Effect of Nitrogen Applied Before Transplanting on NUE in Rice

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Agricultural Sciences in China 2007. 6(7): 842-848

ScienceDirect

July 2007

Effect of Nitrogen Applied Before Transplanting on NUE in Rice ZHENG Yong-mei, DING Yan-feng, WANG Qiang-sheng, LI Gang-hua, WU Hao, YUAN Qi, WANG Hui-zhi and WANG Shao-hua Key Lnhoratory of Crop Growth Regulation, M i n i s t p of AgriculturdNnnjing Agricitlriirnl University, Nanjing 210095, P.R.China

Abstract Nitrogen (N) application before transplanting, where N fertilizers are applied in seedling-bed and carried to the paddy field with seedlings, is a novel method proposed in this article aiming for improving nitrogen utilization efficiency (NUE) in rice.

The effect of this method on mineral N distribution in the rhizosphere soil was investigated in a field experiment with a japonica variety, Ningjing 2, in seasons of 2004 and 2005. There were four levels of N applied 16 h before transplanting: zero N (NO), 207 kg ha-l (NL), 310.5 kg ha-1 (NM), and 414 kg ha1 (NH). The result indicated that N fertilizer before transplantation had positive effect of increasing mineral N content in the rhizosphere soil of rice. Generally, N content in the rhizosphere soil of rice tended to increase with the amount of N fertilizer before transplanting, with the NH treatment having the largest effect. Additionally, N fertilizer before transplanting had significant influence on rice NUE and grain yield. Compared with other treatments, the NM treatment showed the largest influence, with basal-tillering NUE, total NUE, and grain yield being 15%, 12%, and 529.5 kg h a ' higher than those of NO treatment. This result indicated that N fertilizer before transplantation had positive effect on mineral N distribution in the rhizosphere soil of rice, thus improving NUE and grain yield. Key words: rice, nitrogen (N)application before transplanting, nitrogen utilization efficiency (NUE), grain yield

INTRODUCTION

2003). In recent years, water pollution caused by excessive N application has aroused concerns among the societies. To date, great efforts have been made to

N is an essential macronutrient for rice growth, and N

increase NUE by agronomical approaches, such as

application is an effective method for exploiting the maxi-

deep-layer application of fertilizer, formulated

mum yield potential of modern rice cultivars (Liu and Lii 2005). In rice production, to obtain the maximum

fertilization, and balanced fertilization, using urease

yield. farmers often apply additional N fertilizer than the required amount, thus increasing the risk of water pollution. In China, annual N fertilizer consumption has achieved 180 kg N ha-', especially 350 kg ha-' for Jiangsu Province. Researches showed that the NUE of rice in China is markedly lower than that of the world, being 3040% for the entire country and only 20% for

Jiangsu Province (Wang et af. 2003, 2004; Liu er al. Tills paper

15

inhibitors, controlled-release N fertilizer, and site-specific N management (Liu L J et al. 2003,2006; Zheng et al. 2001 ; Liu D L et al. 2002; Wang et al. 2002; Li et al. 2001; Liu Y Y et al. 2006; Dong and Wang 2006; Fan et al. 2005; Ni et al. 2003; Dai et al. 2003; Xue et

al. 2006). NUE varied with the timing, rate, and method of N application, source of N fertilizer, soil chemical and physical properties, climatic conditions, and crop nu-

iranslaird f r o m its Chinese .*eraion in Srienria Agriculrura Sinico

ZHENG Yvng-inri. Ph I). Tel +86-25-84395487. E-mail: 2006201024Bnjau.edu.cn; Correspondence WANG Shao-hua. Professor, Tel: +86-25-8439647.5, E-mail: uangsh@njau edu cn

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Effect of Nitrogen Applied Before Transplanting on NUE in Rice

