趙力瑩, 董文旭, 胡春勝**, 李佳珍, 陳 拓

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耕作方式轉(zhuǎn)變對冬小麥季農(nóng)田溫室氣體排放和產(chǎn)量的影響*

趙力瑩1,2, 董文旭1, 胡春勝1**, 李佳珍1,2, 陳 拓1,2

(1. 中國科學(xué)院遺傳與發(fā)育生物學(xué)研究所農(nóng)業(yè)資源研究中心/中國科學(xué)院農(nóng)業(yè)水資源重點實驗室/河北省節(jié)水農(nóng)業(yè)重點實驗室 石家莊 050022; 2. 中國科學(xué)院大學(xué) 北京 100049)

合理耕作方式對農(nóng)業(yè)可持續(xù)生產(chǎn)和減緩全球氣候變化有重要意義。為評價耕作方式轉(zhuǎn)變對農(nóng)田溫室氣體排放的影響, 本研究針對連續(xù)16年的長期旋耕小麥/玉米農(nóng)田進(jìn)行不同的輪耕處理, 采用原位靜態(tài)箱-氣相色譜法分析了小麥季農(nóng)田土壤3種溫室氣體CH4、CO2、N2O排放規(guī)律。試驗共設(shè)3個處理: 在前期旋耕基礎(chǔ)上分別進(jìn)行翻耕處理(XF)和深松處理(XS), 另外保持旋耕(X)作為對照。試驗結(jié)果表明: CO2排放通量在耕作后1周有明顯排放峰, XF處理顯著低于X和XS處理; N2O排放通量在耕作和灌溉施肥后有明顯排放峰, XS處理顯著高于XF和X處理; 兩種氣體排放通量在越冬期出現(xiàn)最低值。CH4從耕作后到越冬期有持續(xù)明顯的吸收過程, 其中XS處理的吸收通量顯著高于XF和X處理。農(nóng)田土壤在冬小麥生長季表現(xiàn)為CO2的源, 累積排放量為XS(5 241 kg·hm-2)>X(5 160 kg·hm-2)>XF(4 840 kg·hm-2), XS與X處理間差異不顯著, 均顯著高于XF; N2O的源, 累積排放量表現(xiàn)為XS(4.38 kg·hm-2)>XF(2.39 kg·hm-2)>X(2.26 kg·hm-2), XS與XF處理間差異不顯著, 均顯著高于X處理; CH4的匯, 累積吸收量為XS(6.14 kg·hm-2)>XF(5.64 kg·hm-2)>X(3.70 kg·hm-2)。將累積溫室氣體換算為CO2當(dāng)量, 對增溫效應(yīng)的貢獻(xiàn)表現(xiàn)為XF(5.32 t·hm-2)

冬小麥; 旋耕; 翻耕; 深松; 溫室氣體; 產(chǎn)量

由溫室氣體引發(fā)的全球氣候變暖和臭氧層破壞已成為全世界面臨的嚴(yán)重環(huán)境問題[1]。而我們賴以生存的農(nóng)業(yè)向大氣中貢獻(xiàn)了大量的CH4、CO2和N2O[2]。農(nóng)業(yè)產(chǎn)生的溫室氣體通量是復(fù)雜且異質(zhì)的, 但是可以通過有效的農(nóng)業(yè)管理系統(tǒng)實現(xiàn)減排[3]。長期單一的耕作方式會使農(nóng)田土壤環(huán)境不利于作物生長發(fā)育[4], 如長期翻耕因作業(yè)深度淺及機械碾壓等因素加劇耕層變淺, 導(dǎo)致養(yǎng)分庫容降低[5]; 長期深松的土壤有機碳、氮儲量表現(xiàn)為表層富集現(xiàn)象[4], 農(nóng)作物病蟲害加重[6]; 而長期旋耕使土壤耕層變淺[7], 亞表層容重增加[8], 土壤的緊實度增大[9], 使養(yǎng)分易聚集在土壤表層, 不利于作物根部對養(yǎng)分的吸收, 影響作物的產(chǎn)量, 且長期旋耕的土壤表現(xiàn)為碳的凈損失[10], 不利于土壤質(zhì)量提高和農(nóng)田碳減排。農(nóng)田土壤采用單一耕作模式, 導(dǎo)致土壤肥力和作物產(chǎn)量衰減期, 而實行不同的土壤輪耕模式有利于保持和提高土壤肥力, 確保持續(xù)高產(chǎn)[11]。

