Greenhouse gas fluxes and NO release from a Chinese subtropical rice-winter wheat rotation system under nitrogen fertilizer management

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1 JOURNAL OF GEOPHYSICAL RESEARCH: BIOGEOSCIENCES, VOL. 118, , doi:1.12/jgrg.261, 213 Greenhouse gs fluxes nd NO relese from Chinese subtropicl rice-winter whet rottion system under nitrogen fertilizer mngement Zhisheng Yo, 1 Xunhu Zheng, 1 Rui Wng, 1 Hibo Dong, 1 Bohu Xie, 1 Boling Mei, 1 Zixing Zhou, 1 nd Jinguo Zhu 2 Received 24 Jnury 213; revised 29 Mrch 213; ccepted 3 April 213; published 8 My 213. [1] Although synthetic nitrogen fertilizers ply n importnt role in incresing cerel grin yields, there hve been incresed concerns bout their intensive utiliztion nd environmentl consequences. The overll gol of this study is to gin n insight into the integrted evlution of greenhouse gs emission nd nitric oxide (NO) relese nd grin yield s ffected by nitrogen fertiliztion in subtropicl rice-whet rottion system. The ssessment ws bsed on four consecutive yerly mesurements of the fluxes of methne (CH 4 ), nitrous oxide (N 2 O) nd ecosystem respirtion (CO 2 ), nd the simultneous observtion of NO emissions in nonrice sesons under three fertiliztion prctices (i.e., the conventionl frmers prctice with common nitrogen ppliction rte, n lterntive prctice with reduced nitrogen input, nd no nitrogen ppliction s control). Clerly, these trce gs fluxes showed lrgely intr-nnul nd internnul vritions, highlighting the importnce of entire yer mesurement for multiple yers to chieve representtive nnul estimtes. The nnul men CH 4 fluxes vried from 95 kg C h 1 (7.8 kg C t 1 grin) for the frmers prctice to 25 kg C h 1 (25.7 kg C t 1 grin) for the control, indicting tht nitrogen fertiliztion inhibited CH 4 emissions. Across ll the yers, the nnul N 2 Oemissions incresed exponentilly with n incresing nitrogen rte nd hrvested boveground biomss. The nnul N 2 O emission verged kgNh 1 ( g N t 1 grin) for ll tretments. The nnul direct emission fctors of N 2 O-N tended to increse with incresing nitrogen rte nd verged.61% nd.85% for the lterntive nd frmers prctices, respectively. Over ll nonrice sesons, the sesonl men NO emissions rnged from.15 to 1.4 kg N h 1 (58 253gNt 1 grin), nd were equivlent to.43% to.54% of the pplied nitrogen. Averging cross the 4 yers, the nnul ggregte emissions of CH 4 nd N 2 Owere7.4tCO 2 -eq h 1 (928 kg CO 2 -eq t 1 grin) for the control nd t CO 2 -eq h 1 ( kg CO 2 -eq t 1 grin) for the fertilized tretments. Despite the comprble greenhouse effect between the lterntive nd frmers prctices, reducing the common N rte by 37% resulted in decresed NO emission nd incresed nitrogen use efficiency, nd negligible effects on economic return from grin yields. Cittion: Yo, Z., X. Zheng, R. Wng, H. Dong, B. Xie, B. Mei, Z. Zhou, nd J. Zhu (213), Greenhouse gs fluxes nd NO relese from Chinese subtropicl rice-winter whet rottion system under nitrogen fertilizer mngement, J. Geophys. Res. Biogeosci., 118, , doi:1.12/jgrg.261. Additionl supporting informtion my be found in the online version of this rticle. 1 Stte Key Lbortory of Atmospheric Boundry Lyer Physics nd Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Acdemy of Sciences, Beijing, Chin. 2 Stte Key Lbortory of Soil nd Sustinble Agriculture, Nnjing Institute of Soil Sciences, Chinese Acdemy of Sciences, Nnjing, Chin. Corresponding uthor: X. Zheng, Stte Key Lbortory of Atmospheric Boundry Lyer Physics nd Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Acdemy of Sciences, Beijing 129, Chin. (xunhu.zheng@post.ip.c.cn) 213. Americn Geophysicl Union. All Rights Reserved /13/1.12/jgrg Introduction [2] The exchnge of crbon dioxide (CO 2 ), methne (CH 4 ), nitrous oxide (N 2 O), nd nitric oxide (NO) between griculturl ecosystems nd the tmosphere considerbly influences globl wrming nd tmospheric chemistry [Intergovernmentl Pnel on Climte Chnge (IPCC), 27]. Agriculturl prctices hve been estimted to relese Pg CO 2 -equivlent yr 1 nd 1.6 Tg NO-N yr 1, ccounting for 1 12% nd 5% of the globl nthropogenic greenhouse gs (GHG) nd NO emissions, respectively [IPCC, 27]. The estimtes for GHG nd NO emissions from griculturl fields on the regionl nd globl scles re highly uncertin becuse the mesurements conducted to dte re insufficient for 623

2 temporl nd sptil representtions of the climte, soil, nd mngement conditions [Stehfest nd Bouwmn, 26]. The mjority of the field mesurements of GHG nd NO emissions were conducted in temperte regions, nd there hve been few flux mesurements in tropicl nd subtropicl cropping systems [Stehfest nd Bouwmn, 26; Wng et l., 211]. Stehfest nd Bouwmn [26] summrized the informtion from 18 mesurements of N 2 O fluxes in griculturl fields nd indicted tht 13% nd 14% of the mesurements were performed in tropicl nd subtropicl climtes, respectively. [3] It is well known tht in griculturl soils C- nd N- trce gses re produced or consumed by microbil processes, but the mgnitude of the exchnges between the soil nd the tmosphere is lrgely ffected by the soil temperture, inorgnic N(NH 4 + nd NO 3 ) content, nd moisture content [Conrd, 1996, 22]. Agriculturl prctices such s nitrogen fertiliztion tht drive soil N vilbility my significntly chnge the globl tmospheric budgets of these gses [IPCC, 27]. It hs been generlly recognized tht the ppliction of synthetic nitrogen fertilizers is one of the min sources of nthropogenic N 2 O nd NO emissions into the tmosphere [Mtson et l., 1998], nd reserchers hve shown the depressive effects of this prctice on CH 4 consumption in uplnd griculturl soils [Aronson nd Helliker, 21]. Previous reports regrding the effect of N fertiliztion on CH 4 emission from pddy fields re controversil. Some reserchers observed tht the ddition of synthetic N fertilizers incresed CH 4 emission from rice fields [Lindu et l., 1991; Corton et l., 2], lthough other studies reported no chnge or reduced CH 4 emission fter N fertiliztion [Ci et l., 27; Xie et l., 21; Yo et l., 