石鵬飛，鄭媛媛，楊東玉，黨 靜，王貴彥

(河北農(nóng)業(yè)大學(xué)農(nóng)學(xué)院，河北 保定 071001)

種養(yǎng)一體規(guī)?；r(nóng)場(chǎng)溫室氣體排放量分析

石鵬飛，鄭媛媛，楊東玉，黨 靜，王貴彥①

(河北農(nóng)業(yè)大學(xué)農(nóng)學(xué)院，河北 保定 071001)

為準(zhǔn)確評(píng)估華北平原種養(yǎng)一體規(guī)?；r(nóng)場(chǎng)溫室氣體排放量，以河北某種養(yǎng)一體規(guī)模化農(nóng)場(chǎng)為例，應(yīng)用生命周期評(píng)價(jià)方法,根據(jù)《IPCC 2006國(guó)家溫室氣體清單指南》中的排放系數(shù)，計(jì)算該農(nóng)場(chǎng)運(yùn)行過(guò)程中溫室氣體排放量。結(jié)果表明，農(nóng)場(chǎng)運(yùn)行過(guò)程中年溫室氣體總排放量(以CO2當(dāng)量計(jì),下同)為32 528.02 t，其中農(nóng)田生產(chǎn)系統(tǒng)排放占28.09%，養(yǎng)殖場(chǎng)排放占71.91%，其中糞便貯存管理、飼料生產(chǎn)和加工、腸道發(fā)酵及氮素生產(chǎn)和施用等生產(chǎn)環(huán)節(jié)是溫室氣體主要排放源，分別占總排放量的34.66%、21.24%、15.48%和20.08%。生產(chǎn)1 t小麥、玉米籽粒的溫室氣體排放量分別為1 059.39和411.92 kg；生產(chǎn)1 kg原奶和1 kg按蛋白質(zhì)和脂肪糾正的牛奶(FPCM)的溫室氣體排放量分別為1.04和1.14 kg，低于全球平均水平；生產(chǎn)1 kg活體豬、肉牛的溫室氣體排放量分別為2.58和10.00 kg，與國(guó)內(nèi)其他集約化養(yǎng)殖場(chǎng)的排放量相當(dāng)。通過(guò)情景分析發(fā)現(xiàn)，種植生產(chǎn)中采取減氮(化肥)以及提高畜禽糞便廢棄物處理能力等措施，加強(qiáng)農(nóng)場(chǎng)氮素管理，改善飼料結(jié)構(gòu)，可直接或間接減少農(nóng)場(chǎng)水平溫室氣體排放。

種養(yǎng)一體規(guī)?；?；農(nóng)場(chǎng)水平；溫室氣體；減排潛力

氣候變暖是當(dāng)今國(guó)際社會(huì)普遍關(guān)注的全球性環(huán)境問(wèn)題,也是人類面臨的最嚴(yán)峻的挑戰(zhàn)之一,而溫室氣體(GHG)的增加是造成氣候變暖的重要原因。其中涉及農(nóng)業(yè)源的溫室氣體有二氧化碳(CO2)、甲烷(CH4)和氧化亞氮(N2O)[1]。聯(lián)合國(guó)糧食及農(nóng)業(yè)組織(FAO)指出,種植業(yè)和畜牧業(yè)溫室氣體排放分別占全球人為溫室氣體排放的30%和18%[2]。根據(jù)聯(lián)合國(guó)政府間氣候變化專門(mén)委員會(huì)(Intergovernmental Panel on Climate Change,IPCC)第五次評(píng)估報(bào)告,全球范圍內(nèi)農(nóng)業(yè)排放CH4和N2O分別占人類活動(dòng)造成的CH4和N2O排放總量的50%和60%[3]。中國(guó)農(nóng)業(yè)源溫室氣體排放占全國(guó)溫室氣體排放總量的17%,其中農(nóng)業(yè)活動(dòng)排放的CH4和N2O分別占全國(guó)CH4和N2O排放量的50.15%和92.47%[1]。