843

trition status (Sharmaa et al. 2005; Peng et al. 2006; Chao W L and Chao C C 1997; Zhang et al. 2004). Related researches have shown that low NEE in the present rice production is associated with low basaltillering NUE of 1520% (Ding et al. 2004; Ling et al. 2005). Surface application, one of the most common practices, is capable of elevating N level in rhizosphere soil of rice, but not the rhizosphere, thus increasing the risk of N leaching and losing. However, NUE of panicle fertilizer was found to be higher than that of surface application, with a range of 50-60% and the highest being 80% (Peng et al. 2002). It is well established that the amount of N requirement for rice varied in the different growth stages. At the returning green stage and long time tillering stage, young rice plants grow slowly and have relatively low requirement for N, because their roots are small and underdeveloped, absorbing relatively little amount of fertilizer around the root boundary. In China, the most common rice cultivation practice is transplanting, and fertilizer applied mainly is basal-tillering fertilizer(Liu et al. 2002). N application before transplanting, in which N fertilizers are applied in seedling-bed and carried to the paddy field with seedlings, is a novel method proposed in this article to improve NUE in rice. This study was done to investigate the effect of N fertilizer before transplanting on rice NUE and grain yield, by analysis of the movement and spatial-temporal distribution of N fertilizer in the rhizosphere of paddy field.

There were four treatments of N fertilizer (urea) before transplanting in rice seedling bed: zero N (NO), 207 kg ha-' (NL), 311.5 kg ha-' (NM), and 414 kg ha-' (NH). The N fertilizer was fertilized on the plastic plate in the afternoon, and the seedlings were then transplanted to the paddy field the next morning. The time period between fertilization and transplanting were 16 hours to avoid deleterious effect of high N concentration on seedlings. The other managerial practices were in the same way during the seedling period. The seedlings were transplanted on June 19, 2004, with soil ball, 2.2 cm in top diameter, 1.O cm in bottom diameter, and 2.0 cm in basing height. To calculate NUE,a zero N fertilizer treatment (CK) was done in the field. The experiment was a completely randomized block design with triplication. Plot was 4 x 4 m2 and separated by a ridge wrapped with plastic film, 40 cm high, and 35 cm wide. N fertilizer (303.6 kg ha-') was applied 25% at basal, 25% at tillering, and 50%at panicle initiation. Phosphorus fertilizer (1 32 kg ha-') was applied before transplanting. Potassium fertilizer (185 kg ha-') was applied as basal and elongation fertilizer, with a ratio of 1:1. In analysis of NUE, the amount of N fertilizer before transplanting was calculated as the basal fertilizer. Thus, the total amount of N for the five treatments was 0, 303.6, 307.3, 309.2, and 3 11.11 kg ha-', respectively.

MATERIALS AND METHODS

The soil was sampled every 3 days from transplanting to 21 days after transplanting. The depth of the soil sample was 0-10 cm. There were 3 sample spots in each plot. There were 5 samples in each sample spot. They were S1, S2, S3, S4, and S5, which were 1,4, 7, 10, and 13 cm apart from rice plant, respectively (Fig.

Experimentaldesign The experiments were done at the Tuqiao Experimental Station of Nanjing Agricultural University, China in seasons of 2004 and 2005. The soil of experiment farm was sandy loam, with 0.9 g kg-' total N, 34 mg kg-' available P, and 114 mg kg-' available K. A japonica variety, Ningjing 2, was sown on May 22,2004, and the seedlings were raised through the holes of a plastic plate. The area per plastic plate was 0.2 m2 with 352 holes. Two-thirds volume of each hole was filled with sifted soil. After sowing, the remaining space of each hole was covered with sifted soil and the plastic plate transferred to the wet seedling bed.

Sampling and analysis

1). Samples were air-dried, crushed using a disintegrator, and sifted through 1 mm sifter. Mineral N were extracted in 2 mol L-' KCL solution for 1 h and determined using a consecutive flowing analyzer (Li et al. 2006). Considering that the N form in wet soil is mainly NH,+-N, data presented in this article are based on NH,+-N. From transplanting to anthesis, tillers number was investigated every 3-7 days, with prophase being every

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ZHENG Yone-mei er al.