212]. In ddition, severl studies indicted tht the correltion between nitrogen input nd NO nd N 2 O emissions my be more complicted [Ludwig et l., 21; Mcswiney nd Robertson, 25]. For instnce, N-trce gs emissions from griculturl fields exhibit threshold response to nitrogen fertiliztion. At fertiliztion rtes less thn or equl to those required for crop uptke, the utiliztion of synthetic nitrogen fertilizers tended to crete positively liner response in NO nd N 2 Oemissions[Liu et l., 25; Hlvorson et l., 28]. When fertilizer rtes were in excess of the crop requirement, N-trce gs emissions often exponentilly incresed with incresing N inputs [Vn Groenigen et l., 21; M et l., 21; Hoben et l., 211]. Overll, nitrogen fertiliztion not only potentilly regultes N 2 O nd NO emissions nd CH 4 fluxes, but it lso strongly ffects crop productivity nd CO 2 emissions [Treseder, 28]. The ddition of nitrogen fertilizer cn rise crop yield nd biomss, which my hve positive effect on soil C sequestrtion s result of the biomss input into the soil from crop residues nd roots [Vn Groenigen et l., 26; Liu nd Grever, 29]. Accordingly, comprehensive ssessment of the nitrogen fertiliztion effects on GHG fluxes requires considering the net exchnges of the C- nd N-trce gses simultneously becuse of the trdeoffs mong them [Liu nd Grever, 29; Shng et l., 211]. Menwhile, it hs been suggested tht GHG emissions (or globl wrming potentil (GWP)) should be ssessed s function of crop yield, i.e., yield-scled GWP [Shng et l., 211; Linquist et l., 212]. [4] As reported by Heffer [29], more thn 5% of the globl synthetic nitrogen fertilizers re pplied in the production of the mjor cerels (i.e., rice, whet, nd mize). Chin is mjor griculturl producer, nd recent studies hve shown tht Chinese frmers hve demonstrted n excessively high utiliztion or overuse of synthetic nitrogen fertilizers [Ju et l., 29]. For exmple, the verge utiliztion of synthetic nitrogen fertilizers in Chin ws in excess of 2 kg N h 1 in 2, which ws much higher thn the norml use in Indi (under 1 kg N h 1 ) nd in developed countries (pproximtely 12 kg N h 1 ) [Hung et l., 212]. The widespred overuse of synthetic nitrogen fertilizers hs resulted in lrge nitrogen losses in the form of N-trce gses (e.g., N 2 O nd NO) nd low nitrogen use efficiency (NUE) [Mtson et l., 1998; Ju et l., 29]. Therefore, improving nitrogen fertilizer mngement in high-intensity griculturl systems is of gret importnce in the mitigtion of C- nd N-trce gs fluxes nd in crop production sustinbility. In the Chinese subtropics, n nnul rice-winter whet rottion cropping system is used in pproximtely 13 million hectres, which provides pproximtely 63% of the totl cerel grin yields ( gov.cn/english/sttisticldt/) [Chin Sttisticl Yerbook, 21]. However, the mjority of previous studies on GHG fluxes from pddy fields under N fertiliztion mngement were only performed during the rice growing period [e.g., Ci et l., 1997; Zou et l., 29; Xie et l., 21], nd few yer-long mesurements considered the entire ricewinter whet rottion cycle. In one-yer study conducted in Nnjing, Zou et l. [25] found pronounced liner reltionships between the N 2 O emissions nd the synthetic N ppliction rte during the rice nd winter whet sesons nd in the nnul rottion cycle. The emission fctors of N 2 O-N (i.e., the percentge of nitrogen fertilizer lost s N 2 O-N emission in the current seson or yer) were 1.8%, 1.49%, nd 1.26% for the rice seson, winter whet seson, nd nnul rottion cycle, respectively. The liner correltions between N 2 O emissions nd the synthetic N ppliction rte were lso observed in single-yer field mesurement on rice-whet rottion cropping system under intermittent irrigtion mngement, with n nnul emission fctor of.85% [Liu et l., 21]. Clerly, integrted evlutions of N fertiliztion mngement lterntives in terms of their performnce in decresing C- nd N-trce gs fluxes while remining fesible for sustining grin yields re considerbly lcking for the rice-winter whet rottion cropping system. [5] In this study, we present the results of 4 yer field mesurement in which CH 4,N 2 O, CO 2, nd NO fluxes nd crop productivity were observed simultneously in subtropicl rice-winter whet rottion cropping system under three synthetic N fertiliztion rtes. The min objectives of this study were to () chrcterize the responses of C- nd N-trce gs fluxes to fertiliztion rtes, with fluxes expressed on both n re- nd yield-scled bses; (b) determine the emission fctors of N 2 O nd NO for different fertiliztion rtes nd cropping yers; nd (c) ssess the efficcy of using reduced N fertiliztion to minimize the net GHG emission while sustining grin yield or improving NUE. 2. Mterils nd Methods 2.1. Study Site nd Experimentl Design [6] The field mesurements were conducted in pddy soils ( N, E) tht were locted in the north of Jingsu province, Chin. This region is typicl rice-winter 624

3 whet cropping re, which hs northern subtropicl monsoon climte. The men nnul temperture nd men nnul rinfll re pproximtely 15.9 C nd 924 mm, respectively. The soil is clssified s fluvisol ( Agl/gll/wrb/doc/wrb26finl.pdf) [IUSS Working Group WRB, 26] with sndy lom texture (58% snd nd 14% cly) nd ph of 8. in the upper 15 cm. The soil orgnic crbon nd nitrogen content in the cultivted lyer verged 18.4nd1.45gkg 1, respectively. [7] The experiment ws performed over the course of four consecutive rice-whet rottion cycles from June 24 to June 28. The study consisted of three N fertilizer ppliction rtes, rrnged in rndomized complete block design with three replictions in ech yer (see Tble S1 in the uxiliry mteril). These ppliction rtes included the following: the conventionl frmers prctice (FP) for the region, s determined vi frm survey; the lterntive prctice (AP), which ws in ccordnce with gronomists recommendtions nd pplied less N fertilizer in the rottion cycle; nd control (CK) tht received no N fertilizer. In the locl frmers prctice, 25 nd 225 kg N h 1 of compound fertilizer nd ure were pplied in the rice- nd