華北平原是我國(guó)重要的糧食生產(chǎn)基地,耕地面積占全國(guó)耕地總面積的26.57%[4],糧食產(chǎn)量占全國(guó)糧食總產(chǎn)量的34.39%,氮肥用量占全國(guó)用量的35.02%[5]。冬小麥-夏玉米一年兩熟制是華北平原最主要的種植制度,該區(qū)農(nóng)田管理的主要特點(diǎn)是施用化肥和秸稈全量還田,這就必然伴隨著CO2、CH4和N2O等溫室氣體的產(chǎn)生和排放。目前,推廣減少氮肥施用、無(wú)機(jī)和有機(jī)肥相結(jié)合、測(cè)土配方施肥和秸稈還田綜合管理等措施是農(nóng)田溫室氣體減排的潛力所在[1,6-9]。華北平原農(nóng)區(qū)畜牧業(yè)也發(fā)展迅速,過(guò)去的農(nóng)戶分散養(yǎng)殖已逐漸被規(guī)?；?、集約化的養(yǎng)殖場(chǎng)所取代,大量畜禽糞便等廢棄物在堆置過(guò)程中產(chǎn)生的溫室氣體造成了嚴(yán)重的面源污染。因此,種植和養(yǎng)殖相結(jié)合是解決畜禽廢棄物面源污染的重要途徑[10-11],而改善飼料質(zhì)量、提高動(dòng)物生產(chǎn)力、改進(jìn)糞便貯存管理模式以及建設(shè)沼氣工程等都是集約化養(yǎng)殖場(chǎng)溫室氣體減排的重要措施[12-17]。

河北某種養(yǎng)一體規(guī)模化農(nóng)場(chǎng)采用華北平原典型的農(nóng)牧結(jié)合模式,通過(guò)秸稈回收青貯作飼料、畜禽糞便進(jìn)入沼氣池發(fā)酵和替代部分化肥還田、沼液和沼渣還田等接口技術(shù)鏈接種植和養(yǎng)殖生產(chǎn)環(huán)節(jié),不僅提高了物質(zhì)循環(huán)效率,而且有利于溫室氣體減排。但截至目前,有關(guān)溫室氣體排放的研究大都僅涉及農(nóng)田生產(chǎn)系統(tǒng)和畜牧養(yǎng)殖系統(tǒng)的某個(gè)環(huán)節(jié)或某個(gè)子系統(tǒng),而針對(duì)種養(yǎng)一體規(guī)?；r(nóng)場(chǎng)溫室氣體排放評(píng)估的研究相對(duì)較少。

生命周期評(píng)價(jià)(LCA)是對(duì)一個(gè)產(chǎn)品系統(tǒng)的生命周期中輸入、輸出及潛在環(huán)境影響的匯編和評(píng)價(jià)[18],它提供了一種從系統(tǒng)角度分析問(wèn)題的思路和評(píng)估的標(biāo)準(zhǔn)方法[19]。近年來(lái),不少國(guó)內(nèi)外學(xué)者使用LCA對(duì)農(nóng)田和畜牧生產(chǎn)系統(tǒng)的溫室氣體排放進(jìn)行了評(píng)估[15,20-26]。因此,筆者以河北某種養(yǎng)一體規(guī)?；r(nóng)場(chǎng)為例,利用LCA評(píng)估方法系統(tǒng)分析種養(yǎng)一體規(guī)?；r(nóng)場(chǎng)溫室氣體排放及各生產(chǎn)子系統(tǒng)排放比例,系統(tǒng)分析減排潛力,為提出有效減排措施提供科學(xué)依據(jù),研究結(jié)果對(duì)華北平原農(nóng)業(yè)生產(chǎn)過(guò)程溫室氣體減排具有參考意義。

1 材料與方法

1.1 農(nóng)場(chǎng)生產(chǎn)概況及數(shù)據(jù)來(lái)源

河北某種養(yǎng)一體規(guī)模化農(nóng)場(chǎng)是集種植、養(yǎng)殖、沼氣發(fā)酵、飼料加工和有機(jī)肥加工等多項(xiàng)產(chǎn)業(yè)于一體的國(guó)家級(jí)循環(huán)農(nóng)業(yè)園區(qū),是華北平原典型的循環(huán)農(nóng)業(yè)模式。以農(nóng)場(chǎng)2014年的生產(chǎn)情況為例,分析其溫室氣體排放特點(diǎn)。小麥-玉米一年兩熟是其主要種植制度,種植面積1 000 hm2,小麥單產(chǎn)6 000 kg·hm-2,玉米單產(chǎn)6 750 kg·hm-2。小麥和玉米兩季施氮量為557.88 kg·hm-2,其中化肥氮231.26 kg·hm-2。農(nóng)田生產(chǎn)系統(tǒng)中能源消耗主要為旋耕、播種和收獲等耗柴油188.25 kg·hm-2,作物生長(zhǎng)期間灌溉耗電1 800 kW·h·hm-2。

