氮肥與生物炭施用對稻麥輪作系統(tǒng)甲烷和氧化亞氮排放的影響

李 露, 周自強(qiáng), 潘曉健, 李 博, 熊正琴

(南京農(nóng)業(yè)大學(xué)資源與環(huán)境科學(xué)學(xué)院，南京 210095)

氮肥與生物炭施用對稻麥輪作系統(tǒng)甲烷和氧化亞氮排放的影響

李 露, 周自強(qiáng), 潘曉健, 李 博, 熊正琴*

(南京農(nóng)業(yè)大學(xué)資源與環(huán)境科學(xué)學(xué)院，南京 210095)

【目的】以我國稻麥輪作系統(tǒng)為對象，研究氮肥和小麥秸稈生物炭聯(lián)合施用對CH4和N2O排放規(guī)律的影響；結(jié)合小麥和水稻總產(chǎn)量進(jìn)而評估對該生態(tài)系統(tǒng)綜合溫室效應(yīng)(GWP)和溫室氣體強(qiáng)度(GHGI)的影響，為生物炭在減緩全球氣候變化及農(nóng)業(yè)生產(chǎn)中的推廣應(yīng)用提供科學(xué)依據(jù)?！痉椒ā可锾客ㄟ^小麥秸稈在300～500℃條件下炭化獲得。田間試驗于2012年11月至2013年10月進(jìn)行，為稻麥輪作體系。采用靜態(tài)暗箱—氣相色譜法觀測CH4和N2O排放通量；試驗共設(shè)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)、氮肥與20 t/hm2生物炭配施(N1B1)、氮肥與40 t/hm2生物炭配施(N1B2)等5個處理，各處理3次重復(fù)?！窘Y(jié)果】單施氮肥(N1B0)與不施氮肥(N0B0)處理相比，增加了稻麥輪作產(chǎn)量82.8%，增加了CH4排放0.6倍，增加了N2O排放5.5倍。單施生物炭(N0B1)與不施生物炭(N0B0)處理相比，顯著增產(chǎn)25.4%，卻不能減少CH4和N2O的排放。在施氮的同時，配施20 t/hm2生物炭與單施氮肥處理相比，顯著增加稻麥輪作產(chǎn)量21.6%，小麥和水稻總產(chǎn)量也比配施40 t/hm2生物炭處理高；配施40 t/hm2生物炭與單施氮肥處理相比，顯著降低稻麥輪作系統(tǒng)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。隨著生物炭配施量的增加，CH4和N2O減排效果更明顯。單施生物炭并不能有效地減少GWP，但卻可以顯著增加作物產(chǎn)量，從而減小GHGI。對N0B0、N0B1、N1B0、N1B1四個處理進(jìn)行雙因素方差分析發(fā)現(xiàn)，氮肥和生物炭在CH4和N2O 排放、作物產(chǎn)量、GWP 和GHGI方面都不存在明顯的交互作用。各處理在100 a時間尺度上總GWP由大到小的順序為N1B0 > N1B1 > N1B2 > N0B0 > N0B1，GHGI值由大到小的順序則為N1B0 > N1B1 > N0B0 > N1B2 > N0B1。單施生物炭與配施生物炭都能降低稻麥輪作系統(tǒng)的GWP和GHGI，配施40 t/hm2生物炭處理降低效果更好?！窘Y(jié)論】稻田麥季施用不同水平生物炭都能在保產(chǎn)或增產(chǎn)的同時，降低稻麥輪作系統(tǒng)CH4和N2O的排放及GWP和GHGI。在當(dāng)前稻麥輪作系統(tǒng)中，與20 t/hm2的生物炭施用量相比，40 t/hm2的生物炭施用量顯著降低GWP，但增產(chǎn)效果不明顯，因此二者GHGI相當(dāng)，需要根據(jù)溫室效應(yīng)與作物產(chǎn)量權(quán)衡選擇生物炭實際施用量。

