劉 羽，劉 婕，王朝元,3，施正香,3，李保明,3

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規(guī)模奶牛養(yǎng)殖室外運(yùn)動(dòng)場(chǎng)春季溫室氣體與氨氣排放特性

劉 羽1,2，劉 婕4，王朝元1,2,3※，施正香1,2,3，李保明1,2,3

（1.中國(guó)農(nóng)業(yè)大學(xué)水利與土木工程學(xué)院，北京 100083； 2. 農(nóng)業(yè)農(nóng)村部設(shè)施農(nóng)業(yè)工程重點(diǎn)實(shí)驗(yàn)室，北京 100083； 3. 北京市畜禽健康養(yǎng)殖環(huán)境工程技術(shù)研究中心，北京 100083； 4. 山東省煙臺(tái)市海陽(yáng)招虎山省級(jí)自然保護(hù)區(qū)管理處，煙臺(tái) 265100）

舍外運(yùn)動(dòng)場(chǎng)是中國(guó)傳統(tǒng)奶牛養(yǎng)殖場(chǎng)的組成部分，同時(shí)也是溫室氣體和氨氣（NH3）的重要排放源。由于開(kāi)放式生產(chǎn)設(shè)施污染氣體排放的監(jiān)測(cè)難度大，目前中國(guó)還普遍缺少奶牛運(yùn)動(dòng)場(chǎng)溫室氣體和NH3排放通量的直接監(jiān)測(cè)數(shù)據(jù)。該試驗(yàn)采用梯度法對(duì)北京地區(qū)春季典型開(kāi)放式奶牛運(yùn)動(dòng)場(chǎng)的甲烷（CH4）、氧化亞氮（N2O）、二氧化碳（CO2）等溫室氣體和NH3濃度及其排放通量進(jìn)行了監(jiān)測(cè)分析，討論了排放特征和關(guān)鍵影響因素，為獲取中國(guó)北方地區(qū)奶牛運(yùn)動(dòng)場(chǎng)溫室氣體和NH3的排放通量提供了基礎(chǔ)數(shù)據(jù)支撐。測(cè)試運(yùn)動(dòng)場(chǎng)飼養(yǎng)了52頭荷斯坦奶牛，年均單產(chǎn)約8 t，頭均占地面積為20.77 m2。結(jié)果表明，該奶牛運(yùn)動(dòng)場(chǎng)春季CH4、N2O和CO2的排放通量為155.59、3.60和4 869.37 mg/(m2·h)，分別占溫室氣體排放總量的42.79%、9.37%和47.83%；NH3的排放通量為66.27 mg/(m2·h)；排放峰值一般出現(xiàn)在運(yùn)動(dòng)場(chǎng)清糞之后。環(huán)境溫度與CH4、N2O和NH3排放量呈顯著的正相關(guān)關(guān)系（<0.05），同時(shí)風(fēng)速在一定范圍內(nèi)會(huì)促進(jìn)CH4、N2O和NH3的排放。奶牛場(chǎng)清糞活動(dòng)不僅會(huì)加快污染氣體的排放通量，還會(huì)影響溫度和風(fēng)速對(duì)氣體排放通量的作用效果。

溫室氣體；氨氣；排放控制；奶牛運(yùn)動(dòng)場(chǎng)；梯度法

0 引 言

農(nóng)業(yè)生產(chǎn)活動(dòng)所產(chǎn)生的溫室氣體和NH3是全球空氣污染物排放的重要源頭[1-2]。在中國(guó)，畜禽養(yǎng)殖業(yè)生產(chǎn)活動(dòng)排放的CH4、N2O和CO2占總?cè)珖?guó)人為溫室氣體排放量的37%、65%和9%[3]，而廢棄物儲(chǔ)存及管理過(guò)程是這些溫室氣體的主要來(lái)源[4]，僅畜禽糞便產(chǎn)生的CH4即占農(nóng)業(yè)溫室氣體排放量的15%[5]。北京市規(guī)模化奶牛場(chǎng)產(chǎn)生的主要溫室氣體為CH4和CO2，分為占溫室氣體總排放量的80.15%和11.24%[6]。畜牧生產(chǎn)過(guò)程中的NH3排放則會(huì)對(duì)生態(tài)環(huán)境產(chǎn)生重要影響，另外NH3還是細(xì)顆粒物（PM2.5）的前體物質(zhì)，對(duì)中國(guó)東部地區(qū)PM2.5的貢獻(xiàn)已達(dá)8%～11%[7]。工業(yè)化國(guó)家和地區(qū)大氣中約有80%～90%的NH3排放來(lái)自于農(nóng)業(yè)[8]，而奶牛糞尿是其中的重點(diǎn)之一[9-11]。

