宿敏敏， 況福虹， 呂 陽(yáng)， 趙亞南， 傅先友， 李群英， 雷云飛，張福鎖， 石孝均， 申建波， 劉學(xué)軍*

(1 中國(guó)農(nóng)業(yè)大學(xué)資源與環(huán)境學(xué)院， 北京100093； 2 西南大學(xué)資源與環(huán)境學(xué)院, 重慶400716；3 重慶市江津區(qū)農(nóng)業(yè)技術(shù)推廣中心， 重慶402260)

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不同輪作體系不同施氮量甲烷排放比較研究

宿敏敏1， 況福虹1， 呂 陽(yáng)1， 趙亞南2， 傅先友3， 李群英3， 雷云飛3，張福鎖1， 石孝均2， 申建波1， 劉學(xué)軍1*

(1 中國(guó)農(nóng)業(yè)大學(xué)資源與環(huán)境學(xué)院， 北京100093； 2 西南大學(xué)資源與環(huán)境學(xué)院, 重慶400716；3 重慶市江津區(qū)農(nóng)業(yè)技術(shù)推廣中心， 重慶402260)

甲烷； 輪作； 氮肥； 四川盆地

CH4是生態(tài)系統(tǒng)中重要的溫室氣體，考慮到碳循環(huán)-氣候反饋效應(yīng)，以100年尺度GWP計(jì)算，CH4是CO2的34倍[1]。農(nóng)業(yè)是重要的溫室氣體排放源，中國(guó)農(nóng)業(yè)活動(dòng)產(chǎn)生的CH4約占全國(guó)CH4排放量的50%[2]。

氮肥使用的合理與否也在很大程度上影響稻田和旱地CH4的排放[10-11]，氮肥的優(yōu)化管理能在多大程度上調(diào)控CH4的排放目前仍不是很清楚。本研究通過(guò)田間小區(qū)試驗(yàn)，采用靜態(tài)箱-氣相色譜法對(duì)三種輪作模式和不同氮肥管理水平的CH4排放通量進(jìn)行田間原位測(cè)量，試圖探討輪作模式和氮肥施用對(duì)農(nóng)田CH4排放的影響。

1　材料與方法

1.1試驗(yàn)點(diǎn)概況

田間試驗(yàn)于2012年11月至2014年11月在重慶市江津區(qū)永興鎮(zhèn)(29°03.85′N(xiāo)，106°11.37′E)進(jìn)行。該區(qū)屬亞熱帶季風(fēng)性濕潤(rùn)氣候，試驗(yàn)期間氣象條件見(jiàn)圖1。平壩丘陵區(qū)土壤為沙溪廟紫色母巖經(jīng)水耕熟化發(fā)育而成的水稻土，土壤(0—20 cm)基本理化性質(zhì)為有機(jī)碳15.6 g/kg、 pH 4.9、 全氮1.99 g/kg、 容重為1.15 g/cm3。粘粒含量為24.6%，為粘性土壤。

圖1　試驗(yàn)期間月均溫與月降雨量Fig.1　The monthly mean temperature and precipitation during experimental period

1.2試驗(yàn)設(shè)計(jì)

試驗(yàn)主處理為三種輪作模式：水旱輪作田(水稻-小麥輪作，RW)，水旱輪作田改為旱-旱輪作田(玉米-小麥輪作，MW)，冬水田(水稻-冬季淹水/休閑，RF)。由于第一年開(kāi)展試驗(yàn)，冬小麥季的冬水田田埂沒(méi)有建完，而是處于干旱休閑狀態(tài)，次年春天4月開(kāi)始淹水種稻，水稻收獲后淹水休閑。