生物炭； 稻麥輪作系統(tǒng)； CH4排放； N2O排放； 綜合溫室效應(yīng)； 溫室氣體強(qiáng)度

稻田是全球甲烷(CH4)和氧化亞氮(N2O)等溫室氣體的重要排放源，淹水稻田的CH4排放量占全球總排放量的5% ～ 19%[1]，是溫室氣體減排研究的重點對象[6]。稻田N2O排放主要發(fā)生在旱季[2]，其排放量占全國農(nóng)田排放總量的25% ～ 35%[3]，水稻生長期間烤田會明顯促進(jìn)N2O排放[4-5]。華東地區(qū)稻麥輪作系統(tǒng)是我國最典型的農(nóng)業(yè)種植方式，所以如何有效的減少稻麥輪作系統(tǒng)中溫室氣體的排放便成為當(dāng)前應(yīng)對氣候變化的研究熱點[1]。

生物炭是生物質(zhì)在厭氧或無氧條件下經(jīng)高溫?zé)峤馓炕a(chǎn)生的一類孔隙結(jié)構(gòu)發(fā)達(dá)、含碳量高、比表面積大的固態(tài)物質(zhì)[7]，具有高度穩(wěn)定性和較強(qiáng)的吸附性能[8]。研究表明，生物炭不僅可提供作物生長需要的氮、磷、鉀、鈣、鎂等營養(yǎng)元素[9-10]，還可以增加土壤碳庫儲量、養(yǎng)分循環(huán)與固持、提高作物產(chǎn)量[11-13]。章明奎等[14]研究發(fā)現(xiàn)，生物炭能抑制水稻土CH4排放; Zhang等[15]報道生物炭能減少稻田N2O排放、增加CH4排放; Sohi等[16]發(fā)現(xiàn)生物炭能促進(jìn)作物生長，增加作物產(chǎn)量。因此，生物炭在農(nóng)業(yè)領(lǐng)域的應(yīng)用研究日益受到關(guān)注，逐漸成為農(nóng)業(yè)增產(chǎn)和固碳減排的新途徑[17]。

綜合作物產(chǎn)量與溫室效應(yīng)的溫室氣體強(qiáng)度研究成為綜合評估農(nóng)田管理措施的研究趨勢和研究熱點[18-19]。稻田與旱地相比，水分條件迥異的環(huán)境施用生物炭是否也能減緩綜合溫室效應(yīng)與溫室氣體強(qiáng)度。同時，由于不同類型、不同施用水平生物炭對CH4和N2O排放的影響結(jié)果差異較大[20]。尤其是在稻麥輪作體系稻田大量施用氮肥情況下，旱地小麥季配施生物炭又會如何影響稻田綜合溫室效應(yīng)與溫室氣體強(qiáng)度未有定論[21]。很多研究提出施用較高量如40 t/hm2生物炭，既能提高作物產(chǎn)量又能更好地固碳減排[15,22]，但是對于有機(jī)質(zhì)含量較高、氮充足的土壤可適當(dāng)減少生物炭添加量[23]，以保持土壤肥力并減緩溫室氣體排放。為此，于2012年在小麥季單施或配施不同水平的生物炭，田間原位研究施用氮肥和生物炭對我國稻麥輪作生態(tài)系統(tǒng)中CH4和N2O排放規(guī)律的影響；同時結(jié)合作物產(chǎn)量評估該生態(tài)系統(tǒng)綜合溫室效應(yīng)和溫室氣體強(qiáng)度，為生物炭在減緩全球氣候變化及農(nóng)業(yè)生產(chǎn)中的推廣應(yīng)用提供科學(xué)依據(jù)。

1 材料與方法

1.1 試驗地點

試驗于2012年冬季旱作季節(jié)在江蘇省南京市秣陵鎮(zhèn)(31°58′N，118°48′E)開展。該區(qū)屬北亞熱帶季風(fēng)氣候區(qū)，年均日照2047.9小時，年平均氣溫15.7℃，年平均降水量1050.2 mm。試驗田土壤質(zhì)地為粉壤土，土壤類型為水稻土，常年進(jìn)行稻麥輪作。