whetgrowing sesons, respectively. Compound fertilizer combined with ure ws pplied with three splits for the rice nd whet growing seson s follows: 36% s bsl fertilizer, 24% s tillering fertilizer, nd 4% s pnicle fertilizer in the rice seson, nd 5% s bsl fertilizer, 1% s jointing fertilizer, nd 4% s pnicle fertilizer in the whet seson (Tble S1). In the lterntive prctice, 15 kg N h 1 of compound fertilizer nd ure ws pplied in the rice- nd whet-growing sesons, consistent with the recommended rtes for this region [Zhu nd Chen, 22]. Similr to the frmers prctice, split pplictions of N fertilizer were dopted in the lterntive prctice, with two splits for the rice seson (6% s bsl fertilizer nd 4% s pnicle fertilizer) nd three splits for the whet seson (5% s bsl fertilizer, 1% s jointing fertilizer, nd 4% s pnicle fertilizer). In ddition, bsed on the locl convention, phosphorous nd potssium fertilizers were pplied t equl rtes of 7 nd 75 kg h 1 s bsl fertiliztion for ll tretments during the rice nd whet growing periods, respectively. [8] From 24 to 28, rice seedlings were usully trnsplnted in mid-june nd hrvested in middle or lte October. In the following seson, winter whet is usully sown in erly November nd hrvested in erly June of the following yer (Tble S1). The hrvested crop residues were fully removed from the field for other uses, nd the soil ws plowed prior to rice trnsplnting nd whet sowing. In greement with the common wter prctices in this region nd in other res of Chin, intermittent irrigtion with midseson ertion (i.e., flooding-dringe-reflooding-moist) ws dopted in ll field plots during the rice period, while no rtificil irrigtion occurred in the following whet seson [Yo et l., 21] Crbon- nd Nitrogen-Trce Gs Flux Mesurements [9] The N 2 O nd CH 4 fluxes nd the ecosystem respirtion (CO 2 ) were mesured simultneously over the entire rottion cycles using sttic opque mnul gs smpling chmbers, s described by Yo et l. [29]. Bsed on our previous results, which showed tht up to 97% of the totl NO emissions from rice-whet rottion systems were relesed in the uplnd whet seson [Zhou et l., 27], the NO fluxes in this study were monitored only during the nonrice period (i.e., the fllow nd whet growing seson) using the sme method s in the GHG mesurements [Mei et l., 29]. In the center of ech experimentl plot, rectngulr stinless steel frme (5, 5, nd 15 cm in length, width nd height, respectively) ws inserted into the soil nd mintined in plce throughout the entire rottion cycle, except when it ws removed for necessry frming prctices (e.g., tillge). At the time of the gs smpling, the frme ws covered by vented insulted stinless steel chmber with bottom re of.25 m 2 nd height of 5 or 1 cm depending on crop growth, nd gs smples were tken with 6 ml polypropylene syringe t regulr intervls (, 8, 16, 24, nd 32 min fter covering). The gs concentrtions in the smples were nlyzed within 4 h using gs chromtogrphy instrument (Agilent 489D, Agilent Technologies, Plo Alto, CA, USA) equipped with n electron cpture detector for N 2 O detection nd flme ioniztion detector for CH 4 nd CO 2 detection ( nickel ctlyst pplied for converting CO 2 to CH 4 ). The DN-Ascrite nd DN-CO 2 methods described by Zheng et l. [28] were used for the N 2 O nlysis. Additionl detils for the instrumentl configurtions for nlyzing the gses were s described by Zheng et l. [28]. The fluxes were clculted from the rte of chnge in the gs concentrtions in the enclosed chmber hedspce with time [Hutchinson nd Livingston, 1993]. [1] The NO fluxes were determined by smpling twice from the chmber enclosure tht ws used for the GHG mesurements [Mei et l., 29]. One smple ws tken using KNF/N86KNDC pump (Neuberger Inc., Germny) t the beginning of the enclosed-chmber period, nd the other ws tken t the end of this period, nd the smples were injected into n evcuted bg mde of inert luminum-coted plstic. Within 1 h of collection, the NO in the smpling bgs ws mesured using TE-42C chemiluminescent NO-NO 2 -NO x nlyzer (Thermo Environmentl Instruments Inc., USA). The flux ws clculted from the concentrtion difference between the two smples collected t the beginning nd end of the chmber enclosure period. NO flux ws corrected for the hedspce temperture nd mbient ir pressure effects [Zheng et l., 23]. The NO x nlyzer ws clibrted prior to nd t the end of ech growing seson using TE-146i dilution-titrtion instrument (dynmic gs clibrtor). [11] In ddition, soil CO 2 emission ws mesured using 15 cm 2 cm 2 cm (length width height) polyvinyl chloride chmbers from November 24 to August 25. The chmber frmes were instlled between the rows of the plnts. The gs smples for CO 2 detection were drwn using 2 ml syringes t, 5, 1, 15, nd 2 min, respectively. The detection nd clcultion methods were the sme s described bove for the ecosystem respirtion mesurements. [12] Generlly, the C- nd N-trce gs fluxes were observed between 9: A.M. nd 11: A.M. becuse the soil temperture during this time ws close to the dily men soil temperture [Yo et l., 29]. The gs smples were usully tken pproximtely two to three times per week t intervls of 2 to 3 dys, while mesurements were conducted every dy for pproximtely one week during the expected high emission periods, e.g., in the midseson ertion stge during the rice seson nd following fertiliztion nd substntil precipittion during the nonrice seson. 625