試驗(yàn)副處理為氮肥處理，分別為不施氮對(duì)照(N0)、 優(yōu)化施氮處理(Nopt)、 傳統(tǒng)施氮處理(Ncon)。以尿素為氮肥，小麥季Nopt施肥為N 96 kg/hm2，基肥與追肥比為5 ∶5，Ncon施肥為N 180 kg/hm2, 基肥與追肥比為4 ∶6(或5 ∶5)； 水稻季Nopt施肥為N 150 kg/hm2，基肥 ∶分蘗肥 ∶拔節(jié)肥為5 ∶3 ∶2，Ncon施肥為N 225 kg/hm2，基肥 ∶分蘗肥為5 ∶5; 玉米季Nopt施肥為N 150 kg/hm2，Ncon施肥為N 225 kg/hm2，基肥與追肥比均為5 ∶ 5。以KCl為鉀肥，小麥季施用量為K2O 45 kg/hm2, 水稻季或玉米季為K2O 75 kg/hm2； 以過(guò)磷酸鈣為磷肥，優(yōu)化處理和對(duì)照處理均為P2O560 kg/hm2, 傳統(tǒng)處理為P2O5120 kg/hm2。每個(gè)處理三次重復(fù)，完全隨機(jī)排列。小麥11月中上旬種植，次年5月上旬收獲； 冬水田水稻4月中下旬種植，8月中下旬收獲，水旱輪作水稻5月中下旬種植，9月上旬收獲； 玉米5月中旬種植，8月中下旬收獲。水旱輪作田稻季水分管理采用間歇灌溉方式，即前期灌水、 中期曬田、 后期間隙灌溉，成熟期排干； 冬水田稻季水分管理采用長(zhǎng)期淹水方式。

1.3樣品采集與測(cè)定

1.4數(shù)據(jù)分析

溫室氣體排放通量采用以下公式[14]計(jì)算：

F=ρh×dc/dt×273/(273+t)×p/po

式中，F(xiàn)為溫室氣體排放通量； ρ為標(biāo)準(zhǔn)狀態(tài)下溫室氣體密度； h為采樣箱高度； dc/dt為相應(yīng)溫室氣體排放速率； t為采樣箱內(nèi)氣體平均溫度； p為采樣箱內(nèi)氣壓； po為標(biāo)準(zhǔn)大氣壓。

數(shù)據(jù)采用SAS 8.2軟件進(jìn)行隨機(jī)區(qū)組方差分析, Sigmplot 10.0軟件作圖。

2　結(jié)果與分析

2.1同輪作模式的CH4排放特征

MW、 RW、 RF系統(tǒng)第一年的甲烷排放量分別為CH4-C 13.5、 26.7、 89.8 kg/hm2，第二年為相應(yīng)第一年的6.2%、 85.1%、 263.1%(表1)。RF系統(tǒng)第一年甲烷排放較少，由于第一年種植前為干旱休閑，RW系統(tǒng)兩年排放基本一致，但低于前人在川中丘陵區(qū)的研究[18]。相比前人研究，本研究土壤較粘，且pH<5，這些條件均不利于甲烷的產(chǎn)生[9, 31-32]。就兩年平均值而言，MW、 RW、 RF三個(gè)輪作體系均為甲烷的凈排放，MW體系以玉米季為主，N0、 Nopt、 Ncon處理分別占總體系的87.4%、 87.2%、 76.2%； RW體系以水稻季為主，N0、 Nopt、 Ncon處理分別占總體系的91.4%、 95.7%、 94.9%； RF體系中以水稻季為主，N0、 Nopt、 Ncon處理分別占總體系的84.2%、 84.9%、 84.8%。對(duì)于RF體系而言，淹水休閑季甲烷排放約占總體系年排放的16%，不容忽視。

圖2　不同輪作模式不同氮肥處理CH4排放動(dòng)態(tài)Fig.2　Dynamics of CH4 emission in different rotation systems and N fertilization treatments [注(Note): 向上箭頭表示曬田，向下箭頭表示施肥 Upward arrows denote field drying, downward arrows denote fertilization events.]

2.2不同氮肥處理對(duì)CH4排放通量的影響

RW輪作體系同一年的N0處理CH4排放量與Nopt處理CH4排放量差異不大，WM與RW規(guī)律一樣，但第二年Nopt處理與Ncon處理無(wú)差異。氮肥對(duì)RF輪作系統(tǒng)影響不明顯。本研究中，RW系統(tǒng)的每一季，MW系統(tǒng)第一年的每一季表現(xiàn)出大量施氮(Ncon)抑制甲烷排放，與前人研究結(jié)果一致[21-22]，但小麥季甲烷排放少，主要是甲烷產(chǎn)生少，較小的施氮量(優(yōu)化處理)使得氮肥對(duì)甲烷排放出現(xiàn)抑制作用。MW系統(tǒng)第二年的每一季表現(xiàn)出施用氮肥增加甲烷排放，這主要是因?yàn)榈咎镛D(zhuǎn)化為旱田第二年，土壤硬盤(pán)變少，土塊變小，此時(shí)MW輪作的土壤理化性質(zhì)傾向于傳統(tǒng)旱作，施用氮肥時(shí)促進(jìn)甲烷排放，因顆粒態(tài)甲烷單加氧酶和氨單加氧酶具有同源性，甲烷氧化菌會(huì)氧化氨替代甲烷從而促進(jìn)甲烷排放[33-34]，但因甲烷氧化菌會(huì)優(yōu)先氧化甲烷[35]，所以這種情況僅出現(xiàn)在氨濃度與甲烷濃度之比超過(guò)30的旱地中[22, 36]； 相比較間歇灌溉稻田，氮肥對(duì)甲烷氧化菌的促進(jìn)作用并沒(méi)有在長(zhǎng)期淹水稻田中發(fā)現(xiàn)(表1),這是因?yàn)榧淄檠趸跇O端厭氧條件下失活[23]，盡管肥料減緩了甲烷氧化菌的氮限制，但由于長(zhǎng)期淹水稻田缺氧，甲烷的氧化很少。稻田中不同的水分管理制度和氮肥添加量會(huì)得出氮肥對(duì)稻田土壤甲烷排放效果相矛盾的結(jié)果。