供試生物炭為小麥秸稈在高溫(350 ～ 500℃)限氧條件下炭化所得。試驗土壤和生物炭的基本理化性質(zhì)見表1。

1.2 試驗設(shè)計

試驗田各小區(qū)具有獨立灌排水系統(tǒng)，面積為 20 m2(4 m×5 m)。試驗共設(shè)5個處理，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(氮肥與20 t/hm2生物炭配施)、N1B2(氮肥與40 t/hm2生物炭配施)。各處理隨機(jī)分布，3次重復(fù)。按照試驗設(shè)計及施用水平，2012年在小麥播種時一次性施用全部生物炭。施氮處理尿素用量為每季作物N 250 kg /hm2，以4 ∶3 ∶3的比例分基肥和兩次追肥施用。

1.3 水肥管理

除試驗處理方案外，其余田間管理措施依據(jù)當(dāng)?shù)爻Ｒ?guī)進(jìn)行。旱作麥季不進(jìn)行人工灌溉，只接受自然降水；稻季按照淹水—烤田—復(fù)水—落干的模式管理。小麥和水稻分別以撒播和插秧的方式種植，小麥2012年11月20日播種，2013年6月4日收獲，共197 d；水稻2013年6月17日插秧，2013年10月26日收獲，共132 d。所有處理都在小麥播種和水稻插秧時一次性施入鈣鎂磷肥和氯化鉀作為基肥，每季作物的施用量分別為P2O560 kg/hm2和K2O 120 kg/hm2。施氮處理分基肥和兩次追肥施用，小麥分別在2013年1月24日和2013年3月6日追肥，水稻分別在2013年7月8日和2013年8月8日追肥。

1.4 樣品采集和分析

氣體樣品采用靜態(tài)暗箱觀測法采集。整個作物生長周期內(nèi)每星期至少觀測1次；施肥和水稻烤田期間隔天觀測一次，持續(xù)4～5次。采樣時間為2012年11月20日至2013年10月26日。采樣箱規(guī)格為43 cm×43 cm× 50 cm或43 cm×43 cm×110 cm，隨小麥和水稻生長高度改變箱體高度為50 cm或110 cm。采樣時固定選擇在上午8: 00 ～ 11: 00，將采樣箱扣在底座上，于密封后0、10、20、30 min用20 mL針筒采集氣體樣品，然后帶回實驗室1天內(nèi)用安捷倫氣相色譜儀(Agilent 7890A)測定氣體樣品中CH4和N2O含量。CH4用氫火焰離子化檢測器(FID)測定，N2O用電子捕獲檢測器(ECD)測定。

每次采集氣體樣品的同時測定采樣箱內(nèi)溫度、大氣溫度、10 cm土層溫度、旱地0—15 cm土層含水量以及水稻季水層深度。日降雨量、日均溫等數(shù)據(jù)從鄰近氣象觀測站獲得。每季作物收獲時測定作物產(chǎn)量。

CH4和N2O排放通量計算公式如下

F =ρ×V/A×dC/dt×273/(273+T)

式中，F(xiàn)為CH4或N2O排放通量，單位分別為mg/(m2·h)或μg/(m2·h)；ρ為標(biāo)準(zhǔn)狀態(tài)下CH4-C或N2O-N的密度，分別為0.54 g/L和1.25 g/L；V為采樣箱內(nèi)有效體積(m3)；A為采樣箱所覆蓋的土壤表面積(m2)；dC/dt為CH4或N2O的排放速率，單位分別為μL/(L·h)或nL/(L·h)；T為采樣過程中靜態(tài)箱內(nèi)的平均溫度(℃)。

1.5 綜合溫室效應(yīng)與溫室氣體強(qiáng)度計算

在100 a時間尺度上，單位質(zhì)量CH4和N2O的綜合溫室效應(yīng)(global warming potential，GWP)分別為CO2的25倍和298倍[1]。計算式為:

GWP=RCH4×25+RN2O×298

式中，GWP單位為CO2-eq kg/hm2; RCH4和RN2O為CH4和N2O季節(jié)累積排放量(kg/hm2)。

溫室氣體強(qiáng)度(greenhouse gas intensity，GHGI)是綜合評價溫室效應(yīng)的指標(biāo)[24]。計算式為:

