Rice yield, nitrogen utilization and ammonia volatilization as influenced by modified rice cultivation at varying nitrogen rates

doi:10.4236/as.2010.11002

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Vol.1, No.1, 10-16 (2010)s

doi:10.4236/as.2010.11002

Agricultural Science

Rice yield, nitrogen utilization and ammonia

volatilization as influenced by modified rice cultivation

at varying nitrogen rates

Limei Zhao1,2, Lianghuan Wu1*, Cunjun Dong3, Yongshan Li4

1Ministry of Education Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and

Resource Sciences, Zhejiang University, Hangzhou, China; *Corresponding Author: [email protected]

2College of Ecology and Environmental Science, Inner Mongolia Agricultural University, Huhhot, China

3College of Agriculture & Biotechnology, Zhejiang University, Hangzhou, China

4Cotton Research Institute, Shanxi Academy of Agricultural Sciences, Yuncheng, China

Received 15 March 2010; revised 5 April 2010; accepted 10 April 2010.

ABSTRACT

Field experiments were conducted in 2006 to

investigate the impacts of modified rice cultiva-

tion systems on: grain yield, N uptake, ammonia

volatilization from rice soil and N use efficiency

(ANUE, agronomic N use efficiency; and PFP,

partial factor productivity of applied N). The tri-

als compared rice production using modified

methods of irrigation, planting, weeding and

nutrient management (the system of rice inten-

sification, SRI) with traditional flooding (TF).

The effect s of differen t N application rates (0, 80,

160, 240 kg ha-1) and of N rates interacting with

cultivation methods were also evaluated. Grain

yields ranged from 5.6 to 6.9 t ha-1 with SRI, and

from 4.0 to 6.1 t ha-1 under TF management. On

average, grain yields under SRI were 24% higher

than that with TF. Ammonia volatilization was

increased significantly under SRI compared

with TF and the average total amount of ammo-

nia volatilization loss during the rice growth

stage under SRI was 22% higher than TF. With

increases in application rate, N uptake by rice

increased, and the ratio of N in the seed to total

N in the plant decreased. Furthermore, results

showed that higher ANUE was achieved at a

relatively low N fertilizer rate (80 kg ha-1 N) with

SRI. Results of these studies suggest that SRI

increased rice yield and N uptake and improved

ammonia volatilization loss from rice soil com-

pared with TF. Moreover, there were significant

interactions between N application rates and

cultivation methods. We conclude that it was

the most important to adjust the amount of N

application under SRI, such as reducing the

amount of N application. Research on effects of

N fertilizer on rice yield and environmental pol-

lution under SRI may be worth further studying.

Keywords: Ammonia Volatilization; N Use

Efficiency; Paddy Soil; Rice Yield; The System of

Rice Intensification

1. INTRODUCTION

Nitrogen (N) is the most important nutrient in irrigated

rice production [1], and current high yields of irrigated

rice are usually associated with large applications of

fertilizer N [2] . China is currently the world’s largest

consumer of nitrogen fertilizers, accounting for 35% of

the global N fertilizer consumption [3], and about 7% N

was applied to irrigated rice [4]. Nitrogen use efficiency

for rice is lower about 30-35% and with N losses up to >

50% in China [5]. The unique condition of the paddy can

promote N losses through denitrification, ammonia vola-

tilization and leaching, and N losses not only lead to

decrease in N fertilizer efficiency but also to soil, water

and atmospheric pollution. Therefore, the measurement

and assessment of N losses and increased N use effi-

ciency have been of great significance for sustainable

agriculture and environmental protection. Ammonia vo-

latilization is the major process of N losses in irrigated

rice, accounting for 0.41-40% of applied N as urea in

China [6]. Ghosh and Ravi reported that ammonia vola-

tilization losses in flooded soil ranged from negligible

amounts to 60% of applied N [7]. The impact of ammo-

nia volatilization losses on environmental quality has

attracted a great deal of attention [6,8].