養(yǎng)殖中奶牛存欄量為1 400頭,其中犢牛(平均體重180 kg)420頭,育成牛(平均體重450 kg)700頭,泌乳牛(平均體重600 kg)280頭,年產(chǎn)奶1 460 t;肉牛存欄量為3 000頭,犢牛(平均體重180 kg)1 000 頭,育肥牛(平均體重550 kg)1 400頭,架子牛(平均體重250 kg)600頭;豬場(chǎng)中母豬(平均體重210 kg)存欄量為2 400頭,年出欄生豬(平均體重100 kg)60 000頭。出欄豬育肥過(guò)程中主要經(jīng)過(guò)仔豬(平均體重12 kg,70 d)、生長(zhǎng)豬(平均體重45 kg,30 d)和育肥豬(平均體重90 kg,90 d)3個(gè)生長(zhǎng)階段。公司現(xiàn)已投入使用的沼氣池達(dá)8 000 m3,還有3 000 m3沼氣池待使用,養(yǎng)殖場(chǎng)年產(chǎn)糞尿204 035 t,其中65%直接進(jìn)入沼氣池,35%通過(guò)開(kāi)放厭氧塘糞便處理系統(tǒng)貯存。沼氣發(fā)酵所產(chǎn)沼氣用于發(fā)電,2014年產(chǎn)氣量182.5萬(wàn) m3,年發(fā)電量315.36萬(wàn)kW·h,主要供養(yǎng)殖場(chǎng)和飼料加工及農(nóng)場(chǎng)日常使用。

農(nóng)場(chǎng)中的飼料主要包括青貯玉米、牧草等粗飼料和玉米、麥麩和豆粕等精飼料。養(yǎng)殖年消耗青貯玉米8 000 t、玉米籽粒13 294 t、麥麩6 787 t和豆粕5 781 t。其中麥麩和豆粕全部從農(nóng)場(chǎng)外購(gòu)買(mǎi),玉米籽粒除農(nóng)場(chǎng)生產(chǎn)的6 750 t外,其余的外購(gòu)。外購(gòu)玉米籽粒、麥麩和豆粕的產(chǎn)量和施氮量根據(jù)河北省實(shí)際生產(chǎn)情況取值[27]：玉米產(chǎn)量為6.30 t·hm-2,施氮量為0.21 t·hm-2;小麥產(chǎn)量為6.00 t·hm-2,施氮量為0.225 t·hm-2,小麥加工后出麩率為25%,加工小麥耗電0.048 MW·h·t-1;大豆產(chǎn)量為2.032 t·hm-2,施氮量為0.105 t·hm-2,豆粕為大豆榨油后的副產(chǎn)品,豆粕率為80%,加工大豆耗電0.03 MW·h·t-1[17]。

1.2 系統(tǒng)邊界的確定

根據(jù)農(nóng)場(chǎng)種植和養(yǎng)殖生產(chǎn)過(guò)程中相關(guān)的溫室氣體排放活動(dòng)確定系統(tǒng)邊界。農(nóng)田生產(chǎn)過(guò)程主要為氮肥(化肥和糞肥)施用、化肥氮生產(chǎn)、灌溉耗電以及田間管理等機(jī)械能耗所排放的溫室氣體。養(yǎng)殖場(chǎng)排放源主要包括動(dòng)物腸道發(fā)酵、飼料生產(chǎn)和加工、糞便貯存及養(yǎng)殖場(chǎng)日常管理運(yùn)輸?shù)饶芎乃a(chǎn)生的溫室氣體。另外,根據(jù)碳平衡原理[28],糞便進(jìn)入沼氣池發(fā)酵過(guò)程產(chǎn)生的溫室氣體為0。

1.3 溫室氣體排放量計(jì)算公式

化肥氮和糞肥田間施用過(guò)程中N2O排放、動(dòng)物胃腸道發(fā)酵產(chǎn)生的CH4排放和飼料生產(chǎn)加工過(guò)程中的溫室氣體排放計(jì)算公式參照文獻(xiàn)[17];糞便貯存過(guò)程中N2O排放和糞便貯存過(guò)程中CH4排放的計(jì)算公式參照文獻(xiàn)[14]。

1.4 參數(shù)選擇與說(shuō)明

CO2、CH4和N2O的增溫潛勢(shì)值根據(jù)文獻(xiàn)[29]分別取1、25、298。CO2、CH4和N2O的計(jì)算結(jié)果皆根據(jù)各自的當(dāng)量因子以CO2當(dāng)量表示。

小麥和大豆的種植過(guò)程和加工能耗帶來(lái)的溫室氣體排放根據(jù)分配系數(shù)分配給麥麩和小麥粉、豆粕和豆油。分配系數(shù)參照文獻(xiàn)[17]進(jìn)行計(jì)算。

(1)

式(1)中,Wi為飼料組分i的排放量分配系數(shù);Ri為谷物i加工的副產(chǎn)品產(chǎn)出率(小麥的出麩率或大豆的出豆粕率),%;Pi為谷物i的副產(chǎn)品(麥麩或豆粕)價(jià)格,元·kg-1;Pci為谷物i主產(chǎn)品(小麥面粉或豆油)價(jià)格,元·kg-1。根據(jù)2014年河北省小麥和大豆生產(chǎn)情況,小麥面粉價(jià)格為3.05元·kg-1,麥麩價(jià)格為1.36元·kg-1,大豆豆油價(jià)格為6.75元·kg-1,豆粕價(jià)格為3.4元·kg-1,根據(jù)公式可計(jì)算出麥麩和豆粕的分配系數(shù)分別為0.13和0.67。