耕作方式對農(nóng)田溫室氣體的產(chǎn)生與排放有重要影響。Badagliacca等[12]發(fā)現(xiàn)相比于常規(guī)翻耕, 免耕通過增加土壤容重、孔隙(WFPS, water-filled pore space)提高可獲得有機碳量進(jìn)而促進(jìn)土壤N2O排放, 導(dǎo)致N2O排放量增加。Zhu等[13]在13年長期耕作試驗發(fā)現(xiàn)相比于常規(guī)翻耕, 免耕減少土壤N2O排放的同時減少了CO2的排放。Lamptey等[14]發(fā)現(xiàn)與翻耕和旋耕相比, 免耕和深松增加了土壤孔隙度和土壤飽和導(dǎo)水率, 使土壤排放CO2量顯著降低。

但大多數(shù)學(xué)者多集中在對長期不同耕作方式下溫室氣體排放規(guī)律和總量的研究[15-18], 對在長期旋耕基礎(chǔ)上改變耕作方式后溫室氣體排放特點及對增溫效應(yīng)的貢獻(xiàn)研究鮮有報道。而華北平原是我國小麥()主產(chǎn)區(qū), 小麥的產(chǎn)量占全國的41%[19], 對華北平原小麥季溫室氣體排放的研究有很好的代表性, 且該地區(qū)近年來的常規(guī)耕作方式為旋耕[20], 相對于免耕而言, 旋耕促進(jìn)了農(nóng)田土壤CO2、N2O的排放[21-24], 加強了對CH4的吸收[25-26], 但針對華北平原長期旋耕后調(diào)整耕作方式對溫室氣體排放的影響少有研究。一方面, 長期淺旋耕農(nóng)田經(jīng)深耕后會增加土壤擾動, 促進(jìn)微生物活動而增加CO2等氣體排放; 另一方面深耕使上下土層翻轉(zhuǎn), 把長期旋耕累積表層有機質(zhì)翻轉(zhuǎn)到下層, 可能會抑制CO2排放而有利于有機碳積累。鑒于此, 本研究設(shè)置長期旋耕、長期旋耕后深松和翻耕3種耕作處理, 研究不同耕作方式對溫室氣體排放規(guī)律、排放量、增溫效應(yīng)的貢獻(xiàn)和小麥產(chǎn)量的影響, 探索生態(tài)效益和產(chǎn)量收益“雙贏”的輪耕方式, 為調(diào)整本地區(qū)農(nóng)田的耕作模式和分析溫室氣體排放規(guī)律提供理論依據(jù)。

1 材料與方法

1.1 試驗區(qū)概況

試驗地設(shè)在中國科學(xué)院欒城農(nóng)業(yè)生態(tài)系統(tǒng)試驗站(114°40′E, 37°50′N), 處于太行山山前平原的中部位置, 平均海拔為50.1 m。屬于半濕潤半干旱季風(fēng)氣候, 雨熱同期, 年平均氣溫為12.3 ℃, 年平均降水440 mm, 小麥季氣溫和降雨情況如圖1所示。年輻射總量543.3 kJ·cm-2, 年日照時數(shù)2 608 h, 種植制度為冬小麥-夏玉米()一年兩熟。耕層土壤為粉壤土(含13.8%砂粒、66.3%粉粒、19.9%黏粒)。試驗區(qū)土壤基本理化性質(zhì): 全氮1.06 g·kg-1, 堿解氮111.83 mg·kg-1, 速效磷6.00 mg·kg-1, 速效鉀106.37 mg·kg-1。

圖1 試驗?zāi)攴菅芯繀^(qū)冬小麥季日平均溫度(a)和降雨量(b)

1.2 試驗設(shè)計

該試驗在長期旋耕試驗地上進(jìn)行(始于2001年)。在冬小麥-夏玉米的輪作制度下, 從2016年夏玉米后, 對耕作處理進(jìn)行調(diào)整, 包括長期旋耕(X)、在長期旋耕上改為翻耕(XF)和長期旋耕改為深松(XS)3個處理, 各處理重復(fù)4次。具體措施如下: X, 夏玉米機械收獲, 之后玉米秸稈粉碎還田, 旋耕機進(jìn)行旋耕(耕深為10~12 cm), 冬小麥機械播種, 小麥機械收獲, 小麥秸稈粉碎還田, 玉米機械播種, 最后玉米機械收獲; XF, 夏玉米收獲, 玉米秸稈粉碎還田, 鏵式犁進(jìn)行翻耕(耕深為15~18 cm), 冬小麥機械播種, 小麥機械收獲, 小麥秸稈還田, 玉米機械播種, 最后玉米機械收獲; XS, 夏玉米機械收獲, 之后玉米秸稈粉碎還田, 震動深松鏟深松(耕深為23~25 cm), 冬小麥機械播種, 小麥機械收獲, 小麥秸稈還田, 玉米機械播種, 最后玉米機械收獲。