In addition, irrigation plays a critical role in the ability

of the rice sector to expand production to meet continu-

ally growing demand [9] since about 75% of rice pro-

duction in the world comes from irrigated lowland rice

fields [10]. China’s 31.7 million ha of rice fields account

for about 20% of the world’s rice area and produce about

L. M. Zhao et al. / Agricultural Sciences 1 (2010) 10-16

35% of total rice production [11]. However, fresh water

for irrigation is becoming scarce because of increasing

competition from urban and industrial demand [12-14].

Water resource limitations threaten the sustainability of

irrigated rice systems in many countries, and wa-

ter-saving rice cultivation methods are urgently needed

to keep up with future food demands. Water-saving rice

cultivation is important for rice production systems in

the future.

A water-saving rice cultivation method known as the

System of Rice Intensification (SRI) has been introduced

into China from Madagascar where rice productivity is

reportedly increased by simultaneously modifying sev-

eral practices in rice cultivation [15]. With SRI, changes

in standard management practices include: transplanting

very young seedlings at the 2-3 leaf stage; having just

one seedling per hill with wider spacing in a square pat-

tern rather than rows; maintaining non-flooded soil con-

ditions during the vegetative stage and very shallow ir-

rigation after flowering; soil-aerating hand weeding; and

application of large quantities of organic manure [15,16].

SRI alters the environment for growing rice with no

standing water during the vegetative growth period and

only a thin layer of water on the field (1-2 cm) from

panicle initiation until 10-15 days before harvest. These

practices may be influence on nutrient form in soil and

nutrient uptake and utilization by rice. Lower nitrogen

efficiency with conventional plant/soil/nutrient man-

agement and high nitrogen losses from the soil/plant

system, adversely affecting environmental quality, has

attracted a great deal of attention. However, there is little

information about what happens (specifically, N use ef-

ficiency and N losses as ammonia) with SRI practices.

The objective of this study was to evaluate the impact of

different rice cultivation methods and nitrogen fertiliza-

tion rates on rice yield, N uptake, and N-use efficiency

and ammonia loss.

2. MATERIALS AND METHODS

2.1. Site Description

Located in the northern part of Zhejiang Province, east-

ern China, field experiment was conducted on the farm

of Zhejiang University, Huajia Chi Campus in Hangzhou

(30°16′N, 120°12′E). The elevation is 4.3 m. At the ex-

perimental site, the Hungson paddy soil (clay loamy

typic-hapli-stagnic anthrosol) has a pH of 6.8, organic

matter of 11.2 g kg-1, available N of 104.8 mg kg-1, Ol-

sen-P of 83.6 mg kg-1, and available K of 65.2 mg kg-1.

2.2. Experimental Design, Fertilization and

Cultural Practices

The field experiment utilized a split-plot design with

cultivation methods as main plots (traditional flooding =

TF, or system of rice intensification = SRI), and N rates

as subplots, all with three replications. The subplots

(5.5 m × 4.2 m = 23.1 m2) of the main TF and SRI plots

received, respectively, either 0 kg N ha-1, 80 kg N ha-1,

160 kg N ha-1 or 240 kg N ha-1. 60% of the total N ap-

plication as basal fertilizer (on May 19) was applied (as

urea) one day before transplanting; then 20% of the total

N was applied as tillering fertilizer on June 29 and as

booting fertilizer on July 29, respectively. Other fertiliz-

ers applied were 54 kg P2O5 ha-1 (as calcium phosphate)

and 67.5 kg K2O ha-1 (as potassium chloride), incorpo-

rated one day before transplanting as basal fertilizer.

All plots were surrounded by consolidated bunds lined

with plastic sheets installed to a depth of 0.3 m to pre-

vent seepage between plots. Land preparation for both

TF and SRI was the same, with wet tillage and harrow-

ing. Seedlings of 13 days age for SRI and 20 days age

for TF were transplanted with one seedling per hill.

