY, and MSP treatments in Jingmen in 2008 and the GY of SHY treatment in Honghu and Chibi in 2010 were all slightly lower than the GY of the corresponding FFP treatments (Table 4).

The ATB values of MFP, SHY, and MSP treatments were significantly higher than that of the corresponding CK treatments in all experiments (Table 4). The ATB values of MFP, SHY, and MSP treatments were higher than those of the corresponding FFP treatments in all experiments except MFP treatment in Jingmen 2008. The ATB of MFP treatments was higher than that of the FFP treatment in eight of nine experiments (excluding Jingmen 2008). The ATB of MSP treatments was higher than that of SHY treatment in six of nine experiments (excluding Jingmen 2009, Honghu 2011, and Chibi 2011). The ATB of SHY treatments was higher than that of FFP treatment across all nine experiments (Table 4). The harvest indices (HI) of FFP, MFP, SHY, and MSP treatments were lower than those of the corresponding CK treatments across all scenarios except MSP treatment in Chibi in 2008, MFP treatment in Chibi in 2010, and FFP and MSP treatments in Chibi 2011

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Fig. 1. SPAD value of the fully expended top leaf in the mid-tillering (MT), panicle initiation (PI), heading (HD), and maturity (MS) stages under different fertilizer treatments in 2010 and 2011. A: Honghu; B: Chibi. ANOVA analysis was conducted among different treatments at the same growth stage and bars with different letters indicate the significance at the 0.05 level.

(Table 4). The HI of MFP treatment was lower than that of FFP in seven of nine experiments (excluding Chibi 2008 and Chibi 2010); HI of MSP treatment was higher than that of SHY in six out of nine experiments (excluding Jingmen 2008, Jingmen 2009, and Honghu 2011). The HI of SHY treatment was lower than that of FFP in eight out of nine experiments (excluding Chibi 2008) (Table 4). The numbers of panicles (PN) in FFP, MFP, SHY, and MSP treatments were greater than that of the corresponding CK treatment in all experiments (Table 4). The PN of MFP and SHY treatments was greater than that of FFP treatment in all the experiments. The PN of MSP treatment was greater than that of SHY treatment in seven out of nine experiments (excluding Honghu 2011 and Chibi 2008). The numbers of spikelets per panicle (SPP) of FFP, MFP, SHY, and MSP treatments were greater than that of the corresponding CK treatment across nine experiments. The SPP values of SHY treatments were greater than that of FFP treatment in eight out of nine experiments (excluding Honghu 2011). The 1000-grain weight (GW) and filled-grain percentage (FP) values of SHY treatments were lower than those of FFP treatment in eight out of nine experiments (excluding Honghu 2009 and Jingmen 2009) (Table 4).

The NRE of SHY treatments was lower than that of FFP treatments among seven out of nine experiments (excluding Chibi 2009 and Chibi 2011) (Table 5). Relative to FFP, the NAE of MFP treatment of eight out of nine experiments (excluding Jingmen 2008) showed an increase in ratio ranging from 26.0% to 110.3%. Relative to SHY, the NAE of MSP treatment of eight out of nine experiments (excluding Jingmen 2009) showed an increase in ratio ranging from 5.2% to 151.7%. Relative to FFP, the NPE of MFP treatment in eight out of nine experiments (excluding Chibi 2011) showed an increase in ratio ranging from 1.3% to 46.1%. Relative to SHY, the NPE of MSP treatment of eight out of nine experiments (excluding Honghu 2009) showed an increase in ratio ranging from 7.4% to 82.6% (Table 5). The nitrogen partial factor productivity (PFPN ) of MFP treatments was significantly higher than that of FFP treatment. The PFPN of MSP treatments was higher than that of SHY treatments. The PFPN of SHY treatments was lower than that of FFP treatments across all the experiments (Table 5). 3.3. Influence of modified fertilizer practice on SPAD, LAI, and panicle rate of rice

