Direct N 2 O emissions from rice paddy fields: Summary of available data

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1 GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 19,, doi: /2004gb002378, 2005 Direct N 2 O emissions from rice paddy fields: Summary of available data Hiroko Akiyama and Kazuyuki Yagi National Institute for Agro-Environmental Sciences, Tsukuba, Japan Xiaoyuan Yan Frontier Research Center for Global Change, Yokohama, Japan Received 28 September 2004; accepted 1 December 2004; published 22 January [1] Rice cultivation is an important anthropogenic source of atmospheric nitrous oxide (N 2 O) and methane. We compiled and analyzed data on N 2 O emissions from rice fields (113 measurements from 17 sites) reported in peer-reviewed journals. Mean N 2 O emission ± standard deviation and mean fertilizer-induced emission factor during the rice-cropping season were, respectively, 341 ± 474 g N ha 1 season 1 and 0.22 ± 0.24% for fertilized fields continuously flooded, 993 ± 1075 g N ha 1 season 1 and 0.37 ± 0.35% for fertilized fields with midseason drainage, and 667 ± 885 g N ha 1 season 1 and 0.31 ± 0.31% for all water regimes. The estimated whole-year background emission was 1820 g N ha 1 yr 1. A large uncertainty remains, especially for background emission because of limited data availability. Although midseason drainage generally reduces CH 4 and increases N 2 O emissions, it may be an effective option for mitigating the net global warming potential of rice fields. Citation: Akiyama, H., K. Yagi, and X. Yan (2005), Direct N 2 O emissions from rice paddy fields: Summary of available data, Global Biogeochem. Cycles, 19,, doi: /2004gb Introduction [2] Agricultural soil is a major source of nitrous oxide (N 2 O). N 2 O is a greenhouse gas, and it contributes to the destruction of stratospheric ozone. Early studies found N 2 O emission from paddy fields to be negligible [e.g., Smith et al., 1982]. However, recent studies suggest that rice cultivation is an important anthropogenic source of not only atmospheric methane (CH 4 ) but also N 2 O [e.g., Cai et al., 1997]. [3] The Intergovernmental Panel on Climate Change (IPCC) developed Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories [IPCC, 1997] and Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories [IPCC, 2000] for calculating national inventories of greenhouse gases [IPCC, 1997, 2000]. The current IPCC guidelines use a default fertilizer-induced emission factor (EF) of 1.25% of net N input (based on the unvolatilized portion of the applied N) and a background emission rate for direct emission from agricultural soil of 1 kg N ha 1 yr 1 [IPCC, 1997]. In the guidelines, rice paddy fields were not distinguished from upland fields. However, Bouwman et al. [2002] reported on the basis of data published before 1999 that mean N 2 O emission from rice paddy fields (0.7 kg N 2 O-N ha 1 yr 1 ) was lower than that from upland fields, including grasslands (1.1 to 2.9 kg N 2 O-N ha 1 yr 1 ). Yan et al. [2003] reported Copyright 2005 by the American Geophysical Union /05/2004GB on the basis of data published before 2000 that the EF for rice paddy fields, at 0.25% of total N input, was also lower than that for upland fields, and a background emission of 1.22 kg N 2 O-N ha 1 yr 1 for paddy fields. More measurements of N 2 O emission from rice fields have since been performed, although the number of field measurements is still relatively small compared with those of CH 4 emission from rice paddy fields or N 2 O emission from upland fields. The guidelines are due to be updated in 2006, and a simple method for estimating N 2 O emission from rice fields is urgently needed. Therefore the aim of this study was to assess field measurements available to date to provide a quantitative basis for estimating national or regional N 2 O emission inventories. Available data on tested options for mitigating N 2 O emissions from paddy fields were also reviewed. 2. Materials and Methods 2.1. Data Collection [4] We compiled measurement results of direct N 2 O emission from rice fields published in peer-reviewed journals before summer 2004; the initial data set comprised 147 field measurements of N 2 O collected during the rice-cropping or fallow season from 29 sites. Measurements from atypically managed fields [e.g., Xu et al., 2004], those collected over a period significantly shorter than the cropping season [e.g., Freney et al., 1981], and those in which the measurement period was not specified [e.g., Xing and 1of10