在帶有運(yùn)動(dòng)場(chǎng)的奶牛生產(chǎn)系統(tǒng)中，奶牛在運(yùn)動(dòng)場(chǎng)的活動(dòng)時(shí)間長(zhǎng)、糞尿排泄量大。袁慧軍等[12]研究發(fā)現(xiàn)，殘留在運(yùn)動(dòng)場(chǎng)上的糞便量約占整個(gè)奶牛場(chǎng)糞便總量的一半。因此，奶牛本身、清糞不徹底以及糞尿下滲等會(huì)造成運(yùn)動(dòng)場(chǎng)大量的溫室氣體和NH3排放。

歐美國(guó)家采用反演法等對(duì)運(yùn)動(dòng)場(chǎng)的污染氣體排放進(jìn)行過(guò)探索性的研究。Leytem等[13]對(duì)美國(guó)愛(ài)達(dá)荷州奶牛運(yùn)動(dòng)場(chǎng)的監(jiān)測(cè)結(jié)果表明，CH4、N2O、CO2和NH3的排放通量分別為0.49、0.01、28.1和0.13 kg/(頭·d)，其中N2O、CO2和NH3排放占該場(chǎng)排放總量的57%、80%和78%。Borhan等[14]研究表明，奶牛運(yùn)動(dòng)場(chǎng)N2O、CO2和NH3的排放量分別占全場(chǎng)該氣體產(chǎn)生量的72%、51%和63%～95%。

梯度法作為檢測(cè)氣體排放量的手段已有40多年的歷史[15]，梯度法具有不影響排放源小氣候環(huán)境、可真實(shí)反映氣體排放量與規(guī)律等顯著特點(diǎn)，適用于開(kāi)放性系統(tǒng)氣體排放通量的檢測(cè)[16-17]。1977年起，Denmead等[18]就開(kāi)始采用該方法對(duì)NH3排放進(jìn)行檢測(cè)，之后科研人員在此基礎(chǔ)上對(duì)梯度法進(jìn)行了發(fā)展和優(yōu)化。Griffith等[16]在已知?dú)怏w排放速率的舍飼散養(yǎng)的奶牛舍內(nèi)采用梯度法對(duì)CH4排放進(jìn)行了檢測(cè)，發(fā)現(xiàn)梯度法可較好地反映氣體排放速率，檢測(cè)偏差在10%以內(nèi)。

運(yùn)動(dòng)場(chǎng)是中國(guó)傳統(tǒng)奶牛場(chǎng)的標(biāo)準(zhǔn)配置，多采用三合土、立磚和混凝土地面，目前因?yàn)橹苯訖z測(cè)的難度大，仍然缺乏運(yùn)動(dòng)場(chǎng)溫室氣體和NH3排放的基礎(chǔ)數(shù)據(jù)。同時(shí)，由于與西方國(guó)家在奶牛養(yǎng)殖模式、設(shè)施類型、糞便管理等存在明顯差異，也無(wú)法直接采用歐美發(fā)達(dá)國(guó)家的研究數(shù)據(jù)預(yù)測(cè)國(guó)內(nèi)奶牛運(yùn)動(dòng)場(chǎng)的污染氣體排放。

本文采用梯度法對(duì)中國(guó)北京地區(qū)典型開(kāi)放式奶牛運(yùn)動(dòng)場(chǎng)CH4、N2O、CO2和NH3的排放通量進(jìn)行監(jiān)測(cè)，并探究其排放特征和影響因素，為中國(guó)奶牛運(yùn)動(dòng)場(chǎng)溫室氣體和NH3的排放通量提供基礎(chǔ)數(shù)據(jù)。

1 材料與方法

1.1 試驗(yàn)牛場(chǎng)

試驗(yàn)在北京延慶縣某奶牛養(yǎng)殖中心進(jìn)行（40.30°N，115.56°E），奶牛場(chǎng)平面布置圖及試驗(yàn)運(yùn)動(dòng)場(chǎng)如圖1所示。試驗(yàn)運(yùn)動(dòng)場(chǎng)位于養(yǎng)殖中心東南角，長(zhǎng)40 m、寬27 m，共飼養(yǎng)52頭荷斯坦泌乳奶牛，頭均年單產(chǎn)約8 t，頭均占地面積為20.77 m2。運(yùn)動(dòng)場(chǎng)為立磚地面，運(yùn)動(dòng)場(chǎng)每天下午02:00－04:00用鏟車將表面糞便清理并集中堆放于運(yùn)動(dòng)場(chǎng)的西北角，之后通過(guò)清糞運(yùn)輸車運(yùn)往奶牛場(chǎng)堆糞區(qū)自然堆放（如圖1所示）。