供試冬小麥品種為‘科農(nóng)2011’。冬小麥于2016年9月10日播種, 2017年6月初收獲, 播種量為187.5 kg·hm-2, 行距為15 cm。在耕作前各處理均施底肥(2016年9月10日), 施肥量為375 kg·hm-2磷酸二銨(N=67.5 kg·hm-2, P2O5=172.5 kg·hm-2)和225 kg·hm-2(N=67.5 kg·hm-2)尿素, 在2017年4月23日表面撒施尿素225 kg·hm-2(N=67.5 kg·hm-2)進(jìn)行追肥和灌溉。灌溉方式為噴灌。

1.3 測定項目和方法

1.3.1 氣體采集與分析

氣體采集用常用的靜態(tài)箱法。采樣箱由頂箱和底座兩部分組成, 頂箱用透明的有機玻璃制成, 底座用聚乙烯塑料制成, 采樣箱的寬、長、高為20 cm、60 cm、40 cm。采氣頻率為耕作后兩周內(nèi)2~3 d一次, 施肥、降水、灌溉后3 d內(nèi)采一次, 其他時間每兩周采一次; 采氣時間為上午9:00—11:00。耕作后, 將底座插入到土壤中固定, 在小麥整個生長季不再移動, 去除底座里面的所有植物。采樣時, 在底座的槽內(nèi)填一定量的水, 然后將頂箱扣在底座的槽內(nèi), 同時將箱頂?shù)娘L(fēng)扇打開來混勻箱內(nèi)空氣。在扣箱0 min、15 min、30 min后, 用注射器從箱頂取樣器口抽取50 mL氣體打到真空狀態(tài)下的氣袋內(nèi), 并記錄箱內(nèi)空氣的溫度, 30 min后記錄地表土壤溫度。每次采完氣后, 將頂箱移走, 保留底座不動。每個小區(qū)4個重復(fù)。

采完氣后立即將氣袋帶回實驗室, 采用CA-6氣體樣品進(jìn)樣儀進(jìn)樣, 用Agilent6820(G1180A)型氣象色譜儀分析CO2、N2O、CH4, 采氣后24 h內(nèi)測完。CO2和CH4的檢測器為FID(氫火焰離子檢測器), 檢測器溫度為200 ℃, 柱箱溫度為55 ℃, 載氣(高純N2)流速為30 mL·min-1, 助燃?xì)?空氣)流速為400 mL·min-1, 燃?xì)?H2)流速30 mL·min-1。N2O檢測器為ECD(電子捕獲檢測器), 檢測器溫度為330 ℃, 柱箱溫度為55 ℃, 載氣(高純N2)流速為30 mL·min-1。

1.3.2 氣體通量與總量計算

溫室氣體排放通量計算公式[27]:

式中:為氣體的排放通量(mg·m-2·h-1),為目標(biāo)氣體標(biāo)準(zhǔn)狀態(tài)下的密度(kg·m-3),為采樣箱內(nèi)高度(m),分別為采樣箱內(nèi)的實際溫度(℃),為箱內(nèi)目標(biāo)氣體濃度隨時間變化的回歸曲線斜率。

溫室氣體排放總量計算公式[28]:

式中:為農(nóng)田土壤排放氣體總量(kg·hm-2),為氣體排放通量(mg·m-2·h-1),為第次, (t1t)為兩次采樣間隔天數(shù),為采樣次數(shù)。

1.3.3 土壤含水率和容重

越冬期未測定土壤含水率, 其他時間每個月用環(huán)刀按0~5 cm、5~10 cm、10~20 cm、20~30 cm分層取原狀土, 105 ℃烘干測定土壤含水率。土壤容重在2017年玉米收獲后用環(huán)刀法按0~5 cm、5~10 cm、10~20 cm、20~30 cm分層取原狀土, 105 ℃烘干測定土壤容重。

1.3.4 小麥產(chǎn)量

冬小麥成熟期隨機取20株小麥測量穗粒數(shù)和收獲指數(shù); 每小區(qū)選取有代表性的1 m雙行植株, 6個重復(fù), 測定小麥穗數(shù)和千粒重; 每小區(qū)選取200 cm×125 cm面積收割, 6個重復(fù), 測定小麥產(chǎn)量; 并通過產(chǎn)量和收獲指數(shù)計算地上生物量。