Transplanting spacing between hills was different: 25 cm

× 30 cm for SRI, and 25 cm × 17 cm for TF; plant popu-

lations, respectively, were 13.3 and 23.5 m-1. A japonica

rice variety was used (Bing 98110) transplanted on 13

May and harvested on 13 October.

TF plots were continuously flooded with 2-10 cm wa-

ter depth except at the end of the tillering stage, when

plots were drained 7 days before harvest. SRI plots were

kept saturated the first week after transplanting; thereaf-

ter they were maintained in a moist condition without

standing water covering the field until 15 days after pa-

nicle initiation when a thin layer (2 cm) of water was

maintained. Each main plot was irrigated separately,

with water supplied every 3-7 days, depending on am-

bient temperature affecting evapotranspiration. Irriga-

tion water was provided from a tap to a depth of 2 cm

each time, as measured by a plastic ruler inserted into

the plot.

2.3. Ammonia Sampling and Chemical

Analysis

Ammonia volatilization from soil in rice field was de-

termined by venting method, and the instrument used is

shown in Figure 1 [17]. The diameter and height of the

Figure 1. Design of instrument for collecting

ammonia volatilization from the soil surface.

15 cm

L. M. Zhao et al. / Agricultural Sciences 1 (2010) 10-16

PVC cylinder was 15 cm and 30 cm, respectively. Two

pieces of sponge (2.5 cm thickness) were installed in a

PVC cylinder after being immersed with 15 ml glycerol

phosphoric acid (5%, v/v, phosphoric acid and 4%, v/v,

glycerol). The base of the cylinder was inserted 2 cm

into the soil. The lower sponge was 20 cm distance of

the soil surface and used to absorb ammonia volatilized

from the soil surface in the cylinder, and the upper

sponge was 5.0 cm distance of the lower sponge and was

to absorb ammonia from outside the cylinder and to

prevent its absorption by the lower sponge. After fertil-

izer was applied, the instrument was installed immedi-

ately. Within one week after fertilization, the lower

sponge was replaced with a new one after 24 h, and after

one week, the lower sponge was replaced with a new

one after 48 h. The upper sponge was changed every 3

days. The sponges were extracted with 300 ml of 1 mol/L

KCl for 1 h and analyzed N content by nitrogen auto

analyzer (KDN-102C, China).

2.4. Statistical Analysis

Analysis of variance (ANOVA) was performed on a

split-plot design with cultivation methods as the main

factor and N rates as the sub-factor. When cultivation

methods or N rates effects were significant, pair-wise-

testing with the t-test was done between cultivation

methods or among N rates. The level of confidence was

set at 95%. Statistical procedures were conducted using

the data processing system software [18].

3. RESULTS

3.1. Effects of SRI and N Fertilizer Rate on

Grain Yield

Grain yield ranged from 5.6 to 6.9 t ha-1 under SRI, and

from 4.0 to 6.1 t ha-1 under TF (Table 1). The maximum

grain yield was at N1 level (80 kg N ha-1) under SRI and

at N2 level (160 kg N ha-1) under TF. SRI significantly

increased grain yield compared to TF in N0 and N1;

however, there was no significant difference at N2 and

N3 levels. Over the whole range of N application rates,

SRI gave on average yields 22% higher than TF using

much less irrigation water.

At maturity, grain yield was determined as the mean

of two 5-m2 samples per sub-plot. Plant samples were

taken from 5 hills in every sub-plot to determine the

amount of aboveground biomass after the samples were

dried at 70◦C. Total N content was determined using the

standard Kjeldahl method.

Agronomic N use efficiency (ANUE, kg grain kg N

applied-1) was calculated from the difference in grain

yields N between fertilized and unfertilized plots divided

by the N application rate. Partial factor productivity of

applied N (PFP, kg grain kg N applied-1) was calculated

as grain yields divided by the N application rate.

3.2. N Uptake by Rice and Distribution in

Different Organs

SRI plants had greater N uptake than TF plants (Figure

2). N uptake by rice ranged from 308.8 to 596.4 mg

Table 1. Grain yield of rice under SRI and TF with N rates (n = 3).