3.2. Influence of modified fertilizer practice on N use efficiency The nitrogen harvest index (NHI) of FFP, MFP, SHY, and MSP treatments were lower than that of the corresponding CK treatment across all the nine experiments (Table 5). The NHI values of MFP and SHY treatments were lower than that of FFP treatment among seven (excluding Jingmen 2009 and Chibi 2008) and eight (exclude Chibi 2008) out of the nine experiments, respectively. The NHI of MSP treatments was higher than that of SHY treatments among seven out of nine experiments (excluding Honghu 2010 and Chibi 2009) (Table 5). The nitrogen recovery efficiency (NRE) of MFP treatments was significantly greater than that of FFP treatment among eight out of nine experiments (excluding Jingmen 2008). The NRE of MSP treatments was greater than that of SHY treatments among seven out of nine experiments (excluding Honghu 2011 and Chibi 2011).

The SPAD values of mid-tillering, panicle initiation, and full heading stages in all fertilization treatments were significantly higher than the SPAD values of CK. There was not much difference between treatments. However, the SPAD values of MFP, SHY, and MSP treatments in Chibi in 2010 were significantly higher than the SPAD values of FFP treatment or CK. During the maturity stage, the SPAD values of MFP, SHY, and MSP treatments were higher than those of FFP or CK treatments, and the difference was found to be significant in Honghu in 2011. The SHY treatment showed its highest SPAD value during MS in every experiment (Fig. 1). During the mid-tillering stage, LAI values in Honghu from 2010 to 2011 did not differ visibly across treatments (Fig. 2). In Chibi, LAI value of SHY treatment was significantly higher than those of MSP and CK treatments in 2010; LAI values of all fertilizer applied treatments were significantly higher than that of CK treatment and there

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Fig. 2. Leaf area index (LAI) during the mid-tillering (MT), panicle initiation (PI), and heading (HD) stages under different fertilizer treatments in 2010 and 2011. A: Honghu; B: Chibi. ANOVA analysis was conducted among different treatments at the same growth stage and bars with different letters indicate the significance at the 0.05 level.

a slight decrease in Honghu and Chibi during two years (Fig. 2). During the heading stage, LAI values of all nitrogen fertilizer treatments ranged from 4.5 to 6.4 at Honghu and from 5.2 to 6.6 at Chibi in 2010; from 4.4 to 5.1 at Honghu and from 4.5 to 5.5 at Chibi in 2011. They were significantly higher than those of CK (Fig. 2). Relative to FFP, the LAI of MFP of all the four experiments showed a decreasing trend. Relative to SHY, the LAI of MSP of three of the four experiments showed a decreasing trend at the heading stage. In this study, we investigated the tillering dynamics of midseason rice in Honghu and Chibi from 2010 to 2011 and found that maximum tiller number appeared 30–40 days after transplantation. As shown in Fig. 3, the greatest panicle rate (the ratio of the number of panicles to the maximum tiller number) appeared in Honghu in 2011. The ratios appeared in the following trend: MFP >FFP and MSP > SHY in Honghu and Chibi from 2010 to 2011. The panicle rates of CK were significantly higher than those of FFP in Honghu and Chibi in 2010. 4. General discussion and conclusion Fig. 3. Panicle rate of rice under different fertilizer treatments at Honghu and Chibi in 2010 and 2011. ANOVA analysis was conducted among different treatments at the same growth stage and bars with different letters indicate the significance at the 0.05 level.

4.1. Nitrogen management, grain yield, and nitrogen use efficiency

was not much difference between fertilizer applied treatments in 2011. During the panicle initiation stage, the LAI values of all treatments in Honghu and Chibi in 2010 were much higher than those of the corresponding treatments in Honghu and Chibi in 2011. The LAI values of all nitrogen fertilizer treatments were significantly higher than those of CK treatments (Fig. 2). Relative to FFP, the LAI values of MFP showed a slight decrease in 2010 and a slight increase in 2011. Relative to SHY, the LAI values of MSP showed

In southern China, large-scale farmland management began to replace the farm household model during the early 2000s. However, some traditional misconceptions regarding the use of fertilizer are still deeply rooted among some farmers. The investigation shows that farmers generally rely more on N fertilizers than on P or K fertilizer; more on basal fertilizer than other fertilizers; and more on fertilizer during the tillering stage than during the heading stage (Han et al., 2012). Overuse of N not only wastes of resources but also pollutes the environment. In this study, the results showed the