1.4 數(shù)據(jù)處理

采用單因素方差分析對試驗數(shù)據(jù)進(jìn)行處理, 處理間差異用Duncan法進(jìn)行多重比較。所有數(shù)據(jù)分析均在Microsoft Excel 2016和SPSS 17.0環(huán)境下進(jìn)行, OriginPro 9.0作圖。

2 結(jié)果與分析

2.1 耕作方式轉(zhuǎn)換對土壤溫度、水分、容重和土壤有機質(zhì)的影響

地表土壤溫度在3種耕作處理下變化趨勢一致(圖2a)。土壤溫度在耕作后和收獲季較高, 在1月下旬出現(xiàn)最低值, 4月份灌溉后溫度有所降低, 整體上X和XS土壤溫度顯著高于XF。

圖2 不同耕作處理冬小麥田地表平均溫度(a)和0~20 cm土層土壤重量含水率(b)的變化

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage.

土壤重量含水率變化如圖2b所示, 0~20 cm的土壤含水率在耕作后呈不斷下降趨勢, 直到4月23日灌溉, 之后再次不斷下降。耕作方式改變后提高了土壤水分含量, 11月和5月前后XS和XF處理的土壤含水量顯著高于X處理, 其他時間點差異不顯著。

從圖3可以看出, 小麥?zhǔn)斋@后土壤容重隨著土壤深度的增加而增大。0~5 cm土壤容重各處理間差異不顯著, 5~10 cm、10~20 cm和20~30 cm土壤容重X>XF>XS。說明翻耕和深松后能降低土壤容重, 且深松后的效果更明顯。

圖3 冬小麥?zhǔn)斋@后不同耕作處理不同深度土壤容重

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。同一土層不同字母表示在0.05水平差異顯著。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage. Different letters within a soil depth indicate significant differences at0.05.

土壤有機質(zhì)含量變化如表1所示。長期旋耕基礎(chǔ)上進(jìn)行翻耕和深松處理后0~10 cm土層有機質(zhì)含量降低, 10~20 cm土壤有機質(zhì)含量提高。0~10 cm土壤有機質(zhì)含量: X>XS>XF, 和XS相比XF顯著降低了有機質(zhì)含量; 10~20 cm土壤有機質(zhì)含量: XF>XS>X, 處理之間差異不顯著。旋耕后翻耕降低了20~30 cm土壤有機質(zhì), 但三者無顯著差異。

表1 不同耕作處理下冬小麥田不同土層土壤有機質(zhì)含量

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。數(shù)據(jù)為3次重復(fù)的平均值±標(biāo)準(zhǔn)誤。同行不同字母表示在0.05水平差異顯著。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage. Values are means ± S.E. (=3). Different letters within a row indicate significant differences at0.05.

2.2 耕作方式轉(zhuǎn)變對CH4、CO2、N2O通量的影響

2.2.1 冬小麥季CO2通量

CO2通量在3種耕作處理下變化趨勢一致。在10月初進(jìn)行X、XF、XS耕作處理后, 農(nóng)田排放CO2排放通量有快速的響應(yīng)(圖4), 在短時間內(nèi)排放通量均出現(xiàn)最高值, 分別為353 mg·m-2·h-1、321 mg·m-2·h-1、294 mg·m-2·h-1; 冬季通量降到了最低, 然后隨著溫度的回升, 通量逐漸變大, 到收獲期出現(xiàn)較高的排放峰值, 分別為186 mg·m-2·h-1、206 mg·m-2·h-1、178 mg·m-2·h-1。從實施耕作到10月底期間, 除個別采樣時期外, CO2通量在X和XS處理下顯著高于XF處理, 之后這種趨勢逐漸消失; 11月到3月份, 排放通量較小, 各處理間變化不規(guī)律, 其中XS處理波動較大; 3月中旬到5月中旬, XS下CO2排放通量略高于XF和X處理, 多數(shù)測定時期差異不顯著。

圖4 不同耕作處理下冬小麥田CO2排放通量的變化

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage.

2.2.2 冬小麥季N2O通量

如圖5所示, N2O排放通量在耕作后和施肥灌溉后出現(xiàn)明顯排放峰值, 其他時間段通量差異較小。耕作后第3天, 在X和XF耕作處理下, N2O通量達(dá)到最大值, 分別為0.29 mg·m-2·h-1和0.28 mg·m-2·h-1, 而XS處理下N2O通量最大值出現(xiàn)在耕作后第9天(0.70 mg·m-2·h-1); 10月初到10月底N2O排放通量在XS下顯著高于X和XF處理。4月23日施肥和灌溉后N2O有顯著的排放高峰, 且XF>XS>X。

2.2.3 冬小麥季CH4通量

耕作后冬小麥季CH4通量變化如圖6所示。在3種耕作處理下, CH4通量起伏變化較大。從耕作的短期效應(yīng)看, 耕作1周內(nèi)土壤對CH4的吸收通量表現(xiàn)為XS>XF>X, 耕作后第5天CH4吸收通量明顯增大, XF下最大為-0.32 mg·m-2·h-1, 其次XS為-0.23 mg·m-2·h-1, X最小為-0.15 mg·m-2·h-1, 之后吸收通量均減小。整體上, 在耕作后和2016年12月—2017年3月初通量波動大, 其他時間波動較小。

圖5 不同耕作處理下冬小麥田N2O排放通量的變化

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage.