R 44

Fig. 1 Soil sampling of different spots in the paddy field.

3-4 days and anaphase being every 5-7 days. At the transplanting stage (TS), critical stage of productive tiller (N-n), elongation stage (n-2), and mature stage. 5 holes of rice plant were sampled. Samples were dried at 80°C to constant weight, then ground into powder by a stainless grinder. N contents were determined using the Kjeldahl method (Dong and Wang 2006). Samples of 5 holes were hand-harvested at random at maturity. Spikelets per panicle and 1 000-grain weights were investigated. The percentage of filled grains were calculated as fully matured grains, thus sterile florets and grain weight less than 10 mg were excluded. Half of the plot except the side rows was hand-harvested to evaluate grain yield. NUE of basic and tillering dressing = [Total N absorbed during transplanting to (n-2) of N treatments Total N absorbed during transplanting to (n-2) of nonN treatment]/Total N of basal and tillering fertilizer x

tent of fertilizer treatments was higher than that of NO treatment, with N fertilizer before transplanting treatment being the highest. Mineral N content of S4 and S7 increased first and then decreased during the 15 days after transplanting, with the highest value being on the sixth day after transplanting (Figs.3 and 4). By contrast, mineral N content of NO treatment decreased during the rice-growing period, which was similar to s1. The soil ball with seedlings carried N fertilizer to paddy field. But rice requires relatively little amount of N at the forepart stage, and the fertilizer in the soil ball would move away from the rice root. As illustrated in Figs.2,3. and 4, mineral N contents of all fertilizer treatments were higher than that of NO treatment during the 15 days after transplanting. There was no significant difference in mineral N content between the S4 and S5

I

0

3

6

9

12

15

I

I8

Day5 after transplanting t d )

Fig. 2 The dynamic change of N content in soil of S1 during 15 days after transplanting.

1008.

In this paper, the data of graphs were mean values of the two-year experiment, because the results of the two years were in agreement with each other.

RESULTS Effects of fertilizer before transplanting on mineral N content in the rhizosphere soil 1In

Mineral N content in rhizosphere soil varied sigIllficantly with the days changing after transplanting. During 15 days after transplanting. the mineral N content showed a diminishing trend (Fig.2). However, mineral N con-

I 0

I

3

6

9

I:!

1

18

Days after transplanting ( d )

Fig. 3 The dynamic change of N content in soil of S2 during the 15 days after transplanting.

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Effect of Nitrogen Amlied Before Transplanting on NUE in Rice

during the15 days after transplanting. This result indicated that N before transplanting could increase mineral N content in the rhizosphere soil of rice.

Effect of N before transplantingon N space-time distribution The fertilizer before transplanting showed significant influence on mineral N space-time distribution. On the third day after transplanting, mineral N contents of S 1 and S2 were higher than that of S3, S4, and S5 (Fig.5). For example, mineral N content of S 1 of NH treatment was 2.468 mg kg-' higher than that of S5. However, in the treatment of NO, the trend was the opposite. Generally, soil mineral N content decreased with the increasing distance from the plant. Also, it differed with the timing of rice growth. On the sixth day after transplanting, mineral N content of S 1 was similar to

r

150

those of S3, S4, and S5, whereas that of S2 was significantly higher than that of S3, S4, and S5 (Fig.6). Mineral N distribution of all treatments showed a similar trend on the fifteenth day after transplanting (Fig. 7). These results indicated that the fertilizer before transplanting could increase mineral N content in the soil of rhizosphere. In all N treatments, application before transplanting showed significant effects on mineral N content in the soil near the rice root. Generally, mineral N content in the rhizosphere soil of rice tended to increase with the amount of N fertilizer before transplanting, with the NH treatment having the most favorable effect, because of it not destroying the seedlings.

