氮肥与生物炭施用对稻麦轮作系统甲烷和氧化亚氮排放的影响

李 露, 周自强, 潘晓健, 李 博, 熊正琴

(南京农业大学资源与环境科学学院，南京 210095)

氮肥与生物炭施用对稻麦轮作系统甲烷和氧化亚氮排放的影响

李 露, 周自强, 潘晓健, 李 博, 熊正琴*

(南京农业大学资源与环境科学学院，南京 210095)

【目的】以我国稻麦轮作系统为对象，研究氮肥和小麦秸秆生物炭联合施用对CH4和N2O排放规律的影响；结合小麦和水稻总产量进而评估对该生态系统综合温室效应(GWP)和温室气体强度(GHGI)的影响，为生物炭在减缓全球气候变化及农业生产中的推广应用提供科学依据。【方法】生物炭通过小麦秸秆在300～500℃条件下炭化获得。田间试验于2012年11月至2013年10月进行，为稻麦轮作体系。采用静态暗箱—气相色谱法观测CH4和N2O排放通量；试验共设置不施氮肥不施生物炭(N0B0)、不施氮肥施20 t/hm2生物炭(N0B1)、施氮肥不施生物炭(N1B0)、氮肥与20 t/hm2生物炭配施(N1B1)、氮肥与40 t/hm2生物炭配施(N1B2)等5个处理，各处理3次重复。【结果】单施氮肥(N1B0)与不施氮肥(N0B0)处理相比，增加了稻麦轮作产量82.8%，增加了CH4排放0.6倍，增加了N2O排放5.5倍。单施生物炭(N0B1)与不施生物炭(N0B0)处理相比，显著增产25.4%，却不能减少CH4和N2O的排放。在施氮的同时，配施20 t/hm2生物炭与单施氮肥处理相比，显著增加稻麦轮作产量21.6%，小麦和水稻总产量也比配施40 t/hm2生物炭处理高；配施40 t/hm2生物炭与单施氮肥处理相比，显著降低稻麦轮作系统CH4排放11.3%和N2O排放20.9%，CH4和N2O排放量也比配施20 t/hm2生物炭的排放量低。随着生物炭配施量的增加，CH4和N2O减排效果更明显。单施生物炭并不能有效地减少GWP，但却可以显著增加作物产量，从而减小GHGI。对N0B0、N0B1、N1B0、N1B1四个处理进行双因素方差分析发现，氮肥和生物炭在CH4和N2O 排放、作物产量、GWP 和GHGI方面都不存在明显的交互作用。各处理在100 a时间尺度上总GWP由大到小的顺序为N1B0 > N1B1 > N1B2 > N0B0 > N0B1，GHGI值由大到小的顺序则为N1B0 > N1B1 > N0B0 > N1B2 > N0B1。单施生物炭与配施生物炭都能降低稻麦轮作系统的GWP和GHGI，配施40 t/hm2生物炭处理降低效果更好。【结论】稻田麦季施用不同水平生物炭都能在保产或增产的同时，降低稻麦轮作系统CH4和N2O的排放及GWP和GHGI。在当前稻麦轮作系统中，与20 t/hm2的生物炭施用量相比，40 t/hm2的生物炭施用量显著降低GWP，但增产效果不明显，因此二者GHGI相当，需要根据温室效应与作物产量权衡选择生物炭实际施用量。

生物炭； 稻麦轮作系统； CH4排放； N2O排放； 综合温室效应； 温室气体强度

稻田是全球甲烷(CH4)和氧化亚氮(N2O)等温室气体的重要排放源，淹水稻田的CH4排放量占全球总排放量的5% ～ 19%[1]，是温室气体减排研究的重点对象[6]。稻田N2O排放主要发生在旱季[2]，其排放量占全国农田排放总量的25% ～ 35%[3]，水稻生长期间烤田会明显促进N2O排放[4-5]。华东地区稻麦轮作系统是我国最典型的农业种植方式，所以如何有效的减少稻麦轮作系统中温室气体的排放便成为当前应对气候变化的研究热点[1]。