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following: (1) Grain yield does not always increase as the amount of nitrogen fertilizer increases. For example, the grain yield of SHY and MSP in Jingmen (2008), SHY in Honghu (2010), and SHY in Chibi (2010) were lower than in FFP at these experimental sites (Table 4). This is because too much rain and less sunlight during the growth stage (MS) (Table 1) led to lodge at the experimental sites in Jingmen (2008) and Chibi (2010) and the panicle blast (rottenneck) at experimental sites at Honghu (2010) at the rice harvest stage in the treatments with high levels of nitrogen. This caused serious losses in grain yield. (2) Decreases in the amount of nitrogen fertilizer used does not always cause decreases in grain yield. For example, relative to FFP, the grain yield of MFP treatments in eight out of nine experiments showed an increase ratio ranging from 0.3% to 16.6%. Relative to SHY, grain yield of MSP treatments in seven out of nine experiments showed an increase in ratio ranging from 0.2% to 20.4%, even though less nitrogen fertilizer was used in the latter than in the former (Table 4). Both SSNM and RTNM in rice significantly improve nitrogen use efficiency by a large amount relative to FFP (Pampolino et al., 2007; Peng et al., 2006). In this study, the NRE of SHY treatments was found to be lower than that of FFP treatments in seven out of nine experiments (Table 5). Overtopped nitrogen is found to increase plant uptake of nitrogen. However, most N accumulates in straw rather than be in grain, which decrease NRE (Artacho et al., 2009). The results of this study exhibited NRE, NAE, NPE and PEPN of MFP and MSP treatments increased greatly relative to those of FFP and SHY, respectively, across almost all experiments (Table 5). The use of appropriate amounts of N fertilizer and a rational distribution among different growing stages can lead to high grain yield and efficient use of N. In this study, the five treatments differed from each other in several ways, including plant density (treatments 1 and 2 vs. treatments 3, 4, and 5); total N applied; distribution of N application (top dressing); presence of organic fertilizer (rapeseed cakes, treatments 1, 2, and 3 vs. treatments 4 and 5). Plant density and planting pattern are important to the growth and nutritional requirements of individuals and population of high-yielding rice. Generally, highyield and super-high-yield rice cultures are planted with narrow spaces between plants and wide spaces between rows as needed for ventilation and light. In this study, the seedlings were transplanted with 19.8 cm between plants and 23.1 cm between rows in CK and FFP and with 16.5 cm between plants and 26.4 cm between rows in MFP, SHY, and MSP plots. The plant density in MFP, SHY, and MSP treatments was higher than that of CK and FFP treatments. This pattern increase solar radiation and total sunshine reception and therefore the rate of photosynthesis. It can also reduce the spread of disease and pests. Because high grain yield is caused by the correct combination of many factors, changes in the total fertilizer application rate, topdressing rate, and time of application necessitate changes in relevant cultural practices, such as planting density. All of these factors should be considered. 4.2. SPAD values, LAI values, PN, and GY The rice leaf is an important organ for photosynthesis and the production of organic compounds, and more than 90% of photosynthesis is carried out in the leaves. The SPAD value of rice leaves is significantly positively correlated with unit N content per unit leaf area, the latter of which is significantly correlated with the rate of rice leaf photosynthesis. Because SPAD readings are closely related to leaf N content, the SPAD meter can be used to monitor the N status of rice and to adjust the rate of N fertilization in order to increase the efficiency of N use (Hussain et al., 2000; Varinderpal et al., 2010). In this study, the top dressing rates of N, P, and K in SHY and MSP plots were adjusted based on the SPAD values observed in Honghu and Chibi in 2010 and 2011 (Fig. 1). During the MS, the