2 Zhu, 1997] were excluded. Two data points that were statistical outliers were also excluded [Khalil et al., 1998; Zheng et al., 2000]. In the end, the data set used for our assessment comprised 113 measurements from 17 sites. [5] For each series of measurements, documented information compiled included the N 2 O emission during the cropping season and/or the fallow period, the water regime used during the cropping season, the type and amount of organic amendment and nitrogen fertilization, and the location of the field. The fertilizer-induced N 2 O emission factor (EF), defined as the emission from fertilizer plots minus that of a zero-n control plot, was calculated whenever a zero-n control plot was included in a reported experiment. If the seasonal flux was not directly reported, we estimated it by integrating the average emission over the season s duration or from figures showing the seasonal change in N 2 O fluxes. [6] The water regime during the rice-cropping season was classified as continuous flooding, midseason drainage, wetseason rain-fed, or unknown. The water regime of fields drained one or more times during the rice-cropping season was classified as midseason drainage, because among the compiled measurements only one experiment [Bronson et al., 1997a] involved a single midseason drainage, and because the number of times a field was drained was not clearly documented in some papers. The water regime of fields drained only at the end of the season, without midseason drainage, was classified as continuous flooding, because in many experiments the continuous flooding treatment also included end-season drainage and because farmers usually drain the rice fields before harvest. To our knowledge, N 2 O measurements for deep-water rice fields are not available. [7] When only the amount of organic material input was reported and not the actual N content, the N content (percent N, fresh weight) of the organic materials was estimated as follows: swine manure, 1.35%; cattle manure, 0.71%; rice straw compost, 0.417%; rice straw, 0.54%; wheat straw, 0.33%; vetch, 0.59%; and cowpea residue, 0.47% [National Federation of Agricultural Co-operative Associations, 1980; Ministry of Agriculture, Forestry, and Fisheries of Japan (MAFF), 1982]. The N content of rice straw applied after harvesting the previous season s rice was assumed to be 50% that of rice straw applied just before rice cultivation. Farmyard manure was assumed to be cattle manure. N input by Azolla application [Chen et al., 1997] was estimated to be 50 kg ha Data Analysis [8] To provide a quantitative basis for estimating national and regional N 2 O emissions from rice paddy fields, the mean, standard deviation, and median of N 2 O emission, EF, and background emission for the cropping season were calculated for each water regime. [9] Available data covering the whole fallow period for estimating fallow period N 2 O emission were very limited. Therefore, hourly emissions were first calculated for each measurement series, and then the mean hourly emission was calculated after excluding data collected during a measurement period shorter than 50 days, because emissions values collected over a short period were much higher than those collected over a longer period. Finally, emission during the fallow period was calculated by integrating the mean hourly data over the entire period. [10] Comparisons of mean emissions and EF values among different water regimes were made with SPSS version 12 using one-way analysis of variance followed by a Tukey multiple comparison test (SPSS, Inc.). When the data did not fit a normal distribution but fit a lognormal distribution, they were log-transformed before the statistical test. 3. Results and Discussion 3.1. N 2 O Emissions From Fertilized Fields During the Rice-Cropping Season [11] For each water regime, N 2 O emissions from paddy fields with chemical or organic fertilizer application during the rice-cropping season showed large variation (Tables 1a, 1b, 1c, and 1d, Figure 1). N 2 O emission from continuously flooded fields was generally lower than 1000 g N ha 1 season 1, except in one case [Xu et al., 2004], and low emissions were reported even with large N inputs (>300 kg N ha 1 ) [Chen et al., 1997]. In contrast, large N 2 O emission (>1000 g N ha 1 season 1 ) was often reported for fields with midseason drainage. N 2 O emissions from rain-fed fields were reported only by Abao et al. [2000], and emissions differed among fertilizer treatments and also varied with year. The total N input was not clearly related to N 2 O emission for all water regimes or for continuous flooding. For fields drained midseason, a weak linear relationship was observed (adjusted r 2 = 0.28, P < 0.01); that is, about 28% of the variability was explained by total N input. The amount of chemical N input was also not clearly related to N 2 O emission (data not shown). This result is not surprising because N 2 O emission is affected not only by N input and the water regime but also by many other factors such as fertilizer type, temperature, soil texture, and soil ph [e.g., Granli and Bockman, 1994; Bouwman et al., 2002], which could not be considered here because of limited data. Moreover, we classified all water regimes into one of three categories, but actual water management practices varied within each category, especially in the case of midseason drainage. Among fields with midseason drainage, the timing, number, and duration of drainage periods vary, and the timing and amount of rainfall greatly affect water management of even irrigated rice fields; furthermore, details of drainage practices were not documented in many papers. Food and Agriculture Organization/International Fertilizer Industry Association [2001] also found no clear relationship between the amount of chemical N input and N 2 O emissions in upland fields worldwide. [12] Although N 2 O emissions from paddy fields cannot be described as a simple function of N input (Figure 1), a simple method is required for estimating national or regional N 2 O emission inventories, especially for the Tier 1 methodology of the IPCC guidelines. Also, we expect N 2 O emission to increase with N input under comparable conditions [e.g., Cai et al., 1997]. Therefore we calculated the mean and median N 2 O emission and the fertilizer-induced emission factor (EF), 2of10