生物炭是生物质在厌氧或无氧条件下经高温热解炭化产生的一类孔隙结构发达、含碳量高、比表面积大的固态物质[7]，具有高度稳定性和较强的吸附性能[8]。研究表明，生物炭不仅可提供作物生长需要的氮、磷、钾、钙、镁等营养元素[9-10]，还可以增加土壤碳库储量、养分循环与固持、提高作物产量[11-13]。章明奎等[14]研究发现，生物炭能抑制水稻土CH4排放; Zhang等[15]报道生物炭能减少稻田N2O排放、增加CH4排放; Sohi等[16]发现生物炭能促进作物生长，增加作物产量。因此，生物炭在农业领域的应用研究日益受到关注，逐渐成为农业增产和固碳减排的新途径[17]。

综合作物产量与温室效应的温室气体强度研究成为综合评估农田管理措施的研究趋势和研究热点[18-19]。稻田与旱地相比，水分条件迥异的环境施用生物炭是否也能减缓综合温室效应与温室气体强度。同时，由于不同类型、不同施用水平生物炭对CH4和N2O排放的影响结果差异较大[20]。尤其是在稻麦轮作体系稻田大量施用氮肥情况下，旱地小麦季配施生物炭又会如何影响稻田综合温室效应与温室气体强度未有定论[21]。很多研究提出施用较高量如40 t/hm2生物炭，既能提高作物产量又能更好地固碳减排[15,22]，但是对于有机质含量较高、氮充足的土壤可适当减少生物炭添加量[23]，以保持土壤肥力并减缓温室气体排放。为此，于2012年在小麦季单施或配施不同水平的生物炭，田间原位研究施用氮肥和生物炭对我国稻麦轮作生态系统中CH4和N2O排放规律的影响；同时结合作物产量评估该生态系统综合温室效应和温室气体强度，为生物炭在减缓全球气候变化及农业生产中的推广应用提供科学依据。

1 材料与方法

1.1 试验地点

试验于2012年冬季旱作季节在江苏省南京市秣陵镇(31°58′N，118°48′E)开展。该区属北亚热带季风气候区，年均日照2047.9小时，年平均气温15.7℃，年平均降水量1050.2 mm。试验田土壤质地为粉壤土，土壤类型为水稻土，常年进行稻麦轮作。

供试生物炭为小麦秸秆在高温(350 ～ 500℃)限氧条件下炭化所得。试验土壤和生物炭的基本理化性质见表1。

1.2 试验设计

试验田各小区具有独立灌排水系统，面积为 20 m2(4 m×5 m)。试验共设5个处理，即: N0B0(不施氮肥不施生物炭)、N0B1(不施氮, 施20 t/hm2生物炭)、N1B0(施氮肥不施生物炭)、N1B1(氮肥与20 t/hm2生物炭配施)、N1B2(氮肥与40 t/hm2生物炭配施)。各处理随机分布，3次重复。按照试验设计及施用水平，2012年在小麦播种时一次性施用全部生物炭。施氮处理尿素用量为每季作物N 250 kg /hm2，以4 ∶3 ∶3的比例分基肥和两次追肥施用。

1.3 水肥管理

除试验处理方案外，其余田间管理措施依据当地常规进行。旱作麦季不进行人工灌溉，只接受自然降水；稻季按照淹水—烤田—复水—落干的模式管理。小麦和水稻分别以撒播和插秧的方式种植，小麦2012年11月20日播种，2013年6月4日收获，共197 d；水稻2013年6月17日插秧，2013年10月26日收获，共132 d。所有处理都在小麦播种和水稻插秧时一次性施入钙镁磷肥和氯化钾作为基肥，每季作物的施用量分别为P2O560 kg/hm2和K2O 120 kg/hm2。施氮处理分基肥和两次追肥施用，小麦分别在2013年1月24日和2013年3月6日追肥，水稻分别在2013年7月8日和2013年8月8日追肥。

1.4 样品采集和分析

气体样品采用静态暗箱观测法采集。整个作物生长周期内每星期至少观测1次；施肥和水稻烤田期间隔天观测一次，持续4～5次。采样时间为2012年11月20日至2013年10月26日。采样箱规格为43 cm×43 cm× 50 cm或43 cm×43 cm×110 cm，随小麦和水稻生长高度改变箱体高度为50 cm或110 cm。采样时固定选择在上午8: 00 ～ 11: 00，将采样箱扣在底座上，于密封后0、10、20、30 min用20 mL针筒采集气体样品，然后带回实验室1天内用安捷伦气相色谱仪(Agilent 7890A)测定气体样品中CH4和N2O含量。CH4用氢火焰离子化检测器(FID)测定，N2O用电子捕获检测器(ECD)测定。