對(duì)照處理中，MW、 RW、 RF系統(tǒng)第一年的甲烷排放量分別為CH4-C 17.7、 30.5、 85.7 kg/hm2，優(yōu)化處理分別為相應(yīng)對(duì)照處理的87.5%、 111.3%、 119.4%，傳統(tǒng)處理分別為相應(yīng)對(duì)照處理的41.5%、51.1%、 94.8%； 對(duì)照處理中，MW、 RW、 RF系統(tǒng)第二年的甲烷排放量分別為CH4-C 0.4、 26.0、 227.4 kg/hm2，優(yōu)化處理分別為相應(yīng)對(duì)照處理的240.4%、 103.9%、 104.9%，傳統(tǒng)處理分別為相應(yīng)對(duì)照處理的229.6%、 58.6%、 100.1%(表1)。

表1　不同輪作模式不同氮肥處理CH4排放通量 (CH4-C kg/hm2)

注(Note): 數(shù)值后不同大寫(xiě)字母表示相同季相同施肥處理不同輪作體系差異顯著，小寫(xiě)字母表示相同輪作體系相同季不同施肥處理差異顯著(P<0.05)Capital letters mean significantly different among rotation systems in the same seasons under the same fertilizer, and the lowercase mean significantly different among fertilizer treatments in the same season and rotation systems atP< 0.05.

2.3不同施肥時(shí)期對(duì)CH4排放通量的影響

本研究中，冬水田由于較長(zhǎng)的淹水期導(dǎo)致周年CH4排放最高，可見(jiàn)水分管理對(duì)于稻田CH4排放極為重要，這與很多前人研究結(jié)果相吻合[18, 24]。值得注意的是，本研究水改旱第一年，玉米季CH4明顯排放可能與第一年土壤含水量較高以及相對(duì)較多的活性有機(jī)碳有關(guān)； 還發(fā)現(xiàn)，高量施用氮肥抑制了水旱輪作或旱旱輪作中CH4的排放，這可能與大量施氮促進(jìn)甲烷氧化菌的活性從而抑制CH4排放有關(guān)。

3　結(jié)論

表2　不同輪作模式不同施肥期的CH4的累計(jì)排放 (CH4-C kg/hm2)

注(Note): 甲烷排放是指施肥后15天累計(jì)排放量CH4emissions in the different fertilizing times mean the accumulative CH4-C emissions during the 15 days after fertilizing; 數(shù)值后不同小寫(xiě)字母表示相同輪作體系相同季不同施肥處理差異顯著(P<0.05) Values followed by different lowercase letters mean significantly difference among fertilizer treatments in the same season and year atP< 0.05.

2)大量施氮后，水稻-小麥輪作系統(tǒng)、 玉米-小麥輪作系統(tǒng)第一年的甲烷排放受到抑制； 與對(duì)照處理相比，第二年施氮后玉米-小麥輪作系統(tǒng)的甲烷年排放增加，長(zhǎng)期淹水稻田中，氮肥對(duì)甲烷排放無(wú)明顯影響。

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Impact of N fertilization on CH4emission from paddy field under different rotation systems

SU Min-min1, KUANG Fu-hong1, Lü Yang1, ZHAO Ya-nan2, FU Xian-you3, LI Qun-ying3, LEI Yun-fei3,ZHANG Fu-suo1, SHI Xiao-jun2, SHEN Jian-bo1, LIU Xue-jun1*