211

SPAD values of MFP, SHY, and MSP treatments were higher than those of FFP treatment and CK. The SHY treatment in each experiment showed peak SPAD values during MS (Fig. 1). However, the grain yield at Honghu and Chibi in 2010 showed a slight decrease under the SHY treatment relative to FFP (Table 4). Too much rain during the maturity stage and excessive nitrogen fertilizer input led to lodge and panicle blast took place at these experimental sites. FP and GY decreased (Table 4). Because leaves intercept incident solar radiation, leaf area index is widely used in research involving crop photosynthesis and growth analysis. The critical LAI value at maximum crop photosynthesis is about 5–6 (Yoshida, 1981). In this study, LAI values of all fertilizer treatments were significantly higher than that of CK during the heading stage (Fig. 2). Relative to FFP, the LAI of MFP of all four experiments showed a decreasing trend. Relative to SHY, the LAI of MSP of three out of the four experiments showed a decreasing trend (Fig. 2). This showed that LAI was influenced by the fertilization rate and method as well as by plant density. The LAI values of these treatments during PI and HD stages in Honghu and Chibi were higher in 2010 than in 2011, indicating that LAI was also significantly influenced by the climate, such as by precipitation during growth stage (Table 1). Increased amounts of N were found to increase LAI to a certain degree, facilitating high yield. However, greater LAI also means that the leaves block sunlight from each other, creating a closed system. The growing conditions worsen with intensified competition and increased respiration consumption, which reduce photosynthesis and production. High yield requires optimum LAI, but the optimum LAI is not always the largest LAI. Zhong et al. (2003) demonstrated a down-facing parabolic relationship between rice yield and the population index (the product of SPAD and LAI) during the heading stage. Fertilization influences the yield component. A study by He et al. (2007) showed that RTNM could increase PN significantly. In this study, the PNs of the MFP and SHY treatments were greater than that of the FFP treatment in all experiments. The PN of MSP treatment was greater than that of SHY in seven out of nine experiments (excluding Honghu 2011 and Chibi 2008) (Table 4). The panicle rate is an important index of the quality of the rice population and plays a major role in determining grain yield (Ling, 2000). In our experiments, the panicle rate showed the following trend: MFP  FFP and MSP > SHY in Honghu and Chibi from 2010 to 2011 (Fig. 3). Modified fertilizer practices were found to promote appropriate tillering development and to control the number of unproductive tillers. In this way, it promotes ideal growing conditions for increasing the ratio and grain yield. Liu et al. (2003) showed that SSNM increased the SPP and FP of rice relative to FFP treatment. In our experiments, relative to FFP, the SPP of MFP treatments showed an increasing trend across five of nine experiments. However, relative to SHY, the SPP of MSP treatments increased only at Honghu in 2011. In five out of nine experiments, SPP of MSP treatments decreased significantly relative to SHY (Table 4). Relative to FFP, the FP of MFP treatments showed an increasing trend across only three of nine experiments. Relative to SHY, the FP of MSP treatments increased across only four of nine experiments (Table 4). Greater tiller numbers are not always associated with increased production (Cui et al., 2004; Ling, 2000; Peng et al., 1994; Zhang and Ma, 2004). Excess tillers are found to have a negative influence on SPP, resulting in a lower panicle weight with a lower FP, eventually reducing yield (Wang et al., 2007). The accumulation of ATB is the basis of the formation of crop production. The formation process involves the accumulation and distribution of aboveground biomass. In this paper, the ATB of MFP treatment was found to be higher than that of FFP treatment in eight out of nine experiments. The ATB of MSP treatment was found to be higher than that of SHY treatment in six out of nine