GHGI=GWP/grain yield

式中，GHGI單位為CO2-eq kg/kg；GWP為CO2-eq kg /hm2；grain yield為作物產(chǎn)量(kg/hm2)。文中產(chǎn)量即經(jīng)濟(jì)產(chǎn)量，為收獲的主產(chǎn)品谷物的產(chǎn)量。

1.6 數(shù)據(jù)處理

采用Excel 2010軟件進(jìn)行數(shù)據(jù)計算及圖表制作，采用JMP 9.0軟件進(jìn)行CH4和N2O排放量、作物產(chǎn)量、綜合溫室效應(yīng)和溫室氣體排放的方差分析(α=0.05)。

2 結(jié)果與分析

2.1 施用氮肥和生物炭下稻麥輪作體系周年CH4排放規(guī)律

從周年CH4排放的季節(jié)變化(圖1)可知，麥季CH4排放通量都極其微弱，排放和吸收過程相互交替，較為復(fù)雜，沒有明顯規(guī)律。稻季則以CH4排放為主，淹水初期隨著基肥的施用CH4排放量顯著增加，第一次追肥后出現(xiàn)明顯的排放峰。七月中下旬進(jìn)入烤田期，田面水被排干，CH4排放量迅速下降。在復(fù)水初期CH4排放量仍然較低，之后隨著第二次追肥的進(jìn)行CH4排放量明顯增加，成為整個稻季CH4排放的最高峰值。九月底田面再次落干后，CH4幾乎無排放。

[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; 實線用來區(qū)分小麥和水稻的生長季，虛線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.]

在整個周年變化過程中，各小區(qū)CH4的排放規(guī)律幾乎一致。雖然稻季第二次追肥后施用生物炭處理CH4排放峰值比沒施生物炭處理的高，但累積排放量低于不施生物炭處理。結(jié)合表2可知，N0B1處理CH4累積排放量低于N0B0，但差異不顯著，說明麥季單施生物炭不能顯著的減少稻麥輪作周年CH4排放量。N0B0、N0B1、N1B0、N1B1四個處理通過雙因素方差分析表明，氮肥和生物炭之間不存在明顯的交互作用。在施氮肥的同時，配施20 t/hm2生物炭不能顯著降低CH4排放量，而配施40 t/hm2生物炭能顯著降低CH4排放量11.3%(P<0.05)。隨著生物炭施用量的增加，CH4減排效果更明顯，可能是因為生物炭能加速稻田土壤氧化還原電儉(Eh)下降，為甲烷氧化菌提供適宜生長條件，使產(chǎn)生的大部分CH4被氧化，從而降低稻田土壤CH4排放量[25]。

注(Note): 平均值±標(biāo)準(zhǔn)差Mean±SD,n=3同列數(shù)據(jù)后不同字母表示處理間差異顯著(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麥輪作體系周年N2O排放規(guī)律

從周年N2O排放季節(jié)變化(圖2)可知，在小麥生長季基肥和追肥后都出現(xiàn)的N2O排放峰，第二次追肥期間的強(qiáng)降雨(圖3)導(dǎo)致N2O出現(xiàn)明顯的排放峰，不施氮肥處理沒有出現(xiàn)峰值，配施生物炭處理的排放峰低于單施氮肥處理，此后N2O的排放通量迅速降低。在水稻生長季，基肥和追肥后也都出現(xiàn)N2O排放峰，第一次追肥后的排放峰小，烤田期N2O排放量成為稻季最高N2O排放峰。后期N2O排放通量減弱且平緩。

[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。實線用來區(qū)分小麥和水稻的生長季，虛豎線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]