溫室氣體排放因子參數(shù)見(jiàn)表1[14,29-34]。

表1 溫室氣體排放因子參數(shù)

Table 1 Parameters of factors affecting GHG emission in calculations

參數(shù) 含義描述 單位 排放源取值文獻(xiàn)來(lái)源efNDM糞肥田間施用的N2O直接排放系數(shù)t·t-1土壤排放0.0105[30]efND氮肥田間施用的N2O直接排放系數(shù)t·t-1土壤排放0.0105[30]FGAS氮肥以NH3-N和NOx-N形式揮發(fā)系數(shù)t·t-1氮揮發(fā)0.1[29]FGASM糞肥以NH3-N和NOx-N形式揮發(fā)系數(shù)t·t-1氮揮發(fā)0.2[29]efNH大氣氮沉降N2O排放系數(shù)t·t-1氮沉降0.01[29]FLM糞肥的滲漏損失系數(shù)t·t-1滲漏損失0.25[31]FL氮肥的滲漏損失系數(shù)t·t-1滲漏損失0.25[31]efNL滲漏或徑流氮損失的N2O排放系數(shù)t·t-1氮淋洗0.0075[29]efMAj1奶牛胃腸道發(fā)酵CH4排放系數(shù)kg·頭-1·a-1胃腸道109[29]efMAj2肉牛、犢牛腸道發(fā)酵CH4排放系數(shù)kg·頭-1·a-1胃腸道57[29]efMAj3育肥豬(平均體重100kg)腸道發(fā)酵CH4排放系數(shù)kg·頭-1·a-1胃腸道1[29]Nrate1每1000kg奶牛體重氮排泄率kg·d-10.47[29]Nrate2每1000kg肉牛體重氮排泄率kg·d-10.34[29]Nrate3每1000kg生豬體重氮排泄率kg·d-10.5[29]EF2舍內(nèi)糞污貯存N2O排放kg·kg-1舍內(nèi)0.002[29]BOLT1每頭奶牛(350kg)糞污的最大CH4產(chǎn)生潛力m3·kg-1蓄糞池0.13[29]BOLT2每頭肉牛(319kg)糞污的最大CH4產(chǎn)生潛力m3·kg-1蓄糞池0.1[29]BOLT3每頭生豬(28kg)糞污的最大CH4產(chǎn)生潛力m3·kg-1蓄糞池0.29[29]DCH4CH4密度t·m-3蓄糞池0.00067[32]MCFj開(kāi)放厭氧塘的CH4轉(zhuǎn)換因子蓄糞池70%[29]VSdefault1每頭奶牛日排泄的揮發(fā)性固體干物質(zhì)(默認(rèn)值)kg·d-1蓄糞池2.8[29]VSdefault2每頭肉牛日排泄的揮發(fā)性固體干物質(zhì)(默認(rèn)值)kg·d-1蓄糞池2.3[29]VSdefault3每頭生豬日排泄的揮發(fā)性固體干物質(zhì)(默認(rèn)值)kg·d-1蓄糞池0.3[29]UFb不確定性的修正因子0.94[14]MS進(jìn)入系統(tǒng)內(nèi)的糞污比例35%實(shí)地調(diào)查efNC氮肥生產(chǎn)的CO2排放系數(shù)t·t-14.77[33]EFa電網(wǎng)排放因子t·MW-1·h-1華北電網(wǎng)0.8936[34]EFdiesel柴油燃燒的排放因子t·t-13.16[29]EFKm,CO2道路運(yùn)輸kg·km-11.01[29]

溫室氣體排放系數(shù)根據(jù)河北省飼料作物生產(chǎn)和農(nóng)場(chǎng)的具體情況,結(jié)合國(guó)內(nèi)研究成果和文獻(xiàn)[29]選擇。養(yǎng)殖場(chǎng)中溫室氣體排放基于豬、肉牛和奶牛2014年存欄量進(jìn)行計(jì)算,但由于存欄豬、牛群結(jié)構(gòu)和體重有所不同,因此在計(jì)算動(dòng)物胃腸道發(fā)酵CH4排放、糞便貯存過(guò)程中N2O和CH4排放時(shí),均按照不同類型豬、肉牛、奶牛各階段平均體重及維持時(shí)間,對(duì)照表1進(jìn)行排放因子折算,進(jìn)而計(jì)算溫室氣體排放總量。

