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Estimation of methane and nitrous oxide emissions from paddy fields in Taiwan

Shang-Shyng Yang

a

,

b

,

*

, Chao-Ming Lai

c

, Hsiu-Lan Chang

b

, Ed-Huan Chang

b

, Chia-Bei Wei

b

aDepartment of Biochemical Science and Technology, National Taiwan University, Taipei 10617, Taiwan bInstitute of Microbiology and Biochemistry, National Taiwan University, Taipei 10617, Taiwan cDepartment of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan

a r t i c l e

i n f o

Article history:

Available online 20 January 2009 Keywords: Methane Nitrous oxide Paddy field Intermittent irrigation IPCC

a b s t r a c t

To investigate the greenhouse gases emissions from paddy fields, methane and nitrous oxide emissions were estimated with the local measurement and the IPCC method during 1990–2006 in Taiwan. Annual methane emission ranged from 9001 to 14,980 ton in the first crop season for 135,314–242,298 ha of paddy fields, and it was between 16,412 and 35,208 ton for 101,710–211,968 ha in the second crop season with the local measurement for intermittent irrigation. The value ranged from 31,122 to 55,729 ton of methane emission in the first crop season, and it was between 29,493 and 61,471 ton in the second crop season with the IPCC guideline for continuous flooding. Annual nitrous oxide emission from paddy fields was between 371 and 728 ton in the first crop season, and the value ranged from 163 to 365 ton in the second crop season with the local measurement. Methane emission from paddy fields in Taiwan for intermittent irrigation was only 26.72–28.92%, 55.65–57.32% and 41.19–43.10% with the IPCC guidelines for continuous flooding and mean temperature of transplanting stage in the first crop, the second crop and total paddy fields, respectively. The values were 53.44–57.84%, 111.29–114.55% and 82.38–86.20% with the IPCC guidelines for single aeration and mean temperature of transplanting stage, respectively; and the values were 133.60–144.61%, 282.56–286.62% and 205.96–215.49% with the IPCC guidelines for multiple aeration and mean temperature of transplanting stage, respectively. Intermittent irrigation in paddy fields reduces methane emission significantly; appropriate application of nitrogen fertilizer and irrigation in paddy fields also decreases nitrous oxide emission.

Ó 2008 Published by Elsevier Ltd.

1. Introduction

Global warming induced by increasing greenhouse gases

concentrations in the atmosphere is a matter of great

environ-mental concern. Methane, carbon dioxide, nitrous oxide and

chlo-rofluorocarbons (CFCs) are the greenhouse gases, which have strong

infrared absorption bands and trap part of the thermal radiation

from the earth’s surface. Concentrations of carbon dioxide,

methane, nitrous oxide and CFCs increased from 337 to 360, 1.50 to

1.72, 0.302 to 0.320, and 4.68  10

4

to 7.69  10

4

g m

3

,

respec-tively, during last decade in the atmosphere

[1]

.

About 80% of methane is produced biologically and the major

source sites are rice paddy, wetland, sediment, enteric

fermenta-tion, animal wastes treatment, agricultural waste burning,

savannah burning, landfill and sewage treatment under low redox

potential conditions by obligate anaerobes

[2–12]

. The release of

nitrous oxide was increasing in recent years due to more intensive

agricultural practices. Denitrification of heterotrophic microbes in

oxygen deficient environments, nitrification of autotrophic and

heterotrophic nitrifying microbes and dissimilate nitrate to

ammonium of heterotrophic microbes in aerobic conditions

produced nitrous oxide

[13]

. The contribution of agriculture to the

global annual nitrous oxide emission was estimated at

approxi-mately 35%

[14]

.

In Taiwan, there were 263,188 ha of paddy fields and more than

4 million tons of crop residues in 2006. Rice was cultivated with

intermittent irrigation in Taiwan, while continuous flooding was

used in other countries. There are two crop seasons in Taiwan, the

first crop season is cultivated in February and harvested in July, and

the second crop season is cultivated in August and harvested in

December. Estimation of methane and nitrous oxide emissions

from paddy fields during 1990–2006 with the country-specific

emission factors were used, whereas the local data were

unavail-able and the emission factors recommended by the IPCC guideline

[15,16]

were used.

*Corresponding author. Department of Biochemical Science and Technology,

National Taiwan University, Taipei 10617, Taiwan. E-mail address:ssyang@ntu.edu.tw(S.-S. Yang).

Contents lists available at

ScienceDirect

Renewable Energy

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / r e n e n e

0960-1481/$ – see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.renene.2008.12.016

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2. Materials and methods

2.1. Cultivation area

Cultivation areas of paddies in Taiwan from 1990 to 2006 are

adapted from the Taiwan Agriculture Yearbook from 1991 to 2007

[17,18]

.