Grain yield (t ha-1)

N (kg ha-1) TF SRI Difference

0 (N0) 4.0 b 5.6 b 1.6

80 (N1) 4.9 a 6.9 b 2.0

160 (N2) 6.1 a 6.7 a 0.6

240 (N3) 5.7 b 6.1 a 0.4

Analysis of variance

Cultivation

N level

Cultivation × N rates **

Notes: Values followed by the same letter in a column are not significantly different at the 5% level by LSD; ns = not significant; * = P <

0.05; ** = P < 0.01 between SRI and TF.

200

400

600

800

1000

1200

N0 N1 N2 N3N0 N1 N2 N3

TF SRI

N uptake (mg plant

-1

)

Leaf Stem and sheathsPanic le

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

N0 N1 N2 N3N0 N1 N2 N3

TF SRI

N distribution in different organ

(a) (b)

Notes: The same letter within different N rate under SRI and TF are not significantly different by LSD at the 0.05 level.

Figure 2. N uptake and distribution in stem and sheaths, leaf and panicle at maturing stage.

L. M. Zhao et al. / Agricultural Sciences 1 (2010) 10-16

plant-1 under TF and ranged from 673.1 to 957.4 mg

plant-1 under SRI management. SRI significantly in-

creased total N uptake by individual plants, and N up-

take by leaves, stem-sheaths and panicle irrespective of

the N application rate compared to TF. Total N per plant,

N uptake by leaves and stem-sheaths increased with in-

creased N application rate; however, maximum amount

of N uptake in panicle was in N2 level and then de-

creased under both SRI and TF when N applications

were higher (Figure 2(a)). The ratio of N in leaves and

stem-sheaths to total N uptake increased with increased

N rate, while the ratio of N in panicle to total N uptake

decreased (Figure 2(b)).

3.3. Effects of SRI and N Fertilizer Rate on

Nitrogen Use Efficiency

The interactive effects of cultivation methods and N rate

on ANUE and PFP were significantly different. Values

of agronomic N use efficiency (ANUE) ranged from 7.1

to 12.6 kg grain kg-1 N applied under TF, and from 2.1 to

15.7 kg grain kg-1 N applied under SRI (Table 2). Values

for partial factor productivity of applied N (PFP) ranged

from 23.9 to 61.3 kg grain kg-1 N applied under TF, and

25.5 to 86.0 kg grain kg-1 N applied under SRI. Com-

pared with TF, ANUE with SRI methods was higher in

N1 and lower in N2 and N3. However, PFP under SRI

was higher than TF in each N treatment. N application

and cultivation methods significantly influenced ANUE

and PFP.

3.4. Effects of SRI and N Fertilizer Rate on

Ammonia Volatilization

Changes in ammonia volatilization rate at basal, tillering

and booting stages under both SRI and TF treatments

were similar (Figure 3), and the highest rate appeared 4

days after basal and tillering fertilization and 3 days after

booting fertilization, respectively. The total amount of

ammonia volatilization loss ranged from 2.14 to 13.13

kg ha-1 under TF and from 3.14 to 16.23 kg ha-1 under

SRI, respectively. This accounted for 3.2-5.3% and

3.9-5.8% of the total N applied (Ta b l e 3). Total ammo-

nia volatilization loss increased by 23.6~46.7% with SRI

compared to TF. N fertilizer input significantly led to

higher ammonia volatilization rate and loss than the

N-zero controls for both TF and SRI.

4. DISCUSSION

4.1. Grain Yield

Compared to TF, SRI significantly increased grain yield.

This may be attributed to the increase of the number of

Table 2. Agronomic N use efficiency (ANUE, kg grain kg N applied-1) and partial factor productivity of applied N (PFP,

kg grain kg N applied-1) under SRI and TF with N rate (n = 3).