2 結(jié)果與分析

2.1 農(nóng)場(chǎng)農(nóng)田生產(chǎn)和養(yǎng)殖子系統(tǒng)各環(huán)節(jié)溫室氣體排放量及所占比例

農(nóng)場(chǎng)生產(chǎn)活動(dòng)中,農(nóng)田生產(chǎn)系統(tǒng)排放的溫室氣體(以CO2當(dāng)量計(jì),下同)為9 136.83 t·a-1,占農(nóng)場(chǎng)年總排放量的28.09%(表2)。其中,農(nóng)田系統(tǒng)的化肥氮、糞肥施用以及化肥氮生產(chǎn)過(guò)程中的溫室氣體排放所占比例較高,分別占農(nóng)田生產(chǎn)總排放量和農(nóng)場(chǎng)年總排放量的71.46%和20.08%;其次為機(jī)械和灌溉能耗,占農(nóng)田生產(chǎn)總排放量的28.54%。由此可知,農(nóng)田系統(tǒng)中溫室氣體排放主要來(lái)自氮肥和糞肥施用及生產(chǎn)氮肥所產(chǎn)生的溫室氣體,其中化肥氮生產(chǎn)和田間施用環(huán)節(jié)溫室氣體排放量為4 330.80 t,占農(nóng)田生產(chǎn)總排放量的47.40%,為主要排放源。

表2 農(nóng)田生產(chǎn)系統(tǒng)溫室氣體排放量及占農(nóng)場(chǎng)總排放量的比例

Table 2 GHG emission from the farming system and its contribution to the total from the farm

排放源 排放量/(t·a-1)占農(nóng)場(chǎng)總排放量的比例/%化肥氮生產(chǎn)1872.325.76化肥氮施用2458.487.56糞肥施用2198.686.76機(jī)械能耗998.873.07灌溉能耗1608.484.94合計(jì)9136.8328.09

農(nóng)場(chǎng)養(yǎng)殖系統(tǒng)主要包括生豬、肉牛和奶牛養(yǎng)殖以及飼料生產(chǎn)加工等生產(chǎn)活動(dòng),溫室氣體主要來(lái)源于動(dòng)物腸道發(fā)酵、飼料生產(chǎn)加工、糞便貯存及日常管理等生產(chǎn)過(guò)程。由表3可知,養(yǎng)殖系統(tǒng)溫室氣體年排放總量為23 391.19 t·a-1,占農(nóng)場(chǎng)年排放總量的71.91%。其中,貢獻(xiàn)最大的是糞便貯存過(guò)程排放,為11 275.26 t,占農(nóng)場(chǎng)總排放量的34.66%。由于養(yǎng)殖規(guī)模較大,而且現(xiàn)有沼氣池容積不能容納全部糞便進(jìn)行沼氣發(fā)酵,使得大量糞便集中貯存,從而導(dǎo)致溫室氣體排放增多;農(nóng)場(chǎng)生豬和肉牛飼養(yǎng)量較大,對(duì)精飼料需求較多,因此飼料生產(chǎn)和加工過(guò)程中的溫室氣體排放也占農(nóng)場(chǎng)總排放量的21.24%。由于外購(gòu)了大量的玉米籽粒和麥麩、豆粕等精飼料原料,外購(gòu)飼料生產(chǎn)過(guò)程中的化肥氮施用也排放了大量的溫室氣體。此外,動(dòng)物腸道發(fā)酵的溫室氣體年排放量占年總排放量的15.48%。

表3 養(yǎng)殖生產(chǎn)系統(tǒng)溫室氣體排放量及占農(nóng)場(chǎng)總排放量的比例

Table 3 GHG emission from the livestock rearing system and its contribution to the total of the farm

排放源生產(chǎn)環(huán)節(jié)排放量/(t·a-1)占農(nóng)場(chǎng)總排放量的比例/%腸道發(fā)酵生豬養(yǎng)殖 551.30奶牛養(yǎng)殖2779.00肉牛養(yǎng)殖1705.00合計(jì)5035.3015.48飼料生產(chǎn)與加工1)生豬養(yǎng)殖4935.52奶牛養(yǎng)殖667.24肉牛養(yǎng)殖1305.59合計(jì)6908.3521.24糞便N2O排放生豬養(yǎng)殖131.92奶牛養(yǎng)殖31.41肉牛養(yǎng)殖44.75合計(jì)208.080.64糞便CH4排放生豬養(yǎng)殖9845.44奶牛養(yǎng)殖836.31肉牛養(yǎng)殖385.43合計(jì)11067.1834.02柴油CO2排放2)生豬養(yǎng)殖33.27奶牛養(yǎng)殖80.42肉牛養(yǎng)殖58.59合計(jì)172.280.53總計(jì)23391.1971.91