每次采集气体样品的同时测定采样箱内温度、大气温度、10 cm土层温度、旱地0—15 cm土层含水量以及水稻季水层深度。日降雨量、日均温等数据从邻近气象观测站获得。每季作物收获时测定作物产量。

CH4和N2O排放通量计算公式如下

F =ρ×V/A×dC/dt×273/(273+T)

式中，F为CH4或N2O排放通量，单位分别为mg/(m2·h)或μg/(m2·h)；ρ为标准状态下CH4-C或N2O-N的密度，分别为0.54 g/L和1.25 g/L；V为采样箱内有效体积(m3)；A为采样箱所覆盖的土壤表面积(m2)；dC/dt为CH4或N2O的排放速率，单位分别为μL/(L·h)或nL/(L·h)；T为采样过程中静态箱内的平均温度(℃)。

1.5 综合温室效应与温室气体强度计算

在100 a时间尺度上，单位质量CH4和N2O的综合温室效应(global warming potential，GWP)分别为CO2的25倍和298倍[1]。计算式为:

GWP=RCH4×25+RN2O×298

式中，GWP单位为CO2-eq kg/hm2; RCH4和RN2O为CH4和N2O季节累积排放量(kg/hm2)。

温室气体强度(greenhouse gas intensity，GHGI)是综合评价温室效应的指标[24]。计算式为:

GHGI=GWP/grain yield

式中，GHGI单位为CO2-eq kg/kg；GWP为CO2-eq kg /hm2；grain yield为作物产量(kg/hm2)。文中产量即经济产量，为收获的主产品谷物的产量。

1.6 数据处理

采用Excel 2010软件进行数据计算及图表制作，采用JMP 9.0软件进行CH4和N2O排放量、作物产量、综合温室效应和温室气体排放的方差分析(α=0.05)。

2 结果与分析

2.1 施用氮肥和生物炭下稻麦轮作体系周年CH4排放规律

从周年CH4排放的季节变化(图1)可知，麦季CH4排放通量都极其微弱，排放和吸收过程相互交替，较为复杂，没有明显规律。稻季则以CH4排放为主，淹水初期随着基肥的施用CH4排放量显著增加，第一次追肥后出现明显的排放峰。七月中下旬进入烤田期，田面水被排干，CH4排放量迅速下降。在复水初期CH4排放量仍然较低，之后随着第二次追肥的进行CH4排放量明显增加，成为整个稻季CH4排放的最高峰值。九月底田面再次落干后，CH4几乎无排放。

[注(Note): T0—基肥Basal fertilization date; T1、T2—第一次和第二次追肥 The first and second top dressing dates; 实线用来区分小麦和水稻的生长季，虚线表示水稻季的烤田期 Solid line is used to distinguish between wheat and rice growing season, and dotted line indicates the mid-season drainage period during the rice season.]

在整个周年变化过程中，各小区CH4的排放规律几乎一致。虽然稻季第二次追肥后施用生物炭处理CH4排放峰值比没施生物炭处理的高，但累积排放量低于不施生物炭处理。结合表2可知，N0B1处理CH4累积排放量低于N0B0，但差异不显著，说明麦季单施生物炭不能显著的减少稻麦轮作周年CH4排放量。N0B0、N0B1、N1B0、N1B1四个处理通过双因素方差分析表明，氮肥和生物炭之间不存在明显的交互作用。在施氮肥的同时，配施20 t/hm2生物炭不能显著降低CH4排放量，而配施40 t/hm2生物炭能显著降低CH4排放量11.3%(P<0.05)。随着生物炭施用量的增加，CH4减排效果更明显，可能是因为生物炭能加速稻田土壤氧化还原电俭(Eh)下降，为甲烷氧化菌提供适宜生长条件，使产生的大部分CH4被氧化，从而降低稻田土壤CH4排放量[25]。

注(Note): 平均值±标准差Mean±SD,n=3同列数据后不同字母表示处理间差异显著(P<0.05)Values followed by different letters in the same column are significantly different at 0.05 level among treatments.