4 Temperture ( C) e Precipittion Air temperture Soil temperture b c d f g h Precipittion (mm d -1 ) Floodwter (cm) WFPS Floodwter J.1 A.1 O.1 D.1 F.1 A.1 J.1 A.1 O.1 D.1 F.1 A.1 J.1 A.1 O.1 D.1 F.1 A.1 J.1 A.1 O.1 D.1 F.1 A.1 J.1 Dte (month.dy) WFPS (%) Figure 1. The dynmics of ( d) dily precipittion, ir nd soil (5 cm) tempertures nd (e h) floodwter depth in the rice growing sesons nd WFPS (wter-filled pore spce) t 8 cm soil depth in the nonrice sesons during ech nnul rice-whet cycle of Auxiliry Mesurements [13] The soil temperture t depth of 5 cm ws mesured once dy between 9: A.M. nd 11: A.M. using mnul thermocouple thermometer (JM624, Tinjin Jinming Instrument Co. Ltd., Chin). The ir temperture nd dily precipittion were recorded using n on-site utomtic meteorologicl sttion. The field floodwter depth in the rice seson ws monitored dily using stinless steel ruler, nd the soil ( 8 cm) moisture in the nonrice seson ws mesured dily djcent to the frmes using portble frequency domin reflector probe (RDS Technology Co., Ltd Jingsu, Nnjing, Chin). To determine the inorgnic N (NH 4 + nd NO 3 ) content in the soil, soil smples were tken from three points per experimentl plot t depths of to1 cm t weekly intervls using 3 cm dimeter guge uger. Following the smpling, the smples were bulked for ech tretment, nd the inorgnic N content of the field moist soil smples ws mesured using.1 mol L 1 CCl 2 extrction (soil:wter = 1:1) nd colorimetric techniques [Yo et l., 21]. The soil inorgnic N mesurements were conducted from 1 June 25 to 25 October 26 due to shortge of lbor. In ddition, fter the physiologicl mturity of the rice nd whet, the boveground biomss, including strw nd grin, ws hrvested mnully from five subplots with.36 m 2 in ech experimentl plot. The hrvested boveground biomss ws oven-dried for 3 dys t 8 C nd weighed to obtin the dry strw nd grin yields. The strw nd grin smples were ground nd nlyzed using the potssium dichromte-volumetric method nd the semimicro Kjeldhl method for totl C nd N content, respectively [Liu et l., 212]. The yields of strw-c/n, grin-c/n, nd the totl boveground C/N (strw plus grin) were clculted by multiplying the strw nd grin C/N concentrtions by the dry strw nd grin yields, respectively Dt Processing nd Sttisticl Anlysis [14] The fluxes of N 2 O, NO, nd CH 4 nd the ecosystem respirtion (CO 2 ) for ech tretment nd smpling dte were determined s the men of the three fluxes from the three sptil replictions. The dily C- nd N-trce gs fluxes for the dtes between smplings were estimted using liner interpoltion, nd the totl cumultive emissions were clculted s the sum of ll dily fluxes for the rice seson, nonrice seson, nd entire rottion cycle for ech yer. To more effectively evlute the effects of the fertilizer prctices on the C- nd N-trce gs fluxes, the sesonl nd nnul cumultive emissions were expressed on both n re- nd grin yield-scled bses. The CO 2 equivlents (CO 2 -eq) of sesonl nd nnul CH 4 nd N 2 O fluxes were clculted using GWP indices of 25 nd 298, respectively, over 1 yer time horizon [IPCC, 27]. The fertilizer-induced direct emission fctors (EF d s) for N 2 O-N nd NO-N emissions were clculted by subtrcting the totl cumultive emissions of N 2 O nd NO in the control tretment from the corresponding cumultive emissions in ech fertilized tretment nd dividing the result by the fertilizer ppliction rte. The fertilizer NUE ws clculted by subtrcting the boveground N yield in the control tretment from the boveground N yield in ech fertilized tretment nd dividing the result by the pplied totl mount of N fertilizer. [15] The sttisticl nlyses were conducted using SPSS 12. (SPSS Inc., Chicgo, IL, USA) nd Origin 7. (Origin Lb Corportion, USA). The differences in the totl mounts of N 2 O, CH 4, CO 2, nd NO fluxes from the rice-winter whet systems from 24 to 28, s ffected by the N fertilizer tretment, yer, nd their interction, were exmined using two-wy nlysis of vrince. The differences in the grin yields nd totl 626

5 + NH 4 content (mg N kg -1 SDW) CK AP FP N 2 O emission (μg N m -2 h -1 ) c CK AP FP Overll dt - NO 3 content (mg N kg -1 SDW) b 5-rice Non-rice 6-rice NO emission (μg N m -2 h -1 ) d J.1 A.1 O.1 D.1 F.1 A.1 J.1 A.1 O Dte (month.dy, from 25 to 26) Soil minerl N (NH 4 + +NO3 -, mg N kg -1 SDW) Figure 2. Chnges in ( b) soil NH + 4 nd NO 3 contents, nd (c d) dependency of N 2 O nd NO emissions on soil minerl N (NH + 4 +NO 3 ) contents for ll fertilizer prctices (i.e., the conventionl frmers prctice with common nitrogen ppliction rte (FP), n lterntive prctice with reduced nitrogen input (AP) nd no nitrogen ppliction s control (CK)) during the rice-whet rottion cycle from June 25 to October 26. Regression curves given refer to the significntly positive correltions between soil minerl N (NH + 4 +NO 3 ) contents nd N 2 O emissions (R 2 =.18.62, P <.1) nd NO emissions (R 2 =.36.71, P <.1). For the AP nd FP tretments, liner regression curve best described the correltions between N 2 O nd NO emissions nd soil minerl N contents, but cross ll the tretments, the reltionships between N-trce gs emissions nd soil minerl N contents were best described by the exponentil response curves. SDW is soil dry weight. Verticl brs in Figures 2 nd 2b indicte stndrd errors of 3-sptil replictes. mounts of the C- nd N-trce gs fluxes mong the three tretments during the experimentl period were exmined by one-wy ANOVA with Tukey s multiple rnge test. The reltionships between the NO, N 2 O, CH 4, nd CO 2 fluxes nd the environmentl vribles (e.g., the strw nd grin yields, inorgnic N content, nd fertilizer rte) were evluted using liner or nonliner regression process. Tble 1. The Chrcteristics in Strw nd Grin Yields (Men Stndrd Error, in t h 1 ) nd Their Crbon nd Nitrogen Concentrtions (in %) t Physiologicl Mturity, nd the Estimted Nitrogen Use Efficiency (in %) Under Different Fertilizer Prctices During the Rice nd Whet Sesons of Yer Code b SY TC TN GY TC TN NUE SY TC TN GY TC TN NUE c Rice Seson Whet Seson c CK AP b b b b FP b b b b CK AP b b b FP b b b CK AP b b b FP b b c b CK AP b b b FP b b b CK AP b b b b FP c b b b Men vlues of the four investigted sesons. b CK, no nitrogen fertilizer; AP, the lterntive prctice tht pplied 15 kg N h 1 for both the rice nd whet sesons; FP, the frmers prctice tht pplied 25 nd 225 kg N h 1 for the rice nd whet seson, respectively. c SY, strw yield; TC, totl crbon concentrtion; TN, totl nitrogen concentrtion; GY, grin yield; NUE, nitrogen use efficiency. Different letters within the sme column indicte sttisticlly significnt differences mong tretments in ech seson. 627