1.堆糞場(chǎng) 2.青年牛舍 3.運(yùn)動(dòng)場(chǎng) 4.料庫(kù) 5.宿舍 6.辦公室7.擠奶廳 8.犢牛舍 9.隔離牛舍 10.低產(chǎn)牛舍 11.高產(chǎn)牛舍 12.氣象站 13.門衛(wèi)

a1,a2.測(cè)試區(qū)上邊界1,2，b3,b4.下邊界3,4

1.Waste storage area 2.Heifer barn 3.Open lot 4.Forage & feed storage 5.Accommodation for staff 6.Office building 7.Milking parlour 8.New born calve barn 9.Maternal cow barn 10.Low yield lactating cow barn 11.High yield lactating cow barn 12.Weather station 13.Gatehouse

a1, a2. Upwind boundary 1and 2; b3,b4. Downwind boundary 3 and 4

注：斜線標(biāo)記區(qū)為試驗(yàn)運(yùn)動(dòng)場(chǎng)。

Note: Surveyed open lot is marked with cross lines.

圖1 試驗(yàn)?zāi)膛?chǎng)平面示意圖

Fig.1 Schematic diagram of surveyed dairy farm

1.2 試驗(yàn)裝置構(gòu)建與安裝

梯度法利用質(zhì)量平衡法原理，根據(jù)排放源的主導(dǎo)風(fēng)向，將上風(fēng)向處的邊界定義為上邊界，下風(fēng)向處的邊界定義為下邊界，通過(guò)檢測(cè)排放源不同高度處上下邊界目標(biāo)氣體濃度差，采用質(zhì)量差分法計(jì)算水平氣流的擴(kuò)散速率，氣體的檢測(cè)高度根據(jù)氣體濃度分布和采樣時(shí)間確定[18]。

北京市延慶縣春季以東南風(fēng)為主，按照梯度法測(cè)試要求，將運(yùn)動(dòng)場(chǎng)東側(cè)和南側(cè)定義為上風(fēng)邊界，西側(cè)和北側(cè)定義為下風(fēng)邊界。每個(gè)邊界設(shè)置3個(gè)采樣處以連續(xù)測(cè)試氣體濃度，每個(gè)采樣處設(shè)置3個(gè)高度的采樣點(diǎn)，分別距地面1、2和3 m（圖2）。

奶牛運(yùn)動(dòng)場(chǎng)氣體濃度在線測(cè)量系統(tǒng)由采樣模塊、氣路控制、氣樣分析和基礎(chǔ)參數(shù)采集4部分構(gòu)成。采樣模塊由采氣管和光聲譜氣體監(jiān)測(cè)儀（Photoacoustic Field Gas-monitor 1412i，LumaSense Technology，美國(guó)）構(gòu)成，對(duì)溫室氣體和NH3濃度進(jìn)行連續(xù)監(jiān)測(cè)。通過(guò)自制的多路器系統(tǒng)作為氣路控制模塊實(shí)現(xiàn)在各個(gè)采樣點(diǎn)之間的氣路切換，并由光聲譜氣體監(jiān)測(cè)儀完成氣樣分析和基礎(chǔ)參數(shù)采集。

1. 3分路器 2.采樣點(diǎn) 3.抽樣管道 4. 12分路器 5.氣體分析儀 6.氣象站

自制的多路器系統(tǒng)包括1臺(tái)12路多路器和12臺(tái)3路多路器。每臺(tái)多路器由電磁閥、繼電器、Arduino Mega2560、安全開(kāi)關(guān)、電線、氣路等構(gòu)成。每個(gè)采樣處的3個(gè)采樣點(diǎn)通過(guò)外徑為6 mm的特氟龍管與1個(gè)3路多路器連接，并與12路多路器匯合，通過(guò)分路器將上風(fēng)邊界和下風(fēng)邊界處的氣體分別輸入2臺(tái)氣體監(jiān)測(cè)儀中，以保證同時(shí)獲得上下風(fēng)邊界相對(duì)位置采樣點(diǎn)的氣體濃度。因多路器中氣泵流量為8 L/min，氣體監(jiān)測(cè)儀內(nèi)部氣泵流量為4 L/min，為防止過(guò)大的氣流對(duì)氣體監(jiān)測(cè)儀內(nèi)部氣泵的損傷，故最終通過(guò)三通閥將多路器與光聲譜氣體監(jiān)測(cè)儀連接。檢測(cè)完的廢氣通過(guò)氣管排至距離下風(fēng)向邊界20 m處。