1)包括外購(gòu)麥麩和豆粕在生產(chǎn)和初加工時(shí)的用電排放量及農(nóng)場(chǎng)進(jìn)行精、粗飼料加工時(shí)的用電排放量;2)指養(yǎng)殖場(chǎng)日常管理機(jī)械能耗排放量。

2.2 農(nóng)場(chǎng)內(nèi)產(chǎn)品單位產(chǎn)量GHG排放量

農(nóng)田和養(yǎng)殖過(guò)程中生產(chǎn)單位產(chǎn)品所排放的溫室氣體見(jiàn)表4。由表4可知,生產(chǎn)1 t小麥籽粒的溫室氣體排放量為1 059.39 kg,生產(chǎn)1 t玉米籽粒的溫室氣體排放量為411.92 kg。養(yǎng)殖生產(chǎn)中,生產(chǎn)1 kg單位活體生豬的溫室氣體排放量為2.58 kg,低于BASSET-MENS等[35](3.5 kg)和BLONK等[36](3.7 kg)的研究結(jié)果,與周軍[37]的研究結(jié)果(大規(guī)模養(yǎng)殖戶生命周期內(nèi)單位活體豬CO2排放當(dāng)量為2.978 kg)基本一致;奶牛養(yǎng)殖中生產(chǎn)1 kg原奶的溫室氣體排放量為1.04 kg,和新西蘭、瑞典及德國(guó)的原奶生產(chǎn)溫室氣體排放范圍(0.93～1.3 kg)一致[38],與國(guó)內(nèi)其他規(guī)?；膛ｐB(yǎng)殖場(chǎng)單位產(chǎn)品原奶生產(chǎn)排放1.398 kg溫室氣體[17]的研究結(jié)果相當(dāng)。如果參照文獻(xiàn)[17]折算成按蛋白質(zhì)和脂肪含量糾正的牛奶(FPCM)產(chǎn)量,生產(chǎn)1 kg FPCM的溫室氣體排放量為1.14 kg,低于國(guó)內(nèi)規(guī)?；膛ｐB(yǎng)殖場(chǎng)生產(chǎn)1 kg FPCM溫室氣體排放量(1.71 kg)[39],也低于集約化養(yǎng)殖的全球平均水平(生產(chǎn)1 kg FPCM 排放2.8 kg溫室氣體)[40]。按奶牛養(yǎng)殖場(chǎng)年總排放量折算,每頭存欄奶牛平均年排放溫室氣體3.1 t,低于某些規(guī)?；膛?chǎng)的平均排放量(4.9 t)[14]。養(yǎng)殖生產(chǎn)1 kg單位活體肉牛的溫室氣體排放量為10.00 kg,與國(guó)內(nèi)規(guī)?；馀ｐB(yǎng)殖育肥期間的溫室氣體排放強(qiáng)度(10.16 kg)研究結(jié)果一致[15]。

表4 農(nóng)場(chǎng)各系統(tǒng)單位產(chǎn)量溫室氣體排放量

Table 4 GHG emissions per unit output relative to system in the farm

系統(tǒng) 功能單位排放量/kg作物種植系統(tǒng)1t小麥籽粒1059.391t玉米籽粒411.92豬生產(chǎn)系統(tǒng)1kg活體重2.58奶牛生產(chǎn)系統(tǒng)1kg原奶1.041kgFPCM1.14肉牛生產(chǎn)系統(tǒng)1kg活體重10.00

FPCM為按蛋白質(zhì)和脂肪含量糾正的牛奶。

3 討論

3.1 農(nóng)場(chǎng)農(nóng)田生產(chǎn)系統(tǒng)減氮(化肥)對(duì)溫室氣體減排的影響

目前農(nóng)場(chǎng)的種植結(jié)構(gòu)中,小麥-玉米兩熟的農(nóng)田面積占總種植面積的94.34%,生產(chǎn)過(guò)程基本機(jī)械化。種植過(guò)程中除小麥播種前施入282.10 kg·hm-2糞肥氮作為底肥外,還施用231.26 kg·hm-2化肥氮作為底肥和追肥,再加上玉米播種時(shí)施用的161.26 kg·hm-2化肥氮,小麥、玉米兩季僅化肥氮施用量就達(dá)392.52 kg·hm-2,造成了大量N2O排放,導(dǎo)致農(nóng)田成為N2O的主要排放源。根據(jù)河北平原高產(chǎn)小麥、玉米栽培研究,在產(chǎn)量達(dá)到18 845.25 kg·hm-2的情況下,施氮量為420～480 kg·hm-2[41]。因此,減氮尤其是減少化肥氮的施用,一方面可減少因化肥氮田間施用所排放的溫室氣體,而且也可減少化肥氮生產(chǎn)過(guò)程中的溫室氣體排放,是目前農(nóng)場(chǎng)溫室氣體減排的關(guān)鍵措施之一[6-9,39]。隨著糞肥施用年限的增長(zhǎng),不僅可以改善土壤物理結(jié)構(gòu),改良土壤肥力特性,增加土壤養(yǎng)分,而且能夠顯著提高水分利用效率[42],農(nóng)場(chǎng)可逐漸減少并停止施用化肥氮。根據(jù)情景分析,當(dāng)小麥、玉米種植中的化肥氮施用量減少125.51 kg·hm-2時(shí),在不影響作物產(chǎn)量情況下,溫室氣體可以年減排1 384.79 t,占農(nóng)田生產(chǎn)系統(tǒng)總排放量的15.6%。