6 b c CK AP FP d N 2 O flux (μg N m -2 h -1 ) e f g Rice Non-rice h NO flux (μg N m -2 h -1 ) J.1 A.1 O.1 D.1 F.1 A.1 J.1 A.1 O.1 D.1 F.1 A.1 J.1 A.1 O.1 D.1 F.1 A.1 J.1 A.1 O.1 D.1 F.1 A.1 J.1 Dte (month.dy) Figure 3. Sesonl dynmics in ( d) nitrous oxide (N 2 O) fluxes from ll the fertilizer prctices (i.e., the conventionl frmers prctice with common nitrogen ppliction rte (FP), n lterntive prctice with reduced nitrogen input (AP) nd no nitrogen ppliction s control (CK)) in ech rice-whet rottion cycle of 24 28, nd (e h) nitric oxide (NO) fluxes from ll the tretments in ech nonrice seson of The N 2 O fluxes from the rice growing sesons in Figures 3b, 3c, nd 3d were dpted from Yo et l. [212]. The downwrd blck nd grey rrows indicte the time of fertiliztion for the lterntive nd frmers prctices, respectively. Verticl brs in Figures 3 3h indicte stndrd errors of 3-sptil replictes. 3. Results 3.1. Generl Climtic Vribles [16] The nnul men ir tempertures were 15.6, 15.7, 16.8, nd 15.5 C, respectively, for the 24/25, 25/ 26, 26/27, nd 27/28 cropping yers (Figure 1). The mount of rinfll vried significntly intr-nnully nd internnully. The nnul precipittion ws lower in the 24/25 (659 mm) nd 27/28 (748 mm) cropping yers, higher in 25/26 (1139 mm) nd comprble in 26/27 (98 mm), compred to the multiyer verge (924 mm) for this site. During the rice-growing seson (i.e., June to October), the precipittion is usully sufficient nd 49 7% of the nnul rinfll occurred during this period in the studied yers. [17] The soil (5 cm) temperture showed temporl pttern similr to tht of the ir temperture in the four consecutive rice-whet rottion cycles (Figure 1). The nnul men soil tempertures were 14.8, 15., 15.1, nd 14.5 for the 24/25, 25/26, 26/27, nd 27/28 cropping yers, respectively, which ws lower thn the corresponding verge of the ir temperture. The soil moisture content, expressed s WFPS (wter-filled pore spce) rnged from 35% to 1% WFPS during the nonrice sesons. As result of the substntilly vried rinfll distribution in different yers, the soil WFPS showed significntly different sesonl ptterns during the nonrice sesons becuse it ws regulted by precipittion. During the mesurement period, there were no significnt differences in the soil temperture nd moisture mong the different fertilizer prctices Soil Inorgnic N Content nd Agronomic Vribles + [18] The sesonl vritions in the soil inorgnic N (NH 4 nd NO 3 ) content over the rice-whet rottion cycle were primrily regulted by the N ppliction (Figures 2 nd 2b). The reltively high content of NH + 4 nd NO 3 ws primrily observed within 1 dys fter fertiliztion. The men NH + 4 contents for the control, lterntive nd frmers prctices were 6.1, 8.4, nd 11.7 mg N kg 1 soil dry weight (SDW), respectively, during the two rice sesons nd 5.3, 5.8, nd 8.2 mg N kg 1 SDW during the nonrice seson, respectively. A reverse pttern ws observed for the men NO 3 content, which ws reltively lower in the rice seson (2.2, 2.4, nd 3.9 mg N kg 1 SDW for the control, lterntive nd frmers prctices, respectively) thn in the nonrice seson (4.6, 1.6, nd 11.8 mg N kg 1 SDW for the control, lterntive nd frmers prctices, respectively). During the entire rottion cycles, the nnul men inorgnic N contents were 9.3, 14.2, nd 18.3 mg N kg 1 SDW for the control, lterntive nd frmers prctices, respectively, indicting tht the inorgnic N contents incresed with n incresing N rte. [19] Strw nd grin yields in the fertilized plots (the lterntive nd frmers prctices) were significntly higher compred to the control, but there were no significnt difference between the lterntive nd frmers prctices (Tble 1). Two-wy ANOVA nlyses showed tht the grin yields of rice vried significntly with the fertilizer nd the yer but were independent of the interction of these fctors. The grin yields of whet were significntly ffected by the fertilizer nd yer nd their interction (Tble S2). The 628

7 Tble 2. Sesonl Cumultive Fluxes of Methne (CH 4,inkgCh 1 ), Ecosystem Respirtion (CO 2,intCh 1 ), Nitrous Oxide (N 2 O, in kg N h 1 ) nd Nitric Oxide (NO, in kg N h 1 ), nd Direct Emission Fctors of N 2 O (EFd N 2O, in %) nd NO (EF d NO, in %) Under Different Fertilizer Prctices During the Rice Growing nd Nonrice Sesons of Nonrice Seson c c Rice Seson Yer Code b CO 2 CH 4 N 2 O EFd N 2O CH 4 CO 2 N 2 O EFd N 2O NO EF d NO CK AP b b b b b.31.1 FP b b c c CK AP b b b b b b b.57.6 FP b b b b c b b CK AP b b b b b b FP b b b c c CK AP b b b b b b.23.1 FP b b b b b b CK AP b b b b b.43.9 FP b b c b c Men vlues of the four investigted sesons. b Codes of the different fertilizer prctices re defined in the footnotes of Tble 1 nd in the text. c Dt shown re mens stndrd errors of 3-sptil replictes. Different letters within the sme column indicte sttisticlly significnt differences mong tretments in ech seson. grin yields for the control, lterntive nd frmers prctices rnged from 4.8 to 7.3 t h 1 for rice nd from 2. to 6.1 t h 1 for whet cross the 4 yers. For the N concentrtions of strw nd grin, the frmers prctice tretment did not differ from the lterntive prctice, nd the control hd lower vlues thn the two fertilized tretments. For the C concentrtions of strw nd grin, there were no significnt differences mong the tretments (Tble 1). The fertilizer NUE for rice rnged from 34% to 56% (men: 41%) in the lterntive prctice nd from 27% to 42% (men: 36%) in the frmers prctice, indicting tht the reduced N input improved the NUE of rice. For the whet sesons, the verge NUE ws 6% for the lterntive prctice, which ws higher thn tht observed for the frmers prctice (48%). The nnul vlues for the NUE in the lterntive nd frmers prctices were 51% nd 42%, respectively, when verged cross the 4 yer rottion cycles Nitrous nd Nitric Oxide Emissions [2] In the rice sesons, the N 2 O fluxes were stimulted by ech of the fertilizer pplictions nd then grdully declined. In ddition, nother pronounced flux ppered t the end of ech rice seson, with the exception of the 24 rice seson, due to dringe (Figures 3 3d). Sttisticl nlyses indicted tht the totl cumultive N 2 O emissions over the rice sesons were gretly ffected by fertilizer tretment but were independent of the yer nd the interction of these fctors (Tbles 2 nd S2). Generlly, sesonl N 2 Oemissions incresed with incresing nitrogen rtes for ech rice seson. Over the four rice sesons, re-scled sesonl N 2 O emissions were n verge of 211% higher in the lterntive prctice thn the control (P <.5), nd they were pproximtely 95% higher in the frmers prctice thn in the lterntive prctice (P <.5) (Tble 2). When expressed reltive to rice grin yield, the yield-scled N 2 O emissions, on verge, showed the sme trend s the re-scled emissions except the frmers prctice tretment did not significntly differ from the lterntive prctice (Tble 3). For ll rice sesons, the clculted direct emission fctors of N 2 O-N (EF d s) rnged from.21% to 1.