1.3 氣體濃度及環(huán)境參數(shù)監(jiān)測(cè)方法

現(xiàn)場(chǎng)正式測(cè)試時(shí)間為2016年3月28日到2016年4月3日。3月28日－3月31日氣體濃度采樣時(shí)間為08:00－18:00，4月1日－4月3日氣體采樣時(shí)間從4月1日上午08:00開(kāi)始到4月3日上午08:00結(jié)束，進(jìn)行48 h的連續(xù)監(jiān)測(cè)。

采樣間隔為1 min，每個(gè)采樣點(diǎn)連續(xù)監(jiān)測(cè)3 min，梯度法1個(gè)采樣循環(huán)周期為72 min。光聲譜氣體監(jiān)測(cè)儀對(duì)CH4、N2O、CO2和NH3的測(cè)量精度分別為0.11、0.02、3.34和0.05 mg/m3。

將WS500-UMB氣象站（WS500-UMB，8373.U01，德國(guó)Lufft測(cè)量控制技術(shù)有限公司，德國(guó)）立于運(yùn)動(dòng)場(chǎng)東南角對(duì)環(huán)境溫度、濕度、氣壓、風(fēng)速、風(fēng)向等進(jìn)行實(shí)時(shí)監(jiān)測(cè)。WS500-UMB傳感器距離地面5 m，保證其相同高度處10 m范圍內(nèi)沒(méi)有遮擋物。氣象站溫度測(cè)試范圍?40～60 ℃，精度±0.2 ℃；相對(duì)濕度范圍0～100% RH，精度±2% RH；氣壓范圍300～1 200 hPa，精度±1.5 hPa；風(fēng)速范圍0～60 m/s，精度±0.3 m/s；風(fēng)向范圍0～359.9°，精度<3°。

1.4 氣體排放通量計(jì)算方法

本試驗(yàn)采用綜合流梯度法對(duì)CH4、N2O、CO2和NH3的排放通量進(jìn)行計(jì)算，計(jì)算式如下

為獲取垂直高度距地面1、2和3 m處的實(shí)時(shí)風(fēng)速和風(fēng)向，本試驗(yàn)通過(guò)冪率公式推算各個(gè)高度處的風(fēng)速，公式如式（2）[19]。

式中V和V分別為高度Z和Z處的風(fēng)速，m/s；為風(fēng)切變指數(shù)，取值0.19。

1.5 數(shù)據(jù)處理

如無(wú)特別說(shuō)明，文中風(fēng)速數(shù)據(jù)均為運(yùn)動(dòng)場(chǎng)上方1m處的測(cè)量值。試驗(yàn)數(shù)據(jù)采用Microsoft Excel軟件進(jìn)行數(shù)據(jù)整理，并用SPSS21.0軟件分析。

2 結(jié)果與分析

2.1 運(yùn)動(dòng)場(chǎng)環(huán)境變化

運(yùn)動(dòng)場(chǎng)上溫度、濕度和風(fēng)速隨時(shí)間變化情況如圖3所示。試驗(yàn)期間奶牛運(yùn)動(dòng)場(chǎng)氣溫和相對(duì)濕度呈規(guī)律性的周期變化，范圍分別為3～19 ℃和11%～56%。運(yùn)動(dòng)場(chǎng)上方1 m處風(fēng)速變化范圍為2.9～20.0 m/s。

試驗(yàn)期間大氣壓力變化范圍為94.8～96.7 kPa，3月31日氣壓范圍為94.8～95.3 kPa，為試驗(yàn)期間最低氣壓日，其他幾天氣壓均大于95.3 kPa。

圖3 運(yùn)動(dòng)場(chǎng)溫度、濕度、風(fēng)速變化情況

2.2 運(yùn)動(dòng)場(chǎng)溫室氣體、NH3排放通量

試驗(yàn)期間，運(yùn)動(dòng)場(chǎng)CH4、N2O、CO2和NH3的平均排放通量分別為155.59、3.60、4869.37和66.27 mg/(m2·h)（表1），換算成每頭牛的日均排放量則為77.56、1.79、2 278.05和33.25 g/(頭·d)。

試驗(yàn)期間運(yùn)動(dòng)場(chǎng)溫度、濕度和風(fēng)速變化平穩(wěn)，氣體排放通量總體比較穩(wěn)定。3月31日的CH4、N2O和NH3的排放通量明顯升高（<0.05），由圖3可知當(dāng)天的溫度和濕度變化范圍分別為10.8～18.8 ℃和31.4%～44.4%，在測(cè)試期間屬于高溫高濕天氣，對(duì)糞污中污染氣體的產(chǎn)生與排放產(chǎn)生了影響。運(yùn)動(dòng)場(chǎng)上的CO2主要來(lái)源于奶牛的呼吸，測(cè)試期間的溫?zé)岘h(huán)境處于奶牛舒適區(qū)，CO2排放通量沒(méi)有明顯變化。