圖6 不同耕作處理下冬小麥田CH4排放通量的變化

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage.

2.3 耕作方式轉(zhuǎn)變對冬小麥季溫室氣體累積排放量的影響

表2為3種耕作處理下冬小麥季溫室氣體總排放量、CO2當(dāng)量以及增溫效應(yīng)的貢獻(xiàn)。結(jié)果表明, 冬小麥季華北平原為CO2和N2O的排放源、CH4的吸收匯。CO2排放量在X和XS處理下差異不顯著, 但均顯著高于XF處理。N2O排放量在XS處理下顯著高于X和XF處理, 且后兩者間沒有顯著差異。XS耕作處理下農(nóng)田CH4的吸收量最大, 其次為XF處理, 2個處理間差異顯著。

冬小麥季農(nóng)田CO2當(dāng)量XS處理下最大, 其次是X, XF處理下最小, 且三者差異達(dá)顯著水平。CO2對增溫效應(yīng)的貢獻(xiàn)最大, 占84.15%~91.22%; N2O的貢獻(xiàn)為10.61%~18.62%; CH4的貢獻(xiàn)率最低, 為負(fù)貢獻(xiàn)。

2.4 耕作方式轉(zhuǎn)變對冬小麥產(chǎn)量及其構(gòu)成因素的影響

不同耕作處理產(chǎn)量測定結(jié)果見表3。耕作方式改變對冬小麥產(chǎn)量影響顯著, X最高, 顯著高于XS, XF和兩處理差異均不顯著; 穗數(shù)在不同耕作間差異不顯著; 穗粒數(shù)為X>XS>XF, 處理間差異顯著; 千粒重表現(xiàn)為XF≈X>XS, 且XF和X顯著高于XS, 而X和XF間差異不顯著; 地上部生物量X>XF>XS, XF和XS、X差異不顯著, 但XS顯著低于X; 3種耕作處理下小麥?zhǔn)斋@指數(shù)無顯著差異。結(jié)合表2中CO2當(dāng)量和表3中冬小麥產(chǎn)量計算出不同耕作下冬小麥單位產(chǎn)量CO2當(dāng)量, XS為1.01, XF為0.82, X為0.79。

表2 不同耕作處理下冬小麥田溫室氣體累積排放量和對增溫效應(yīng)的貢獻(xiàn)

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。數(shù)據(jù)為4次重復(fù)的平均值±標(biāo)準(zhǔn)誤。同列不同字母表示在0.05水平下差異顯著。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage. Values are means ± S.E. (=4). Different letters within a column indicate significant differences at0.05.

表3 不同耕作處理對冬小麥產(chǎn)量及其構(gòu)成因素的影響

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。數(shù)據(jù)為6次重復(fù)的平均值±標(biāo)準(zhǔn)誤, 同列不同字母表示0.05水平下差異顯著。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage. Values are means ± S.E. (=6). Different letters within a colum indicate significant differences at0.05.

3 討論

3.1 不同耕作對溫室氣體排放的影響

不同的耕作處理對土壤中的生物、水分和熱量等造成了不同程度的影響[31-32], 這些因素影響著農(nóng)田溫室氣體排放量。冬小麥季土壤對CO2的排放量表現(xiàn)為XS≈X>XF, 對N2O的排放量表現(xiàn)為XS>XF≈X, 對CH4的吸收量表現(xiàn)為XS>XF>X。

