張亦濤,劉宏斌,王洪媛,翟麗梅,劉 申,雷秋良,任天志

1 農(nóng)業(yè)部面源污染控制重點(diǎn)實(shí)驗(yàn)室, 中國(guó)農(nóng)業(yè)科學(xué)院農(nóng)業(yè)資源與農(nóng)業(yè)區(qū)劃研究所, 北京 100081 2 農(nóng)業(yè)部環(huán)境保護(hù)科研監(jiān)測(cè)所,天津 300191

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農(nóng)田施氮對(duì)水質(zhì)和氮素流失的影響

張亦濤1,劉宏斌1,王洪媛1,翟麗梅1,劉 申1,雷秋良1,任天志2,*

1 農(nóng)業(yè)部面源污染控制重點(diǎn)實(shí)驗(yàn)室, 中國(guó)農(nóng)業(yè)科學(xué)院農(nóng)業(yè)資源與農(nóng)業(yè)區(qū)劃研究所, 北京 100081 2 農(nóng)業(yè)部環(huán)境保護(hù)科研監(jiān)測(cè)所,天津 300191

基于ISI Web of Science數(shù)據(jù)庫(kù),利用文獻(xiàn)計(jì)量學(xué)方法分析了自1957年以來(lái)各國(guó)在農(nóng)田氮流失領(lǐng)域的研究發(fā)展態(tài)勢(shì),綜述了農(nóng)田氮流失特征及氮流失防控措施。結(jié)果表明,目前各國(guó)對(duì)農(nóng)田氮流失的研究主要集中在施氮對(duì)水體水質(zhì)的污染和監(jiān)測(cè)方法上,涉及的關(guān)鍵詞主要有Groundwater、Water quality、Surface water、Nitrate pollution、Eutrophication、Contamination、Nonpoint source pollution、Lysimeter、Runoff、Subsurface drainage等。中國(guó)、美國(guó)和加拿大等農(nóng)業(yè)大國(guó)的研究機(jī)構(gòu)在這一領(lǐng)域的研究成果最多發(fā)文量最多的期刊主要分布在荷蘭、美國(guó)和中國(guó)。文獻(xiàn)分析表明,受降水、地形、土壤、施肥等諸多管理措施的影響,不同區(qū)域的農(nóng)田氮流失量差別很大,中國(guó)各類(lèi)農(nóng)田的氮流失量(13.7—347 kg/hm2)明顯高于歐美國(guó)家(4—107 kg/hm2)。我國(guó)單位面積化肥(357.3 kg/hm2)和氮肥(165.1 kg/hm2)施用量均遠(yuǎn)高于世界平均用量(87.5 kg/hm2和52.9 kg/hm2),當(dāng)季氮肥利用率(17%)卻明顯低于世界平均水平(58%),表明氮肥施用過(guò)量且利用率過(guò)低是造成氮流失的關(guān)鍵因素。綜合分析農(nóng)田氮流失防控措施發(fā)現(xiàn),從源頭控制氮流失是最有效的措施,優(yōu)化農(nóng)藝管理措施和氮遷移過(guò)程攔截等分別可減少15%—92%、46%—77%的氮素流失,其中針對(duì)農(nóng)田適宜施氮量的研究最多。然而,面對(duì)糧食生產(chǎn)需求與資源短缺、水體水質(zhì)持續(xù)惡化的現(xiàn)狀,未來(lái)的研究重點(diǎn)應(yīng)從簡(jiǎn)單的表觀(guān)平衡向整個(gè)農(nóng)田生態(tài)系統(tǒng)的氮素循環(huán)過(guò)程轉(zhuǎn)變,更為迫切的是加快探索以水質(zhì)保護(hù)為目標(biāo)的化肥氮施用閾值(造成環(huán)境污染的臨界施氮量),并推廣示范這些有效的氮流失防控措施。