3 Table 1a. N 2 O Emissions From Paddy Fields During the Cropping Season a Amendment b Amendment, kg ha 1 Nitrogen Fertilizer c Tested Mitigation Option d Chemical N, kgn ha 1 N 2 O Emission, gn ha 1 Fertilizer-Induced N 2 O Emission Factor, e % Xu et al. [2004] China Yancheng, Jiangsu no 0 U Chen et al. [1997] China Shenyang no 0 no 0 40 Chen et al. [1997] China Shenyang no 0 U Chen et al. [1997] China Shenyang FYM U Chen et al. [1997] China Shenyang FYM, Azolla U Hou et al. [2000] China Shenyang FYM U Ghosh et al. [2003] India New Delhi no 0 no 0 38 Ghosh et al. [2003] India New Delhi no 0 U Ghosh et al. [2003] India New Delhi no 0 AS Ghosh et al. [2003] India New Delhi no 0 PN Ghosh et al. [2003] India New Delhi no 0 U DCD Ghosh et al. [2003] India New Delhi no 0 AS DCD Ghosh et al. [2003] India New Delhi no 0 PN DCD Pathak et al. [2002] India New Delhi no 0 U Pathak et al. [2002] India New Delhi FYM 6000 U Pathak et al. [2002] India New Delhi no 0 U DCD Pathak et al. [2002] India New Delhi no 0 no Suratno et al. [1998] Indonesia Bogor, West Java no 0 no Suratno et al. [1998] Indonesia Bogor, West Java no 0 U Suratno et al. [1998] Indonesia Bogor, West Java no 0 U Suratno et al. [1998] Indonesia Bogor, West Java no 0 no Suratno et al. [1998] Indonesia Bogor, West Java no 0 U Suratno et al. [1998] Indonesia Bogor, West Java no 0 U Yagi et al. [1996] Japan Ryugasaki, Ibaraki straw NH Bronson et al. [1997a] Philippines Los Baños no 0 U Bronson et al. [1997a] Philippines Los Baños no 0 AS Bronson et al. [1997a] Philippines Los Baños GM U Bronson et al. [1997a] Philippines Los Baños straw 5500 U Bronson et al. [1997a] Philippines Los Baños no 0 U Bronson et al. [1997a] Philippines Los Baños straw 5500 U Smith et al. [1982] USA Louisiana no 0 no 0 74 Smith et al. [1982] USA Louisiana no 0 U Smith et al. [1982] USA Louisiana no 0 U Smith et al. [1982] USA Louisiana no 0 U Smith et al. [1982] USA Louisiana no 0 U a Water regime: continuous flooding. b organic amendment: FYM, farmyard manure; GM, green manure. c Fertilizer type: AS, ammonium sulfate; PN, potassium nitrate; U, urea; NH 4 + : complex fertilizer including NH 4 +. d Mitigation options: DCD, dicyandiamide. e Includes both chemical and organic fertilizers. which is defined as the emission from fertilized plots minus that of a zero-n control plot (Table 2). The difference between the mean and median shows the skewness of the data distribution. Mean N 2 O emission ± standard deviation and EF for continuously flooded fields with chemical or organic fertilizer application during the rice-cropping season were 341 ± 474 g N ha 1 season 1 and 0.22 ± 0.24%, respectively. Mean N 2 O emission and EF for fields with midseason drainage and chemical or organic fertilizer application were 993 ± 1075 g N ha 1 season 1 and 0.37 ± 0.35%, respectively. Mean N 2 O emission and EF for all water regimes were 667 ± 885 g N ha 1 season 1 and 0.31 ± 0.31%, respectively. Mean N 2 O emission from continuously flooded fields was significantly lower than that from fields with midseason drainage, although N 2 O emissions within each water regime showed large variation. However, no significant difference in EF between the continuous flooding and midseason drainage water regimes was observed. Note that fewer EF data were available, because we were able to calculate EF only when zero-n control measurements were available. The mean N 2 O emission from rain-fed fields, provided only by Abao et al. [2000], was lower than but not significantly different from values for fields with other water regimes Background N 2 O Emissions [13] Mean background N 2 O emission (emission from paddy fields without N fertilizer application) during the cropping season was not significantly different between continuous flooding and midseason drainage regimes (Table 3). Large variations were observed within each water regime even in background emissions, and relatively few experiments included zero-n control plots. [14] Data for emission during the fallow period are listed in Table 4. After excluding measurements obtained over periods shorter than 50 days, which were much higher than those obtained over longer periods, we calculated a mean emission of 24 mg m 2 h 1. Note that only one value (16.3 mg m 2 h 1 [Chen et al., 1997]) for a zero-n control plot during cropping season was avail- 3of10