2.2. Measurement of methane and nitrous oxide emissions

Methane and nitrous oxide emissions were measured by

home-made acrylic chamber (length 40 cm, width 40 cm and height

65 cm, about 96 l)

[19]

. Methane and nitrous oxide were analyzed

by gas chromatograph using FID and ECD, respectively

[20]

.

2.3. Methane and nitrous oxide emission factors of paddy fields

Methane and nitrous oxide emission factors from paddy fields of

Taiwan were measured by the local measurement and listed in

Table 1

. Other emission factors were recommended by the IPCC

guidelines

[15]

. Most of the paddies were applied chemical

fertil-izers; only the organic paddies production used organic fertilizers.

2.4. Estimation of methane and nitrous oxide emissions

Methane and nitrous oxide emissions from paddy fields were

calculated from the experimental data and estimated by the

following equation at each growth stage

[7,32]

.

F [ ðV=AÞð

D

C=

D

Where F is the methane or nitrous oxide emission rate

(mg m

2

h

1

), V is the volume of chamber above the soil (m

3

), A is

the cross-section of chamber (m

2

),

D

C is the concentration

difference between zero time and time t (mg m

3

), and

D

t is the

time duration between two sampling period (h). The total

methane or nitrous oxide emission from paddy fields was the

summation of methane and nitrous oxide emissions in all growth

stages of crops.

Table 1

Greenhouse gas emission from paddy fields.

Location Treatment Methane emission Nitrous oxide emission

1st crop 2nd crop 1st crop 2nd crop Full year

g m2

NTU Exper. Station Inter. irrigation 2.55–11.70k 13.73k 0.30–0.39g 0.07–0.75g

Cont. flooding – 28.85k

Taoyuan Dist. AIS Inter. irrigation 1.73–5.23k 10.54–10.56k 0.44–0.54g 0.06–0.40g

W/green manure 5.55k 14.43–30.12k 1.22g

Miaoli farm Inter. irrigation 9.82k 39.50k

NCHU Exper. Station Inter. irrigation 8.18j 1.18j

0.11–0.60a 0.11–0.50a 0.22–1.25a

0.61b

Huatan-CH farm Inter. irrigation 9.00–19.80c,l 12.03–33.11c,l 0.32h 0.48–0.52h,l

Inter. irrigation – 4.76l 0.27l

Chihu-CH farm Inter. irrigation 0.15j 10.45j 0.05–1.11a

Chihu-CH farm Inter. Irrigation 23.06c

Tachen-CH farm Inter. Irrigation 0.94g

Tienwei-CH farm Inter. Irrigation 0.59b

Chiayi farm Inter. irrigation 3.48j 10.17j 0.24–0.99a

Lutsao-Chiayi Inter. Irrigation 4.78d 35.27d 0.44b

Inter. Irrigation 9.20e 49.00e

W/burned rice straw 4.10d 41.79d

W/rice straw 5.72d 80.62d

W/chicken manure 66.90e

W/soybean cake 46.65e

W/rice bran 14.89e

Cont. flooding 55.80e 84.50e

Kaohsiung Dist. AIS Inter. irrigation 2.36j 8.47j 0.05–1.14a

Inter. Irrigation 0.49e

Hwalien-Lotung AIS Inter. irrigation 2.92k 24.64k 0.35–0.78g 0.0–0.06g

Hwalien-Chian AIS Inter. irrigation 1.42–2.42i 0.26–2.33i

W/rice straw 2.77–2.85i 3.13–7.60i

Hwalien-Fuli AIS Inter. irrigation 7.40–13.10i 12.50–24.30i

W/high N fertile. 11.60–19.73i 21.14–48.37i

IPCC Cont. flooding 23f 29f

Single drain 11.50f 14.50f Multiple drains 4.6f 5.8f aChao[21]. b Chao[22]. c Chen et al.[23]. d Huang et al.[24]. e Huang et al.[25]. f IPCC[15]. g Lai[26]. hLai et al.[27]. i Huang et al.[28]. j Wang and Shieh[29]. k Yang and Chang[6,30].

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3. Results and discussion

3.1. Methane emission from paddy fields

There are two crop seasons for paddy rice in Taiwan. Total

growth period of paddy rice in the first crop season (February to

July) was between 122 and 149 days, and it ranged from 112 to 135

days in the second crop season (August to December). The daily

temperature increased gradually during rice cultivation in the first

crop season, and it was reversed in the second crop season. The

mean temperature in the first crop season (February to July) was

19.17–26.25



C, and the value was 19.54–26.56



C in the second

crop season (August to December). While the mean temperature

during the transplanting stages of rice cultivation was 16.27–

24.10



C in the first crop season (February to April), and the value

was 21.20–28.37



C in the second crop season (August to October).

Most of mean temperatures in the second crop were higher than

those in the first crop except in 1991 and some areas in 1994, 1999,

2001, 2002, 2003 and 2004. This is different from the single crop

season countries such as Japan, Korea, USA and Italy

[33–36]

.