養(yǎng)殖生產(chǎn)中,每年需要從農(nóng)場(chǎng)外購(gòu)買(mǎi)6 544.47 t玉米籽粒、6 787 t麥麩和5 781 t豆粕,外購(gòu)玉米、麥麩和豆粕主要來(lái)自農(nóng)戶種植,而目絕大部分農(nóng)戶基本不施用有機(jī)肥,外購(gòu)玉米、麥麩和豆粕的生產(chǎn)消耗1 609.53 t化肥氮,間接增加農(nóng)場(chǎng)溫室氣體排放。因此,可采取相關(guān)措施減少外購(gòu)精飼料,間接減少化肥氮施用,這也是農(nóng)場(chǎng)溫室氣體減排的潛力所在。

3.2 改善糞便綜合管理方式對(duì)農(nóng)場(chǎng)溫室氣體減排的影響

隨著農(nóng)場(chǎng)養(yǎng)殖規(guī)模的不斷擴(kuò)大,動(dòng)物糞便堆積貯存時(shí),在厭氧條件下會(huì)產(chǎn)生大量CH4和N2O等溫室氣體,對(duì)環(huán)境構(gòu)成極大威脅。當(dāng)有限的耕地不能全部容納養(yǎng)殖廢棄物時(shí),有必要綜合利用多種廢棄物處理和資源化利用方式來(lái)達(dá)到更好的經(jīng)濟(jì)和環(huán)境效益[43]。在可供選擇的動(dòng)物糞便污染控制技術(shù)中,沼氣發(fā)酵可減少溫室氣體排放[16,28,44-47]。

農(nóng)場(chǎng)通過(guò)建設(shè)沼氣池對(duì)畜禽糞便進(jìn)行綜合利用,除已投入使用的8 000 m3沼氣池外,還將投入建造一套3 000 m3的沼氣發(fā)酵設(shè)施,當(dāng)農(nóng)場(chǎng)沼氣發(fā)酵池達(dá)到11 000 m3時(shí),年處理糞便量可增加11%,與不使用沼氣發(fā)酵相比可多減排15.68%。另外,目前農(nóng)場(chǎng)沼氣發(fā)電替代國(guó)家電網(wǎng)電力可間接減排溫室氣體2 818.06 t·a-1。根據(jù)調(diào)查,農(nóng)場(chǎng)建造沼氣池雖然可以得到政府的相應(yīng)補(bǔ)貼,但仍需要投入大量資金進(jìn)行維護(hù),而處理廢棄物的經(jīng)濟(jì)利潤(rùn)較低[43]。因此,相關(guān)部門(mén)應(yīng)根據(jù)當(dāng)?shù)氐呐欧艠?biāo)準(zhǔn)和環(huán)保要求等給予一定的經(jīng)濟(jì)補(bǔ)貼和獎(jiǎng)勵(lì)。另外,對(duì)不能進(jìn)入沼氣池發(fā)酵的糞便,在貯存過(guò)程中可添加小麥秸稈生物質(zhì)炭和過(guò)磷酸鈣等物質(zhì),已有研究表明這些措施均可顯著降低堆肥過(guò)程中的溫室氣體排放[48-49]。

3.3 改善飼料結(jié)構(gòu)對(duì)農(nóng)場(chǎng)溫室氣體減排的影響

目前,農(nóng)場(chǎng)養(yǎng)殖的奶牛和肉牛粗飼料以青貯玉米秸稈為主,只添加少量的高丹草和苜蓿等優(yōu)質(zhì)牧草。根據(jù)WANG等[39]的研究,對(duì)奶牛養(yǎng)殖而言,溫室氣體排放量和牛奶產(chǎn)量與飼料中的精飼料、青貯飼料及苜蓿等成分密切相關(guān),改善飼料構(gòu)成可減少生產(chǎn)單位質(zhì)量蛋白質(zhì)的溫室氣體排放。研究表明,當(dāng)采用3 kg苜蓿替代1.5 kg精飼料時(shí),牛奶產(chǎn)量將提高11%,如果苜蓿生產(chǎn)中不施用化肥,總溫室氣體排放量將增加2%,但生產(chǎn)1 kg FPCM的溫室氣體排放將減少8%;而當(dāng)替代的苜蓿生產(chǎn)施用化肥情況下,總溫室氣體排放量將增加5%,但生產(chǎn)1 kg FPCM的溫室氣體排放將減少5%[39]。因此,在奶牛養(yǎng)殖時(shí)增加苜蓿和高丹草等優(yōu)質(zhì)牧草,雖然總溫室氣體排放量有所增加,但可降低單位產(chǎn)品的溫室氣體排放。