4 Table 1b. N 2 O Emissions From Paddy Fields During the Cropping Season a Amendment b Amendment, kg ha 1 Nitrogen Fertilizer c Tested Mitigation Option d Chemical N, kgn ha 1 N 2 O Emission, gn ha 1 Fertilizer-Induced N 2 O Emission Factor, e % Cai et al. [1999] China Fenqiu SM 5000 ABC, U Cai et al. [1999] China Fenqiu SM 5000 ABC, U Cai et al. [1999] China Fenqiu SM 5000 ABC, U Cai et al. [1997] China Nanjing no 0 No Cai et al. [1997] China Nanjing no 0 AS Cai et al. [1997] China Nanjing no 0 AS Cai et al. [1997] China Nanjing no 0 U Cai et al. [1997] China Nanjing no 0 U Xiong et al. [2002] China Yingtan, Jangxi vetch U Xiong et al. [2002] China Yingtan, Jangxi vetch No Xiong et al. [2002] China Yingtan, Jangxi no 0 U Xiong et al. [2002] China Yingtan, Jangxi no 0 No Xiong et al. [2002] China Yingtan, Jangxi no 0 U Xiong et al. [2002] China Yingtan, Jangxi no 0 No Xiong et al. [2002] China Yingtan, Jangxi no 0 U Xiong et al. [2002] China Yingtan, Jangxi no 0 No Khalil et al. [1998] China Beijing no 0 ABC Zheng et al. [2000] China Jiangsu no 0 ABC Zheng et al. [2000] China Jiangsu no 0 ABC Zheng et al. [2000] China Jiangsu no 0 ABC Zheng et al. [2000] China Jiangsu no 0 No Zheng et al. [2000] China Jiangsu no 0 No Zheng et al. [2000] China Jiangsu compost U Zheng et al. [2000] China Jiangsu no 0 U Kumar et al. [2000] India New Delhi no 0 No 0 46 Kumar et al. [2000] India New Delhi no 0 U Kumar et al. [2000] India New Delhi no 0 AS Kumar et al. [2000] India New Delhi no 0 U DCD Kumar et al. [2000] India New Delhi no 0 AS DCD Kumar et al. [2000] India New Delhi no 0 U TS Majumdar et al. [2000] India New Delhi no 0 No 0 34 Majumdar et al. [2000] India New Delhi no 0 U Majumdar et al. [2000] India New Delhi no 0 U DCD Majumdar et al. [2000] India New Delhi no 0 U NEU Majumdar et al. [2000] India New Delhi no 0 U NIU Pathak et al. [2002] India New Delhi no 0 U Pathak et al. [2002] India New Delhi FYM 6000 U Pathak et al. [2002] India New Delhi no 0 U DCD Pathak et al. [2002] India New Delhi no 0 No Suratno et al. [1998] Indonesia Bogor, West Java no 0 No Suratno et al. [1998] Indonesia Bogor, West Java no 0 U Suratno et al. [1998] Indonesia Bogor, West Java no 0 U Suratno et al. [1998] Indonesia Bogor, West Java no 0 No Suratno et al. [1998] Indonesia Bogor, West Java no 0 U Suratno et al. [1998] Indonesia Bogor, West Java no 0 U Yagi et al. [1996] Japan Ryugasaki, Ibaraki straw NH Nishimura et al. [2004] Japan Tsukuba, Ibaraki straw 2100 U Bronson et al. [1997a] Philippines Los Baños no 0 U Bronson et al. [1997a] Philippines Los Baños no 0 AS Bronson et al. [1997a] Philippines Los Baños GM U Bronson et al. [1997a] Philippines Los Baños straw 5500 U Bronson et al. [1997a] Philippines Los Baños no 0 U Bronson et al. [1997a] Philippines Los Baños straw 5500 U a Water regime: midseason drainage. b organic amendment: SM, swine manure; FYM, farmyard manure; GM, green manure. c Fertilizer type: ABC, ammonium bicarbonate; AS, ammonium sulfate; PN, potassium nitrate; U, urea; NH 4 + : complex fertilizer including NH 4 +. d Mitigation options: DCD, dicyandiamide; NEU, neem-coated urea; NIU, nimin-coated urea; TS, thiosulfate. e Both chemical and organic fertilizer are included. able for the fallow period among the compiled data. On the basis of the mean hourly emission, the total N 2 O emission during the fallow period was estimated to be 1495 g N ha 1 period 1, when the cropping season was assumed to be 110 days long. The estimated emission for the fallow period has large uncertainty because the number of measurements was limited, although fallow rice fields are considered to be an important source of N 2 O. It is not clear why measured N 2 O emissions were higher during short measurement periods [Bronson et al., 4of10

5 Table 1c. N 2 O Emissions From Paddy Fields During the Cropping Season a Amendment b Amendment, kg ha 1 Nitrogen Fertilizer c Tested Mitigation Option d Chemical N, kgn ha 1 N 2 O Emission, gn ha 1 Abao et al. [2000] Philippines Los Baños no 0 U Abao et al. [2000] Philippines Los Baños no 0 U Slow-U 90 4 Abao et al. [2000] Philippines Los Baños no 0 U Abao et al. [2000] Philippines Los Baños GM 3000 U Abao et al. [2000] Philippines Los Baños no 0 U Abao et al. [2000] Philippines Los Baños straw 3000 U a Water regime: Rain-fed, wet season. b organic amendment: GM, green manure (cowpea residue in this case). c Fertilizer type: U, urea. d Mitigation options: slow-u, slow-release urea. e Both chemical and organic fertilizer are included. Fertilizer-Induced N 2 O Emission Factor, e % 1997b]. Note that winter cropping and dry season cropping after the rice harvest were not considered here. The background emission for an entire year was estimated as 1820 g N ha 1 yr 1 from the sum of the mean background emission for all water regimes and the estimated fallow period emission Options for Mitigation of N 2 O Emissions From Rice Fields During the Rice-Cropping Season [15] Among tested options for mitigation of N 2 O emissions from rice fields during the growing season (Table 5), nitrification inhibitors (dicyandiamide and thiosulfate) and slow-release urea significantly (P < 0.05) reduced N 2 O emissions, although the data are few and the effectiveness of each mitigation option showed large variation. Neemcoated urea and nimin-coated urea, which are supposed to have nitrification inhibition properties and to be more locally available in India, did not significantly reduce N 2 O emissions [Majumdar et al., 2000] Trade-Off of CH 4 and N 2 O Emissions From Rice Paddy Fields [16] Midseason drainage is considered to be an effective option for mitigating methane emissions from rice fields [e.g., Yagi et al., 1997]. A statistical analysis of a large field-measurement data set indicated that compared with continuous flooding, a single midseason aeration can reduce the average seasonal CH 4 emission by 40%, and multiple aeration reduces it by 48% (X. Yan et