Therefore, the methane emission patterns of the two crop seasons

in Taiwan were also different from other locations with single crop

season. Methane emission was high at the active tillering, booting,

flowering and ripening stages for the active degradation of organic

Table 2

Methane emission from paddy fields in Taiwan with local measurement from 1990 to 2006 (ton).

Year Taipei, Keelung I-lan Taoyuan, Hsinchu Miaoli Taichung, Changhua, Nantou Yuanlin, Chiayi, Tainan Kaohsiung, Pingtung Taitung, Hwalien Total 1990 1st crop 265.9 319.2 989.4 1,327.8 6,161.8 4,510.8 496.0 908.6 14,979.5 2nd crop 240.4 1,371.9 3,823.0 5,372.3 6,058.6 15,009.1 1,702.5 1,631.1 35,208.4 Sub-total 506.3 1,691.0 4,812.4 6,700.1 12,220.3 19,519.9 2,198.5 2,539.7 50,187.9 1991 1st crop 206.1 286.0 934.1 1,219.0 5,800.0 4,357.4 435.7 862.9 14,101.2 2nd crop 198.8 1,272.1 3,778.9 4,828.2 5,950.1 14,104.4 1,502.4 1,526.7 33,161.6 Sub-total 404.9 1,558.1 4,712.9 6,047.1 11,750.1 18,461.8 1,938.1 2,389.7 47,262.8 1992 1st crop 167.1 288.5 909.9 1,136.3 5,648.2 3,641.9 390.9 851.5 13,034.3 2nd crop 131.1 819.7 3,587.5 4,711.2 5,675.3 13,303.0 1,233.1 1,496.0 30,956.9 Sub-total 298.2 1,108.3 4,497.3 5,847.5 11,323.5 16,944.9 1,623.9 2,347.6 43,991.2 1993 1st crop 142.1 276.7 862.7 1,079.7 5,337.4 4,272.2 357.4 798.8 13,127.0 2nd crop 96.9 754.9 3,468.9 4,388.4 5,448.4 12,952.9 1,053.0 1,451.5 29,614.9 Sub-total 239.0 1,031.5 4,331.6 5,468.1 10,785.8 17,225.1 1,410.4 2,250.3 42,741.9 1994 1st crop 99.6 278.3 723.2 1,055.4 5,077.6 3,808.2 375.3 816.4 12,234.0 2nd crop 84.4 480.4 3,185.6 4,270.2 5,187.7 12,377.6 988.7 1,457.0 28,031.6 Sub-total 184.0 758.7 3,908.8 5,325.6 10,265.3 16,185.8 1,364.0 2,273.4 40,265.6 1995 1st crop 106.2 270.2 782.5 982.6 4,923.9 4,033.6 329.4 799.0 12,227.4 2nd crop 76.8 301.5 3,239.9 4,264.1 4,985.1 12,182.0 895.9 1,543.7 27,489.0 Sub-total 182.9 571.7 4,022.3 5,246.8 9,909.0 16,215.6 1,225.3 2,342.7 39,716.4 1996 1st crop 76.0 267.5 655.9 951.3 4,777.2 3,540.9 316.5 870.2 11,455.5 2nd crop 71.9 264.7 3,115.5 3,994.9 4,875.2 12,400.8 925.8 1,632.9 27,281.7 Sub-total 147.9 532.2 3,771.4 4,946.2 9,652.4 15,941.7 1,242.3 2,503.1 38,737.2 1997 1st crop 86.5 282.6 783.1 960.1 4,923.3 4,205.9 303.7 963.9 12,509.1 2nd crop 64.4 207.3 3,231.5 4,102.1 4,787.6 11,886.0 813.4 1,728.0 26,820.3 Sub-total 150.9 489.8 4,014.5 5,062.2 9,710.9 16,091.9 1,117.1 2,691.9 39,329.4 1998 1st crop 72.0 275.2 792.5 956.0 4,782.2 4,260.3 305.5 977.0 12,420.7 2nd crop 60.7 29.1 3,108.1 3,886.5 4,624.2 11,759.0 720.2 1,677.9 25,865.7 Sub-total 132.7 304.3 3,900.7 4,842.4 9,406.4 16,019.3 1,025.8 2,654.9 38,286.4 1999 1st crop 67.1 272.7 747.1 897.7 4,680.9 4,174.5 303.5 970.9 12,114.4 2nd crop 53.2 76.5 2,821.6 3,776.8 4,639.2 11,910.1 789.2 1,745.6 25,812.2 Sub-total 120.3 349.2 3,568.7 4,674.6 9,320.1 16,084.6 1,092.7 2,716.5 37,926.6 2000 1st crop 62.7 268.0 710.4 904.0 4,518.1 4,252.0 317.7 978.6 12,011.5 2nd crop 50.0 42.6 2,461.2 3,245.3 4,449.9 11,095.6 695.9 1,693.3 23,734.7 Sub-total 112.7 310.6 3,171.6 4,149.3 8,968.0 15,347.6 1,013.6 2,671.9 35,745.3 2001 1st crop 56.8 258.9 667.6 853.1 4,499.4 4,078.3 307.3 917.8 11,639.2 2nd crop 49.7 8.5 2,325.6 2,889.6 4,485.3 11,304.4 656.4 1,726.6 23,446.1 Sub-total 106.6 267.4 2,993.2 3,742.7 8,984.8 15,382.7 963.8 2,644.5 35,085.3 2002 1st crop 50.9 236.3 538.6 723.1 4,430.7 3,939.3 289.8 946.0 11,154.7 2nd crop 43.8 7.2 1,714.6 2,790.9 4,257.3 10,354.1 518.1 1,587.6 21,273.6 Sub-total 94.7 243.5 2,253.2 3,514.0 8,688.1 14,293.4 807.9 2,533.6 32,428.3 2003 1st crop 42.0 234.0 269.5 743.7 4,309.1 3,637.1 286.5 900.3 10,422.2 2nd crop 40.1 0.3 1,136.9 2,305.3 3,843.3 9,000.5 425.5 1,476.0 18,227.9 Sub-total 82.1 234.3 1,406.4 3,049.0 8,152.4 12,637.6 712.0 2,376.3 28,650.1 2004 1st crop 39.6 215.9 133.9 546.4 4,181.3 2,733.4 270.9 879.8 9,001.1 2nd crop 43.4 0.8 944.0 2,039.3 3,760.0 7,786.7 323.6 1,514.0 16,411.7 Sub-total 83.0 216.7 1,077.8 2,585.7 7,941.3 10,520.1 594.4 2,393.8 25,412.8 2005 1st crop 38.2 215.2 342.9 654.6 4,247.0 3,560.0 268.9 879.7 10,206.5 2nd crop 39.1 0.3 1,103.2 2,305.7 3,866.4 9,133.9 295.9 1,544.3 18,288.8 Sub-total 77.3 215.5 1,446.1 2,960.3 8,113.4 12,693.9 564.7 2,424.0 28,495.3 2006 1st crop 33.0 215.1 287.8 620.7 4,188.9 3,591.1 243.5 906.4 10,086.5 2nd crop 33.6 0.5 886.5 2,135.1 3,730.0 9,357.3 219.0 1,580.0 17,942.0 Sub-total 66.6 215.6 1,174.3 2,755.8 7,918.9 12,948.4 462.5 2,486.4 28,028.5 Average 1st crop 94.8 262.4 654.8 918.3 4,852.2 3,917.5 329.3 895.8 11,924.6 2nd crop 81.1 331.7 2,584.3 3,606.2 4,742.6 11,524.6 809.3 1,589.0 25,268.8 Sub-total 175.9 594.1 3,239.1 4,524.5 9,594.8 15,442.1 1,138.6 2,484.8 37,193.4