表1 奶牛運(yùn)動(dòng)場(chǎng)CH4、N2O、CO2和NH3的排放通量

該結(jié)果中CH4、N2O和CO2的排放通量分別是Ding等[20]采用靜態(tài)箱法對(duì)北京某奶牛運(yùn)動(dòng)場(chǎng)CH4、N2O和CO2的排放通量的3.6倍、2.6倍和1.7倍。主要是因?yàn)殪o態(tài)箱法僅能測(cè)得其所罩住的排放源（即殘留的糞污）的氣體排放通量，而梯度法所測(cè)氣體排放通量為運(yùn)動(dòng)場(chǎng)糞污以及奶牛本身所產(chǎn)生的氣體排放量之和。此外，Ding等[20]的試驗(yàn)布置9個(gè)測(cè)量點(diǎn)，測(cè)量點(diǎn)數(shù)量以及靜態(tài)箱所覆蓋地面上殘留糞便量的差異也會(huì)對(duì)測(cè)量精度產(chǎn)生一定的影響。

運(yùn)動(dòng)場(chǎng)上的奶牛飼養(yǎng)密度以及糞便管理方式等，顯著影響運(yùn)動(dòng)場(chǎng)氣體排放量。Leytem等[13]對(duì)美國(guó)愛(ài)達(dá)荷州某奶牛運(yùn)動(dòng)場(chǎng)的測(cè)定結(jié)果表明，CH4、N2O和NH3的排放通量分別為52.91、7.5和98.33 mg/(m2·h)。CH4排放通量低于本試驗(yàn)監(jiān)測(cè)結(jié)果，因?yàn)镃H4主要來(lái)源于奶牛的胃腸道發(fā)酵[21-22]，而測(cè)試運(yùn)動(dòng)場(chǎng)的每頭牛占地面積為55.00 m2/頭，高于本研究的20.77 m2/頭，因此排放通量更低。另外，在Leytem等[13]試驗(yàn)中，工作人員每天會(huì)對(duì)奶牛運(yùn)動(dòng)場(chǎng)耙犁一遍，加快了糞便中N2O和NH3的排放，因此其排放均高于本試驗(yàn)結(jié)果。Borhan等[14,23]采用動(dòng)態(tài)箱法對(duì)散養(yǎng)青年母牛運(yùn)動(dòng)場(chǎng)的N2O和CO2的排放通量進(jìn)行了監(jiān)測(cè)，其中N2O和CO2的排放通量分別為2.2～7.5 和2 824～5 392 g/(頭·d)，較本研究的N2O和CO2排放通量更高。分析認(rèn)為，主要是因?yàn)槠湓囼?yàn)運(yùn)動(dòng)場(chǎng)每年僅清理2次糞污，糞尿的大量殘留導(dǎo)致了更高的污染氣體排放量。

2.3 運(yùn)動(dòng)場(chǎng)溫室氣體排放量

春季該奶牛運(yùn)動(dòng)場(chǎng)上通過(guò)奶牛生理活動(dòng)和糞便發(fā)酵產(chǎn)生的CH4、N2O和CO2的排放量占比分別為42.79%、9.37%和47.83%，CH4和CO2的排放量占溫室氣體排放總量的比例相當(dāng)。不同氣體排放量占比會(huì)受到測(cè)試季節(jié)、飼養(yǎng)密度以及糞便管理制度等因素的影響。Ding等[20]的研究結(jié)果表明，奶牛運(yùn)動(dòng)場(chǎng)殘留糞便全年的CH4、N2O和CO2的排放量所占比例分別為15.95%、18.75%和65.30%。Leytem等[13]對(duì)美國(guó)愛(ài)達(dá)荷州某牛場(chǎng)CH4、N2O和CO2的排放量進(jìn)行了測(cè)算，該牛場(chǎng)每頭牛占地面積為55.00 m2/頭，并且每天對(duì)運(yùn)動(dòng)場(chǎng)耙犁一遍，測(cè)算得CH4、N2O和CO2的排放量比例分別為30.85%、5.96%和63.19%。此外，由于各個(gè)牛場(chǎng)使用的飼料因地區(qū)和季節(jié)不同而有所差異，因此推測(cè)CH4、N2O和CO2的排放量比例上的差異也可能與飼料成分有關(guān)。

