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Estimate of CH4 emissions from permanently flooded rice fields in China

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Running Title: CH4 EMISSIONS FROM FLOODED RICE FIELDS

[A shortened title used as a running head and should be less than 50 letters including space between words]



Estimate of CH4 Emissions from Year-Round Flooded Rice Fields During Rice Growing Season in China*1[Foundation items concerning this research should be given as a footnote and marked with ‘*1’ behind the title] [All first letters of the substantives should be in capitalization]



CAI Zu-Cong1,*2, KANG Guo-Ding2, H. TSURUTA3 and A. MOSIER4 [The last name of any author should be in capitalization. The first and middle names for the foreign authors should be in abbreviation while those for the Chinese authors in full name]


1Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China)

2Department of Demography and Economics, Nanjing College for Population Program Management, Nanjing 210093 (China)

3Tokyo University of Agriculture and Technology, Tokyo (Japan)

4USDA/ARS, Ft. Collins, CO (USA)


(Received , 2004; revised , 2004)



ABSTRACT


A special kind of rice field exists in China that is flooded year-round. These rice fields have substantially large CH4 emissions during the rice-growing season and emit CH4 continuously in the non-rice growing season. CH4 emission factors were used to estimate the CH4 emissions from year-round flooded rice fields during the rice-growing season in China. The CH4 emissions for the year-round flooded rice fields in China for the rice growing season over a total area of 2.66 Mha were estimated to be 2.44 Tg CH4 year-1. The uncertainties of these estimations are discussed as well. However, the emissions during the non-rice growing season could not be estimated because of limited available data. Nevertheless, methane emissions from rice fields that were flooded year-round could be several times higher than those from the rice fields drained in the non-rice-growing season. Thus, the classification of “continuously flooded rice fields” in the International Panel on Climate Change (IPCC) [A full name must be given when the abbreviation appears in both the abstract and text for the first time] Guidelines for National Greenhouse Gas Inventories is suggested to be revised and divided into “continuously flooded rice fields during the rice growing season” and “year-round flooded rice fields”.


Key Words: IPCC methodology, methane emission, rice fields, year-round flooded [ 5 in alphabetical order]

Citation：Cai, Z. C., Kang, G. D., Tsuruta, H. and Mosier, A. 201???. Estimate of CH4 emissions from year-round flooded rice fields during rice growing season in China. Pedosphere. 2???(???): ???--???.



INTRODUCTION [All letters should be in capitalization]


Rice is widely produced in China, from south to north and from east to west. In general terms, there are two distinct seasons in Chinese rice-based agriculture, i.e. a rice growing season (RGS) [A full name must be given when the abbreviation appears in both the abstract and text for the first time] and a non-rice growing season (non-RGS). The former starts in late March and ends in early November, and varies greatly from south to north China and with rice cropping systems. The interval between two rice crop seasons is the non-RGS. The water regime for rice production is relatively homogenous and in China intermittent irrigation has been widely adopted during the RGS. In contrast, the water regime during the non-RGS is substantially different even for the same area. From the water regime point of view in the non-RGS, rice fields in China can be classified into two types. One is drained and either planted with upland winter crops, such as winter wheat, oil seed rape, green manure, or fallowed with drained conditions. The second is year-round flooded rice fields that retain a floodwater layer with no planting in the non-RGS (locally named as winter-flooded rice fields).

According to the book of Paddy Soils in China (Lee, 1992[In case of 1 author]), the total area of year-round flooded rice fields was estimated to range from 2.7 to 4.0 Mha in China mainly distributed in mountainous areas of south and southwestern China. There were 3 reasons as to why the fields were flooded year-round. First, drainage conditions of the fields are too poor to drain floodwater from the soil completely due to depressions in topography. Second, irrigation systems are not well developed and are dependent more or less on rainfall. If the field is drained in winter and the precipitation in spring is insufficient, the field could not be flooded for rice transplanting. Finally, farmers unconsciously keep the floodwater layer until the following rice-planting period after the rice harvest.