al., Statistical analysis of the major variables controlling methane emission from rice fields, submitted to Global Change Biology, 2004) (hereinafter referred to as Yan et al., submitted manuscript, 2004). However, midseason drainage increases N 2 O emission by creating saturated or nearly saturated soil conditions, which promote N 2 O production [e.g., Zheng et al., 2000]. Cai et al. [1999] reported that the global warming potential (GWP) of N 2 O emissions was even higher than that of CH 4 emissions from Chinese paddy fields with midseason drainage when large amounts of chemical fertilizer (364.5 kg N ha 1 )or farmyard manure (5 t ha 1 ) were applied. Bronson et al. [1997a] found that the total GWP of continuously flooded fields was lower than that of fields drained midseason when no straw was applied, but it was higher when straw was applied. [17] When CH 4 emissions estimated by a statistical model proposed by Yan et al. (submitted manuscript, 2004) and mean N 2 O emissions calculated here (Table 2) were compared between continuous flooding and midseason drainage water regimes with no organic fertilizer or straw application (Table 6), midseason drainage appears to be generally the more effective option for mitigating net GWP; however, 15% to 20% of the benefit gained by decreasing CH 4 emission was offset by the increase in N 2 O emission. Yan et al. (submitted manuscript, 2004) estimated that application of rice straw at 6 t ha 1 (dry weight) before rice planting, which is roughly all the rice straw harvested, would increase CH 4 emission 3.1-fold, compared with that from soils without any organic amendment, for both continuous flooding and midseason drainage water regimes. Therefore, midseason drainage may also be an effective mitigation option when straw is applied. [18] Li et al. [2004] also reported that midseason drainage reduces net GWP compared with continuous Table 1d. N 2 O Emissions From Paddy Fields During the Cropping Season a Amendment Amendment, kg ha 1 Nitrogen Fertilizer Tested Mitigation Option Chemical N, kgn ha 1 N 2 O Emission, gn ha 1 Minami, 1987 Japan Konosu, Ibaraki no 0 unknown Minami, 1987 Japan Tsukuba, Ibaraki no 0 unknown Minami, 1987 Japan Mito, Ibaraki no 0 unknown a Water regime: unknown. Fertilizer Induced N 2 O Emission Factor, % 5of10

6 Figure 1. Relationships between total N input and N 2 O emission during the growing season for (a) all water regimes, including continuous flooding, midseason drainage, and rain-fed; (b) continuous flooding; (c) midseason drainage (MSD); and (d) rain-fed, wet season. Only Abao et al. [2000] reported data on a wet-season rain-fed water regime. Note that the scales of the axes differ among the graphs. flooding; 65% of the benefit gained by decreasing CH 4 emissions from rice fields in China was offset by an increase in N 2 O emissions, as determined by the denitrification-decomposition (DNDC) model. Frolking et al. [2004] used the DNDC model and an atmospheric model to simulate the effect of a change in water management from continuous flooding to midseason drainage on N 2 O and CH 4 emissions from rice fields and the relative radiative impact over 500 years. They found that, initially, a change in radiative forcing was dominantly the result of a decrease in CH 4 emissions, but long-term radiative forcing was dominantly the result of the increase of N 2 O emissions; thus, an initial 36-year cooling effect was followed by a long-term warming effect (e.g., 100 years or longer). They also suggested that the overall complexity of the radiative forcing response to the change in water management could not be captured by conventional GWP calculations Seasonal Pattern of N 2 O Emissions From Rice Fields [19] We tried to find a general seasonal pattern of N 2 O emissions from paddy fields during the rice-cropping period even though many different patterns were reported. Table 2. N 2 O Emissions From Rice Paddy Fields With Chemical or Fertilizer Applied During the Cropping Season a Water Regime Mean b Standard Deviation Median n Maximum Minimum N 2 O Emission, gn ha 1 Continuous flooding 341a Midseason drainage 993b Rain-fed, wet season 188ab All water regimes c Fertilizer-Induced N 2 O Emission Factor, % Continuous flooding 0.22a Midseason drainage 0.37a Rain-fed, wet season d ND ND ND ND ND ND All water regimes a N 2 O emissions from tests of mitigation options are not included. b Means followed by the same letter are not significantly different at P < c Includes unknown water regimes. Thus n of this category is greater than the sum of n for continuous flooding, midseason drainage, and rain-fed water regimes. d ND, no data, because no zero-n control data were available. 6of10

