Estimation of methane and nitrous oxide emission from
paddy fields and uplands during 1990–2000 in Taiwan
Shang-Shyng Yang
a,b,*, Chung-Ming Liu
c, Chao-Ming Lai
a, Yen-Lan Liu
ca
Department of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan
b
Graduate Institute of Biotechnology, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan
c
Department of Atmospheric Sciences, National Taiwan University, Taipei 10617, Taiwan Received 25 July 2002; received in revised form 10 December 2002; accepted 20 December 2002
Abstract
To investigate the greenhouse gases emissions from paddy fields and uplands, methane and nitrous oxide emissions were estimated from local measurement and the IPCC guidelines during 1990–2000 in Taiwan. Annual methane emission from 182 807 to 242 298 ha of paddy field in the first crop season ranged from 8062 to 12 066 ton, and it was between 16 261 and 25 007 ton for 144 178–211 968 ha in the second crop season with local measurement. The value ranged from 12 132 to 17 465 ton, and from 16 046 to 24 762 ton of methane in the first and second crop season with the IPCC guidelines for multiple aeration treatments, respectively. Annual nitrous oxide emission was between 472 and 670 ton and between 236 and 359 ton in the first and second crop season, respectively. Methane and nitrous oxide emissions from uplands depend on crop, growth season, fertilizer application and environmental conditions. Annual methane emission from upland crops, vegetable, fruit, ornamental plants, forage crops and green manure crops was 138–252, 412–460, 97–100, 3–5, 4–5 and 3–51 ton, respectively. Annual nitrous oxide emission was 1080–1976, 1784–1994, 2540– 2622, 31–54, 43–53 and 38–582 ton, respectively. Annual nitrous oxide emission ranged from 91 to 132 ton for 77 593– 112 095 ton of nitrogen-fixing crops, from 991 to 1859 ton for 3 259 731–6 183 441 ton of non-nitrogen-fixing crops, and from 1.77 to 2.22 Gg for 921 169–1 172 594 ton of chemical fertilizer application. In addition, rice hull burning emitted 19.3–24.2 ton of methane and 17.2–21.5 ton of nitrous oxide, and corn stalk burning emitted 2.1–4.2 ton of methane and 1.9–3.8 ton of nitrous oxide. Methane emission from the agriculture sector was 26 421–37 914 ton, and nitrous oxide emission was 9810–11 649 ton during 1990–2000 in Taiwan. Intermittent irrigation in paddy fields reduces sig-nificantly methane emission; appropriate application of nitrogen fertilization and irrigation in uplands and paddy fields also decreases nitrous oxide emission.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Methane; Nitrous oxide; Paddy field; Upland; Intermittent irrigation
1. Introduction
Global warming induced by increasing greenhouse gases concentrations in the atmosphere is a matter of
great environmental concern. Methane, carbon dioxide, nitrous oxide and chlorofluorocarbons are the green-house gases, which have strong infrared absorption bands and trap part of the thermal radiation from the earthÕs surface. Atmospheric concentrations of carbon dioxide, methane and nitrous oxide increased from 337 to 360, 1.50 to 1.72 and 0.302 to 0.320 ppmv, respectively, during last decade (Rasmussen and Khalil, 1986; Battle et al., 1996).
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*
Corresponding author. Address: Department of Agricul-tural Chemistry, National Taiwan University, Taipei 10617, Taiwan. Tel.: +886-2-23621519; fax: +886-2-23679827.
E-mail address:ssyang@ccms.ntu.edu.tw(S.-S. Yang).
0045-6535/03/$ - see front matterÓ 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0045-6535(03)00029-8
About 80% of methane is produced biologically and the major source sites are rice paddies, wetlands, sediments, enteric fermentation, animal wastes treat-ment and landfills under low redox potential conditions by obligate anaerobes (Watson et al., 1992; Liu et al., 1996; Yang, 1998; Yang and Chang, 1999; Yang et al., 2001). The release of nitrous oxide has been increasing in recent years due to intensive agricultural prac-tices. Denitrification by heterotrophic microbes in oxy-gen deficient environments, nitrification by autotrophic and heterotrophic nitrifying microbes and dissimila-tion of nitrate to ammonium by heterotrophic microbes in aerobic conditions all produce nitrous oxide (David-son et al., 1986; Yu et al., 2001). The contribution of agriculture to the global annual nitrous oxide emission has been estimated at approximately 35% (Isermann, 1994).