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matter and high concentration of root secretes

[6,7]

. However,

drainage was practiced at the flowering and ripening stages in the

intermittent irrigation system, and the methane emission rate

decreased at these stages. Methane emission was high at the

flooding and the transplanting stages in the second crop season for

organic matter degradation with high temperature. While methane

emission was low at the flooding and the transplanting stages in the

first crop season for low temperature, and it was also low at the

flowering and the ripening stages for the intermittent irrigation

and high redox potential repressed methane emission. Therefore,

methane emission from paddy field in the second crop season was

higher than those in the first crop season.

Methane emission was between 0.15 and 19.80 g m

2

with

intermittent irrigation in the first crop season, and it ranged from

1.18 to 49.00 g m

2

in the second crop season. Methane emission

increased with green manure, burn rice straw, rice straw, rice bran,

soybean cake and chicken manure amendment. It was 1.06–3.20,

0.86, 1.18–1.95, and 1.62 times higher than those with intermittent

irrigation and convention chemical fertilizer application for green

manure, burn rice straw, rice straw and rice bran amendment in the

first crop season, respectively; and the value was 1.36–2.85, 1.18,

1.34–3.26, 1.37, and 0.95 times higher than those with intermittent

irrigation for green manure, burn rice straw, rice straw, chicken

manure and soybean cake amendment in the second crop season,

respectively

[6,24,25,28,30]

. High nitrogen fertilizer application

also enhanced 1.51–1.57 and 1.69–1.99 times of methane emission

higher than those with convention nitrogen chemical fertilizer

application in the first and second crop seasons, respectively

[28]

.

Green manure amendment stimulated methane emission rate and

it also increased the soil organic matter content

[6,30]

. Similar

results were also found in rice cultivated during dry and wet crop

seasons in the Philippines paddy fields

[37]

.