2.4 環(huán)境因素對(duì)奶牛運(yùn)動(dòng)場(chǎng)氣體排放通量的影響

2.4.1 溫度對(duì)氣體排放通量的影響

圖4為4月1日至3日CH4、N2O、CO2和NH3的排放通量隨溫度變化的情況。統(tǒng)計(jì)結(jié)果顯示，溫度對(duì)CH4、N2O和NH3的排放通量有顯著的正相關(guān)性影響（<0.05），而對(duì)CO2的影響不顯著。崔曉東等[24]研究也發(fā)現(xiàn)溫度與CO2排放通量相關(guān)性不顯著。

圖4 CH4、N2O、CO2和NH3的排放通量與溫度變化規(guī)律

Fig.4 Emission rate of CH4, N2O, CO2and NH3related of temperature

Ding等[20]研究發(fā)現(xiàn)奶牛運(yùn)動(dòng)場(chǎng)上的溫室氣體在夏季排放速率最大，在冬季排放速率最小。說(shuō)明溫度對(duì)溫室氣體的產(chǎn)生有非常積極的影響。Pereira等[25-26]研究表明，當(dāng)環(huán)境溫度從5 ℃上升至35 ℃的過(guò)程中，CH4、N2O、CO2和NH3的排放通量明顯增加。當(dāng)溫度低于10 ℃時(shí)，脲酶活性下降；當(dāng)溫度處于10～40 ℃時(shí)，脲酶活性升高[27]。脲酶活性增加會(huì)促進(jìn)NH4+的生成，進(jìn)而促進(jìn)硝化作用和反硝化作用的進(jìn)行，導(dǎo)致N2O產(chǎn)量的增大[26]。同時(shí)NH4+濃度的增加會(huì)使液相NH4+/NH3失衡，促使液態(tài)NH3轉(zhuǎn)化為氣態(tài)NH3[27]。隨著溫度的升高，微生物的生物活性和呼吸作用增加，加快了生物降解速率，促進(jìn)了糞尿中揮發(fā)性脂肪酸等含有有機(jī)碳化合物的降解，導(dǎo)致CO2和CH4的產(chǎn)生量增加，從而提高氣體的排放通量[28]。本試驗(yàn)后期，CO2排放量與溫度變化趨勢(shì)相反，可能與當(dāng)時(shí)的奶牛活動(dòng)有關(guān)。

2.4.2 風(fēng)速對(duì)氣體排放通量的影響

風(fēng)速與氣體排放速率有很強(qiáng)的相關(guān)性[29]，會(huì)通過(guò)改變排放源表面?zhèn)髻|(zhì)系數(shù)而影響氣體的排放[30]。表2列出了每天17:00時(shí)（運(yùn)動(dòng)場(chǎng)剛清完糞）所發(fā)生的不同風(fēng)速條件下（距地面1 m處）奶牛運(yùn)動(dòng)場(chǎng)CH4、N2O、CO2和NH3的排放通量。這段時(shí)間，風(fēng)速范圍為4.05～18.85 m/s，CH4、N2O、CO2和NH3的排放通量范圍分別為180.60～214.26、2.59～8.63、5 546.68～6 795.20及71.00～92.29 mg/(m2·h)。由表2可知風(fēng)速對(duì)各個(gè)氣體的排放通量有不同程度的影響。

當(dāng)風(fēng)速為4.05和4.75 m/s時(shí)，CH4和NH3的排放通量沒(méi)有顯著性差異（>0.05）。然而，當(dāng)風(fēng)速增大到5.16 m/s時(shí)，CH4和NH3的排放通量顯著高于風(fēng)速為4.75 m/s時(shí)的氣體排放通量（<0.05）。在4.05～5.16 m/s的風(fēng)速范圍內(nèi)，N2O的排放通量隨風(fēng)速的增加顯著增加（<0.05）。當(dāng)風(fēng)速為18.85 m/s時(shí)，CH4、N2O和NH3的排放通量顯著低于風(fēng)速為5.16 m/s時(shí)的情況（<0.05）。雖然風(fēng)速增大時(shí)，糞堆內(nèi)外表面由于壓差增大會(huì)促進(jìn)氣體的排放[31]，但是隨著風(fēng)速的增大，糞堆表層水分的蒸發(fā)會(huì)加快，加速糞堆表面結(jié)痂，從而減少氣體的排放[32]。風(fēng)速對(duì)CO2的排放通量沒(méi)有顯著性影響（>0.05）。因?yàn)?7:00時(shí)，奶牛場(chǎng)開(kāi)始進(jìn)行組織擠奶，大部分奶牛不在運(yùn)動(dòng)場(chǎng)，導(dǎo)致此時(shí)的CO2的排放通量貢獻(xiàn)主要來(lái)自于運(yùn)動(dòng)場(chǎng)糞污發(fā)酵。

表2 不同風(fēng)速條件下CH4、N2O、CO2和NH3的排放通量

Table 2 Emission rate of CH4, N2O, CO2 and NH3 under different wind speed

注：不同小寫(xiě)字母表示0.05水平差異顯著。

Note: Different letters indicate significant difference at 0.05 level.