(1CollegeofResourcesandEnvironmentalSciences,ChinaAgriculturalUniversity,Beijing100193,China;2CollegeofResourcesandEnvironmentalSciences,SouthwestUniversity,Chongqing400716,China;3JiangjinCentreofAgri-Techniques,Chongqing402260,China)

【Objectives】 A field experiment was conducted at Jiangjin District of Chongqing City, the differences and characteristics of methane(CH4) emissions as influenced by nitrogen fertilization were examined and evaluated under different cropping systems which were originally derived from single rice system. 【Methods】 The main factor was three cropping systems: maize-wheat (MW), rice-wheat (RW) and rice-winter flooded fallow (RF) system. The subtreatments were N application levels: N0 (no N application), Nopt(96 kg/hm2in wheat, 150 kg/hm2in maize or rice) and Ncon (180 kg/hm2in wheat, 225 kg/hm2in maize or rice), respectively.insitustatic chamber-gas chromatography system was used to collect and measure the emmision of CH4in frequency of one to three times a week during the whole year’s experimental period.【Results】 The highest CH4emissions was found in RF system while the lowest in MW cropping system. The annual average CH4emissions from MW, RW and RF systems were CH4-C 13.5, 26.7, 89.8 kg/hm2in the first experimetal year (2013/2014), and 0.8, 22.7, 236.3 kg/hm2in the second year (2014/2015), respectively. N fertilization did not affect CH4emissions significantly across three cropping systems except for treatment Nopt in RW and RF systems. In the first year, the CH4fluxes of N0 treatemnts in the MW, RW, RF systems were respectively 17.7, 30.5, 85.7 kg/hm2, and those in Nopt treatments were 87.5%, 111.3%, 119.4%, and in Ncon treatments were 41.5%, 51.1%, 94.8% of corresponding N0 treatments, respectively. In the second year, the CH4fluxes in N0 treatemnts of MW, RW, RF rotation systems were CH4-C 0.4, 26.0, 227.4 kg/hm2, respectively, and those in Nopt treatments were 240.4%, 103.9%, 104.9%, and in Ncon treatments were 229.6%, 58.6%, 100.1% of the corresponding N0 treatments, respectively. The net CH4emissions were all occured from MW, RW and RF systems on average for two years’s period. In MW system, the highest emissions was measured in the maize season, averaged accounting for 87.7%, 87.2%, 76.2% of the system for the N0, Nopt and Ncon treatment, respectively; In RW system, the highest was in rice season, averagedly accounted for 91.4%, 95.7%, 94.9% of the system in the N0, Nopt and Ncon treatments, respectively; Similarly in the RF system, the highest emissions were in the rice season, accounted for 84.2%, 84.9%, 84.8% of those from the system for the N0, Nopt and Ncon treatments, respectively. CH4emissions durning fertilizing periods accounted for 9%-32% of wheat growing seasons; CH4emissions during fertilizing periods accounted for 6%-11% of maize growing seasons in the first year but 30%-45% of maize seasons in the second year; CH4emissions during fertilizing periods accounted for 37%-50% of rice seasons in RW systems; CH4emissions during fertilizing periods accounted for 21%-28% of rice growing seasons in RF systems. Flooded fallow seasons also contributed about 16% of annual CH4emissions for RF system.【Conclusions】Total net emission of CH4was highest in rice-flooding fallow system, followed by rice-wheat rotation system and the lowest in maize-wheat rotation system. In the first year after the single rice system was changed to maize-wheat rotation, there was an emission peak in the maize season, but not in the second year, and the total emission was similar in the two year’s time. In the second year of the rice-flooding fallowe system, the CH4emissions increased significantly. The net CH4emissions occured in all the three systems, and mianly in the maize or rice season. Nitrogen fertilization inhibited the CH4fluxes in maize-wheat and rice-wheat rotation systems, but not in rice-flooding fallow system.

methane flux; rotation; N fertilization; Sichuan basin

2015-11-23接受日期: 2016-02-26

國(guó)家杰出青年科學(xué)基金(40425007)； 自然科學(xué)基金(31471944)； 教育部植物-土壤相互作用重點(diǎn)實(shí)驗(yàn)室資助。

宿敏敏(1985—)， 女， 黑龍江省虎林市人， 博士研究生， 主要從事植物營(yíng)養(yǎng)與肥料方面的研究。E-mail: suminmin@cau.edu.cn

E-mail: liu310@cau.edu.cn

S513.062； S153.6+1

A

1008-505X(2016)04-0913-08