ANUE PFP

N (kg ha-1)

TF SRI Difference TF SRI Difference

80 (N1) 10.6 a 15.7 a 5.1

** 61.3 a 86.0 a 24.7

160 (N2) 12.6 a 7.0 b -5.6

** 37.9 b 42.1 b 4.2

240 (N3) 7.1 b 2.1 c -5.0

** 23.9 b 25.5 c 1.6

Analysis of variance ANUE PFP

Cultivation * **

N level ** **

Cultivation × N rate ** **

Notes: Values followed by the same letter in a column are not significantly different at the 5% level by LSD; ns = not significant; *

= P < 0.05; ** = P < 0.01.

Table 3. Ammonia volatilization losses after N fertilizer application at basal, tillering and booting stages (kg N ha-1) (n = 3).

ultivation N rates Basal fertilizer Tillering fertilizer Booting fertilizer Total NH3 loss

TF N0 1.02 a 0.80 a 0.32 a 2.14 a

N1 3.77 b 1.58 b 1.08 b 6.44 b (5.37)

N2 4.91 c 3.03 c 1.84 c 9.78 c (4.77)

N3 6.33 d 4.19 d 2.61 d 13.13 d (4.58)

SRI N0 1.38 a 1.03 a 0.72 a 3.14 a

N1 4.22 b 1.98 b 1.67 b 7.88 b (5.93)

N2 6.06 c 3.65 c 2.48 c 12.19 c (5.66)

N3 7.78 d 5.04 d 3.41 d 16.23 d (5.45)

Notes: Values followed by the same letter within one column are not significantly different by LSD at the 0.05 level under the same cul-

tivation system. The number in parentheses indicated the percentage of the amount of applied N.

L. M. Zhao et al. / Agricultural Sciences 1 (2010) 10-16

100

120

1234567912345679 12345679

Bas alTilleringBoo tin g

Days after fertilize

volatilization rate (mg N m

-2

-1

)

SRI

Figure 3. Average ammonia volatilization rates with four N

rates after N fertilizer application at basal (May 19), tillering

(June 29) and booting (July 29) stage under SRI and TF.

tiller and effective panicles and higher chlorophyll [19];

furthermore, the leaf N content (chlorophyll SPAD) is

closely related to photosynthetic rate and biomass pro-

duction [20]. Another explanation was SRI had greater

root activity and delayed root and leaf senescence during

later growth stages according to research [21,22].

The interactive effects on grain yield between cultiva-

tion and N rate was significant. The yield-increasing ef-

fect with SRI was affected by N fertilizer applied, and the

maximum yield difference in grain yield was in N1 (80

kg ha-1) level, and there were no significantly difference

at N2 (160 kg ha-1) and N3 (240 kg ha-1) level. These

results were explained that SRI plots likely had higher N

uptake from the indigenous supply due to the changes in

the environment for growing rice and had a better root

system under SRI. The SRI changes the environment of

rice growth from anaerobic to aerobic soil conditions,

with no standing water during the vegetative growth pe-

riod and only a thin layer of water on the field (1-2 cm)

from panicle initiation until 10-15 days before harvest.

These practices may affect the structure and functioning

of soil biota, nutrient status and cycling, and root system.

Bonkowski [23] indicated that under more aerobic soil

conditions, there will be larger populations of soil mi-

crobes that contribute to biological processes for supply-

ing N needs of plants. Hence, yield increase with SRI

should not rely on increased nitrogen application, the

moderate water requirements and nitrogen management

under SRI should be paid more attention.