In Taiwan, there were 339 235 ha of paddy fields, 692 697 ha of uplands and more than 4 million tons of crop residues in 2000. Rice is cultivated with intermittent irrigation in Taiwan, while continuous flooding, con-tinuous flooding with single aeration or multiple aera-tions are used in other countries (Sass et al., 1992). 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. Estimating methane and nitrous oxide emissions from paddy fields and uplands during 1990– 2000 with country-specific emission factors was applied, whereas the local data were unavailable, the emission factors recommended by the IPCC guidelines (IPCC, 1997a,b) were used.
2. Materials and methods 2.1. Cultivation area
Cultivation areas of paddies and uplands in Taiwan from 1990 to 2000 are adapted from the Taiwan Agri-culture Yearbook from 1991 to 2001 (Department of Agriculture and Forest/Provincial Taiwan Gov-ernment, 1991–2000; Council of Agriculture/ROC, 2001). Uplands include upland crops, vegetables, fruits, ornamental plants, forage crops and green manure crops.
2.2. Amount of crop residue production
The amount of crop residue production was calcu-lated according to Yang et al. (1991) and recom-mended by the IPCC guidelines. The dry weight content of crop, N/C ratio, percent of burning and oxida-tion were adapted from the IPCC guidelines (IPCC, 1997a,b).
2.3. Methane andnitrous oxide emissions
Methane and nitrous oxide emissions from paddy fields and uplands were measured by homemade acrylic chamber (length 40 cm, width 40 cm and height 65 cm, about 96 l) (Chang and Yang, 1997). Methane and ni-trous oxide emission rates were determined at a 0.5 h interval for 1.0 h by measuring the changes of methane and nitrous oxide concentrations (the net change be-tween greenhouse gas emission and sink) in the acrylic chamber. Methane and nitrous oxide were analyzed by gas chromatograph using FID and ECD, respectively (Yang et al., 1994; Chao, 1997; Chang et al., 2000). 2.4. Methane andnitrous oxide emission factors
Methane and nitrous oxide emission factors of paddy fields and uplands are listed in Table 1. Most of paddies applied both chemical and organic fertilizers; while or-ganic paddies production used only oror-ganic fertilizer. Methane emission factors of paddy fields and uplands were measured by Chung et al. (1997), Wang and Shieh (1997), Yang and Chang (1997, 1999, 2001a,b), Perng and Huang (1998) and Huang et al. (1999). Nitrous oxide emission factors were determined by Chao (1997) and Lai (1998, 2000). Other emission factors were rec-ommended by the IPCC guidelines.
2.5. Estimation of methane andnitrous oxide emissions Methane and nitrous oxide emissions from paddy fields and uplands were calculated from the experimental data and estimated by the following equation at each growth stage (Rolston, 1986):
F ¼ ðV =AÞðDC=DtÞ
where F is the methane or nitrous oxide emission rate (mg m2h1), V is the volume of chamber above soil
(m3), A is the cross-section of chamber (m2), DC is the
concentration difference between time zero and time t
(mg m3), and Dt is the time duration between two
sampling periodðhÞ. The total methane or nitrous oxide emission from paddy fields or uplands was the summa-tion of methane and nitrous oxide emissions in all growth stages of crops (Chao, 1997; Yang and Chang, 1998).
2.6. Methane andnitrous oxide emissions from crop
residue burning
Methane and nitrous oxide emissions from crop residue burning were calculated from annual crop pro-duction, crop residue ratio, dry matter content, burning and oxidation percent, carbon content, nitrogen content, N/C ratio, emission factor and conversion factor as
stated by the IPCC guidelines (IPCC, 1997a,b). Nitrous oxide emission from crop residue was calculated as fol-lowing:
N2O emission¼ 2 ½CropO FracNCROþ CropBF
FracNCRBF ð1 FracRÞ
ð1 FracBURNÞ EF
Conversion ratio
where CropO¼ production of non-nitrogen-fixing crops
in country, FracNCRBF¼ fraction of nitrogen in
nitrogen-fixing crops, FracNCRO¼ fraction of nitrogen in
non-nitrogen-fixing crops, FracR¼ fraction of crop residue
that is removed from the field as crop, FracBURN¼
frac-tion of crop residue that is burned rather than left on
field, CropBF¼ production of nitrogen-fixing crops,
EF¼ emission coefficient, and Conversion ratio ¼ 44/28. 2.7. Nitrous oxide emission from cultivated soils
Nitrous oxide emitted from the application of chemical and organic fertilizers, animal wastes, nitro-gen-fixing and non-nitronitro-gen-fixing crops. Nitrous oxide emission from cultivated soils was estimated from the amount of chemical and organic fertilizers application,
annual production of crops, nitrogen content, cultiva-tion area, total nitrogen in the atmosphere, emission factor and conversion factor as described in the IPCC guidelines.