CO2通量變化趨勢呈三峰態(tài), 變化趨勢與Liu等[33]的研究結(jié)果相似。耕作后短期內(nèi)CO2出現(xiàn)排放高峰, 因為耕作對土壤的擾動破壞了原有的結(jié)構(gòu), 使得土壤有機質(zhì)有一個較高的轉(zhuǎn)化率[34]。長期旋耕會使土壤養(yǎng)分表聚, 相對于XS和XF, X表層土壤會為微生物提供更多的養(yǎng)分, 促進(jìn)CO2排放。到第2和第3個峰時, 植物根呼吸占主體, 同時溫度較高, 促進(jìn)微生物活動, 使CO2通量較高。本研究中X處理CO2排放總量高于XF處理, 這與前人的研究結(jié)果[21]不一致。主要因為長期旋耕使農(nóng)田土壤有機質(zhì)表聚, 經(jīng)過翻耕和深松處理后將土壤表層有機質(zhì)混合到較深層土壤中, 而0~10 cm土層的土壤呼吸強度高于10~20 cm土層[35]。其次因為X和XS處理地表溫度均高于XF處理, 而CO2排放通量與土壤溫度呈正相關(guān)關(guān)系[36], 使XF和XS處理下土壤有機質(zhì)礦化速率降低, 抑制了CO2的產(chǎn)生。XF處理0~10 cm有機質(zhì)含量下降, 而深層含量呈升高的趨勢。因此, 本研究證明長期旋耕農(nóng)田進(jìn)行單次翻耕處理, 并未造成土壤CO2排放升高, 這為農(nóng)田輪耕管理提供有力的數(shù)據(jù)支撐。

N2O通量在耕作和施肥灌溉后出現(xiàn)明顯的峰值, 在冬季出現(xiàn)最低值。Krauss等[37]試驗結(jié)果也發(fā)現(xiàn)在耕作后短時間內(nèi), 會出現(xiàn)高N2O排放通量。因為耕作后農(nóng)田表層土壤孔隙度增大, 秸稈和底肥為微生物提供了碳和氮源, 有利于N2O的產(chǎn)生和釋放。在耕作后接近1個月時間XS處理N2O排放通量顯著高于XF和X處理, 因為XS處理土壤大孔隙增多, 利于土壤水分下滲和存儲, 加之該時期降雨量大,激發(fā)了深層土壤中N的釋放。且XS增加土壤的上下通透性, 利于N2O向土壤表層擴(kuò)散。而XF將粉碎的秸稈和肥料翻到了土壤深層, 底層土壤溫度較低且深層土壤微生物含量較少, 不利于N2O的形成[38]。與前人研究一致[38-42], N2O排放通量在施氮肥和灌溉后出現(xiàn)峰值。因為氮肥為土壤硝化和反硝化微生物提供了充足的氮源[43], 使微生物更加活躍, 促進(jìn)N2O產(chǎn)生; 灌溉后, 土壤孔隙不斷地充滿水, 使土壤中氧氣不斷減少, 進(jìn)而促進(jìn)了反硝化作用, 也加速了N2O的產(chǎn)生[44]。冬小麥季農(nóng)田土壤N2O累積排放量表現(xiàn)為XS>XF≈X。與本研究結(jié)果相同, 張賀等[23]和Forte等[45]也得出N2O排放量在翻耕和旋耕處理下差異不顯著的結(jié)論, Tian等[46]發(fā)現(xiàn)土壤經(jīng)深松后比旋耕后排放更多N2O。已有研究確定影響農(nóng)田土壤N2O排放的關(guān)鍵因素是水分、溫度和硝態(tài)氮含量[47]。本研究經(jīng)耕作處理后, XS和XF土壤中水分含量高于X, 而N2O產(chǎn)生和排放與水分呈正相關(guān)關(guān)系[48]; 且有研究發(fā)現(xiàn)深松處理下植物根際土壤的硝態(tài)氮含量比翻耕和旋耕高[49], 促進(jìn)了反硝化作用, 使N2O排放量較高。

在耕作的同時施用了底肥, 增加了土壤中NH4+的含量, 部分CH4氧化菌參加氨氧化[50], 影響了甲烷氧化菌的氧化作用, 使耕作后短期內(nèi)CH4的吸收通量很低。隨著時間推移, NH4+含量逐漸減少, 更多的甲烷氧化菌參與到氧化CH4的過程中, 到耕作后第5天耕作與甲烷氧化菌共同作用使CH4吸收通量增大。冬小麥整個生育季農(nóng)田土壤對CH4吸收量表現(xiàn)為XS>XF>X。Wolff等[51]也發(fā)現(xiàn)對土壤擾動最小的耕作方式土壤CH4吸收量最小。其原因是XS、XF處理比X處理更好地改善了土壤的通氣狀況, 使甲烷氧化菌群更容易獲得適宜的生存條件和好氧環(huán)境[25], 提高了土壤對CH4的氧化能力, 使CH4吸收通量更高[26]。董玉紅等[52]已表明通氣狀況良好的土壤是CH4的最大吸收匯。冬小麥季CH4通量的變化起伏大, 因為不同的耕作影響土壤的物理性狀、肥力狀況、生物學(xué)特性、水分和溫度[53], 這些因素對CH4的產(chǎn)生和傳輸產(chǎn)生影響, 但是具體的影響機制尚不清楚, 需要更深一步的研究。

