不同轮作体系不同施氮量甲烷排放比较研究

宿敏敏， 况福虹， 吕 阳， 赵亚南， 傅先友， 李群英， 雷云飞，张福锁， 石孝均， 申建波， 刘学军*

(1 中国农业大学资源与环境学院， 北京100093； 2 西南大学资源与环境学院, 重庆400716；3 重庆市江津区农业技术推广中心， 重庆402260)



不同轮作体系不同施氮量甲烷排放比较研究

宿敏敏1， 况福虹1， 吕 阳1， 赵亚南2， 傅先友3， 李群英3， 雷云飞3，张福锁1， 石孝均2， 申建波1， 刘学军1*

(1 中国农业大学资源与环境学院， 北京100093； 2 西南大学资源与环境学院, 重庆400716；3 重庆市江津区农业技术推广中心， 重庆402260)

甲烷； 轮作； 氮肥； 四川盆地

CH4是生态系统中重要的温室气体，考虑到碳循环-气候反馈效应，以100年尺度GWP计算，CH4是CO2的34倍[1]。农业是重要的温室气体排放源，中国农业活动产生的CH4约占全国CH4排放量的50%[2]。

氮肥使用的合理与否也在很大程度上影响稻田和旱地CH4的排放[10-11]，氮肥的优化管理能在多大程度上调控CH4的排放目前仍不是很清楚。本研究通过田间小区试验，采用静态箱-气相色谱法对三种轮作模式和不同氮肥管理水平的CH4排放通量进行田间原位测量，试图探讨轮作模式和氮肥施用对农田CH4排放的影响。

1　材料与方法

1.1试验点概况

田间试验于2012年11月至2014年11月在重庆市江津区永兴镇(29°03.85′N，106°11.37′E)进行。该区属亚热带季风性湿润气候，试验期间气象条件见图1。平坝丘陵区土壤为沙溪庙紫色母岩经水耕熟化发育而成的水稻土，土壤(0—20 cm)基本理化性质为有机碳15.6 g/kg、 pH 4.9、 全氮1.99 g/kg、 容重为1.15 g/cm3。粘粒含量为24.6%，为粘性土壤。

图1　试验期间月均温与月降雨量Fig.1　The monthly mean temperature and precipitation during experimental period

1.2试验设计

试验主处理为三种轮作模式：水旱轮作田(水稻-小麦轮作，RW)，水旱轮作田改为旱-旱轮作田(玉米-小麦轮作，MW)，冬水田(水稻-冬季淹水/休闲，RF)。由于第一年开展试验，冬小麦季的冬水田田埂没有建完，而是处于干旱休闲状态，次年春天4月开始淹水种稻，水稻收获后淹水休闲。

试验副处理为氮肥处理，分别为不施氮对照(N0)、 优化施氮处理(Nopt)、 传统施氮处理(Ncon)。以尿素为氮肥，小麦季Nopt施肥为N 96 kg/hm2，基肥与追肥比为5 ∶5，Ncon施肥为N 180 kg/hm2, 基肥与追肥比为4 ∶6(或5 ∶5)； 水稻季Nopt施肥为N 150 kg/hm2，基肥 ∶分蘖肥 ∶拔节肥为5 ∶3 ∶2，Ncon施肥为N 225 kg/hm2，基肥 ∶分蘖肥为5 ∶5; 玉米季Nopt施肥为N 150 kg/hm2，Ncon施肥为N 225 kg/hm2，基肥与追肥比均为5 ∶ 5。以KCl为钾肥，小麦季施用量为K2O 45 kg/hm2, 水稻季或玉米季为K2O 75 kg/hm2； 以过磷酸钙为磷肥，优化处理和对照处理均为P2O560 kg/hm2, 传统处理为P2O5120 kg/hm2。每个处理三次重复，完全随机排列。小麦11月中上旬种植，次年5月上旬收获； 冬水田水稻4月中下旬种植，8月中下旬收获，水旱轮作水稻5月中下旬种植，9月上旬收获； 玉米5月中旬种植，8月中下旬收获。水旱轮作田稻季水分管理采用间歇灌溉方式，即前期灌水、 中期晒田、 后期间隙灌溉，成熟期排干； 冬水田稻季水分管理采用长期淹水方式。

1.3样品采集与测定

1.4数据分析

温室气体排放通量采用以下公式[14]计算：

F=ρh×dc/dt×273/(273+t)×p/po

式中，F为温室气体排放通量； ρ为标准状态下温室气体密度； h为采样箱高度； dc/dt为相应温室气体排放速率； t为采样箱内气体平均温度； p为采样箱内气压； po为标准大气压。