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experiments (Table 4). HI of MFP treatment was lower than that of FFP in seven of nine experiments. However, the HI values of MSP treatment were higher than that of SHY in six out of nine experiments (Table 4). These results indicate that modified fertilizer treatments can increase the ATB and even increase the HI concurrently, and so increase the grain yield. The results of this paper suggest that decreasing the total amount of nitrogen applied, redressing the proportion of basal fertilizer, tiller fertilizer, and panicle fertilizer, adding organic fertilizers, and engaging in reasonable planting density can produce adequate numbers of effective panicles, foster a high panicle rate, delay senescence of functional leaves, and promote a healthy population, all of which improve grain yield and efficiency of fertilizer. Adequate PN is the basis of high yield, and coordinating the relationships between PN, SPP, and FP and the relationships between FP and ATB can increase grain yield. Acknowledgments We are grateful to Mr. Zhongqing Yao (Soil and Fertilizer Station of Chibi County, Hubei, China), Mr. Ximing Xiao (Soil and Fertilizer Station of Jingmen County, Hubei, China), and Mr. Yongwu Liu (Honghu, Hubei, China) for their help in the field trials. Financial support was provided by the Special Fund for Agro-scientific Research in the Public Interest in China (Project Nos. 201103003, 201003016 and 200803030). References Artacho, P., Bonomelli, C., Meza, F., 2009. Nitrogen application in irrigated rice grown in Mediterranean conditions: effects on grain yield, dry matter production, nitrogen uptake, and nitrogen use efficiency. J. Plant Nutr. 32, 1574–1593. Cabangon, R.J., Castillo, E.G., Tuong, T.P., 2011. Chlorophyll meter-based nitrogen management of rice grown under alternate wetting and drying irrigation. Field Crops Res. 121, 136–146. Chen, X., Cui, Z., Vitousek, P.M., Cassman, K.G., Matson, P.A., Bai, J., Meng, Q., Hou, P., Yue, S., Römheld, V., Zhang, F., 2011. Integrated soil–crop system management for food security. Proc. Natl. Acad. Sci. 108, 6399–6404. Cui, K., Peng, S., Xing, Y., Yu, S., Xu, C., 2004. Molecular dissection of the relationships among tiller number, plant height and heading date in rice. Plant Prod. Sci. 7, 309–318. Dobermann, A., White, P.F., 1999. Strategies for nutrient management in irrigated and rainfed lowland rice systems. Nutr. Cycl. Agroecosyst. 53, 1–18. Dobermann, A., Witt, C., Dawe, D., Gines, H.C., Nagarajan, R., Satawathananont, S., Son, T.T., Tan, P.S., Wang, G.H., Chien, N.V., Thoa, V.T.K., Phung, C.V., Stalin, P., Muthukrishnan, P., Ravi, V., Babu, M., Chatuporn, S., Kongchum, M., Sun, Q., Fu, R., Simbahan, G.C., Adviento, M.A.A., 2002. Site-specific nutrient management for intensive rice cropping systems in Asia. Field Crops Res. 74, 37–66. Godfray, H.C.J., 2010. Food security: the challenge of feeding 9 billion people. Science 327, 812–818. Guo, J., Liu, X., Zhang, Y., Shen, J., Han, W., Zhang, W., Christie, P., Goulding, K.W., Vitousek, P.M., Zhang, F., 2010. Significant acidification in major Chinese croplands. Science 327, 1008–1010. Han, B., Shi, L., Xu, F., Huang, J., Zeng, X., Ma, X., Guo, L., 2012. Evaluation and present situation of fertilization for rice in Hubei Province. Hubei Agric. Sci. 51, 2430–2435 (in Chinese, with English abstract). He, F., Huang, J., Cui, K., Zeng, J., Xu, B., Peng, S., Buresh, R.J., 2007. Effect of real-time and site-specific nitrogen management on rice yield and quality. Sci. Agric. Sin. 40, 123–132 (in Chinese, with English abstract). Huang, J., He, F., Cui, K., Buresh, R.J., Xu, B., Gong, W., Peng, S., 2008. Determination of optimal nitrogen rate for rice varieties using a chlorophyll meter. Field Crops Res. 105, 70–80. Hussain, F., Bronson, K.F., Yadvinder, S., Bijay, S., Peng, S., 2000. Use of chlorophyll meter sufficiency indices for nitrogen management of irrigated rice in Asia. Agron. J. 92, 875–879. Ju, X., Xing, G., Chen, X., Zhang, S., Zhang, L., Liu, X., Cui, Z., Yin, B., Christie, P., Zhu, Z., Zhang, F., 2009. Reducing environmental risk by improving N management in intensive Chinese agricultural systems. Proc. Natl. Acad. Sci. 106, 3041–3046.

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