Previous studies have demonstrated that water regimes in the non-RGS significantly affected CH4 emissions during the following RGS. Flooding in the non-RGS stimulated CH4 emissions (Cai et al., [In case of 3 authors; et al in Italic] 2000; Xu et al., 2003; Yao and Conrad, 2000[In case of 2 authors]) because it kept soil Eh low and Fe and Mn as reduced statues (Liu et al., 2003), as well as was favorable for survival of methanogens (Ueki et al., 1997). In the same region the CH4 emission from year-round flooded rice fields was substantially larger, up to 3.81 times that of rice fields drained in non-RGS season (Kang et al., 2002). The largest emissions (up to 203 g CH4 m-2) measured in China were observed in year-round flooded rice fields during the RGS (Cai et al., 2000). Moreover, year-round flooded rice fields maintain CH4 emissions in the non-RGS because continuous flooding sustains anaerobiosis (Cai et al., 2003).

The importance of year-round flooded rice fields as an atmospheric CH4 source has not been adequately recognized. In the IPCC (International Panel on Climate Change) Guidelines for National Greenhouse Gas Inventories, the basic method for estimating emissions from each country included estimates based on rice ecosystems relating to the water regime (IPCC, 1997). However, the methodology took into account the water regime during the RGS, not the non-RGS. In this paper, the CH4 emissions from year-round flooded rice fields in China during the RGS are estimated using CH4 emission factors with a discussion of the estimate uncertainties.


Materials and Methods


For estimating CH4 emissions during the RGS, available data were integrated from the literature. According to the similarities of climate and topography and depending on the data available, year-round flooded rice fields were then classified into five regions (Fig. 1) and emission factors in the RGS were allocated to these regions (Table I). [Any illustration and table should be clearly marked with the figure or table number in the text and listed just behind the paragraph mentioned.]


Fig. 1 [Illustrations: all illustrations must be readable when reduced to a width of 70 mm or 157 mm. Photographs, charts and diagrams are all to be referred to as “Figure (abbreviated to ‘Fig.’)”. They should accompany the Ms, but should not be included within the text. Each figure should have a caption. Please note that photocopies of photographs are not acceptable. A legend for identifying graph lines should not be included in figure captions. This information should be in the drawing itself.]

Fig. 1 Regionalization of year-round rice fields in China for estimating CH4 emission during the rice growing period.


TABLE I [All tables must be self-explanatory. Vertical lines between the columns are not allowed. Table captions should not include the units of measurements. These units should be listed in the body of the table. ]


Estimated methane emissions from year-round flooded rice fields during rice growing and non-rice growing seasons in China

Region

Area

Rice growing season

Emission factor

Site for measurement

CH4 emission


103 ha

g CH4 m-2 year-1


Gg CH4 year-1

I

469

57.2a)

Jurong

268

II

608

67.2b)

Chongqing

408

III

442

76.0c)

Guangzhou

336

IV

684

104c)

Changsha

708

V

457

159c)

Yingtan

724

Total

2 660



2 444

a)Cited from Li et al. (1993); b)Cited from Cai et al. (2003); c)Cited from Kang et al. (2002).[All notes for a table must be marked with a), b), c), …]


There were no data available for year-round flooded rice fields in the whole north China, however Li et al. (1993) measured CH4 emissions from a year-round flooded rice field in Jurong, Jiangsu Province during the rice-growing period in 1992. The climate and management for rice production in Jurong were not identical with those in north China, but they were the most similar among the sites where CH4 emissions from year-round flooded rice fields were measured. Thus, CH4 emissions from the field measurements in Jurong (Li et al., 1993) were utilized as the emission factor for Region I. The CH4 emission factor of Region II, which included Sichuan, Yunnan, and Guizhou Provinces along with Chongqing Municipality, was obtained from a field measurement in Chongqing Municipality. Region III included Guangdong Province, Guangxi Zhuang Autonomous Region, and Hainan Province with the CH4 emission being measured in Guangzhou, Guangdong Province. A field measurement was carried out in Changsha, Hubei Province and the measured CH4 emissions from a winter-flooded rice field was taken as the emission factor for Region IV, which included Hunan and Hubei Provinces. Region V was composed of Jiangxi, Fujian, and Zhejiang Provinces and the CH4 emission factor was obtained from the field measurement in Yingtan, Jiangxi Province (Fig. 1).