2.4.3 糞污管理制度對(duì)氣體排放通量的影響

由圖4可知CH4、N2O、CO2和NH3的排放通量會(huì)在17:00－18:00之間出現(xiàn)峰值，主要是因?yàn)樵撨\(yùn)動(dòng)場(chǎng)每天15:00－16:30會(huì)進(jìn)行清糞，新鮮糞尿的暴露會(huì)促進(jìn)氣體的排放。Leytem等[13]和Bjorneberg等[33]監(jiān)測(cè)的奶牛運(yùn)動(dòng)場(chǎng)每天除了定時(shí)清糞以外，還會(huì)對(duì)運(yùn)動(dòng)場(chǎng)進(jìn)行耙犁一遍，導(dǎo)致其測(cè)出的N2O、CO2和NH3排放通量高于本試驗(yàn)結(jié)果，也說(shuō)明了清糞活動(dòng)會(huì)加快氣體的排放速率。Borhan等[14,23]的試驗(yàn)牛場(chǎng)每年僅清理2次糞污，大量的糞污滯留在運(yùn)動(dòng)場(chǎng)使溫室氣體和NH3的產(chǎn)量快速增加，從而提高氣體的排放通量。說(shuō)明過(guò)量或過(guò)少地清除運(yùn)動(dòng)場(chǎng)糞污對(duì)溫室氣體和NH3的排放都有很大的影響，合理的糞污管理制度對(duì)控制有害氣體排放非常重要。

從圖4還可看出每天氣體排放通量峰值僅在清糞后（17:00后）出現(xiàn)，而在14:00－15:00之間當(dāng)天的氣溫就會(huì)達(dá)到最高值，如果氣體排放通量?jī)H受溫度影響，則其監(jiān)測(cè)值應(yīng)該先持續(xù)增長(zhǎng)一段時(shí)間然后下降，但是在14:00－17:30之間氣體排放通量持續(xù)增加，說(shuō)明清糞活動(dòng)在促進(jìn)氣體排放的同時(shí)也放大了溫度對(duì)氣體排放的影響。

此外，糞便管理制度也會(huì)改變風(fēng)速對(duì)氣體排放的影響效果。圖5反映了奶牛運(yùn)動(dòng)場(chǎng)4月2日白天CH4、N2O、CO2和NH3的排放通量和風(fēng)速的變化情況，由圖5可看出運(yùn)動(dòng)場(chǎng)在下午清糞期間（15:00－16:30）風(fēng)速持續(xù)下降，這本應(yīng)該會(huì)降低氣體的排放通量，但是氣體排放通量卻持續(xù)增加，說(shuō)明清糞活動(dòng)對(duì)氣體排放通量的促進(jìn)作用覆蓋了風(fēng)速對(duì)氣體排放的影響效果。

圖5 奶牛運(yùn)動(dòng)場(chǎng)4月2日CH4、N2O、CO2和NH3排放通量

3 結(jié) 論

本文通過(guò)對(duì)北京地區(qū)奶牛運(yùn)動(dòng)場(chǎng)春季溫室氣體和NH3的排放通量的現(xiàn)場(chǎng)測(cè)試，證明梯度法可應(yīng)用于開(kāi)放式系統(tǒng)的氣體排放通量監(jiān)測(cè)。結(jié)果表明，春季奶牛運(yùn)動(dòng)場(chǎng)CH4、N2O、CO2和NH3的排放通量分別為155.59、3.60、4 869.37和66.27 mg/(m2·h)，在每天清糞之后出現(xiàn)排放峰值。環(huán)境溫度顯著影響CH4、N2O和NH3的排放量，風(fēng)速在一定范圍內(nèi)會(huì)促進(jìn)CH4、N2O和NH3的排放。奶牛場(chǎng)清糞活動(dòng)不僅會(huì)加快氣體的排放量，還會(huì)影響溫度和風(fēng)速對(duì)氣體排放通量的作用效果。

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Emission characteristic of greenhouse gases and ammonia from open lot of scale dairy farm in spring