% nd from.3% to 1.22%, with men vlues of.53% nd.76% for the lterntive nd frmers prctices, respectively (Tble 2). [21] Similr to the rice seson, the nitrogen fertilizer events pplied in the nonrice seson triggered the emission of lrge mounts of N 2 O but no lrge increse in emission occurred following the first topdressing (i.e., the jointing fertilizer ppliction). For the NO fluxes, their sesonl vritions showed similr pttern to those of N 2 O (Figure 3). The cumultive N 2 O emissions over the nonrice seson vried significntly with fertilizer tretment nd yer, but the totls were not significntly ffected by the interction of these fctors. In contrst, the sesonl NO emissions were significntly ffected by the interctions between the fertilizer nd the yer, prt from by the fertilizer nd yer seprtely (Tbles 2 nd S2). Compred to the control, the ppliction of nitrogen fertilizer in the lterntive nd frmers prctices significntly incresed N 2 O nd NO emissions. In the lterntive nd frmers prctices, there ws liner reltionship between the NO emissions nd soil inorgnic N (NH 4 + +NO 3 ) content during the nonrice seson (R 2 =.36.67, P <.1, Figure 2d). However, cross ll the tretments, NO emissions incresed exponentilly with 629

8 Tble 3. Yield-Scled Sesonl Fluxes of Methne (CH 4,inkgCt 1 ), Ecosystem Respirtion (CO 2,intCt 1 ), Nitrous Oxide (N 2 O, in g N t 1 ) nd Nitric Oxide (NO, in g N t 1 ) Under Different Fertilizer Prctices During the Rice Growing nd Nonrice Sesons of Yer Code b Yield-scled CH 4 Yield-scled CO 2 Yield-scled N 2 O Yield-scled CH 4 Yield-scled CO 2 Yield-scled N 2 O Yield-scled NO c Rice Seson Nonrice Seson c CK AP b b.18.8 b b b b FP b b.14.2 b b b CK AP b.17.3 b b b FP b.15.2 b b CK AP b b b FP b b b b b CK AP b.34.2 b b b b FP b.44.3 b b b b CK AP b b b FP b b b Men vlues of the four investigted sesons. b Codes of the different fertilizer prctices re defined in the footnotes of Tble 1 nd in the text. c Dt shown re mens stndrd errors of 3-sptil replictes. Different letters within the sme column indicte sttisticlly significnt differences mong tretments in ech seson. incresing soil inorgnic N contents (R 2 =.71, P <.1, Figure 2d). Menwhile, cross ll nonrice sesons, sesonl NO emissions showed n exponentil response to both the nitrogen rte nd the boveground biomss (strw plus grin) (Figures 4c nd S1). Over the four nonrice sesons, the re-scled sesonl N 2 O emissions were incresed n verge of 1.2 nd 2.4 times higher in the lterntive nd frmers prctices, respectively, compred to the control (P <.5). However, there ws no significnt difference in the yield-scled N 2 O emissions mong the tretments (Tble 4). With respect to the verged NO emissions over ll of the nonrice sesons, s expressed either on n re bsis or reltive to whet yield, the lterntive nd frmers prctices showed drmticlly higher emissions thn did the control. However, the lterntive nd frmers prctices did not significntly differ from ech other (Tbles 2 nd 3). Similr to the rice seson, the EF d sofn 2 O-N nd NO-N in the nonrice sesons showed temporl vritions for different yers. The men EF d s for ll nonrice sesons were.72% nd.97% for N 2 O-N in the lterntive nd frmers prctices, respectively, nd.43% nd.54% for NO-N in the lterntive nd frmers prctices, respectively (Tble 2). Sesonl N 2 O emissions (kg N h -1 ) Sesonl NO emissions (kg N h -1 ) Rice seson f(x) =.81 exp(.35 x) (R 2 =.7, P<.1) c. Non-rice seson f(x) =.19 exp(.35 x) (R 2 =.86, P<.1) b. Non-rice seson f(x) =.4 exp(.15 x) (R 2 =.51, P<.1) d. Annul rottion f(x) =.15 exp(.13 x) (R 2 =.7, P<.1) Sesonl N 2 O emissions Annul N 2 O emissions (kg N h -1 ) (kg N h -1 ) Aboveground biomss of strw nd grin (t h -1 ) Figure 4. Reltionships (, b, nd d) between cumultive nitrous oxide (N 2 O) emissions nd boveground biomss of strw nd grin cross ll rice growing nd nonrice sesons nd nnul rottion cycles, nd (c) between sesonl nitric oxide (NO) emissions nd boveground biomss of strw nd grin over ll nonrice sesons. Verticl nd horizontl brs indicte stndrd errors of 3-sptil replictes. 63

9 Tble 4. Annul Cumultive Emissions of Methne (CH 4 ), Ecosystem Respirtion (CO 2 ) nd Nitrous Oxide (N 2 O) Expressed on Both n Are- nd Yield-Scled Bsis, nd Annul Direct Emission Fctors of N 2 O (EFd N 2O), Grin Yields (GY) nd Nitrogen Use Efficiency (NUE) Under Different Fertilizer Prctices During the Rice-Whet Rottion Cycles of Annul Rice-Whet Rottion c Yield-scled N 2 O(gNt 1 ) Yield-scled CO 2 (t C t 1 ) Yield-scled CH 4 (kg C t 1 ) CH 4 (kg C h 1 ) CO 2 (t C h 1 ) N 2 O (kg N h 1 ) EFd N 2O (%) GY (t h 1 ) NUE (%) Yer Code b CK AP b b b b b b FP b b c b b b b CK AP b b b b FP b b b b b CK b AP b b b b b b FP b b b c b b b CK AP b b b b FP b b b b CK AP b b b b b FP b b b b b Men vlues of the four investigted nnul cycles. b Codes of the different fertilizer prctices re defined in the footnotes of Tble 1 nd in the text. c Dt shown re mens stndrd errors of 3-sptil replictes. Different letters within the sme column indicte sttisticlly significnt differences mong tretments in ech nnul cycle. [22] Over the four consecutive nnul rottion cycles, the cumultive N 2 O emissions rnged from 1.12 to 1.63 kg N h 1 for