7 Table 3. N 2 O Emissions (in gn ha 1 ) From Rice Paddy Fields With No N Fertilizer Input During the Cropping Season Water Regime Mean a Standard Deviation Median n Maximum Minimum Continuous flooding 211a Midseason drainage 372a Rain-fed, wet season b ND ND ND ND ND ND All water regimes a Means followed by the same letter are not significantly different at P < b ND, no data; because no zero-n control data were available. We assessed figures showing seasonal changes in N 2 O flux for measurement series that include data on chemical or organic fertilizer input and measurements from zero-n control plots, but excluded mitigation option experiments. [20] One or more N 2 O peaks after transplanting or sowing were observed in about 70% of 79 measurements. During the flooded period, N 2 O peaks were reported in about 35% of measurements. N 2 O peaks were also reported in about 50% of measurements associated with an end-season drainage period, which is common practice both for middle season drainage and continuous flooding regimes. [21] In the case of fields with midseason drainage, N 2 O peaks were observed in 51 of 52 measurements during the midseason drainage period. N 2 O peaks have been generally observed after top dressing application [e.g., Cai et al., 1999], but some reports showed N 2 O peaks during the midseason drainage that were not related to the application of top dressing [e.g., Cai et al., 1997; Xiong et al., 2002]. Zheng et al. [2000] reported that N 2 O emission peaked during the midseason drainage and suggested that soil moisture is the most sensitive factor regulating N 2 O emissions. They reported explosive emissions of N 2 O when soil moisture was near 110% of the soil water holding capacity or the water-filled pore space was 99%. It is notable that N 2 O peaks during the midseason drainage have been reported for both fertilized and unfertilized fields [e.g., Cai et al., 1997], but N 2 O peaks from unfertilized fields are generally smaller than those from fertilized fields. In contrast, no N 2 O peak was reported by Yagi et al. [1996] during the midseason drainage in Japan, even after the application of top dressing. Table 4. N 2 O Emissions From Paddy Fields During the Fallow Period N 2 O Flux, mg m 2 h 1 N 2 O Emission, gn ha 1 Measurement Period in Fallow Season, Days Chen et al. [1997] China Shenyang Chen et al. [1997] China Shenyang Chen et al. [1997] China Shenyang Hou et al. [2000] China Shenyang Zheng et al. [2000] China Jiangsu Nishimura et al. [2004] Japan Tsukuba, Ibaraki Tsuruta et al. [1997] Japan Ryuugasaki, Ibaraki Xiong et al. [2002] China Yingtan, Jangxi Xiong et al. [2002] China Yingtan, Jangxi Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Bronson et al. [1997b] Philippines Los Baños Abao et al. [2000] Philippines Los Baños Abao et al. [2000] Philippines Los Baños Abao et al. [2000] Philippines Los Baños Abao et al. [2000] Philippines Los Baños Abao et al. [2000] Philippines Los Baños Abao et al. [2000] Philippines Los Baños Abao et al. [2000] Philippines Los Baños Abao et al. [2000] Philippines Los Baños of10

8 Table 5. Available Data on Possible Mitigation Options Tested Mitigation Option c Chemical N, kgn ha 1 Emission of Tested Mitigation Option Plot, d % Water Regime a Nitrogen Fertilizer b Kumar et al. [2000] India New Delhi MSD U DCD e Kumar et al. [2000] India New Delhi MSD AS DCD e Kumar et al. [2000] India New Delhi MSD U TS e Majumdar et al. [2000] India New Delhi MSD U DCD e Majumdar et al. [2000] India New Delhi MSD U NEU Majumdar et al. [2000] India New Delhi MSD U NIU Ghosh et al. [2003] India New Delhi CF U DCD e Ghosh et al. [2003] India New Delhi CF AS DCD e Ghosh et al. [2003] India New Delhi CF PN DCD e Pathak et al. [2002] India New Delhi CF U DCD e Pathak et al. [2002] India New Delhi MSD U DCD e Abao et al. [2000] Philippines Los Baños RF U Slow-U 90 3 e,f a Water regime: MSD, midseason drainage; CF, continuous flooding; RF, rain-fed, wet-season. b Fertilizer type: AS, ammonium sulfate; PN, potassium nitrate; U, urea. c Mitigation options: DCD, dicyandiamide; NEU, neem-coated urea; NIU, nimin-coated urea; TS, thiosulfate; slow-u, slow-release urea. d Fertilizer-induced N 2 O-N emission of the tested mitigation option plot compared with that of the conventional fertilizer plot. e Significantly different from conventional fertilizer plot at P < 0.05 by Duncan s multiple range test. Statistical test results are from the original papers. f Fertilizer-induced N 2 O emission could not be calculated because no zero-n control plot was available. Thus the percent of N 2 O-N emission (including background emission) from the tested mitigation option plot is compared with that from conventional fertilizer plot is shown. [22] After the rice has been harvested, large N 2 O peaks are commonly observed; in many cases, these peaks are larger than those observed during the cropping season [e.g., Hou et al., 2000; Nishimura et al., 2004]. Most measurements, however, were terminated at harvest and thus did not capture N 2 O emissions afterward. [23] Although water management has a large effect on N 2 O emission [e.g., Zheng et al., 2000], this pattern analysis can be expected to contain errors caused by the difficulty of determining the water regime, because details of water management (timing, number, and duration of drainage) were not described in many papers. In only seven papers among those reviewed were the seasonal changes in water depth for the entire cropping period reported [Yagi et al., 1996; Cai et al., 1997, 1999; Suratno et al., 1998; Zheng et al., 2000; Ghosh et al., 2003; Nishimura et al., 2004]. In addition, details of fertilizer management (timing and application method for both basal and supplemental fertilizer application, N content of organic fertilizer) or the actual cropping period (date of transplanting and harvest) were not described in