Liu Yu1,2, Liu Jie4, Wang Chaoyuan1,2,3※, Shi Zhengxiang1,2,3, Li Baoming1,2,3

(1.100083,; 2.100083,; 3.100083,; 4.265100)

Climate change is currently a global concern, which is mainly caused by excessive emission of greenhouse gases to the atmosphere, in particular the emission of CH4, N2O and CO2from agricultural production process. Greenhouse gas produced from manure management in livestock and poultry production is an important source of greenhouse gas emission. Besides, fermentation process of animal manure may generate large amount of NH3, which is considered as an important contaminant gas to the environmental and ecological system. Among agricultural sector, dairy farm is a big source of greenhouse gas and NH3emission. In China, a barn with a fully open lot, where the cows are freely accessible, is a typical operation for dairy cattle. Manure on the surface of the open lots is typically removed from days to weeks depending the climate and management in the farms, while the remained manure, liquid penetration and the cows on the lot are important sources of contaminated gas emissions. However, there are few field studies on the emissions from the lot because of its open characterization, relative low gas concentration and the potential impact on the daily management of the farms. In this paper, an integrated horizontal flux method, based on the mass balance principle, was used to calculate the emission fluxes of CH4, N2O, CO2and NH3from a typical dairy open lot in Beijing in spring season by continuous measurement of their concentrations with the purpose to provide fundamental information on the emissions. As the emission source, the open lot, which was 40 m in length by 27 m in width and kept with 52 milking cows, was divided into upwind boundary and downwind boundary according to the dominating wind directions. The emission rate was calculated based on the concentration differences of the target gases continuously measured from the upwind and downwind boundaries at three different heights of 1, 2 and 3 m by a photoacoustic field gas-monitor (INNOVA 1412i) and self-developed multiplexer. The results showed the overall emission rates of CH4, N2O, CO2and NH3from the dairy open lot were 155.59, 3.60, 4 869.37 and 66.27 mg/(m2·h) during the field measurement, respectively. The emissions of all the gases reached their daily peaks after manure removal in late afternoon. The emissions of CH4, N2O and CO2(based on CO2equivalents) of the open lot accounted for 42.79%, 9.37% and 47.83% of the total greenhouse gases emissions, respectively; and their proportions were related to the climate, manure management strategies of the lot, and feed in gredients as well. Additionally, CH4, N2O and NH3emission rates were significantly and positively affected by ambient temperature (<0.05). CH4, N2O and NH3emission rates could also be enhanced by wind speed within some limits. When the surface wind speed was around 5.16 m/s, which was measured on the point 1 m above the ground, the emissions of the three gases were significantly differed from those under 4.05 and 4.75 m/s (<0.05). While, when the wind speed was at 18.85 m/s, the emission rates were decreased, which could be explained by the crust formed on the manure surface due to the drying process under much higher wind speed and its prevention on the emissions. Besides, manure removal activity increased the emissions of gases, and the impacts of ambient temperature and wind speed on the gas emission may also be altered to some extent.

greenhouse gases; ammonia; emission control; dairy open lot; integrated horizontal flux method

劉 羽，劉 婕，王朝元，施正香，李保明. 規(guī)模奶牛養(yǎng)殖室外運(yùn)動(dòng)場(chǎng)春季溫室氣體與氨氣排放特性[J]. 農(nóng)業(yè)工程學(xué)報(bào)，2018，34(22)：178－184. doi：10.11975/j.issn.1002-6819.2018.22.022 http://www.tcsae.org

Liu Yu, Liu Jie, Wang Chaoyuan, Shi Zhengxiang, Li Baoming. Emission characteristic of greenhouse gases and ammonia from open lot of scale dairy farm in spring[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2018, 34(22): 178－184. (in Chinese with English abstract) doi：10.11975/j.issn.1002-6819.2018.22.022 http://www.tcsae.org

10.11975/j.issn.1002-6819.2018.22.022

S815.4

A

1002-6819(2018)-22-0178-07

2018-05-29

2018-09-29

國(guó)家自然科學(xué)基金（31472132、31172244）、國(guó)家奶牛產(chǎn)業(yè)技術(shù)體系（CARS-36）

劉 羽，博士生，研究方向?yàn)樵O(shè)施畜禽養(yǎng)殖環(huán)境與控制。 Email：xiaohaizhibei@cau.edu.cn

王朝元，教授，博士生導(dǎo)師，研究方向?yàn)樵O(shè)施畜禽養(yǎng)殖過(guò)程控制與環(huán)境。Email：gotowchy@cau.edu.cn

中國(guó)農(nóng)業(yè)工程學(xué)會(huì)高級(jí)會(huì)員：王朝元（E041200616S）