農(nóng)田施氮；Web of Science；水體水質(zhì)；氮流失；防控措施；施氮閾值

A bibliometric analysis of status and trend of international research on field nitrogen application effects on nitrogen losses and water quality

氮是作物生長(zhǎng)和產(chǎn)量形成的最重要營(yíng)養(yǎng)元素,氮肥施用為滿(mǎn)足全球70億人口的糧食需求做出了突出貢[1],農(nóng)田氮肥施用對(duì)發(fā)達(dá)國(guó)家糧食增產(chǎn)的貢獻(xiàn)率在40%以上[2],對(duì)發(fā)展中國(guó)家糧食增產(chǎn)貢獻(xiàn)率高達(dá)55%[3]。迫于人口持續(xù)增長(zhǎng)對(duì)糧食需求的壓力,農(nóng)田生態(tài)系統(tǒng)氮素投入越來(lái)越多,然而,農(nóng)田氮素利用率卻逐年下降,投入的過(guò)量氮素或者殘留在土壤中,或以氨、氧化亞氮的形式揮發(fā),或以徑流、淋溶等方式進(jìn)入水體,即使是殘留在土壤中的氮素,最終也會(huì)以揮發(fā)或流失的形式進(jìn)入環(huán)境[4],造成了嚴(yán)重的環(huán)境風(fēng)險(xiǎn)或直接的環(huán)境污染。然而,作物對(duì)氮素的利用效率受氣候、土壤、農(nóng)田管理等多因素的影響,當(dāng)前全球大多數(shù)作物種植系統(tǒng)的氮盈余量大[5],氮肥利用率低[6],水溶性氮流失及氣態(tài)氮損失量高[7],農(nóng)田氮流失嚴(yán)重,并成為農(nóng)區(qū)地表水富營(yíng)養(yǎng)化和地下水硝酸鹽污染的重要原因[8-9]。

過(guò)量施氮及施氮后的損失造成了嚴(yán)重的環(huán)境問(wèn)題[10],氮素管理與環(huán)境質(zhì)量及人類(lèi)健康的關(guān)系受到了廣泛的關(guān)注,多年來(lái),相關(guān)研究論文發(fā)表數(shù)量持續(xù)增長(zhǎng)。文獻(xiàn)計(jì)量學(xué)是對(duì)文獻(xiàn)進(jìn)行定量分析研究的科學(xué),被廣泛應(yīng)用于分析各種學(xué)科研究的科研成果和研究趨勢(shì)[11- 14]。ISI (Institute for Scientific Information)Web of Science數(shù)據(jù)庫(kù)收錄了全球8700多種各學(xué)科領(lǐng)域的領(lǐng)先期刊的SCI(Science Citation Index)論文,覆蓋面最廣,是文獻(xiàn)計(jì)量分析最常用的數(shù)據(jù)庫(kù)[15]。針對(duì)特定領(lǐng)域研究的文獻(xiàn)計(jì)量分析可以多方面的揭示各領(lǐng)域研究發(fā)展態(tài)勢(shì)和研究熱點(diǎn)問(wèn)題,為科研工作者探索學(xué)科新方向提供依據(jù)。

本文將從農(nóng)田施氮對(duì)水體水質(zhì)的影響、氮流失影響因素及防控措施等多個(gè)角度,探討農(nóng)田氮流失(農(nóng)田向水體遷移損失的那部分氮,不包括氣態(tài)形式的氮損失)對(duì)水體水質(zhì)的影響發(fā)展態(tài)勢(shì),揭示影響氮素流失的主要影響因素,分析當(dāng)前有效的氮流失防控措施,并明確優(yōu)化氮肥施用量是從源頭控制氮素流失的最有效措施之一,為確定基于水質(zhì)保護(hù)的化肥氮施用閾值(即水質(zhì)污染突變時(shí)的農(nóng)田施氮量)提供依據(jù)。