the control, from 2.21 to 4.98 kg N h 1 for the lterntive prctice, nd from 3.65 to 7.63 kg N h 1 for the frmers prctice. The nnul N 2 O emissions were significntly ffected by fertilizer nd yer nd by the interction of these fctors (Tbles 4 nd S2). Compred to the control, the 4 yer men nnul N 2 O emissions were significntly incresed by 141% nd 38% for the lterntive nd frmers prctices, respectively (P <.5). When expressed reltive to grin yield, the yield-scled N 2 O emissions were consistently lower for the control thn for the frmers prctice (P <.5), but there ws no significnt difference between the control nd lterntive prctice (Tble 3). Across the smpling dtes from June 25 to October 26, during which the N 2 O fluxes nd soil inorgnic N content were mesured simultneously, positive liner correltion ws found between the N 2 O emissions nd the totl inorgnic N (NH 4 + +NO 3 ) content in the lterntive nd frmers prctices (R 2 =.18.55, P <.1, Figure 2c). However, cross ll the tretments, nonliner response curve best described the increses in the N 2 O emissions with incresing soil inorgnic Ncontent(R 2 =.62,P <.1, Figure 2c). In ddition, for the dt mesured in different time scles, the exponentil model best described the correltion between the cumultive N 2 O emissions nd the nitrogen rte or the boveground biomss (strw plus grin) for the rice seson, nonrice seson nd nnul rottion cycle (Figures 4 nd S1). For the nnul rottion cycles, the EF d sofn 2 O-N were estimted to be n verge of.61% nd.85% s result of the fertilizer mngement of the lterntive nd frmers prctices, respectively Methne Fluxes nd Ecosystem Respirtion [23] During the rice growing periods, the CH 4 fluxes incresed grdully in the erly stge nd decresed shrply in the midseson ertion stge. The mplitudes of the CH 4 fluxes were then primrily regulted by dry nd wet soil conditions, i.e., wter regimes (Figures 1 nd 5e 5h). The three fertiliztion tretments (CK, AP, nd FP) hd similr sesonl ptterns but vried in the mgnitudes of the CH 4 fluxes for ech of the rice sesons. The sesonl cumultive CH 4 emissions depended gretly on the fertilizer ddition, yer, nd the interction of these fctors (Tbles 2 nd S2). Compred to the control, the lterntive prctice tended to decrese the sesonl CH 4 emissions, lthough this influence ws not sttisticlly significnt. However, the frmers prctice significntly decresed the sesonl CH 4 emissions by n verge of 54% compred to the control (Tble 2). Across ll rice sesons, the trend nd mgnitude of the fertiliztion effects on the yield-scled CH 4 emissions reltive to the control were similr to their effects on the re-scled CH 4 (Tbles 2 nd 3). [24] In the nonrice sesons, the CH 4 fluxes out of or into the soil were often spordic. There were no regulr nd consistent sesonl ptterns for the field tretments (Figure S2). For the nonrice sesons, ll of the tretments cted s smll net sinks of tmospheric CH 4. The sesonl CH 4 uptke rnged from.63 kg C h 1 for the control in the 24/ 25 nonrice seson to 1.99 kg C h 1 for the frmers prctice in the 27/28 nonrice seson. The 4 yer men uptke ws between 1.16 nd 1.25 kg C h 1, with no significnt difference observed mong the tretments (Tble 2). Obviously, substntil CH 4 emission ws observed during 631

10 Ecosystem respirtion CH (mg CO 2 m -2 h -1 4 flux (mg CH 4 m -2 h -1 ) ) e b f c g Rice CK AP FP Non-rice d h Ecosystem respirtion CH 4 flux (mg CH 4 m -2 h -1 ) (mg CO 2 m -2 h -1 ) J.1A.1O.1D.1F.1A.1J.1A.1O.1D.1F.1A.1J.1A.1O.1D.1F.1A.1J.1A.1O.1D.1F.1A.1J.1 Dte (month.dy) Figure 5. Sesonl dynmics in ( d) ecosystem respirtion (CO 2 ) emissions nd (e h) methne (CH 4 ) fluxes from ll the fertilizer prctices (i.e., the conventionl frmers prctice with common nitrogen ppliction rte (FP), n lterntive prctice with reduced nitrogen input (AP) nd no nitrogen ppliction s control (CK)) in ech rice-whet rottion cycle of The CH 4 fluxes from the rice growing sesons Figures 5f, 5g, nd 5h were dpted from Yo et l. [212]. Verticl brs in Figures 5 5h indicte stndrd errors of 3-sptil replictes. the rice seson, which ws significntly greter thn the uptke in the nonrice seson. Therefore, ll of the tretments cted s net source of tmospheric CH 4 over the time period of one yer. The sttisticl nlyses showed tht nnul CH 4 emissions vried significntly with the fertilizer nd yer (Tbles 4 nd S2). Compred to the control, there ws no significnt influence of N fertilizer on the men nnul CH 4 emissions in either the lterntive or the frmers prctices, lthough the men nnul CH 4 emissions tended to be lower by 38 54%. However, when expressed reltive to grin yield, the verge nnul CH 4 emission cross the 4 yer rottion cycles ws significntly inhibited by 7% in the frmers prctice compred to the control (Tble 4). [25] In this study, the CO 2 emission ws mesured t the ecosystem level (including soil nd plnts) using drk sttic chmber. There were similr sesonl ptterns of ecosystem respirtion in ll tretments during the rice-growing nd nonrice sesons (Figures 5 5d). During the rice growing periods, the ecosystem respirtion grdully incresed following rice trnsplnting nd reched pek in mid- August with the mximum biomss of plnts. In contrst, the CO 2 emissions decresed grdully from the beginning of the nonrice seson to mid-februry becuse of lower tempertures. As the whet turned green nd the temperture incresed, the ecosystem respirtion slowly reched its pek in mid-my (Figures 1 nd 5). The mounts of CO 2 emitted over the rice or nonrice sesons were significntly influenced by the ppliction of nitrogen fertilizer (Tble S2). The incresed fertilizer ppliction rte (i.e., in the lterntive nd frmers prctices) stimulted the ecosystem respirtion both in the rice nd in the nonrice sesons (Tble 2). When the mounts of ecosystem respirtion from the rice nd nonrice sesons were combined, the nnul CO 2 emissions rnged from n verge of to t C h 1 over the four nnul rottion cycles. Across the different fertilizer rtes nd crop yers, liner response curve best described the correltions