Nitrous oxide emission from nitrogen-fixing crops was estimated from the following equation that pro-posed by the IPCC guidelines (IPCC, 1997a,b): N2O emission¼ 2 CropBF FracNCRBF EF
Conversion ratio
where CropBF¼ production of nitrogen-fixing crops,
and FracNCRBF¼ fraction of nitrogen in nitrogen-fixing
crops.
Nitrous oxide emission from chemical fertilizer ap-plication was calculated from the following equation: N2O emission¼ NFERT ð1 FracGASFÞ EF
Conversion ratio
where NFERT¼ total application of chemical fertilizer
in country (kg N/yr), and FracGASF¼ fraction of total
chemical fertilizer nitrogen that is emitted as NOx+ NH3
(kg N/kg N).
Table 1
Greenhouse gas emission from paddy fields
Location Treatment Methane emission (g m2) Nitrous oxide emission (g m2)
First crop Second crop First crop Second crop Full year NTU Exper. Station Inter. irrigation 2.55–11.70a 13.73a 0.30–0.39b 0.07–0.75b –
Cont. flooding – 28.85a – – –
Taoyuan Dist. AIS Inter. irrigation 1.73–5.23a 10.54–10.56a 0.44–0.54b 0.06–0.40b –
W/green manure 5.55a 14.43–30.12a – 1.22b –
Miaoli farm Inter. irrigation 9.82a 39.50a – – –
Hwalien-Lotung AIS Inter. Irrigation 2.92a 24.64a 0.35–0.78b 0.0–0.06b –
Huatan-CH farm Inter. irrigation – 5.58 – 0.48
– 4.76 – 0.27
NCHU Exper. Station Inter. irrigation 8.18c 1.18c )0.11–0.60d )0.11–0.50d 0.22–1.25d
Chihu-CH farm Inter. irrigation 0.15c 10.45c – – )0.05–1.11d
Chiayi farm Inter. irrigation 3.48c 10.17c – – 0.24–0.99d
Kaohsiung Dist. AIS Inter. irrigation 2.36c 8.47c – – 0.05–1.14d
Hwalien-Chian AIS Inter. irrigation 1.42–2.42e 0.26–2.33e – – –
W/rice straw 2.77–2.85e 3.13–7.60e – – –
Hwalien-Fuli AIS Inter. irrigation 7.40–13.10e 12.50–24.30e – – –
W/high N fertile 11.60–19.73e 21.14–48.37e – – –
IPCC Cont. flooding 35.64f 38.94f – – –
Single drain 18.70f 20.43f
Multiple drains 4.42f 7.24f a
Yang and Chang (1998, 1999, 2001a).
bLai (1998, 2000). cWang and Shieh (1997). dChao (1997).
ePerng and Huang (1998) and Huang et al. (1999). fIPCC (1997a,b).
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 sea-son (February–July) was between 122 and 149 days, and it ranged from 112 to 135 days in the second crop season (August–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 was 22.46–24.68°C,
and the value was 23.07–25.72 °C in the second crop
season. This is different from the single crop season countries such as Japan, Korea, USA and Italy (Hol-zapfel-Pschorn and Seiler, 1986; Minami and Neue, 1994; Lindau et al., 1995; Shin et al., 1995). Therefore, the methane emission patterns of the two crop seasons in Taiwan were also different to 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 matter and high concen-tration of root secretes. However, drainage was prac-ticed at the flowering and ripening stages in the intermittent irrigation system, and methane emission rate decreased at these stages. Methane emission was high at the flooding and transplanting stages in the second crop season for organic matter degradation at high temperature. While methane emission was low at the flooding and transplanting stages in the first crop season for organic matter degradation at low tempera-ture, and it was also low at the flowering and ripening stages for the intermittent irrigation and high redox potential repressed methane emission (Yang and Chang, 1999, 2001b). Therefore, methane emission in the second crop season was higher than that in the first crop season because of high organic matter degradation with high temperature at the flooding, transplanting and active tillering stages in the second crop season.