4.2. N Uptake and Utilization

SRI increased the ratio of panicle N among four N fer-

tilizer levels compared with TF. ANUE and PFP both

decreased with increased N application rates, while the

ANUE in N2 (80 kg ha-1) level was at a maximum under

SRI. These results showed that SRI methods benefited

nitrogen uptake by rice and could promote the transfer of

nitrogen in leaves and stem-sheaths to the panicle, while

high-levels of nitrogen may have resulted just in luxury

uptake of N by rice. These results were supported by

other research [24,25]. Abha and Salokhe [26] indicated

that younger seedlings performed better than older seed-

lings when transplanted into either flooded or non-

flooded soils with greater uptake of nitrogen and man-

ganese than older seedlings. Higher available N in soil

resulting higher N uptake from soil under SRI manage-

ment compared to TF due to increased root biomass and

activity with SRI [21,25], while higher soil microbial

activity contributed to soil processes for supplying

plants’ nitrogen needs [23]. This was supported by Ru-

pela et al. [27] who reported that microbial biomass N,

microbial biomass carbon, dehydrogenase, root mass,

root density and root volume were higher under SRI than

in flooded rice.

4.3. Ammonia Vocalization Loss

N fertilizer significantly increased ammonia volatiliza-

tion loss of both SRI and TF, and ammonia volatilization

loss increased generally with higher N fertilizer rate. The

greatest loss of ammonia volatilization for both SRI and

TF was at the basal stage, next was at tillering stage, and

the smallest loss was at booting stage. This may suggest

that largest ammonia volatilization was affected by high

N fertilizer input and the different ratios of N fertilizer

applied at basal, tiller and booting stage. Higher ammo-

nia volatilization loss at basal stage was due to the root

systems having little sink capacity for N so early in the

crop cycle [28], especially with transplanting young

seedlings (about 15 days old) in our study. Though same

amount of N fertilizer was applied at tillering and boot-

ing stage, there is less loss at booting stage than tillering

stage, suggesting that at booting stage, well-developed

canopies reduced the ammonia volatilization loss due to

lower ammonia gas concentrations and restricted air

movement. Therefore, such results indicated that opti-

mum ratio of N fertilizer at different stages was impor-

tant to reduce ammonia volatilization losses.

Ammonium volatilization is consistently higher under

SRI than TF, suggesting a potentially more intensive N

loss under SRI, though with no significant difference

between both. This may suggest that non-flooded rice

led to higher concentration of NH4

+ in the soil and soil

solution than with flooding, which may have benefited

the long-term nitrogen availability for rice growth under

SRI. There was a significant correlation between NH4

in the soil, soil solution and ammonia volatilization loss

[29]. Cui et al. [30] have reported that ammonia volatili-

zation loss under water-saving irrigation was higher by

22.9% than with continuous flooding. Moreover, trans-

planting young seedlings with wider spacing under SRI

could be another reason to create higher ammonia vola-

tilization loss.

5. CONCLUSIONS

Our results showed that the highest grain yield of rice,

L. M. Zhao et al. / Agricultural Sciences 1 (2010) 10-16

ANUE and PFP were achieved at a relatively low rate of

N fertilization (80 kg ha-1 N) under the system of rice

intensification (SRI). SRI significantly increased N up-

take during rice growth and promoted N translocation to

the panicle. Though SRI caused higher ammonium vola-

tilization loss than TF, the percentage of loss at 80 kg

ha-1 N is at the similar magnitude to that at higher N fer-

tilizer input rates (160~240 kg ha-1), which were charac-

terized by the decreasing grain yield and N use effi-

ciency (Tables 1-3). To increase N use efficiency and to

decrease N losses, as well as to maintain or improve soil

fertility for sustainable crop production, research efforts

are needed to focus on the effects of SRI on soil fertility

and nitrogen management. Due to the increasing fertil-

izer costs, irrigation water shortages, and growing pollu-

tion/environmental problems in the future decades, the

current study can help further investigate the different

cultivation system and fertilization strategy for the sake

of sustainable rice production and soil management at a

single-season experiment and long-term purpose.

6. ACKNOWLEDGEMENTS

This research was supported by the Key Project of Agricultural Con-

struction Adjustment of Ministry of Agriculture of China (No. 2003-

01-02A), Key Project of Ministry of Science and Technology of China

(2008ZX07101-006) and Key Projects in the National Science & Tech-

nology Pillar Program (No. 2008BADA4B03).

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