在整個周年變化過程中，各小區(qū)N2O的排放規(guī)律幾乎一致。氮肥的施用促進(jìn)稻田土壤N2O的排放。N0B0、N0B1、N1B0、N1B1四個處理通過雙因素方差分析表明，氮肥和生物炭之間不存在明顯的交互作用。結(jié)合表2可知，N0B0與N0B1差異不顯著，說明單施20 t/hm2生物炭不能減少N2O的排放。N1B1和N1B2都低于N1B0，說明配施生物炭的排放通量低于單施氮肥，N1B1與N1B0沒有顯著差異，而N1B2比N1B0顯著減少20.9%(P<0.05)，說明配施20 t/hm2生物炭不能顯著降低稻田N2O排放，而40 t/hm2生物炭能顯著降低稻田N2O排放，配施40 t/hm2生物炭對稻田N2O的減排效果明顯優(yōu)于配施20 t/hm2生物炭。由于生物炭具有高C/N比，會限制氮素的微生物轉(zhuǎn)化和反硝化[26]，因此高量生物炭減緩N2O排放的效果更好。Liu等[27]則明確指出，土壤N2O排放量隨生物炭施用量的增加而降低。

2.3 施用氮肥和生物炭對稻麥輪作周年作物產(chǎn)量、綜合溫室效應(yīng)及溫室氣體強(qiáng)度的影響

由表3可知，施用氮肥能明顯增加作物產(chǎn)量。N0B0與N0B1對作物產(chǎn)量的影響具有顯著性差異，單施20 t/hm2生物炭能顯著增加作物產(chǎn)量25.4%(P<0.05)。N1B0與N1B1有顯著性差異，而N1B0與N1B2卻沒有，說明在施氮的同時，配施40 t/hm2生物炭不能顯著增加作物產(chǎn)量，而配施20 t/hm2生物炭卻能顯著增產(chǎn)21.6%(P<0.05)。這種隨生物炭用量增加而降低的增產(chǎn)效應(yīng)與前人研究一致[28]。這與生物炭礦質(zhì)養(yǎng)分含量低及C/N高，易降低土壤養(yǎng)分有效性有關(guān)，更易出現(xiàn)在有效養(yǎng)分低或低氮土壤上[29]。

由表3各處理在100 a時間尺度上的綜合溫室效應(yīng)和溫室氣體強(qiáng)度可知，施氮與不施氮處理之間GWP存在顯著差異而GHGI卻差異不顯著，N0B0與N0B1的GWP之間沒有顯著差異而GHGI之間表現(xiàn)出了顯著差異。可見單施生物炭并不能有效地減少GWP，但卻可以顯著增加作物產(chǎn)量，從而減小GHGI。N0B0、N0B1、N1B0、N1B1四個處理通過雙因素方差分析表明，氮肥和生物炭之間對產(chǎn)量、GWP和GHGI都不存在明顯的交互作用。

注(Note): 同列數(shù)據(jù)后不同字母表示處理間差異顯著(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與N1B1、N1B0與N1B2之間GWP差異從不顯著變?yōu)轱@著，說明配施40 t/hm2生物炭對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減少越明顯。N1B0與N1B1和N1B2之間GHGI都表現(xiàn)出顯著差異，配施生物炭在降低溫室氣體排放的同時又增加了作物產(chǎn)量，故可以有效降低單位產(chǎn)量的GWP，即GHGI；表明配施生物炭能有效降低GHGI。與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，但增產(chǎn)效果不明顯，因此二者GHGI相當(dāng)，需要根據(jù)溫室效應(yīng)與作物產(chǎn)量之間的平衡決定生物炭實際施用量。N1B0處理GWP和GHGI明顯高于其他處理，說明單施氮肥會增加各處理GWP和GHGI，在施用氮肥的同時配施生物炭便能減少各處理GWP和GHGI。

3 討論

3.1 施用生物炭對稻麥輪作周年CH4和N2O排放的影響

本試驗中在施氮的同時，配施20和40 t/hm2生物炭，CH4排放量比單施氮肥分別降低了3.7%和11.3%(P<0.05)，說明隨著生物炭施用量的增加，CH4排放通量減少，這可能是因為生物炭能改善土壤的通透性，減少了厭氧狀態(tài)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機(jī)碳，從而抑制CH4排放[14]。Forbes等[31]、Cheng等[32]和Liang等[33]研究發(fā)現(xiàn)，生物質(zhì)炭還能夠刺激土壤中微生物，影響微生物特性，改變微生物群落結(jié)構(gòu)，降低土壤中CH4排放量。Feng等[34]發(fā)現(xiàn)生物炭能增加稻田土壤甲烷氧化菌的豐度，降低產(chǎn)甲烷菌與甲烷氧化菌的豐度比，從而抑制產(chǎn)甲烷菌的活性或增強(qiáng)甲烷氧化菌的活性，進(jìn)而降低CH4排放。