some papers Other Factors Affecting N 2 O Emissions From Rice Fields [24] N 2 O emissions from rice paddy fields are affected by many factors, including type of fertilizer, climate, and soil type. However, those factors were not considered here because of limited data availability. For example, fertilizer type varied little; most measurements were from fields to which urea had been applied as fertilizer. Interannual variation was also not considered here, even though large interannual variation in N 2 O emissions from rice fields has been reported [e.g., Khalil et al., 1998]. [25] This analysis is also affected by the water regime classification scheme. We classified the water regime into three categories, but actual water management is more varied, especially in the case of midseason drainage. Local practices regarding the timing, number, and duration of drainage periods vary by region, and the timing and amount Table 6. Comparison of Estimated CH 4 Emission Determined by the Model of Yan et al. (submitted manuscript, 2004) and the Mean N 2 O Emission Found by This Study for Continuous Flooding and Midseason Drainage CH 4 Emission, mg m 2 h 1 CH 4 Emission, a kg ha 1 Season 1 N 2 O Emission, gn ha 1 Season 1 CO 2 Equivalent, b kg ha 1 Season 1 Reduced GHG by Drainage, CO 2 Equivalent, kg ha 1 Season 1 CH 4 Emission, Estimated From Model of Yan et al. (Without Fertilizer or Straw) Continuous flooding Single drainage Multiple drainage Mean N 2 O Emission by This Study (Without Fertilizer but Including Plots With Straw Application) Continuous flooding Midseason drainage a The cropping season assumed to be 110 days. b Calculated by using the global warming potential (GWP) for a time horizon of 100 years: CH 4 =23andN 2 O=296[IPCC, 2001]. 8of10

9 of rainfall greatly affect water management even for irrigated rice fields. Moreover, the details of drainage were not documented in many papers. [26] Some of the data were obtained by automated N 2 O flux monitoring [Bronson et al., 1997a, 1997b; Abao et al., 2000; Zheng et al., 2000; Nishimura et al., 2004]. Those results showed sharp peaks in N 2 O emissions from paddy fields, especially during periods of intermittent drainage. Most of the available data, however, were obtained manually once or twice a week by the static chamber method, so sharp peaks might have been missed, causing seasonal N 2 O emissions to be underestimated. Also, only two papers reported measurements covering the entire year [Zheng et al., 2000; Nishimura et al., 2004], although many data were available on N 2 O emissions during the rice-cropping period. 4. Conclusions [27] We reviewed published reports of N 2 O emissions from rice paddy fields and tried to establish a quantitative basis on which to develop national or regional emission inventories. We propose a value of 0.31 ± 0.31% for the fertilizer-induced emission factor during the rice-cropping period and a value of 1820 g N ha 1 yr 1 for background emission for an entire year. The estimated background emission value has large uncertainty, because available measurements were very limited, especially for the fallow period, even though fallow rice fields are considered an important source of N 2 O. [28] Midseason drainage is an effective option for mitigating methane emissions and net GWP from rice fields, although mean N 2 O emission is increased by midseason drainage compared with continuous flooding. Available data on tested options for the mitigation of emissions from rice fields during the growing season were also assessed. Although few data are available, we found that application of a nitrification inhibitor or slow-release urea significantly reduced N 2 O emissions. More field measurements, especially for the entire year, including the fallow period, and experiments that include a zero-n control are required for further analyses. [29] Acknowledgment. This work was supported by the Global Environment Research Fund, Ministry of the Environment, Japan. References Abao, E. B., Jr., K. F. Bronson, R. Wassmann, and U. Singh (2000), Simultaneous records of methane and nitrous oxide emissions in ricebased cropping systems under rainfed conditions, Nutr. Cycling Agroecosyst., 58, Bouwman, A. F., L. J. M. Boumans, and N. H. Batjes (2002), Emissions of N 2 O and NO from fertilized fields: Summary of available measurement data, Global Biogeochem. Cycles, 16(4), 1058, doi: / 2001GB Bronson, K. F., H. U. Neue, U. Singh, and E. B. Abao Jr. (1997a), Automated chamber measurements of methane and nitrous oxide flux in a flooded rice soil: I. Residue, nitrogen, and water management, Soil Sci. Soc. Am. J., 61, Bronson, K. F., U. Singh, H. U. Neue, and E. B. Abao Jr. (1997b), Automated chamber measurements of methane and nitrous oxide flux in a flooded rice soil: II. Fallow period emissions, Soil Sci. Soc. Am. J., 61, Cai, Z., G. Xing, X. Yan, H. Xu, H. Tsuruta, K. Yagi, and K. Minami (1997), Methane and nitrous oxide emissions from rice paddy fields as affected by nitrogen fertilizers and water management, Plant Soil, 196, Cai, Z., G. Xing, G. Shen, H. Xu, X. Yan, H. Tsuruta, K. Yagi, and K. Minami (1999), Measurements of CH 4 and N 2 O emissions from rice paddies in Fengqiu, China, Soil Sci. Plant Nutr., 45, Chen, G. X., G. H. Huang, B. Huang, K. W. Yu, J. Wu, and