2.2 施用氮肥和生物炭稻麦轮作体系周年N2O排放规律

从周年N2O排放季节变化(图2)可知，在小麦生长季基肥和追肥后都出现的N2O排放峰，第二次追肥期间的强降雨(图3)导致N2O出现明显的排放峰，不施氮肥处理没有出现峰值，配施生物炭处理的排放峰低于单施氮肥处理，此后N2O的排放通量迅速降低。在水稻生长季，基肥和追肥后也都出现N2O排放峰，第一次追肥后的排放峰小，烤田期N2O排放量成为稻季最高N2O排放峰。后期N2O排放通量减弱且平缓。

[注(Note): T0—基肥Basal fertilization date; T1和T2—第一次和第二次追肥The first and second top dressing dates。实线用来区分小麦和水稻的生长季，虚竖线表示水稻季的烤田期Solid line is used to distinguish between wheat and rice growing season and dotted vertical line indicates mid-season drainage during the rice season]

在整个周年变化过程中，各小区N2O的排放规律几乎一致。氮肥的施用促进稻田土壤N2O的排放。N0B0、N0B1、N1B0、N1B1四个处理通过双因素方差分析表明，氮肥和生物炭之间不存在明显的交互作用。结合表2可知，N0B0与N0B1差异不显著，说明单施20 t/hm2生物炭不能减少N2O的排放。N1B1和N1B2都低于N1B0，说明配施生物炭的排放通量低于单施氮肥，N1B1与N1B0没有显著差异，而N1B2比N1B0显著减少20.9%(P<0.05)，说明配施20 t/hm2生物炭不能显著降低稻田N2O排放，而40 t/hm2生物炭能显著降低稻田N2O排放，配施40 t/hm2生物炭对稻田N2O的减排效果明显优于配施20 t/hm2生物炭。由于生物炭具有高C/N比，会限制氮素的微生物转化和反硝化[26]，因此高量生物炭减缓N2O排放的效果更好。Liu等[27]则明确指出，土壤N2O排放量随生物炭施用量的增加而降低。

2.3 施用氮肥和生物炭对稻麦轮作周年作物产量、综合温室效应及温室气体强度的影响

由表3可知，施用氮肥能明显增加作物产量。N0B0与N0B1对作物产量的影响具有显著性差异，单施20 t/hm2生物炭能显著增加作物产量25.4%(P<0.05)。N1B0与N1B1有显著性差异，而N1B0与N1B2却没有，说明在施氮的同时，配施40 t/hm2生物炭不能显著增加作物产量，而配施20 t/hm2生物炭却能显著增产21.6%(P<0.05)。这种随生物炭用量增加而降低的增产效应与前人研究一致[28]。这与生物炭矿质养分含量低及C/N高，易降低土壤养分有效性有关，更易出现在有效养分低或低氮土壤上[29]。

由表3各处理在100 a时间尺度上的综合温室效应和温室气体强度可知，施氮与不施氮处理之间GWP存在显著差异而GHGI却差异不显著，N0B0与N0B1的GWP之间没有显著差异而GHGI之间表现出了显著差异。可见单施生物炭并不能有效地减少GWP，但却可以显著增加作物产量，从而减小GHGI。N0B0、N0B1、N1B0、N1B1四个处理通过双因素方差分析表明，氮肥和生物炭之间对产量、GWP和GHGI都不存在明显的交互作用。

注(Note): 同列数据后不同字母表示处理间差异显著(P<0.05)Values followed by different letters are significantly different at 0.05 level among treatments. GWP—Global warming potential; GHGI— Greenhouse gas intensity.

N1B0与N1B1、N1B0与N1B2之间GWP差异从不显著变为显著，说明配施40 t/hm2生物炭对GWP的降低效果比配施20 t/hm2生物炭更好，生物炭施用越多GWP减少越明显。N1B0与N1B1和N1B2之间GHGI都表现出显著差异，配施生物炭在降低温室气体排放的同时又增加了作物产量，故可以有效降低单位产量的GWP，即GHGI；表明配施生物炭能有效降低GHGI。与20 t/hm2的生物炭施用量相比，40 t/hm2的生物炭施用量更加降低GWP，但增产效果不明显，因此二者GHGI相当，需要根据温室效应与作物产量之间的平衡决定生物炭实际施用量。N1B0处理GWP和GHGI明显高于其他处理，说明单施氮肥会增加各处理GWP和GHGI，在施用氮肥的同时配施生物炭便能减少各处理GWP和GHGI。