Methane emission was between 0.15 and 13.10 g m2
with intermittent irrigation in the first crop season, and it ranged from 1.18 to 39.50 g m2 in the second crop
season (Table 1) (Wang and Shieh, 1997; Perng and Huang, 1998; Yang and Chang, 1998, 1999; Huang et al., 1999). Methane emission with green manure amendment was 1.06–3.20 times higher than those with intermittent irrigation and convention chemical fertilizer application in the first crop season, and the value was between 1.37 and 2.85-fold in the second crop season (Yang et al., 1994; Yang and Chang, 2001a). Methane emission with rice straw application was 1.17–1.95 and 3.26–12.03 times higher than those with convention chemical fertilizer application in the first and second crop season, respectively (Perng and Huang, 1998). High nitrogen fertilizer application also enhanced 1.50–1.56 and 1.69–1.99 times of methane emission higher than those with convention nitrogen level of chemical fertil-izer application in the first and second crop season, re-spectively (Huang et al., 1999). The scaling factor of methane emission for organic matter amendment in the most of Taiwan paddy fields was slightly lower than 2 to 5-fold that proposed by the IPCC guidelines. This phe-nomenon might be due to the differences among the environmental conditions, the amount of organic matter amendment and irrigation management of paddy fields. Green manure amendment stimulated methane emission rate and it also increased the soil organic matter content. Similar results were also found in rice cultivated with dry and wet crop seasons in the Philippines paddy fields (Denier van der Gon and Neue, 1995). Methane emis-sion of paddy field at different locations in Taiwan is presented in Table 2. The values were the average of local measurement at different years and different paddy fields in each location. Methane emission in the second crop season was higher than those in the first crop sea-son with intermittent irrigation; the reverse was true in the pot cultivation or in the paddy fields with continuous flooding (Yang et al., 1994; Yang and Chang, 1997, 1999). There was a 10–15 cm depth of flooding in the soil surface during the rice cultivation in Italian, Loui-siana and California paddy fields (Cicerone et al., 1983; Schutz et al., 1989; Lindau et al., 1993). Methane emission with continuous flooding was 2.02 times higher than that with intermittent irrigation in the second crop
Table 2
Methane and nitrous oxide emission factors of paddy fields in Taiwan
Location CH4emission coefficient (mg m2h1) N2O emission coefficient (mg m2h1)
First crop Second crop First crop Second crop
Taipei 2.12 4.85 0.128 0.031
I-lan 0.69 8.93 0.174 0.001
Taoyuan, Hsinchu 0.89 4.15 0.169 0.062
Miaoli 2.92 13.70 0.169 0.062
Taichung, Changhua, Nantou 2.84 2.54 0.088 0.068 Yuanlin, Chiayi, Tainan 1.21 3.53 0.045 0.051 Kaohsiung, Pingtung 0.82 2.94 0.020 0.105 Hwalien, Taitung 2.11 4.21 0.174 0.001
season (Yang et al., 1994; Yang and Chang, 2001a). The scaling factor of methane emission with continuous flooding in Taiwan fell within the range of 2 with con-tinuous flooding for single aeration and 5 for multiple aerations that was proposed by the IPCC guidelines. However, the intermittent irrigation 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 with intermittent irrigation was around 20–50% lower than with continuous flooding treatment. Miaoli area had high methane emission due to the high soil organic matter content (Yang and Chang, 2001b). Annual methane emission from paddy field is calculated with the emission factors in each location and cultivation area, and the results are illustrated in Table 3. Annual meth-ane emission decreased with the decreasing of rice cul-tivation area. Total methane emission was 37 073 ton in 1990 and it decreased to 25 678 ton in 2000. Methane emission from paddy fields in Taiwan that was proposed by the IPCC guidelines ranged from 117 198 to 169 864, 72 727 to 105 568 and 29 091 to 42 227 ton with contin-uous flooding, contincontin-uous flooding for single aeration and continuous flooding for multiple aerations, respec-tively. Methane emission from paddy fields in Taiwan was only 20.45–21.90%, 33.93–37.74% and 84.83– 87.79% of those calculated with the IPCC guidelines, respectively. Methane emission from paddy fields of Houston with midseason drain and three aerations was 52.46% and 12.40% of that with continuous flooding, respectively (Sass et al., 1992). The differences among these paddy fields might be due to the different irrigation managements. Paddy fields in Taiwan had multiple ae-rations (more than three aeae-rations) during the flowering and ripening stages. Therefore, methane emission from paddy fields in Taiwan was slightly lower than that with three aeration treatments, but the value fell within the ranges that was proposed by the IPCC guidelines with multiple aeration treatments.
3.2. Nitrous oxide emission from paddy fields
Agriculture is the main source of most nitrous oxide emissions. Nitrous oxide is produced from soil processes as an intermediate product of microbial nitrification and denitrification. Nitrous oxide emission was between )0.11 and 0.78 g m2 with intermittent irrigation in the
first crop season, and it ranged from)0.11 to 0.75 g m2
in the second crop season (Table 1). Nitrous oxide emission also increased 3–20 times with green manure amendment (Lai, 1998). Green manure amendment stimulated nitrous oxide emission rate due to the in-crease of soil organic matter and nitrogen content.