無論是哪種耕作方式下CO2-eq均為正值, 即土壤排放的3種溫室氣體對增溫的綜合效應(yīng)均為正效應(yīng)。其中CO2對增溫效應(yīng)貢獻(xiàn)最大, N2O對增溫效應(yīng)的貢獻(xiàn)較小, 而CH4對增溫效應(yīng)最小為負(fù)貢獻(xiàn); XF處理下CO2-eq是最低的, 即增溫貢獻(xiàn)最小, 相對于X和XS處理, 利于緩解農(nóng)田溫室氣體的增溫貢獻(xiàn)率。相對于X處理, XS處理盡管明顯提高CH4的吸收量, 但由于N2O排放量更大, 總體上顯著增加了綜合溫室效應(yīng)。因此, 在本區(qū)域內(nèi)實施深松改善土壤結(jié)構(gòu)的耕作管理時, 應(yīng)綜合考慮水分效應(yīng), 減少綜合溫室氣體排放。

3.2 不同耕作下的冬小麥產(chǎn)量

在長期旋耕的基礎(chǔ)上進(jìn)行翻耕和深松, 雖然改善了土壤的通透性, 但沒有提高小麥的產(chǎn)量, 而使產(chǎn)量降低。這與前人的研究結(jié)果有所不同, 于淑婷等[4]發(fā)現(xiàn)冬小麥產(chǎn)量在翻耕/旋耕輪耕模式顯著高于連年旋耕模式。研究發(fā)現(xiàn)[27,54], 農(nóng)田深松有利于作物產(chǎn)量的提高。鄭侃等[55]通過Meta分析我國北方地區(qū)深松對作物產(chǎn)量的影響, 也得出小麥產(chǎn)量在旋耕深松耕作模式下比連年旋耕下的要高。本研究中, 雖然深松改善了土壤的物理性狀, 但對小麥的產(chǎn)量沒有提高, 可能是因為XS后粉碎的秸稈仍保留在表層土壤中, 有機質(zhì)沒有進(jìn)入到深層土壤中(表1), 對深層土壤環(huán)境改善效果不顯著, 使作物產(chǎn)量受到了影響, 這與Pierce等[56]的研究結(jié)果相似。也有研究[57]認(rèn)為深松技術(shù)雖有較好的保土保水作用, 但是耕層松緊不一, 土塊較大, 不利于作物的生長發(fā)育。經(jīng)過翻耕后小麥穗數(shù)降低, 可能是因為在出苗期降雨量較大且XF后土壤溫度低影響了出苗率; 而XF和X處理千粒重顯著高于XS處理, 可能是因為灌漿期XS處理表層土壤水分蒸發(fā)快, 影響了粒重; 改變耕作方式后, 穗粒數(shù)均降低, 具體影響機理尚不清楚。輪耕對作物產(chǎn)量影響需要針對不同氣候年型進(jìn)一步深入研究。

4 結(jié)論

冬小麥季農(nóng)田在長期旋耕基礎(chǔ)上經(jīng)深松和翻耕后, CO2、N2O、CH4排放有顯著變化, 但農(nóng)田土壤均表現(xiàn)為CO2和N2O的源、CH4的匯, 溫室氣體換算為CO2當(dāng)量排序為: XS>X>XF。綜合來看經(jīng)過翻耕后, 農(nóng)田溫室氣體排放顯著降低。

從當(dāng)前短期影響看, 冬小麥產(chǎn)量經(jīng)過XF和XS后較X有所降低, XF和X單位產(chǎn)量下CO2當(dāng)量均小于XS。綜合考慮溫室氣體排放和冬小麥產(chǎn)量, 短期看旋耕深松模式不利于華北農(nóng)田小麥生產(chǎn)和控制溫室氣體排放, 旋耕翻耕可能是較適宜的輪耕模式, 但需要加強對不同輪耕模式長期效應(yīng)研究, 為確定合理的耕作模式提供依據(jù)。

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Effect of tillage method change on soil greenhouse gas emission and yield during winter-wheat growing season*

ZHAO Liying1,2, DONG Wenxu1, HU Chunsheng1**, LI Jiazhen1,2, CHEN Tuo1,2

(1. Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences / Key Laboratory of Agricultural Water Resources, Chinese Academy of Sciences / Hebei Key Laboratory of Water-Saving Agriculture, Shijiazhuang 050022, China; 2. University of Chinese Academy of Sciences, Beijing 100049, China)