Effectsof N beforetransplantingon N assimilation and utilization There were significant differences in rice plant N ac-

+NM+NH

+NL

+NO

845

+NL

110 3

0

6

9

12

150

r

120

I

18

15

+NM-A-NH

+NL

+NM-A-NH

7

4

13

10

Distance from plant (crn)

Fig. 4 The dynamic change of N content in soil of S3 during the 15 days after transplanting.

r

I

I

I

Days after transplanting (d)

150

+NO

Fig. 6 The spatial distribution of N in soil on the sixth day after transplanting.

+NO

+NL

+NM-A-NH

+NO

135 -r

130

125

120

120

J

1 I5

1

4

7

10

13

Distance from plant (cm)

Fig. 5 The spatial distribution of N in soil on the third day after transplanting.

I

4

7

10

13

Distance from plant (cm)

Fig. 7 The spatial distribution of N in soil on the fifteenth day after transplanting.

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ZHENG Yone-mei et al.

816

cumulation from transplanting to N-n stage among the treatments, with the order of NM > NH > NL > NO (Table 1). The basal-tillering N fertilizer utilization efficiency was elevated as the N assimilation increased, with NH, NM, and NL treatments being 12, 15, and 5% higher than NO treatment, respectively. Although the proportion of N fertilizer before transplanting in the basal and tillering N fertilizer was rather low. it significantly improved the pedormance of rice plant. As shown in Table 1. there were dramatic variations in the accumulation of N during rice growing period among all treatments, with NM treatment having the largest value of 243.15 kg ha-'. In addition, differences in NUE between NO treatment and N fertilizer before transplanting treatments were statistically significant. with NM treatment being 44% higher than NO treatment. NUE of NL and NH treatments were not

signficantly different. This result showed that the treatments of N before transplanting had more tillers than NO treatment, and the tillers developed earlier than that of NO treatment. To N-n leaf-age period, tillers number of NO treatment was lower than that of N before transplanting treatments. In NL, NM, and NH treatments, rice plants grew well and root system was more developed than those of NO, thus increasing N accumulation and NUE of rice plant. In this study, the difference in grain yield among all treatments was significantly different. Grain yield of NM treatment was 529.5 kg ha.' higher than NO treatment, whereas that of NH treatment was 166.5 kg ha-' lower than NM treatment. Additionally, the difference between the two years was statistically significant. The results indicated that N application before transplanting could significantly increase rice grain yield.

Table 1 N utilization efficiency and vield as affected by N before transplanting TIcatment

Z iiptahe between SN-(n-2)

Total N uptake ikg ha I )

Total NUE

(%)

44 X S D

12.06 D

204.15 D

32 C

274.8

5 2 YS

17 39 C

27 1 7 A

217.95 C 243.15 A

36 BC 44A

287 7 C 312.75 A

8470.5 C 8814.0 A

24.70 B

227.25 B

39 AB

294.6 B

8647.5 B

130.05 E

5 830.65 E

(kg ha ' 1 __

67

x

('

A

64.05 B 26 5 5 E

SUE of BT

106.5 E

Tiller No. at the stage of (N-n) (ten thousand ha I)

D

Yield (kg ha-!) 8 284.51)

The I e t t c r i indicate significance at P < 0 01 level. The same as helou

Table 2 Grain yield as dtfected by N before transplanting Treaunent

Keprat 1

Repeat 2

Repeat 3

Average

:001

YO

8200

x

8313 0

8 195 7

8216 5 E

'I lrld ihr h,i

\L

8457 h

8358 2

8704 7

8759 0

8442 8 8 847 9

8419 5 DE

\v \H

Xi28 1

8585 6

8 608 4

8770 5 AB 85740C

(K

5788 H

58124

5741 9

5781 0 G

(J

8268 0

8319 5

8410 1

8 732 5 EF

Yield

\L

8474 3

85109

8 579 4

8521 5 CD

ihg h'i I

\v

8860 I

8915 3

8797 2

8857 5 A

hH CK

8 660 4

8 709 0

8793 6

8721 0 B

5 865 6

5902 7

5 872 7

5 880 3 G

2olli

DISCUSSION The high input rate of fertilizer N and improper timing of N application in farmers' N fertilizer management have resulted in low N U E of irrigated rice in China. Scvcral researches have been done to develop practiceh to improve NUE. with emphasis on the significance of rnanagement of N inputs for reducing N losses and increase N uptake by rice.