Ni-trous oxide emission increased with the increasing of Ta
ble 3 Meth ane and nitrous oxide emissio ns fr om padd y fields in Taiwan Yea r First crop season Second crop season Total
Cultiv. area (ha)
CH 4 em ission (ton) N2 O em is-sion (ton) Cultiv. area (ha)
CH 4 emissio n (ton) N2 O em is-sion (to n)
Cultiv. area (ha)
CH 4 emissio n (to n) N2 O
emis- sion (ton)
Loca l IP C C co nt. IPC C sing le
IPCC multi- ple
Loca l IPCC cont. IPC C sing le
IPCC multi- ple
Loca l IPCC cont. IPCC single IP CC mu lti-ple 1990 242 298 12 066 87 323 43 662 17 465 670 211 968 25 007 82 541 61 906 24 762 359 454 266 37 073 169 864 105 568 42 227 1029 1991 227 417 11 239 81 051 40 526 16 210 639 201 385 23 515 78 420 58 815 23 526 359 428 802 34 754 159 471 99 341 39 736 998 1992 209 474 10 498 74 656 37 328 14 931 591 187 676 21 852 73 080 54 810 21 924 317 397 150 32 350 147 736 92 138 36 855 908 1993 211 790 10 400 75 482 37 741 15 096 577 179 137 20 780 69 757 52 318 20 927 300 390 927 31 180 145 239 90 059 36 023 877 1994 196 317 9736 69 882 34 941 13 976 535 169 520 19 604 66 011 49 508 19 803 284 365 837 29 340 135 893 84 449 33 779 819 1995 197 571 8062 60 660 30 330 12 132 472 145 170 17 398 56 529 42 397 16 959 239 342 741 25 460 117 198 72 727 29 091 711 1996 182 807 9129 65 153 32 577 13 031 503 164 955 18 841 64 234 48 176 19 270 273 347 762 27 970 129 387 80 753 32 301 776 1997 202 010 9871 71 998 35 999 14 400 554 162 202 18 773 63 162 47 372 18 949 267 364 212 28 644 135 160 83 371 33 349 821 1998 201 424 9779 71 787 35 894 14 357 552 156 263 17 947 60 848 45 636 18 254 258 357 687 27 726 132 635 81 530 32 611 810 1999 197 123 9559 70 253 35 127 14 051 536 155 942 17 813 60 724 45 543 18 217 256 353 065 27 372 130 977 80 670 32 268 792 2000 195 057 9417 69 517 34 759 13 903 526 144 178 16 261 53 485 40 114 16 046 236 339 235 25 678 123 002 74 873 29 949 762
nitrogen fertilizer application and decreased with the nitrification inhibitor addition (Lai, 2000). Nitrous oxide emission from paddy field in different locations of Tai-wan is also summarized in Table 2. It was between 0.02 and 0.17 mg m2h1 in the first crop season, and the
value ranged from 0.00 to 0.11 mg m2h1in the second
crop season. Nitrous oxide emission in the first crop season was higher than those in the second crop season because of intermittent irrigation and high temperature at the later growth stage. Slow-release N fertilizer ap-plication reduced nitrous oxide emission (Abao et al., 2000). Annual nitrous oxide emission from paddy fields was calculated with the emission factor in each location and cultivation area, and the results are also presented in Table 3. Annual nitrous oxide emission decreased with the decreasing of cultivation area of paddy. Total ni-trous oxide emission was 1029 ton in 1990 and the value decreased to 762 ton in 2000. Nitrous oxide derived from N fertilizer in paddy field was between 0.05% and 0.28% in central and southern Taiwan (Chao, 1997).
3.3. Methane emission from uplands
Methane emission from uplands depends on crop, variety, soil type, water management, fertilizer applica-tion and environmental condiapplica-tions. Methane emission
was )0.01 to 1.06 (average was 0.09 g m2 for seven
locations), )0.40 to 1.00 (average was 0.24 g m2 for
eight locations),)0.46 to 0.59 (average was 0.43 g m2
for five locations), and)0.62 to 0.44 (average was )0.17 g m2 for three locations) g m2 in upland crops,
vege-tables, fruit, and ornamental plants, respectively (Chung et al., 1997; Wang and Shieh, 1997; Young, 1997). Total cultivation area of upland crops (included other cereals, pulses, root crops, and special crops), vegetables, fruits, ornamental plants, forage crops, and green manure crops was 153 697–281 309, 170 182–190 946, 222 812– 229 972, 6206–10 973, 8646–10 641, and 7717–117 893 ha, respectively. Annual methane emission from upland crops, vegetables, fruit, ornamental plants, forage crops, and green manure crops was 138–252, 412–460, 97–100, 3–5, 4–5 and 3–51 ton, respectively (Table 4). Annual methane emission from uplands was between 721 and 816 ton in 687 629 to 726 731 ha of cultivation area. Methane emission from upland crops and forage crops decreased due to the decreasing of cultivation area, while the value from vegetables, fruit, ornamental plants and green manure crops increased gradually because of the transfer planning encouragement and the change of living custom.