Results and Discussion

CH4 emissions [Italic]

CH4 emissions from rice fields have been intensively investigated in China since the late of 1980’s. Measurements of CH4 emissions from year-round flooded rice fields are, however, still limited, with even less data available on CH4 emissions during the non-RGS. The Data of Soil Survey of China listed 2.524 Mha of gleyic paddy soils distributed in 23 provinces, excluding Guizhou and Shandong Provinces. For Guizhou and Shandong provinces, the areas of 0.108 and 0.028 Mha were calculated, respectively, from the Soil Species of China, Volume 1 (Office for the National Soil Survey, 1993). Thus, the total area of gleyic paddy soils estimated from the Data of Soil Survey of China and the Soil Species of China was 2.66 Mha [there should be a space prior to a unit], distributed throughout 25 provinces. This value was very close to the low range (2.7--4.0 Mha[“--” is used to express the range in the manuscript]) for the area of winter-flooded rice fields reported by Lee (1992).

The CH4 emissions in the RGS, measured from rice fields as shown in Table I were much larger than those measured for the same region in the rice fields drained during the RGS (Kang et al., 2002). These values were also larger than those reported from other parts of the world (e.g. the data from Wassmann et al., 2000). The CH4 emission rates from Japanese rice fields were reported to range from 13.4 to 20.8 g CH4 m-2 year-1 (Soil Science Society of Japan, 1996); from Indian rice fields from 8 to 44 g CH4 m-2 year-1 for waterlogged fields and from 0.1 to 2.1 g CH4 m-2 year-1 for intermittently flooded irrigated fields (Parashar et al., 1994); and from rice fields in Thailand 9.8 g CH4 m-2 year-1 from deepwater rice fields and 7.4 g CH4 m-2 year-1 from irrigated rice fields (Chareonsilp et al., 2000).

The large CH4 emissions from year-round flooded rice fields resulted from the low soil Eh that was maintained under continuous flooding (Cai et al., 2003; Xu et al., 2003). As a result, in contrast to fields that were drained in the non-RGS, soil Eh was no longer a limiting factor for CH4 production in year-round flooded rice fields. For the rice fields that were drained in the non-RGS, reduced chemicals, such as NH4+, Mn2+, and Fe2+, could be re-oxidized in the non-RGS under the aerobic conditions. The presence of Mn4+ and Fe3+ depresses CH4 production and emission (Liu et al., 2003). After re-flooding it took some time to reduce these oxidized chemicals and lower the soil Eh to a value suitable for CH4 production. Thus, soil Eh was a dominant factor controlling CH4 emission in the rice fields drained in the non-RGS, but not in year-round flooded rice fields (Xu et al., 2003). Another factor was that continuous flooding created a favorable condition for survival of methanogens, which possibly decreased when soils were aerated in the non-RGS (Ueki et al., 1997).

Based on CH4 emissions measured and projected in the different regions (Table I), the CH4 emissions from year-round flooded rice fields in the RGS in China were estimated to be 2.44 Tg CH4 year-1, which accounted for 31.8% of the total CH4 emission of 7.67 Tg CH4 year-1 from all rice fields in China that were recently estimated by Yan et al. (2003).

Similar to that observed in the rice fields drained in the non-RGS, there was a large spatial variation for CH4 emission factors from year-round flooded rice fields in China (Table I). Within China, the spatial variations of CH4 emissions from the rice fields drained in non-RGS could be mainly explained by soil moisture in the non-RGS (Kang et al., 2002). For the year-round flooded rice fields soil moisture in non-RGS would not be a dominant factor in determining the spatial variations of CH4 emissions because the fields were water-saturated continuously. The factors determining the spatial variation of CH4 emissions from the year-round flooded rice fields have not been identified and need further research.