Methane emission factors of paddy fields at different locations

in Taiwan with the local measurement were the average of the local

measurement at different years and different paddy fields in each

location. Methane emission in the second crop season was 1.15–

12.94 times higher than those in the first crop season with

inter-mittent irrigation; the reverse was true in the pot cultivation with

continued flooding

[6,38]

. There was a 10–15 cm depth of flooding

in the soil surface during the rice cultivation in Italian, Louisiana

and California paddy fields

[4,37]

. However, the intermittent

irri-gation system was very popular in the late stage of paddy rice

cultivation in Taiwan to reduce the water resource for rice growth,

to increase the rice yield and to eliminate toxic substances in the

rice root. The accumulative methane emission was around 47–58%

lower with intermittent irrigation than with continuous flooding

treatment. Miaoli area had high methane emission due to the high

soil organic matter content

[7]

.

Cultivation area of paddy fields in the first crop was 1.14 times

higher than that of the second crop in 1990, the value increased

gradually to 1.45 times in 2003, and then the value slightly

decreased to 1.44 in 2006. Cultivation area of paddy fields in the

first crop was higher than the second crop due to the cultivation of

vegetable and upland crop, and the low rice productivity (71–91%

of the first crop) in the second crop season. Cultivation area of

paddy fields was also decreased because of the change of culture

system and agriculture policy in Taiwan. The first crop, second crop

and total cultivation area were 242,298, 211,968 and 454,266 ha in

1990, respectively and the cultivation areas decreased to 155,248,

107,940 and 263,188 ha in 2006. Taichung, Changhua, Nantou,

Yuanlin, Chiayi, and Tainan in the central Taiwan are the major

cultivation area. It had 59.06–67.71%, and 60.48–71.49% of total

paddy cultivation area in the first and the second crop, respectively,

and the ratio increased gradually due to the change of land use and

culture system in the northern and southern Taiwan.

Annual methane emission from paddy fields was calculated

with the emission factors and cultivation area at each location and

the results are illustrated in

Table 2

. Annual methane emission

decreased with the decreasing of cultivation area of rice. Total

methane emissions were 14,980 and 35,208 ton at the first and the

second crop seasons in 1990, respectively, and it decreased to

10,087 and 17,942 ton in 2006. Although the cultivation area of the

first crop was higher than that of the second crop, however,

methane emission of the second crop season was higher than that

of the first crop season. Methane emission of the second crop

season was 2.35 times higher than that of the first crop season in

1990, and the value decreased to 1.78 times in 2006 due to the

cultivation of vegetable and upland crop and the decreasing of

cultivation area of rice paddy in the second crop.

Table 3

Methane emission from paddy fields in Taiwan calculated with local measurement and IPCC guidelines from 1990 to 2006(ton).