between the totl ecosystem respirtion nd boveground biomss (strw plus yield) t the sesonl nd nnul scles (R 2 =.49.65, P <.1). Reltive to the control, the men nnul ecosystem respirtion ws incresed by 28% nd 34% for the lterntive nd frmers prctices, respectively (Tble 4). When expressed bsed on grin yields, the totl CO 2 emissions did not differ significntly between the tretments for the rice nd nonrice sesons or for the nnul cycles (Tbles 3 nd 4) Sesonl nd Annul Aggregte Emissions of CH 4 nd N 2 O [26] As shown in Figure 6, the ggregte emissions of CH 4 nd N 2 O during the rice sesons rnged from 3.5 t CO 2 -eq h 1 in the frmers prctice of the 25 rice seson to 12.8 t CO 2 -eq h 1 in the control of the 24 rice seson, with men vlue of 5.38 t CO 2 -eq h 1. Over the four rice sesons, the verged ggregte emissions of CH 4 nd N 2 O rnged from 4.26 to 7.5 t CO 2 -eq h 1, nd nitrogen fertiliztion tended to decrese the net GHG emissions. Similrly, the ppliction of N fertilizer showed inhibitory effects on the men yield-scled ggregte emissions of CH 4 nd N 2 O, which rnged from 649 to 129 kg CO 2 -eq t 1. [27] During the nonrice periods, the ggregte emissions of CH 4 nd N 2 O were between.33 nd 1.94 t CO 2 -eq h 1 nd verged to.89 t CO 2 -eq h 1. Among the tretments, the lterntive nd frmers prctices significntly incresed the GHG emissions by 131% nd 264% on verge, respectively, compred to the control (P <.5). However, there were no significnt differences in the yield-scled ggregte emissions of CH 4 nd N 2 O( kg CO 2 -eq t 1 )forny tretments (Figure 6). [28] The ggregte emissions of CH 4 nd N 2 O for the ricegrowing sesons, expressed on re nd grin yield bses, 632

11 Rice seson d Are-scled ggregte emissions of CH 4 nd N 2 O (t CO 2 -eq h -1 ) b c Non-rice seson Annul rottion b b CK AP FP e f Yield-scled ggregte emissions of CH 4 nd N 2 O (kg CO 2 -eq t -1 ) Yer Yer Figure 6. Aggregte emissions of methne (CH 4 ) nd nitrous oxide (N 2 O) for ll fertilizer prctices (i.e., the conventionl frmers prctice with common nitrogen ppliction rte (FP), n lterntive prctice with reduced nitrogen input (AP) nd no nitrogen ppliction s control (CK)) in the rice growing sesons, nonrice sesons nd nnul rottion cycles, expressed on n re- nd yield-scled bsis. Verticl brs indicte stndrd errors of three or four replictes. For 4 yer mens, brs with the sme letters indicte no significnt differences mong tretments. were pproximtely 5. nd 3.6 times higher thn those of the nonrice sesons. During the rice sesons, the GHG emissions were lrgely regulted by the CH 4 emissions, which, on verge, ccounted for 97%, 88%, nd 71% of the ggregte emissions for the control, lterntive nd frmers prctices, respectively. In contrst, the N 2 O emissions substntilly influenced the combined climtic impct for the nonrice sesons, which contributed pproximtely % of the ggregte emissions for ll tretments. Averged over the 4 yers, the rnges of the nnul ggregte emissions of CH 4 nd N 2 O for ll tretments were t CO 2 -eq h 1 when expressed on n re bsis nd kgCO 2 -eq t 1 when expressed on grin yield bsis (Figure 6). Although the ppliction of N fertilizer incresed the ggregte emissions of CH 4 nd N 2 O during the nonrice periods, the nnul ggregte emissions tended to be higher for the control thn for the fertilized tretments (i.e., the lterntive nd frmers prctices) due to the substntil decreses in the CH 4 emissions from the fertilized tretments in the rice sesons. 4. Discussion [29] It is noteworthy tht in this study the exchnges of N 2 O, NO, CH 4, nd CO 2 between the rice-whet rottion groecosystem nd the tmosphere were mesured using sttic mnul chmbers with the pproprite smpling schedule (i.e., preferbly smpling dily for severl dys fter fertiliztion, during midseson ertion stge in the rice seson, nd fter substntil precipittion in the nonrice seson nd otherwise smpling t progressively wider intervls). This smpling method provides relible results in terms of coping with the temporl vribility of these gses, but it introduces n extent of uncertinty into the flux estimte, e.g., n pproximtely 18% overestimtion for the N 2 O mesurements [Yo et l., 29] Nitrogen Fertiliztion Affecting GHG nd NO Fluxes [3] Our findings corroborte the rgument tht the ppliction of synthetic N fertilizers strongly ffects the emissions of environmentlly importnt trce gses, such s CH 4,CO 2, N 2 O, nd NO from griculturl fields [Chu et l., 27; IPCC, 27]. Over the entire nnul rottion cycle, the rice-whet systems re sources for tmospheric CH 4 becuse the totl CH 4 emissions in the rice sesons were only mrginlly offset by CH 4 uptke in the nonflooded whet sesons. Nonetheless, our results indicte tht the ppliction of synthetic N fertilizers cused generl suppression of nnul CH 4 emissions cross multiyer mesurements, irrespective of their expression on either n re- or yield-scled bses (Tble 4). Numerous studies hve demonstrted tht CH 4 production, oxidtion nd trnsport re ffected by synthetic nitrogen fertilizers. However, the mgnitude nd even the direction of these responses vried mong field studies, which observed positive, negtive nd no influences of nitrogen inputs on CH 4 emissions [Bodelier nd Lnbroek, 24; Cietl., 27]. In the mjority of ecosystems, CH 4 production nd consumption occur simultneously [Liu nd Grever, 29], nd so the decrese in nnul CH 4 emissions under the fertilized tretments ws presumbly cused by the ctivities of methnogenic rche nd methnotrophic bcteri. In rice pddy fields, the utiliztion of synthetic N fertilizers, especilly mmoniumbsed fertilizers, hs been shown to improve the growth nd ctivities of methne-oxidizing bcteri, especilly in the rhizosphere of rice [Bodelier et l., 2], thus resulting in the oxidtion of more CH 4. For our studied lluvil soil with sndy lom texture, probbly CH 4 consumption under ure-bsed fertiliztion ws further stimulted by prtilly erobic soil conditions due to the porous nd highly percolting nture of the soil. Menwhile, the toxicity of nitrite (NO 2 ), NO nd 633