In the case of slopeland and forest, methane emission was between)7.91 and 1.87 g m2in banana cultivation
(average was)0.46 g m2) and between)1.80 and 3.80
g m2 in mango cultivation (average was 0.22 g m2).
Annual methane emission from slopeland and forest
increased from 445 to 734 ton for 203 377–335 296 ha of cultivation area (Wang and Shieh, 1997).
3.4. Nitrous oxide emission from uplands
Nitrous oxide emission from upland crops, vegeta-bles, fruits, and ornamental plants was between 0.11 and 17.61 (average was 0.70 g m2 for seven locations), 0.36
and 2.81 (average was 1.04 g m2 for eight locations),
0.56 and 2.23 (average was 1.14 g m2for five locations),
and 0.21 and 0.77 (average was 0.49 g m2for three
lo-cations) g m2, respectively (Chao, 1997; Lai, 1998). The
nitrogen fertilizer application was high in vegetable and fruit cultivations; therefore, nitrous oxide emission was also higher than those of upland crops and ornamental plants. Annual nitrous oxide emission ranged from 1080 to 1976, 1784 to 1994, 2540 to 2622, 31 to 54, 43 to 53, and 38 to 582 ton from upland crops, vegetables, fruit, ornamental plants, forage crops and green manure crops, respectively. Annual nitrous oxide emission from uplands was between 6167 and 6653 ton (Table 4). Ni-trous oxide emission from upland crops and forage crops decreased gradually due to the decreasing of cul-tivation area. While nitrous oxide emission from vege-tables, fruit, ornamental plants and green manure crops increased for the changes of living style and the market demand. In the case of slopeland and forest, nitrous oxide emission was in the range from 0.16 to 0.96 g m2
for banana cultivation and from 0.10 to 1.16 g m2 for
mango cultivation. Annual nitrous oxide emission from slopeland and forest increased gradually from 1110 to 1831 ton.
3.5. Nitrous oxide emission from chemical fertilizer application
Nitrous oxide emission was stimulated by nitrogen fertilizer application. Nitrous oxide emission from ni-trogen fertilizer application in paddy field of Taiwan ranged from 0.05% to 0.28% (Chao, 1997). The chemical fertilizers include ammonium sulfate, urea, calcium ammonium nitrate, and combined fertilizer. Nitrous oxide emission from chemical fertilizer application is demonstrated in Table 5. Ammonium sulfate, urea and combined fertilizer are the major nitrogen fertilizer, while calcium ammonium nitrate is the minor. Nitrous oxide emission was high in 1996 (22 177 ton), and then decreased gradually for the decreasing of cultivation area (1768 ton in 2000).
3.6. Nitrous oxide emission from nitrogen-fixing and non-nitrogen-fixing crops
Nitrous oxide emission from nitrogen-fixing and non-nitrogen-fixing crops is presented in Table 5.
Nitrogen-fixing crops include soybean, peanut, common bean, adzuki bean, and mung bean; while non-nitrogen-fixing crops include sweet potato, cassava, potato, tea, tobacco, sugar cane, sesame, repeseed, and perfume plants. An-nual production of nitrogen-fixing crops was between 77 593 and 112 095 ton, and annual nitrous oxide
emis-sion ranged from 91 to 132 ton. The maximal value was in 1995 and the minimal was in 1999. In the case of non-nitrogen-fixing crops, annual production decreased from 6 153 079 ton in 1990 to 3 259 731 ton in 2000. Annual nitrous oxide emission from non-nitrogen-fixing crops also decreased from 1847 ton in 1990 to 991 ton in 2000.