Year Local measurement IPCC continuous IPCC single aeration IPCC multiple aeration 1990 1st crop 14,979.5 55,728.9 27,864.3 11,145.7 2nd crop 35,208.4 61,470.7 30,735.4 12,294.1 Sub-total 50,187.9 117,199.6 58,599.7 23,439.8 1991 1st crop 14,101.2 52,305.2 26,152.6 10,461.0 2nd crop 33,161.6 58,399.3 29,199.7 11,679.9 Sub-total 47,262.8 110,704.5 55,352.3 22,140.9 1992 1st crop 13,034.3 48,178.1 24,089.1 9,635.6 2nd crop 30,956.9 54,424.3 27,212.2 10,884.9 Sub-total 43,991.2 102,602.4 51,301.2 20,520.5 1993 1st crop 13,127.0 48,711.7 24,355.9 9,742.3 2nd crop 29,614.9 51,949.7 25,974.9 10,389.9 Sub-total 42,741.9 100,661.4 50,330.7 20,132.3 1994 1st crop 12,234.0 45,152.9 22,576.5 9,030.6 2nd crop 28,031.6 49,160.8 24,580.4 9,832.2 Sub-total 40,265.6 94,313.7 47,156.9 18,862.7 1995 1st crop 12,227.4 45,441.3 22,720.7 9,088.3 2nd crop 27,489.0 48,113.3 24,056.7 9,622.7 Sub-total 39,716.4 93,554.6 46,777.3 18,711.0 1996 1st crop 11,455.5 42,045.6 21,022.8 8,409.1 2nd crop 27,281.7 47,837.0 23,918.5 9,567.4 Sub-total 38,737.2 89,882.6 44,941.3 17,976.5 1997 1st crop 12,509.1 46,462.3 23,231.2 9,292.5 2nd crop 26,820.3 47,038.3 23,519.1 9,407.7 Sub-total 39,329.4 93,500.6 46,750.3 18,700.2 1998 1st crop 12,420.7 46,327.5 23,163.8 9,265.5 2nd crop 25,865.7 45,316.3 22,658.1 9,063.3 Sub-total 38,286.4 91,643.8 45,821.9 18,328.8 1999 1st crop 12,114.4 45,338.3 22,669.1 9,067.7 2nd crop 25,812.2 45,223.2 22,611.6 9,044.6 Sub-total 37,926.6 90,561.5 45,280.8 18,112.3 2000 1st crop 12,011.5 44,862.7 22,431.3 8,972.5 2nd crop 23,734.7 41,918.3 20,959.2 8,383.7 Sub-total 35,746.2 86,781.0 43,390.5 17,356.2 2001 1st crop 11,639.2 43,367.2 21,683.6 8,673.4 2nd crop 23,446.1 41,489.1 20,744.6 8,297.8 Sub-total 35,085.3 84,856.3 42,428.2 16,971.3 2002 1st crop 11,154.7 40,913.3 20,456.7 8,182.7 2nd crop 21,273.6 37,397.2 18,698.6 7,479.4 Sub-total 32,428.3 78,310.5 39,155.3 15,662.1 2003 1st crop 10,422.2 37,072.3 18,536.2 7,414.5 2nd crop 18,227.9 32,172.6 16,086.3 6,434.5 Sub-total 28,650.1 69,244.9 34,622.5 13,849.0 2004 1st crop 9,001.1 31,122.2 15,561.1 6,224.4 2nd crop 16,411.7 29,493.3 14,746.6 5,898.7 Sub-total 25,412.8 60,615.5 30,307.7 12,123.1 2005 1st crop 10,206.5 36,444.0 18,222.0 7,288.8 2nd crop 18,288.8 32,065.6 16,032.8 6,413.1 Sub-total 28,495.3 68,509.6 34,254.8 13,701.9 2006 1st crop 10,080.5 35,707.0 17,853.5 7,141.4 2nd crop 17,944.1 31,302.9 15,651.4 6,260.6 Sub-total 28,024.6 67,009.9 33,504.9 13,402.0 Average 1st crop 11,924.6 43,834.1 21,917.1 8,766.8 2nd crop 25,268.8 44,398.3 22,199.2 8,879.7 Sub-total 37,193.4 88,232.4 44,116.3 17,646.5

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Average methane emission factors from paddy fields with 52

samples in 11 locations of the world except Taiwan were

26.00 g m

2

. Hour et al.

[39]

reported the average methane

emis-sion factors from the Japan, Korea, Philippines, Thailand and Texas

were 20 g m

2

. The methane emission factors were 20 and

26 g m

2

in northern and southern Taiwan at the first crop season,

respectively; while the values were 25 and 30 g m

2

at the second

crop season, respectively. From the mean temperature of the first

and the second crop growth season, it showed that the average

temperatures of 7 locations from 1990 to 2006 were 23.93 and

24.43



C during the growth period at the first crop (February to

July) and the second crop (August to December) season,

respec-tively. While the mean temperatures during the flooding and the

transplanting stage at the first crop (February to April) and the

second crop (August to October) were 20.41 and 26.53



C,

respec-tively. Methane emission from paddy fields is high at the flooding

and the transplanting stages for the organic matter degradation

and the submerged state

[30,38]

. A positive linear correlation

between

methane

production

(Y)

and

temperature

(X)

(Y ¼ 0.22X  3.94) (r

2

¼ 0.93) between 15 and 37



C was described

in previous paper

[30]

. Therefore, the methane emission factors

calculated with the IPCC guideline and mean temperature of the

flooding and the transplanting stages are estimated as 23 and

29 g m

2

.

Annual methane emissions from the paddy fields in Taiwan with

the IPCC guideline from 1990 to 2006 are calculated in

Table 3

.

Table 4

Nitrous oxide emission from paddy fields in Taiwan with local measurement from 1990 to 2006 (ton).