1 農(nóng)田施氮對(duì)水體水質(zhì)影響的文獻(xiàn)計(jì)量分析

農(nóng)田施用的氮肥除被作物吸收利用外,剩余氮素大部分以揮發(fā)、淋溶或徑流等形式損失進(jìn)入大氣和水體[16],硝態(tài)氮和銨態(tài)氮是流失氮素的主要形態(tài),水分?jǐn)_動(dòng)產(chǎn)生的懸浮土壤顆粒及其溶出的養(yǎng)分可隨地表徑流水遷移流失[17],而由水分溶解的土壤氮也可垂直向下遷移出根區(qū)[18]。

早在19世紀(jì),科學(xué)家們就注意到了氮素流失帶來(lái)的環(huán)境問(wèn)題,并將用于研究水分平衡的滲濾池技術(shù)應(yīng)用到了元素的淋失研究[19],此后100a間研究的主要內(nèi)容是對(duì)養(yǎng)分淋失量及其形態(tài)進(jìn)行觀(guān)測(cè),但并未深入研究淋洗的剖面特征和動(dòng)態(tài)。20世紀(jì)40年代以來(lái),氮肥大量施用造成的嚴(yán)重環(huán)境問(wèn)題凸顯出來(lái),引發(fā)了70年代以來(lái)的氮素問(wèn)題研究熱潮,農(nóng)田氮素遷移逐漸受到重視,15N示蹤技術(shù)開(kāi)始應(yīng)用于土壤肥料效應(yīng)研究,此后科學(xué)家開(kāi)始關(guān)注區(qū)域尺度上的氮素流失情況,并對(duì)影響流失的因素和有效控制措施進(jìn)行了深入研究和模擬,同時(shí)多學(xué)科交叉合作日益增多,并形成了諸多新興研究領(lǐng)域。1976年,美國(guó)最早提出了面源污染的概念,并進(jìn)行了面源污染研究[20- 21]；20世紀(jì)80年代初,我國(guó)湖泊、水庫(kù)富營(yíng)養(yǎng)化調(diào)查和河流水質(zhì)規(guī)劃是中國(guó)面源污染研究的重要開(kāi)端,但該時(shí)期我國(guó)農(nóng)田肥料投入量并未顯著增加,農(nóng)田養(yǎng)分的流失監(jiān)測(cè)也未作為研究的重點(diǎn),然而隨著氮肥施用量的不斷增加和農(nóng)田灌溉條件的改善,面源污染問(wèn)題日益突出,相關(guān)研究迅速發(fā)展起來(lái),自20世紀(jì)90年代起,我國(guó)的農(nóng)田面源污染實(shí)地監(jiān)測(cè)也開(kāi)展起來(lái),氮流失問(wèn)題備受重視[22]。

以ISI Web of Science數(shù)據(jù)庫(kù)的全部期刊為檢索對(duì)象,限定發(fā)表時(shí)間為1957年至2014年8月,對(duì)“農(nóng)田氮肥施用”主題的SCI論文進(jìn)行檢索、數(shù)據(jù)清理、文獻(xiàn)分類(lèi)和主題分析,檢索策略：(TOPIC: ((Farmland or field or agriculture or farming) and (“nitrogen fertiliz*” or “N fertiliz*” or“fertiliz* nitrogen” or “fertiliz* N”))),共檢索出全部論文7460篇,然后從7460篇論文的關(guān)鍵詞中檢索出與“水體水質(zhì)”相關(guān)的文獻(xiàn)(共305篇),此類(lèi)文獻(xiàn)主要涉及氮肥施用對(duì)地下水、地表水水質(zhì)的影響及其施用造成的硝酸鹽污染、水體富營(yíng)養(yǎng)化等。