Table 4
Methane and nitrous oxide emissions from uplands in Taiwan
Year Upland crops Vegetable Fruit Ornamental plants Cultiv. area (ha) CH4 emis-sion (ton) N2O emis-sion (ton) Cultiv. area (ha) CH4 emis-sion (ton) N2O emis-sion (ton) Cultiv. area (ha) CH4 emis-sion (ton) N2O emis-sion (ton) Cultiv. area (ha) CH4 emis-sion (ton) N2O emis-sion (ton) 1990 281 309 252.2 1976.4 188 249 453.7 1965.9 222 812 96.5 2540.1 6206 2.7 30.7 1991 274 126 245.8 1925.9 190 946 460.2 1994.1 226 143 98.0 2578.0 6670 2.9 33.0 1992 269 541 241.7 1893.7 188 736 454.9 1971.0 226 274 98.0 2579.5 7580 3.3 37.5 1993 264 296 237.0 1856.9 184 309 444.2 1924.7 228 281 98.9 2602.4 9089 3.9 44.9 1994 261 859 234.8 1839.7 170 812 411.7 1783.8 226 380 98.1 2580.7 9401 4.1 46.4 1995 254 487 228.2 1787.9 173 048 417.1 1807.1 228 719 99.1 2607.4 9661 4.2 47.7 1996 233 203 209.1 1638.4 176 774 426.0 1846.1 229 972 99.7 2621.7 9968 4.3 49.2 1997 213 094 191.1 1497.1 180 209 434.3 1881.9 226 519 98.2 2582.3 10 427 4.5 51.5 1998 182 748 163.9 1283.9 180 072 434.0 1880.5 227 144 98.4 2589.4 10 172 4.4 50.3 1999 159 992 143.5 1124.1 183 600 442.5 1917.3 224 806 97.4 2562.8 10 765 4.7 53.2 2000 153 697 137.8 1079.8 177 057 426.7 1849.0 224 431 97.2 2558.5 10 973 4.8 54.2
Forage crops Green manure crops Total Cultiv. area (ha) CH4 emis-sion (ton) N2O emis-sion (ton) Cultiv. area (ha) CH4 emis-sion (ton) N2O emis-sion (ton) Cultiv. area (ha) CH4 emis-sion (ton) N2O emis-sion (ton) 1990 10 297 4.5 50.9 7717 3.3 38.1 716 590 812.9 6602.1 1991 10 066 4.4 49.7 11 642 5.0 57.5 719 593 816.3 6638.2 1992 10 564 4.6 52.2 24 036 10.4 118.7 726 731 812.9 6652.6 1993 10 048 4.4 49.6 27 778 12.0 137.2 723 801 800.4 6615.7 1994 10 641 4.6 52.6 41 041 17.8 202.7 720 134 771.1 6505.9 1995 10 121 4.4 50.0 39 859 17.3 196.9 715 895 770.3 6497.0 1996 9666 4.2 47.8 45 225 19.6 223.4 704 808 762.9 6426.6 1997 9337 4.1 46.1 54 491 23.6 269.2 694 077 755.8 6328.1 1998 9054 3.9 44.7 78 439 34.0 387.5 687 629 738.6 6236.3 1999 8856 3.8 43.7 104 338 45.2 515.4 692 357 737.1 6216.5 2000 8646 3.8 42.7 117 893 51.1 582.4 692 697 721.4 6166.6
Upland crops include corn, wheat, millet, sorghum, soybean, peanut, common bean, adzuki bean, mung bean, sweet potato, tea, tobacco, sugar cane, sesame, repeseed, perfume plants and others.
Vegetables include radish, carrot, other root vegetable, ginger, taro, scallion, scallion bulb, onion, garlic, garlic bulb, water chestnut, leek, bamboo shoot, asparagus, water bamboo, other stem vegetable, leaf mustard, water convolvulus, celery, cabbage, Chinese cabbage, Chinese mustard, other leaf vegetable, cauliflower, lily flower, oriental picking melon, cucumber, white gourd, bitter gourd, eggplant, tomato, pepper, kidney bean, pea, vegetable soybean, other fruit vegetable, watermelon, muskmelon, cantaloupe, seed watermelon, strawberry, and mushroom.
Fruits include banana, pineapple, citrus-ponkan, citrus-tankan, wentan pomelon, citrus-tou pomelon, pai pomelon, satsuma orange, citrus-valencias, liuchengs, lemon, grapefruit, other citrus, longans, mango, betel nut, guava, wax apple, grape, loquat, plum, peach, persimmon, Japanese apricot, lichee, olive, carambola, pear, apple, papaya, jujube, sugar apple, passion fruit, coconut and others. Ornamental plants include cut flower, bulb, herbaceous flower seed, nurseries and potted flower.
Forage crops include oat, pangola grass, napier grass and others.
Green manure crops include raphanus sativus, sesbania sesbean, soybean, field pea, astragalus sinicus, velvet bean, crotataria, rape, tephrosia, ber seem clover, other single sowing and other mixed sowing.