Under long-term rotary tillage, soil bulk density, carbon decomposition and nutrient in sub-surface soil in the shallow plow layer significantly increase, but wheat growth and soil carbon sequestration become limited. However, subsoiling and deep plowing can break the bottom of the plow layer and reduce soil bulk density, which are conducive for good growth of plant root and absorption of nutrients to ensure high crop yield. The objectives of this study were to analyze changes in greenhouse gases emission and wheat yield after 16 years (2001-2016) of rotary tillage (X) treatment and conversion into other tillage treatments, including rotary tillage-deep plowing (XF) and rotary tillage-subsoiling (XS) treatments in 2016, and to determine the best rational tillage strategy. Carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4)emission fluxes in the three tillage treatments were sampled and measured using static chamber-gas chromatography. Soil temperature at the 0 cm depth, soil gravimetric moisture content, soil bulk density at different depths and other related factors were monitored during wheat growth period and winter wheat yield analyzed after harvest. The experimental results showed prominent high fluxes of CO2and N2O one week after the three tillage treatments and during harvest, with minimum emission fluxes of CO2and N2O during winter period. Compared with XF treatment, X and XS treatments significantly increased CO2emission fluxes from the start of the three tillage treatments to the end of October. Compared with X and XF treatments, N2O fluxes under XS treatment were significant high after tillage treatment, fertilization and irrigation. CH4fluxes fluctuated from November 2016 to February 2017, and became more stable from March 2017. From January 2017 to the harvest season, soil uptake of CH4under XS treatment was higher than those under XF and X treatments. The fields under the three tillage treatments during winter wheat growth were the sources of CO2and N2O. The cumulative fluxes of the three tillage treatments served as CH4sink. In winter wheat fields, cumulative CO2emission was in order of XS > X > XF, with total CO2emissions of 5 241 kg·hm-2, 5 160 kg·hm-2and 4 840 kg·hm-2, respectively. Cumulative N2O emission was in order of XS > XF > X, with total N2O emissions of 4.38 kg·hm-2, 2.39 kg·hm-2and 2.26 kg·hm-2, respectively. Cumulative CH4sink was in order of XS > XF > X, with total CH4absorptions of 6.14 kg·hm-2, 5.64 kg·hm-2and 3.70 kg·hm-2, respectively. The contribution of cumulative greenhouse gases to CO2-equivalents was expressed as XS > X > XF, which were 6.23 t·hm-2, 5.66 t·hm-2and 5.32 t·hm-2, respectively. Using deep plowing and subsoiling, soil organic matter decreased in the 0–10 cm soil depth, but increased in the 10–20 cm soil depth. Soil organic carbon was the main source of CO2. Reduction in soil organic matter led to reduction in CO2. Winter wheat grain yield under X treatment was higher than that under XS and XF treatments. Considering the changes in soil physical properties, greenhouse gas emission and wheat yield, XF treatment was the most suitable tillage practice. However, more and longer research work was needed to determine an ideal tillage treatment to ensure future ecological benefits and grain yield.

Winter wheat; Rotary tillage; Deep plowing tillage; Subsoiling tillage; Greenhouse gases; Yield

, E-mail: cshu@sjziam.ac.cn

Mar. 7, 2018;

May 30, 2018

S157.4+2; S512.1+1

A

1671-3990(2018)11-1613-11

10.13930/j.cnki.cjea.180219

* 公益性行業(yè)(農(nóng)業(yè))科研專項(201503117-5)和國家重點研發(fā)計劃項目(2017YFD0800601)資助

胡春勝, 主要研究方向為農(nóng)田生態(tài)系統(tǒng)碳、氮、水循環(huán)及土壤生態(tài)過程。E-mail: cshu@sjziam.ac.cn

趙力瑩, 主要研究方向為農(nóng)田生態(tài)系統(tǒng)碳循環(huán)。E-mail: zlydlkx@163.com

2018-03-07

2018-05-30

* This study was supported by the Special Fund for Agro-scientific Research in the Public Interest of China (201503117-5) and the National Key Research and Development Program of China (2017YFD0800601).

趙力瑩, 董文旭, 胡春勝, 李佳珍, 陳拓. 耕作方式轉(zhuǎn)變對冬小麥季農(nóng)田溫室氣體排放和產(chǎn)量的影響[J]. 中國生態(tài)農(nóng)業(yè)學(xué)報, 2018, 26(11): 1613-1623

ZHAO L Y, DONG W X, HU C S, LI J Z, CHEN T. Effect of tillage method change on soil greenhouse gas emission and yield during winter-wheat growing season[J]. Chinese Journal of Eco-Agriculture, 2018, 26(11): 1613-1623