對(duì)檢索出的相關(guān)文獻(xiàn)利用Excel統(tǒng)計(jì)數(shù)據(jù)信息,利用高頻關(guān)鍵詞和相關(guān)關(guān)系圖對(duì)研究熱點(diǎn)進(jìn)行研究分析,采用發(fā)文數(shù)量和被引頻次對(duì)研究機(jī)構(gòu)、出版期刊等進(jìn)行分析,統(tǒng)計(jì)分析過(guò)程中均選擇第一作者、第一研究機(jī)構(gòu)。利用湯森路透公司研發(fā)的TDA(Thomson Data Analyzer)軟件,將主題關(guān)鍵詞與全部關(guān)鍵詞進(jìn)行相關(guān)分析組成相互關(guān)系數(shù)矩陣,并據(jù)此繪制相互關(guān)系圖,相關(guān)關(guān)系圖揭示了各關(guān)鍵詞之間關(guān)聯(lián)性的緊密程度,圖中點(diǎn)的大小表示包含這一關(guān)鍵詞的文獻(xiàn)量多少,點(diǎn)之間線(xiàn)的粗細(xì)表示兩個(gè)關(guān)鍵詞之間的相關(guān)程度,線(xiàn)越粗相關(guān)程度越緊密。

1.1 研究熱點(diǎn)

農(nóng)田氮素施用對(duì)水體水質(zhì)的影響研究中涉及的高頻關(guān)鍵詞主要涉及到與水體類(lèi)型相關(guān)的如Groundwater、Water quality、Surface water、Wastewater等,與水體污染相關(guān)的如Nitrate pollution、Eutrophication、Contamination、Nonpoint source pollution、Nitrogen pollution等,與含氮污染物相關(guān)的如Nitrate concentration、Nitrogen availability、Nitrate nitrogen、Nitrate-N等,還有與氮素流失監(jiān)測(cè)相關(guān)的Runoff、Lysimeter、Subsurface drainage等(表1)。通過(guò)繪制這些高頻詞之間的相關(guān)關(guān)系圖,發(fā)現(xiàn)各主題詞之間的關(guān)聯(lián)關(guān)系(圖1),地下水(Groundwater)、水質(zhì)(Water quality)、氮(Nitrate)、磷(Phosphorus)、農(nóng)業(yè)(Agriculture)、施肥(Fertilization)、污染(Pollution；Contamination)和環(huán)境(Environment)之間關(guān)聯(lián)密切；說(shuō)明農(nóng)田化肥的施用與面源污染尤其是水體水質(zhì)是存在密切聯(lián)系的,當(dāng)前的農(nóng)田施肥已經(jīng)導(dǎo)致了水體中養(yǎng)分含量的變化。此外,水稻田(Paddy field)的氮素?fù)p失(Nitrogen loss)以及氨(Ammonia)的關(guān)聯(lián)關(guān)系也較為集中。

1.2 研究機(jī)構(gòu)

開(kāi)展農(nóng)田氮肥施用對(duì)水體水質(zhì)研究的機(jī)構(gòu)很多,但發(fā)表SCI論文最多的10個(gè)研究機(jī)構(gòu)主要分布北美和亞洲的中國(guó),其中有5家美國(guó)研究機(jī)構(gòu)、4家中國(guó)研究機(jī)構(gòu)、1家加拿大研究機(jī)構(gòu)(表2)。中國(guó)科學(xué)院在該領(lǐng)域發(fā)表了26篇SCI研究論文,排名全球第一,美國(guó)農(nóng)業(yè)部排名第二,發(fā)表SCI論文22篇,加拿大農(nóng)業(yè)及農(nóng)業(yè)食品部和中國(guó)農(nóng)業(yè)大學(xué)排名并列第三,各發(fā)表SCI論文10篇。這些關(guān)注農(nóng)田氮肥施用與水體水質(zhì)關(guān)系的研究機(jī)構(gòu)主要分布在農(nóng)田面積大、農(nóng)業(yè)生產(chǎn)活動(dòng)頻繁的國(guó)家,這些國(guó)家的農(nóng)田氮素投入均很大,而作物每年從農(nóng)田帶走的氮素卻極其有限,部分農(nóng)田氮流失進(jìn)入水體并不斷累積從而導(dǎo)致水質(zhì)下降,直接威脅人們的飲水安全,因此備受關(guān)注。