3.7. Methane andnitrous oxide emission from crop residues burning
The ratio of crop residue to crop (or grain) depends on the variety of crop. The ratio of crop residue to crop is low (0.2) in sugar beet and high (2.1) in mung bean and soybean. The relative coefficients of greenhouse gas emission from crop residue burning are not available in local measurement, and all of these coefficients are adapted by the IPCC guidelines (IPCC, 1997a,b). Rice and corn are the major crops in Taiwan; therefore, methane and nitrous oxide emissions from the burning of rice hull and corn stalk are calculated and presented in Table 6. Methane and nitrous oxide emissions from rice hull burning were in the range from 19.4 to 24.2 ton, and from 17.2 to 21.5 ton, respectively. In the case of corn stalk burning, methane and nitrous oxide emissions
was between 2.1 and 4.2 ton and between 1.8 and 3.8 ton, respectively.
From the mention results, methane and nitrous oxide emissions from paddy fields and uplands during 1990– 2000 in Taiwan are summarized in Fig. 1. Methane emission is higher than those of nitrous oxide in paddy fields. Annual methane and nitrous oxide emissions were 37 073 and 1029 ton in 1990, respectively, and the values decreased gradually to 25 678 and 762 ton in 2000. Methane emission from paddy fields in local measure-ment with intermittent irrigation is lower than those calculated by the IPCC guidelines with continuous flooding, and the value was consistent with continuous flooding for multiple aerations. While in the uplands, nitrous oxide emission is higher than those of methane emission. Annual methane and nitrous oxide emissions were 813 and 6602 ton in 1990, respectively. They had
Table 5
Nitrous oxide emission from chemical nitrogen fertilizers, nitrogen-fixing and non-nitrogen-fixing crops
Year Chemical nitrogen fertilizer Nitrogen-fixing crops Non-nitrogen-fixing crops Application (ton) N2O emission (ton) Yield (ton) N2O emission (ton) Yield (ton) N2O emission (ton) 1990 1 060 917 2039.5 89 840 105.9 6 153 079 1847.4 1991 1 135 096 2160.8 104 592 123.3 5 134 846 1558.3 1992 1 105 114 2087.6 95 399 112.4 6 183 441 1859.4 1993 1 140 480 2118.6 99 562 117.3 5 097 723 1545.7 1994 1 156 835 2132.8 104 041 122.6 5 797 750 1751.8 1995 1 140 412 2175.8 112 095 132.1 5 155 242 1569.6 1996 1 172 594 2216.9 102 785 121.1 4 698 543 1430.1 1997 1 004 616 1914.3 101 117 119.1 4 444 101 1355.2 1998 982 082 1862.2 79 985 94.3 4 057 935 1230.5 1999 966 679 1805.2 77 593 91.4 3 597 715 1094.1 2000 921 169 1768.3 87 377 103.0 3 259 731 991.3 Chemical nitrogen fertilizer include ammonium sulfate, urea, calcium ammonium nitrate and combined fertilizer. Nitrogen-fixing crops include soybean, peanut, common bean, adzuki bean, and mung bean.
Non-nitrogen-fixing crops include sweet potato, cassava, potato, tea, tabacco, sugar cane, sesame, rapeseed and perfume plants.
Table 6
Methane and nitrous oxide emissions from crop residue burning Year Rice yield
(ton)
Rice hull Corn yield (ton) Corn stalk CH4emission (ton) N2O emission (ton) CH4emission (ton) N2O emission (ton) 1990 2 283 670 23.9 21.3 398 875 4.1 3.7 1991 2 311 638 24.2 21.5 374 810 3.9 3.5 1992 2 069 880 21.6 19.3 389 869 4.1 3.6 1993 2 232 933 23.3 20.8 405 999 4.2 3.8 1994 2 061 403 21.5 19.2 397 118 4.2 3.7 1995 2 071 968 21.7 19.3 375 571 3.9 3.5 1996 1 930 897 20.2 18.0 395 412 4.1 3.7 1997 2 041 843 21.3 19.0 337 617 3.5 3.2 1998 1 859 157 19.4 17.3 243 792 2.6 2.3 1999 1 916 305 20.0 17.9 201 195 2.1 1.9 2000 1 843 227 19.9 17.8 138 315 1.4 1.3
the maximum value in 1993, and then decreased to 721 and 6167 ton in 2000. Total annual methane and nitrous oxide emissions from the agriculture sector were 37 914 and 11 649 ton in 1990, respectively, and the value de-creased to 26 421 and 9810 ton in 2000. Methane emis-sion is high from paddy fields, while nitrous oxide emission is high from uplands and chemical nitrogen fertilizer application. Intermittent irrigation and appro-priate application of fertilizer might reduce methane and nitrous oxide emissions from agriculture practices.
Acknowledgements
The authors thank Professors Y.P. Wang, L.P. Lin, C.C. Young, C.C. Chao, S.N. Huang and R.S. Chung for their helpful assistances and comments, National Science Council and Environmental Protection Admin-istration of Republic of China for financial supports.
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