数据采用SAS 8.2软件进行随机区组方差分析, Sigmplot 10.0软件作图。

2　结果与分析

2.1同轮作模式的CH4排放特征

MW、 RW、 RF系统第一年的甲烷排放量分别为CH4-C 13.5、 26.7、 89.8 kg/hm2，第二年为相应第一年的6.2%、 85.1%、 263.1%(表1)。RF系统第一年甲烷排放较少，由于第一年种植前为干旱休闲，RW系统两年排放基本一致，但低于前人在川中丘陵区的研究[18]。相比前人研究，本研究土壤较粘，且pH<5，这些条件均不利于甲烷的产生[9, 31-32]。就两年平均值而言，MW、 RW、 RF三个轮作体系均为甲烷的净排放，MW体系以玉米季为主，N0、 Nopt、 Ncon处理分别占总体系的87.4%、 87.2%、 76.2%； RW体系以水稻季为主，N0、 Nopt、 Ncon处理分别占总体系的91.4%、 95.7%、 94.9%； RF体系中以水稻季为主，N0、 Nopt、 Ncon处理分别占总体系的84.2%、 84.9%、 84.8%。对于RF体系而言，淹水休闲季甲烷排放约占总体系年排放的16%，不容忽视。

图2　不同轮作模式不同氮肥处理CH4排放动态Fig.2　Dynamics of CH4 emission in different rotation systems and N fertilization treatments [注(Note): 向上箭头表示晒田，向下箭头表示施肥 Upward arrows denote field drying, downward arrows denote fertilization events.]

2.2不同氮肥处理对CH4排放通量的影响

RW轮作体系同一年的N0处理CH4排放量与Nopt处理CH4排放量差异不大，WM与RW规律一样，但第二年Nopt处理与Ncon处理无差异。氮肥对RF轮作系统影响不明显。本研究中，RW系统的每一季，MW系统第一年的每一季表现出大量施氮(Ncon)抑制甲烷排放，与前人研究结果一致[21-22]，但小麦季甲烷排放少，主要是甲烷产生少，较小的施氮量(优化处理)使得氮肥对甲烷排放出现抑制作用。MW系统第二年的每一季表现出施用氮肥增加甲烷排放，这主要是因为稻田转化为旱田第二年，土壤硬盘变少，土块变小，此时MW轮作的土壤理化性质倾向于传统旱作，施用氮肥时促进甲烷排放，因颗粒态甲烷单加氧酶和氨单加氧酶具有同源性，甲烷氧化菌会氧化氨替代甲烷从而促进甲烷排放[33-34]，但因甲烷氧化菌会优先氧化甲烷[35]，所以这种情况仅出现在氨浓度与甲烷浓度之比超过30的旱地中[22, 36]； 相比较间歇灌溉稻田，氮肥对甲烷氧化菌的促进作用并没有在长期淹水稻田中发现(表1),这是因为甲烷氧化菌在极端厌氧条件下失活[23]，尽管肥料减缓了甲烷氧化菌的氮限制，但由于长期淹水稻田缺氧，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会得出氮肥对稻田土壤甲烷排放效果相矛盾的结果。

对照处理中，MW、 RW、 RF系统第一年的甲烷排放量分别为CH4-C 17.7、 30.5、 85.7 kg/hm2，优化处理分别为相应对照处理的87.5%、 111.3%、 119.4%，传统处理分别为相应对照处理的41.5%、51.1%、 94.8%； 对照处理中，MW、 RW、 RF系统第二年的甲烷排放量分别为CH4-C 0.4、 26.0、 227.4 kg/hm2，优化处理分别为相应对照处理的240.4%、 103.9%、 104.9%，传统处理分别为相应对照处理的229.6%、 58.6%、 100.1%(表1)。

表1　不同轮作模式不同氮肥处理CH4排放通量 (CH4-C kg/hm2)

注(Note): 数值后不同大写字母表示相同季相同施肥处理不同轮作体系差异显著，小写字母表示相同轮作体系相同季不同施肥处理差异显著(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不同施肥时期对CH4排放通量的影响

本研究中，冬水田由于较长的淹水期导致周年CH4排放最高，可见水分管理对于稻田CH4排放极为重要，这与很多前人研究结果相吻合[18, 24]。值得注意的是，本研究水改旱第一年，玉米季CH4明显排放可能与第一年土壤含水量较高以及相对较多的活性有机碳有关； 还发现，高量施用氮肥抑制了水旱轮作或旱旱轮作中CH4的排放，这可能与大量施氮促进甲烷氧化菌的活性从而抑制CH4排放有关。

3　结论

表2　不同轮作模式不同施肥期的CH4的累计排放 (CH4-C kg/hm2)

注(Note): 甲烷排放是指施肥后15天累计排放量CH4emissions in the different fertilizing times mean the accumulative CH4-C emissions during the 15 days after fertilizing; 数值后不同小写字母表示相同轮作体系相同季不同施肥处理差异显著(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-小麦轮作系统、 玉米-小麦轮作系统第一年的甲烷排放受到抑制； 与对照处理相比，第二年施氮后玉米-小麦轮作系统的甲烷年排放增加，长期淹水稻田中，氮肥对甲烷排放无明显影响。

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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

国家杰出青年科学基金(40425007)； 自然科学基金(31471944)； 教育部植物-土壤相互作用重点实验室资助。

宿敏敏(1985—)， 女， 黑龙江省虎林市人， 博士研究生， 主要从事植物营养与肥料方面的研究。E-mail: suminmin@cau.edu.cn

E-mail: liu310@cau.edu.cn

S513.062； S153.6+1

A

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