Year Taipei, Keelung I-lan Taoyuan, Hsinchu Miaoli Taichung, Changhua, Nantou Yuanlin, Chiayi, Tainan Kaohsiung, Pingtung Taitung, Hwalien Total 1990 1st crop 16.05 80.49 187.87 76.85 147.54 120.96 22.99 74.93 727.68 2nd crop 1.54 1.54 57.12 24.31 116.01 99.87 60.80 3.87 365.06 Sub-total 17.59 82.03 244.99 101.16 263.55 220.83 83.79 78.80 1,092.72 1991 1st crop 12.44 72.12 177.37 70.55 138.87 116.85 20.19 71.16 679.55 2nd crop 1.27 1.42 56.46 21.85 113.94 93.85 53.66 3.63 346.08 Sub-total 13.71 73.54 233.83 92.40 252.81 210.70 18.11 74.79 1,025.63 1992 1st crop 10.09 72.76 172.77 65.76 135.24 97.66 44.04 70.22 668.54 2nd crop 0.84 0.92 53.60 21.32 108.68 88.52 62.15 3.55 339.58 Sub-total 10.93 73.68 226.37 87.08 243.92 186.18 106.19 73.77 1,008.12 1993 1st crop 8.58 69.76 163.81 62.49 127.80 114.56 16.56 65.87 629.43 2nd crop 0.62 0.85 51.82 19.86 104.33 86.19 37.61 3.45 304.73 Sub-total 9.20 70.61 215.63 82.35 232.13 200.75 54.17 69.32 934.16 1994 1st crop 6.01 70.18 137.32 61.08 121.58 102.12 17.39 67.32 583.00 2nd crop 0.54 0.54 47.59 19.33 99.34 82.36 35.31 3.46 288.47 Sub-total 6.55 70.72 184.91 80.41 220.92 184.48 52.70 70.78 871.47 1995 1st crop 6.41 68.15 148.58 56.87 117.90 108.16 15.27 65.89 587.23 2nd crop 0.49 0.34 48.40 19.30 95.46 81.06 32.00 3.67 280.72 Sub-total 6.90 68.49 196.98 76.17 213.36 189.22 47.27 69.56 867.95 1996 1st crop 4.59 67.45 124.55 55.06 114.38 94.95 14.67 71.76 547.41 2nd crop 0.46 0.30 46.54 18.08 93.35 82.51 33.06 3.88 278.18 Sub-total 5.05 67.75 171.09 73.14 207.73 177.46 47.73 75.64 825.59 1997 1st crop 5.22 71.26 148.69 55.57 117.88 112.78 14.07 79.49 604.96 2nd crop 0.41 0.23 48.28 18.56 91.68 79.09 29.05 4.10 271.40 Sub-total 5.63 71.49 196.97 74.13 209.56 191.87 43.12 83.59 876.36 1998 1st crop 4.35 69.40 150.49 55.33 114.50 114.24 14.16 80.57 603.04 2nd crop 0.39 0.03 46.43 17.59 88.55 78.24 25.72 3.99 260.94 Sub-total 4.74 69.43 196.92 72.92 203.05 192.48 39.88 84.56 863.98 1999 1st crop 4.05 68.77 141.87 51.96 112.08 111.94 14.06 80.06 584.79 2nd crop 0.34 0.09 42.15 17.09 88.84 79.25 28.19 4.15 260.10 Sub-total 4.39 68.86 184.02 69.05 200.92 191.19 42.25 84.21 844.89 2000 1st crop 3.79 67.57 134.89 52.32 108.18 114.02 14.72 80.70 576.19 2nd crop 0.33 0.05 36.77 14.69 85.21 73.83 24.85 4.02 239.75 Sub-total 4.12 67.62 171.66 67.01 193.39 187.85 39.57 84.72 815.94 2001 1st crop 3.43 65.29 126.77 49.37 107.73 109.36 14.24 75.69 551.88 2nd crop 0.32 0.01 34.74 13.08 85.89 75.22 23.44 4.10 236.80 Sub-total 3.75 65.30 161.51 62.45 193.62 184.58 37.68 79.79 788.68 2002 1st crop 3.07 59.59 102.27 41.85 106.09 105.63 13.43 78.01 509.94 2nd crop 0.28 0.01 25.62 12.63 81.52 68.89 18.51 3.77 211.23 Sub-total 3.35 59.60 127.89 54.48 187.61 174.52 31.94 81.78 721.17 2003 1st crop 2.53 59.02 51.17 43.04 103.18 97.53 13.28 74.24 443.99 2nd crop 0.26 0.00 16.99 10.43 73.59 59.89 15.20 3.51 179.87 Sub-total 2.79 59.02 68.16 53.47 176.77 157.42 28.48 77.75 623.86 2004 1st crop 2.39 54.45 25.42 31.62 99.07 73.30 12.55 72.55 371.36 2nd crop 0.28 0.01 14.10 9.23 72.00 51.84 11.56 3.60 162.60 Sub-total 2.67 54.46 39.52 40.85 171.07 125.14 24.11 76.15 533.96 2005 1st crop 2.31 54.28 65.10 37.89 100.63 95.46 12.46 72.55 440.67 2nd crop 0.25 0.01 16.48 10.43 74.04 60.81 10.57 3.67 176.25 Sub-total 2.56 54.29 81.59 48.32 174.66 156.28 23.03 76.22 616.92 2006 1st crop 1.99 54.25 53.50 35.93 99.25 96.30 11.28 74.74 427.24 2nd crop 0.22 0.01 13.24 9.66 71.43 62.30 7.82 3.76 168.43 Sub-total 2.21 54.26 66.74 45.59 170.68 158.60 19.10 78.50 595.67 Average 1st crop 5.72 66.16 124.26 53.15 115.99 105.05 16.79 73.87 560.99 2nd crop 0.52 0.37 38.61 16.32 90.82 76.69 29.97 3.78 257.07 Sub-total 6.14 66.53 162.87 69.47 206.81 181.74 46.76 77.65 818.06