本試驗在施氮同時，配施生物炭都能一定程度上降低N2O排放。 Spokas等[35]發(fā)現(xiàn)這主要是由于生物炭增加土壤通透性，促進(jìn)氧氣擴(kuò)散，有利于土壤中有機(jī)物質(zhì)利用N2O發(fā)生非生物反應(yīng)，Yanai等[36]研究發(fā)現(xiàn)生物炭可提高土壤pH，增強(qiáng)反硝化微生物的活性，從而降低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、增加通氣性，從而限制硝化和反硝化作用的氮底物，促進(jìn)氮素固持，降低N2O排放[37-38]。本試驗中，配施不同水平生物炭各處理N2O排放通量變化趨勢基本一致，但配施20 t/hm2生物炭不能而配施40 t/hm2生物炭能顯著降低N2O排放，這與Zhang等[15]報道的40 t/hm2生物炭對稻田N2O減排效果優(yōu)于20 t/hm2生物炭一致。但Spokas等[35]嘗試添加不同水平的生物炭均能一定程度上抑制土壤N2O的釋放，但并未發(fā)現(xiàn)生物炭的添加量與土壤N2O排放量之間存在線性關(guān)系，說明生物炭種類、施炭量、土壤類型對N2O排放的影響并無一致結(jié)論。

3.2 施用生物炭對稻麥輪作產(chǎn)量及GWP和GHGI的影響

GWP常被用來估計CH4和N2O對氣候變化的綜合效應(yīng)[45]；GHGI表示農(nóng)業(yè)中生產(chǎn)單位產(chǎn)量的糧食對氣候的影響，是一個將環(huán)境效益與經(jīng)濟(jì)效益相協(xié)調(diào)統(tǒng)一的綜合評價指標(biāo)[46]。本試驗中，單施氮肥顯著增加GWP而對GHGI影響卻不顯著，單施生物炭或配施生物炭都能在一定程度上降低GWP和GHGI，這與Renner[18]報道的草地土壤施用生物炭能夠降低其CH4和N2O排放，提高作物生產(chǎn)力和產(chǎn)量，進(jìn)而降低GWP和GHGI的結(jié)果一致。

4 結(jié)論

氮肥施用增加CH4和N2O排放，增加稻麥輪作產(chǎn)量；20 t/hm2生物炭與氮肥配施能在一定程度上降低稻麥輪作系統(tǒng)CH4和N2O排放量，顯著增加小麥和水稻的總產(chǎn)量；40 t/hm2生物炭和氮肥配施能顯著降低稻麥輪作系統(tǒng)CH4和N2O排放量，可保持產(chǎn)量穩(wěn)定或在一定程度上有增產(chǎn)效果。而單施生物炭沒有減排效果卻能顯著增加產(chǎn)量。因此，稻田麥季施用不同水平生物炭都能在保產(chǎn)或增產(chǎn)的同時，降低稻麥輪作系統(tǒng)CH4和N2O的排放及GWP和GHGI，配施20 t/hm2與40 t/hm2生物炭二者具有相似較低的GHGI。但由于生物炭具有后續(xù)效應(yīng)[47]，因此還有待對生物炭的作用機(jī)理進(jìn)行長期深入的定位試驗研究。

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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 網(wǎng)絡(luò)出版日期: 2015-02-12

國家自然科學(xué)基金(41171238; 41471192)；“十二五”農(nóng)村領(lǐng)域國家科技計劃課題農(nóng)業(yè)生態(tài)系統(tǒng)固碳減排技術(shù)研發(fā)集成與示范2013BAD11B01；教育部高等學(xué)校博士點科研基金項目(20110097110001)資助。

李露(1989—)，男，安徽宣城人，碩士研究生，主要從事農(nóng)田溫室氣體減排研究。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