4 結(jié)論

種養(yǎng)一體規(guī)?；r(nóng)場(chǎng)在正常運(yùn)行狀態(tài)下的溫室氣體年總排放量為32 528.02 t,其中農(nóng)田生產(chǎn)系統(tǒng)排放占28.09%,養(yǎng)殖場(chǎng)排放占71.91%。糞便貯存管理、飼料生產(chǎn)和加工、腸道發(fā)酵、氮素生產(chǎn)和施用等生產(chǎn)環(huán)節(jié)是農(nóng)場(chǎng)溫室氣體的主要排放源,分別占總排放量的34.66%、21.24%、15.48%和20.08%。生產(chǎn)1 t小麥和玉米籽粒的溫室氣體排放量分別為1 059.39和411.92 kg;生產(chǎn)1 kg牛奶(原奶)和FPCM的溫室氣體排放量分別為1.04和1.14 kg,低于全球平均水平;生產(chǎn)1 kg活體豬和肉牛的溫室氣體排放量分別為2.58和10.00 kg,與國(guó)內(nèi)其他集約化養(yǎng)殖場(chǎng)的排放量相當(dāng)。

農(nóng)場(chǎng)中,化肥氮生產(chǎn)和施用、外購(gòu)大量的玉米等精飼料原料及糞便貯存過(guò)程排放了大量的溫室氣體,是減排的潛力所在。通過(guò)情景分析,在減少化肥氮施用、增加進(jìn)入沼氣發(fā)酵池糞便等情形下,可直接或間接減少大量的溫室氣體排放,減排潛力巨大。另外,加強(qiáng)糞便貯存管理和改善飼料結(jié)構(gòu),也是直接或間接減排的重要措施。

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(責(zé)任編輯： 許 素)

Estimation of Greenhouse Gas Emissions in Scaled Crop-Livestock Integrated Farms in North China Plain.

SHIPeng-fei,ZHENGYuan-yuan,YANGDong-yu,DANGJing,WANGGui-yan

(College of Agronomy, Agricultural University of Hebei, Baoding 071001, China)

The North China Plain is one of the most important crop and livestock production regions, and large-scaled crop and livestock integrated farms are common and typical of the region and thought to be an effective way to solve the environment pollution. Emission of greenhouse gases from the crop and livestock system is already accepted as a main cause of climate change. The objective of this study is to quantify greenhouse gas (GHG) emission from a farm of such a nature in the North China Plain. The life-cycle-based assessment method was used to estimate GHG emission during the operation of the farm by referring to the calculation methodology and emission coefficients specified in the “IPCC 2006 National Guide for and List of GHG” . Results show that the annual total GHG emission from the farm was 32 528.02 t (CO2-equivalence, the same below), among which the farming system contributed 28.09%, and the livestock system did 71.91%. During the operation of the farm, the processes of livestock waste handling and storage, animal feed production and processing, intestinal fermentation and nitrogen production and application were the main sources of GHG emission, contributing 34.66%, 21.24%, 15.48% and 20.08% to the total, respectively. The production of 1 kg of wheat and maize grains emitted 1 059.39 and 411.92 kg, respectively; the production of 1 kg of raw milk and 1 kg of fat-protein corrected milk (FPCM) did 1.04 and 1.14 kg, respectively, which was lower than the average of the world; and production of 1 kg of live pig and beef cattle did 2.58 and 10.00 kg, respectively, similar to those from other intensive animal farms in the country. Scenario analysis shows that to reduce N (fertilizer) application rate, improve the capacity of handling and treating livestock waste, intensify N management and modify feed composition may directly or indirectly mitigate GHG emissions from such farms.

mixed farm; farm level; greenhouse gas; emission reduction potential

2016-04-18

國(guó)家科技支撐計(jì)劃(2012BAD14B07-06-02)

X511

A

1673-4831(2017)03-0207-08

10.11934/j.issn.1673-4831.2017.03.003

石鵬飛(1989—),男,陜西榆林人,碩士生,主要研究方向?yàn)榧s持續(xù)農(nóng)作制度。E-mail： spf1023@sina.com

① 通信作者E-mail： guiyanwang@sina.com