H. Xu (1997), Nitrous oxide and methane emissions from soil-plant systems, Nutr. Cycling Agroecosyst., 49, Food and Agriculture Organization/International Fertilizer Industry Association (FAO/IFA) (2001), Global Estimate of Gaseous Emissions of NH 3, NO and N 2 O from Agricultural Land, Rome. Freney, J. R., O. T. Denmead, I. Watanabe, and E. T. Craswell (1981), Ammonia and nitrous oxide losses following applications of ammonium sulfate to flooded rice, Aust. J. Agric. Res., 32, Frolking, S., C. Li, R. Braswell, and J. Fuglestvedt (2004), Short- and longterm greenhouse gas and radiative forcing impacts of changing water management in Asian rice paddies, Global Change Biol., 10, , doi:10.111/j x. Ghosh, S., D. Majumdar, and M. C. Jain (2003), Methane and nitrous oxide emissions from an irrigated rice of North India, Chemosphere, 51, Granli, T., and O. C. Bockman (1994), Nitrogen oxide from agriculture, Norw. J. Agric. Sci., 12, 128 pp. Hou, A. X., G. X. Chen, Z. P. Wang, O. Van Cleemput, and W. H. Patrick Jr. (2000), Methane and nitrous oxide emissions from a rice field in relation to soil redox and microbiological processes, Soil Sci. Soc. Am. J., 64, International Panel on Climate Change (IPCC) (1997), Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories Workbook, vol. 2, Cambridge Univ. Press, New York. International Panel on Climate Change (IPCC) (2000), Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories, Cambridge Univ. Press, New York. International Panel on Climate Change (IPCC) (2001), Climate Change 2001, the Scientific Basis, Cambridge Univ. Press, New York. Khalil, M. A. K., R. A. Rasmussen, M. J. Shearer, Z. L. Chen, H. Yao, and J. Yang (1998), Emissions of methane, nitrous oxide, and other trace gases from rice fields in China, J. Geophys. Res., 103(D19), 25,241 25,250. Kumar, U., M. C. Jain, H. Pathak, S. Kumar, and D. Majumdar (2000), Nitrous oxide emission from different fertilizers and its mitigation by nitrification inhibitors in irrigated rice, Biol. Fertil. Soils, 32, Li, C., A. Mosier, R. Wassmann, Z. Cai, X. Zheng, H. Yao, H. Tsuruta, J. Boonjawat, and R. Lantin (2004), Modeling greenhouse gas emissions from rice-based production systems: Sensitivity and upscaling, Global Biogeochem. Cycles, 18, GB1043, doi: /2003gb Majumdar, D., S. Kumar, H. Pathak, M. C. Jain, and U. Kumar (2000), Reducing nitrous oxide emission from an irrigated rice field of North India with nitrification inhibitors, Agric. Ecosyst. Environ., 81, Minami, K. (1987), Emission of nitrous oxide (N 2 O) from agro-ecosystem, Jpn. Agric. Res. Q., 21, Ministry of Agriculture, Forestry, and Fisheries of Japan (MAFF) (1982), Conservation of Soil Fertility, vol. 60, Quality of Manures and Fertilizers (in Japanese), Tokyo. National Federation of Agricultural Co-operative Associations (1980), Fertilizer Guide (in Japanese), Tokyo. Nishimura, S., T. Sawamoto, H. Akiyama, S. Sudo, and K. Yagi (2004), Methane and nitrous oxide emissions from a paddy field with Japanese conventional water management and fertilizer application, Global Biogeochem. Cycles, 18, GB2017, doi: /2003gb Pathak, H., A. Bhatia, S. Prasad, S. Singh, S. Kumar, M. C. Jain, and U. Kumar (2002), Emission of nitrous oxide from rice-wheat systems of Indo-Gangetic plains of India, Environ. Monit. Assess., 77, Smith, C. J., M. Brandon, and W. H. Patrick Jr. (1982), Nitrous oxide emission following urea-n fertilization of wetland rice, Soil Sci. Plant Nutr., 28(2), Suratno, W., D. Murdiyarso, F. G. Suratmo, I. Anas, M. S. Saeni, and A. Rambe (1998), Nitrous oxide flux from irrigated rice fields in West Java, Environ. Pollut., 102(1, Suppl. 1), Tsuruta, H., K. Kanda, and T. Hirose (1997), Nitrous oxide emission from a rice paddy field in Japan, Nutr. Cycling Agroecosyst., 49, Xing, G. X., and Z. L. Zhu (1997), Preliminary studies on N 2 O emission fluxes from upland soils and paddy soils in China, Nutr. Cycling Agroecosyst., 49, Xiong, Z. Q., G. X. Xing, H. Tsuruta, G. Y. Shen, S. L. Shi, and L. J. Du (2002), Measurement of nitrous oxide emissions from two ricebased cropping systems in China, Nutr. Cycling Agroecosyst., 64, of10

10 Xu, Y. C., Q. R. Shen, M. L. Li, K. Dittert, and B. Sattelmacher (2004), Effect of soil water status and mulching on N 2 O and CH4 emission from lowland rice field in China, Biol. Fertil. Soils, 39, Yagi, K., H. Tsuruta, K. Kanda, and K. Minami (1996), Effect of water management on methane emission form a Japanese rice paddy field: Automated methane monitoring, Global Biogeochem. Cycles, 10, Yagi, K., H. Tsuruta, and K. Minami (1997), Possible mitigation options from rice cultivation, Nutr. Cycling Agroecosyst., 49, Yan, X., H. Akimoto, and T. Ohara (2003), Estimation of nitrous oxide, nitric oxide and ammonia emissions from croplands in East, Southeast and South Asia, Global Change Biol., 9, Zheng, X., M. Wang, Y. Wang, R. Shen, J. Gou, J. Li, J. Jin, and L. Li (2000), Impact of soil moisture on nitrous oxide emission from croplands: A case study on the rice-based agro-ecosystem in southeast China, Chemosphere Global Change Sci., 2, H. Akiyama and K. Yagi, National Institute for Agro-Environmental Sciences, Kannondai, Tsukuba , Japan. (ahiroko@affrc. go.jp) X. Yan, Frontier Research Center for Global Change, Shaowa-machi , Yokohama , Japan. 10 of 10