(6)

Methane emission from the paddy fields in Taiwan that were

proposed by the IPCC guidelines ranged from 31,122.2 to 55,728.9,

29,493.3 to 60,615.5 and 69,244.9 to 117,119.6 ton with continuous

flooding at the first crop, the second crop and the total paddy field

during 1990 to 2006, respectively. Methane emission from the

paddy fields with the local measurement were 26.72–28.11%,

55.65–57.32% and 41.19–43.10% of those calculated with the IPCC

guideline for continuous flooding method at the first crop,

the second crop and total paddy field, respectively. However, the

intermittent irrigation management at the latter stage of rice

growth was used in Taiwan to decrease the toxic substances

accumulation in the flooding soil and the water requirement for

rice growth. Methane emissions from the paddy fields with

continuous flooding for single aeration and continuous flooding for

multiple aerations were 50% and 20% of that with continuous

flooding

[15]

. Sass et al.

[40]

also reported that the paddy fields of

Houston with midseason drain and three aerations were 52.46%

and 12.4% of that continuous flooding, respectively. Methane

emissions from the paddy fields with the local measurement were

53.44–57.84%, 111.29–114.07% and 82.38–86.20% of those calculated

with the IPCC guidelines for continuous flooding and single

aera-tion at the first crop, the second crop and total paddy fields,

respectively. However, the values were 133.60–144.61%, 278.32–

286.62% and 205.96–215.49% of those calculated with the IPCC

guidelines for continuous flooding and multiple aerations at the

first crop, the second crop and total paddy fields, respectively. The

differences among these paddy fields might be due to the different

irrigation managements. Paddy fields in Taiwan had multiple

aerations (more than three aerations) during the flowering and

ripening stages. However, the temperature was low in the flooding

and transplanting stages at the first crop season with continuous

flooding and temperature was high in the flowering and ripening

stages with drain; while the temperature was high in the flooding

and transplanting stages at the second crop season and the

temperature was low in the flowering and ripening stages.

There-fore, methane emission from the paddy fields in Taiwan was lower

than that with continuous flooding and single aeration treatments

in the first crop season, while the value was reversed in the second

crop season. Methane emission from the paddy fields in Taiwan was

lower than those with continuous flooding or continuous flooding

with single aeration, but the value was higher than those with

continuous flooding and multiple aerations by the IPCC guideline in

both crop seasons.

3.2. Nitrous oxide emission from paddy fields

Agriculture is the main source of most nitrous oxide emissions.

Nitrous oxide was produced from soil processes as an intermediate

product of microbial nitrification and denitrification. Nitrous oxide

emission was between 0.11 and 0.78 g m

2

with intermittent

irrigation in the first crop season, and it ranged from 0.11 to

0.75 g m

2

in the second crop season (

Table 1

)

[21,26,31]

. Nitrous

oxide emission also increased with green manure amendment

[26]

.

It was 3 to 20 times higher than those with convention chemical

fertilizer. Green manure amendment stimulated nitrous oxide

emission rate due to the increase of soil organic matter and

nitrogen content. Nitrous oxide emission increased with the

increasing of nitrogen fertilizer application and decreased with

the nitrification inhibitor added

[41]

.

Nitrous oxide emission coefficient of paddy field at different

locations in Taiwan was between 0.038 and 0.174 mg m

2

h

1

in the

first

crop

season,

and

the

value

ranged

from

0.010

to

0.105 mg m

2

h

1

in the second crop season. Nitrous oxide

emis-sion coefficient in the first crop season was higher than those in the

second crop season because of the intermittent irrigation and high

temperature at the later growth stage. Slow-release N fertilizer

application reduced nitrous oxide emission

[40]

. Annual nitrous

oxide emission from paddy fields was calculated with the local

emission factors at each location and cultivation area, and the

results are also presented in

Table 4

. Annual nitrous oxide emission

decreased with the decreasing of cultivation area of paddy. Total

nitrous oxide emission was 1092 ton in 1990 and the value

decreased to 596 ton in 2006. Nitrous oxide derived from N

fertil-izer in paddy field was between 0.05 and 0.28% in the central and

southern Taiwan

[41]

. Appropriate fertilization could reduce the

nitrous oxide emission from the paddy fields.

Acknowledgements

The author thanks Professors H. P. Wu, C. C. Chao, S. N. Huang, R.

M. Liou, J. J. Horng, U. Hegde, and I. C. Lin for their helpful

assis-tances and comments, National Science Council and Environmental

Protection Administration of Taiwan for financial supports.

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數據

Table 1. Other emission factors were recommended by the IPCC guidelines [15]. Most of the paddies were applied chemical  fertil-izers; only the organic paddies production used organic fertilizers.

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