The study was conducted under the condition of raising seedlings by means of plastic plate and transplanting with soil and fertilizer. The results indicated that fertilizing a day before transplanting could improve mineral N content in rhizosphere soil. So it could satisfy the larger N demand for the rapid growth of rice root by improving mineral N content in rhizosphere soil. However, there are few researches dealing with the planting method for increasing N content in rhizo-

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Effect of Nitrogen Applied Before Transplanting on NUE in Rice

sphere soil. Thus, the method proposed by this study is of significance for improving rice NUE and grain yield. The analysis of spatial-temporal distribution of mineral N content in soil of all N treatments indicated that N content differences in the soil mostly existed within 7 cm apart from each plant. The differences among all treatments were largest on the sixth day after transplanting. The characteristic of mineral N accumulation and movement in soil was in agreement with the results of some researchers (Yang et al. 2003; Gao et al. 2005; Wang et al. 2005; Shi et al. 2002). Surface broadcasting of basal-tillering N fertilizer elevated N content mainly in the non-rhizosphere soil. However, the N in non-rhizosphere soil cannot be used for rice, thus increasing the loss of N in the soil by contrary (Peng et al. 2002). In this experiment, all N fertilizers before transplanting treatments increased the N content in rhizosphere soil, thus optimizing the N distributing in soil, and enhancing the absorbance and use of N fertilizer. Thus, it had the advantages of improving NUE by altering the distribution of N in the rhizosphere soil (Gao et al. 2005; Wang et al. 2005). However, since the content of N fertilizer of NH treatment was so high that it had a negative impact on tiller developing in the paddy field. The absorption and utilization of N fertilizer were lower in the treatment of NH. Moreover, in comparison with other treatments, the NM treatment significantly increased the mineral N content in rhizosphere soil, thus improving tiller development, basaltillering N fertilizerutilization efficiency,and grain yield. Therefore, the proper amount of N fertilizer is capable of having positive effect on absorption and utilization of N fertilizer. NUE is a scientific criterion for evaluating the approaches aiming for higher grain yield. The result indicated that N fertilizer before transplanting had a positive effect on rice N accumulation and W E . Moreover, the NM treatment showed the most significant effect, with NUE of basal-tillering and whole growing period being 15 and 12% higher than NO treatment, respectively. These results indicated that applying N fertilizer before transplanting is an effective method for improving rice NUE. In addition, the amount of fertilizer needs to be calculated exactly to obtain higher NUE and rice yield.

847

CONCLUSION N fertilizer before transplanting had significantly positive effect on mineral N content in rhizosphere soil. Mineral N content of NL, NM, and NH treatments were higher than NO treatment. The mineral N content of S2 of NH treatment was 18.5331 mg kg-' higher than that of NO treatment on the sixth day. Fifteen days after transplanting, mineral N content of N fertilizer before transplanting treatments of S2 and S3 increased first and then decreased thereafter. By contrast, mineral N content of NO treatment showed a diminishing trend. On the fifteenth day after transplanting, the spatial distribution of mineral N in soil of all treatment was not significantly different. As the distance between plants decreased, mineral N content reduced gradually, but in the same distance, mineral N content in the soil of N fertilizer treatment was higher than that of NO treatment. The results indicated that N fertilizer before transplanting had positive effect on rice N accumulation and NUE. It also significantly increased tiller number at the stage of N-n and rice yield. Compared with other treatments, the NM treatment showed the largest influence, with basal-tillering NUE, total NUE, and rice yield being 15%, 12%, and 529.5 kg ha-' higher than those of NO treatment. It is emphasized that the amount of N fertilizer before transplanting must be calculated exactly to improve the N distribution,NUE, and subsequently grain yield.

Acknowledgements The study was supported by the National Commissariat Fertility TechnologiesProgram, China (2004BA520A03, BE2004387).

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