3 讨论

3.1 施用生物炭对稻麦轮作周年CH4和N2O排放的影响

本试验中在施氮的同时，配施20和40 t/hm2生物炭，CH4排放量比单施氮肥分别降低了3.7%和11.3%(P<0.05)，说明随着生物炭施用量的增加，CH4排放通量减少，这可能是因为生物炭能改善土壤的通透性，减少了厌氧状态的存在，降低土壤中水溶性碳的含量[30]，生物炭可以吸附固定土壤中的水溶性有机碳，从而抑制CH4排放[14]。Forbes等[31]、Cheng等[32]和Liang等[33]研究发现，生物质炭还能够刺激土壤中微生物，影响微生物特性，改变微生物群落结构，降低土壤中CH4排放量。Feng等[34]发现生物炭能增加稻田土壤甲烷氧化菌的丰度，降低产甲烷菌与甲烷氧化菌的丰度比，从而抑制产甲烷菌的活性或增强甲烷氧化菌的活性，进而降低CH4排放。

本试验在施氮同时，配施生物炭都能一定程度上降低N2O排放。 Spokas等[35]发现这主要是由于生物炭增加土壤通透性，促进氧气扩散，有利于土壤中有机物质利用N2O发生非生物反应，Yanai等[36]研究发现生物炭可提高土壤pH，增强反硝化微生物的活性，从而降低N2O的排放。生物炭由于具有高碳氮比，施入土壤后可吸附和保持水分、降低土壤容重、增加通气性，从而限制硝化和反硝化作用的氮底物，促进氮素固持，降低N2O排放[37-38]。本试验中，配施不同水平生物炭各处理N2O排放通量变化趋势基本一致，但配施20 t/hm2生物炭不能而配施40 t/hm2生物炭能显著降低N2O排放，这与Zhang等[15]报道的40 t/hm2生物炭对稻田N2O减排效果优于20 t/hm2生物炭一致。但Spokas等[35]尝试添加不同水平的生物炭均能一定程度上抑制土壤N2O的释放，但并未发现生物炭的添加量与土壤N2O排放量之间存在线性关系，说明生物炭种类、施炭量、土壤类型对N2O排放的影响并无一致结论。

3.2 施用生物炭对稻麦轮作产量及GWP和GHGI的影响

GWP常被用来估计CH4和N2O对气候变化的综合效应[45]；GHGI表示农业中生产单位产量的粮食对气候的影响，是一个将环境效益与经济效益相协调统一的综合评价指标[46]。本试验中，单施氮肥显著增加GWP而对GHGI影响却不显著，单施生物炭或配施生物炭都能在一定程度上降低GWP和GHGI，这与Renner[18]报道的草地土壤施用生物炭能够降低其CH4和N2O排放，提高作物生产力和产量，进而降低GWP和GHGI的结果一致。

4 结论

氮肥施用增加CH4和N2O排放，增加稻麦轮作产量；20 t/hm2生物炭与氮肥配施能在一定程度上降低稻麦轮作系统CH4和N2O排放量，显著增加小麦和水稻的总产量；40 t/hm2生物炭和氮肥配施能显著降低稻麦轮作系统CH4和N2O排放量，可保持产量稳定或在一定程度上有增产效果。而单施生物炭没有减排效果却能显著增加产量。因此，稻田麦季施用不同水平生物炭都能在保产或增产的同时，降低稻麦轮作系统CH4和N2O的排放及GWP和GHGI，配施20 t/hm2与40 t/hm2生物炭二者具有相似较低的GHGI。但由于生物炭具有后续效应[47]，因此还有待对生物炭的作用机理进行长期深入的定位试验研究。

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Combined effects of nitrogen fertilization and biochar incorporation on methane and nitrous oxide emissions from paddy fields in rice-wheat annual rotation system

LI Lu, ZHOU Zi-qiang, PAN Xiao-jian, LI Bo, XIONG Zheng-qin*

(CollegeofResourcesandEnvironmentalSciences,NanjingAgriculturalUniversity,Nanjing210095,China)