The year-round flooded rice fields are continuously flooded after the rice harvest; thus the anaerobic conditions for CH4 production are sustained in the non-RGS. According to a 4-year measurement carried out in Chongqing (Cai et al., 2003), the year-round flooded rice field continuously emitted CH4 in the non-RGS though the fluxes are lower than that in the RGS. The CH4 emission rate for the non-RGS measured in Chongqing, where a single rice crop was cultivated and the of non-RGS


Conclusions


By using the CH4 emission factor method described here, the CH4 emission from year-round flooded rice fields in China during the RGS was estimated to be 2.44 Tg CH4 year-1. However, due to limitations of available field-measured data for CH4 emissions as well as uncertainties with area measurements and location of year-round flooded rice fields, there were still uncertainties with the CH4 emissions estimates. The shortage of field measured data on CH4 emissions from year-round flooded rice fields during the non-RGS limited the estimate of CH4 emissions during the season as well as the total annual CH4 emissions from year-round flooded rice fields in China. Nevertheless, it was shown that methane emissions from rice fields that were flooded year-round could be several times higher than those from the rice fields drained in the non-RGS. Therefore, it was suggested that classification of “continuously flooded rice fields” in the IPCC Guideline be revised and divided into “continuously flooded rice fields during the rice growing season” and “year-round flooded rice fields”.

[In addition, significance should be expressed as P ＝ 0.01 or P ＜ 0.05 etc.＝



REFERENCES

[All references listed should be formally published except for dissertations and should have been cited in the text. All authors must be listed here and ‘et al.’is not allowed in the references.]


Bouwman, A. F. 1990. Exchange of greenhouse gases between terrestrial ecosystems and the atmosphere. In Bouwman, A. F. (ed.) Soils and the Greenhouse Effect. John Wiley & Sons, New York. pp. 61--127.［For a chapter reference from a book or a symposium proceedings］

Cai, Z. C., Tsuruta, H. and Minami, K. 2000. Methane emission from rice fields in China: Measurements and influencing factors. J. Geophysi. Res. 105(13): 17 231--17 242. [For all authors in the references, the first and middle names of the authors should be given in initials and put behind the last name]

Cai, Z. C., Tsuruta, H., Gao, M., Xu, H. and Wei, C. F. 2003. Options for mitigating methane emission from a permanently flooded rice field. Glob. Changy Biol. 9(1): 37--45. [Use international abbreviations such as ISI Journal Title Abbreviations for abbreviations of journal names, and when in doubt give full name of the periodical; The name of journal should be italic; The volume number should be in bold face, while the issue number must be involved in the parentheses]

Chareonsilp, N., Buddhaboon, C., Promnart, P., Wassmann, R. and Lantin, R. S. 2000. Methane emission from deepwater rice fields in Thailand. Nutri. Cycl. Agroecosys. 58(1): 121--130.

International Panel on Climate Change (IPCC). 1997. Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories Workbook. Volume 2. Cambridge University Press, Cambridge. 140pp. [For a book name, all first letters of the substantives should be in capitalization][The publisher and the city as well as the total pages should be given]

Kang, G. D., Cai, Z. C. and Feng, X. Z. 2002. Importance of water regime during the non-rice growing period in winter in regional variation of CH4 emissions from rice fields during following rice growing period in China. Nutri. Cycl. Agroecosys. 64(1--2): 95--100.

Lee, C. K. 1992. Paddy Soils in China (in Chinese). Science Press, Beijing. pp. 1--10.

Li, D. B., Zhang, J. N. and Li, W. X. 1993. Effect of various agricultural measures on methane emission fluxes from rice paddies. Rural Eco-Environ. (in Chinese). 35: 13--18. [Publications in languages other than English should be translated into English <Always use the English title, English journal or book name, etc. provided by the journal or book itself if possible>, and a notation such as “(in German)”, “(in Chinese)”, “(in Japanese)” and “(in Russian)” must be added behind the name of the periodical or book]

Liu, K. X., Liao, Z. W., Wang, S. C. and You, Z. L. 2003. Effects of Fe and Mn in paddy soils derived from different parent materials on methane production and emission. Pedosphere. 13(4): 337--344.

Office for the National Soil Survey. 1993. Soil Species of China (in Chinese). Volume 1. China Agricultural Press, Beijing. 924pp.

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1Supported by the National Distinguished Young Scholar, China (No. 40125004), and the Knowledge Innovation Program of the Chinese Academy of Sciences (No. KZCX1-SW-01-05). [All the foundation items concerning this research should be given here as a footnote and marked with ‘*1’ behind the title of the article]

2*Corresponding author. E-mail: [email protected].


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