【Objectives】The potentials of biochar application in mitigating global warming in agriculture systems need assessed through field experiments. The effects of combined N fertilization and biochar incorporation on the global warming potential(GWP)caused by CH4and N2O emissions, the greenhouse gas intensities(GHGI), and grain yield are need to be investigated to provide a scientific base for the biochar application in a rice-wheat annual rotation system. 【Methods】Biochar used in the study was prepared by carbonization of wheat straw at 350-500℃. A field experiment was carried out during the wheat and rice seasons between November 2012 and October 2013. Five treatments were adopted in triplicate: no N fertilization without biochar amendment(N0B0), no N fertilization with 20 t/hm2biochar amendment(N0B1), 250 kg/hm2N fertilization without biochar amendment(N1B0), 250 kg/hm2N fertilization with 20 t/hm2biochar amendment(N1B1), 250 kg/hm2N fertilization with 40 t/hm2biochar amendment(N1B2). The CH4and N2O gas emission fluxes were monitored with a static chamber and gas chromatography method.【Results】In N1B0 treatment, the yield of rice and wheat was increased by 82.8%, the CH4and N2O emissions were 1.6 and 6.5 times of those in N0B0 treatment. In N0B1 treatment, the wheat and rice production was significantly increased by 25.4%, no pronounced difference in CH4and N2O emissions was found with in the N0B0 treatment. In contrast with the N1B0 treatment, CH4emission decreased by 3.7% and 11.3%(P<0.05), N2O emission decreased by 6.1% and 20.9%(P<0.05), the yield of rice and wheat increased by 21.6%(P<0.05)and 10.0% in the N1B1 and N1B2 treatments, respectively. The N1B2 treatment significantly reduced the CH4and N2O emissions than in N1B1 treatment. The mitigation effect on CH4and N2O emissions became more noticeable with higher biochar amendment. Based on a 100 years horizon, the order of ranks in the annual total GWPs of CH4and N2O total emissions over the entire rotation cycle was N1B0 > N1B1 > N1B2 > N0B0 > N0B1, the GWPs per unit crop grain yield were in order of N1B0 > N1B1 > N0B0 > N1B2 > N0B1. Significant difference in the GWPs existed between the treatments with and without N fertilizer, not in the GHGIs. There was no significant difference between the N0B0 and N0B1 treatments in the GWPs, but significant in the GHGIs. The noticeably higher GWP and GHGI were found in the N1B0 than in other treatments, which indicated that the single N fertilization could increase the GWP and GHGI. Both nitrogen and biochar combination treatments could reduce the GWP and GHGI. The single biochar amendment did not effectively reduce the GWP, but significantly increased crop yield and reduced GHGI. A two-way analysis of variance for treatments of N0B0, N0B1, N1B0 and N1B1 indicated that no obvious interaction between N fertilizer and biochar on CH4and N2O emissions, crop yield, GWP and GHGI. All the single biochar application and the combined application with N fertilizer could reduce the GWPs and GHGIs, and biochar incorporation of 40 t/hm2produced better results than that of 20 t/hm2. 【Conclusion】 The single N fertilization, and the biochar and N incorporation in wheat season increase the wheat and rice production, decrease CH4and N2O emissions, thus simultaneously lowered GWP and GHGI in a rice-wheat rotation system. Biochar amendment of 40 t/hm2could mitigate more GHG emissions than that of 20 t/hm2, while improved insignificant grain yields. Thus the two biochar amendments produce comparable GHGI. It is therefore an unanswered issue for decision when balanced between GHG mitigation and grain yield.

biochar; rice-wheat rotation system; CH4; N2O; global warming potential; greenhouse gas intensity

2014-05-14 接受日期: 2014-08-24 网络出版日期: 2015-02-12

国家自然科学基金(41171238; 41471192)；“十二五”农村领域国家科技计划课题农业生态系统固碳减排技术研发集成与示范2013BAD11B01；教育部高等学校博士点科研基金项目(20110097110001)资助。

李露(1989—)，男，安徽宣城人，硕士研究生，主要从事农田温室气体减排研究。E-mail: 2012103110@njau. edu. cn *通信作者E-mail: zqxiong@njau.edu.cn

X501；S161.9

A

1008-505X(2015)05-1095-09