表1 水體水質(zhì)主題前20位關(guān)鍵詞頻詞

表2 水體水質(zhì)主題發(fā)文量前10位的機(jī)構(gòu)

1.3 主流期刊和高被引論文

刊發(fā)農(nóng)田氮肥施用對(duì)水體水質(zhì)影響研究論文排名前10位的英文期刊主要在歐美國(guó)家,中國(guó)的優(yōu)秀英文期刊也對(duì)這一研究領(lǐng)域較為關(guān)注(表3),從期刊發(fā)文量來(lái)看,發(fā)文量最多的3個(gè)期刊均來(lái)自荷蘭,分別是AGRICULTURAL WATER MANAGEMENT (21篇)、AGRICULTURE ECOSYSTEMS & ENVIRONMENT(21篇)和NUTRIENT CYCLING IN AGROECOSYSTEMS(13篇),來(lái)自中國(guó)的PEDOSPHERE刊發(fā)了10篇相關(guān)文章,排在了并列第四位。歐美國(guó)家之所以重視這一領(lǐng)域研究論文的刊發(fā),一方面在于其研究水平較高,另一方面在于發(fā)達(dá)國(guó)家對(duì)于生態(tài)環(huán)境與人類(lèi)健康關(guān)系的關(guān)注；歐美國(guó)家的水體水質(zhì)也曾經(jīng)歷了不斷惡化的階段,但在農(nóng)業(yè)面源污染的概念提出以來(lái),農(nóng)田施氮與人體健康的關(guān)系也備受關(guān)注,并出臺(tái)了一系列防控措施,最具代表性的就是歐盟頒布并實(shí)施的《硝酸鹽法令》,一些國(guó)家對(duì)特定農(nóng)田、特定肥料的用量也均有限制施用標(biāo)準(zhǔn)。

該研究領(lǐng)域SCI論文被引頻次排名前五位的文章主要出自美國(guó)、新西蘭、中國(guó)和以色列(表4),被引頻次最高的文章是波士頓大學(xué)的Valiela, I于1997年在《ECOLOGICAL APPLICATIONS》雜志上發(fā)表的論文《Nitrogen loading from coastal watersheds to receiving estuaries: New method and application》,被引用了220次,該文詳述了估算入湖負(fù)荷的新方法。新西蘭林肯大學(xué)的Di, HJ綜述了各類(lèi)型土地利用方式的硝態(tài)氮淋失,闡述了合理施氮減少硝態(tài)氮淋失的重要性,其論文被引用了152次。中國(guó)農(nóng)業(yè)大學(xué)的Ju, XT研究了中國(guó)山東地區(qū)作物系統(tǒng)的地下水硝態(tài)氮濃度差異,指出了氮肥過(guò)量施用可能是造成地下水硝態(tài)氮濃度超標(biāo)的重要原因,其論文被引用了124次。中國(guó)農(nóng)業(yè)大學(xué)Liu, XJ教授詳述了不同施氮條件下,深層(0—300 cm)土壤硝態(tài)

圖1 水體水質(zhì)主題相關(guān)關(guān)系圖Fig.1 Affinity diagram on the topic of water quality

氮的多年分布特征,指出硝態(tài)氮淋失出100 cm是華北小麥-玉米輪作氮損失的主要途徑,其論文被引用了103次。以色列理工學(xué)院的Shaviv, A綜述了緩控釋肥的農(nóng)學(xué)效應(yīng)和環(huán)境效應(yīng),闡明了控釋肥施用對(duì)作物生長(zhǎng)的促進(jìn)作用,也詳述了氮肥施用(其中包括氮淋失)對(duì)環(huán)境的不利影響,這有助于我們?nèi)嬲J(rèn)識(shí)肥料效應(yīng),其論文被引用了101次。

表3 水體水質(zhì)主題發(fā)文量前10位的期刊

表4 水體水質(zhì)主題排名前5位熱點(diǎn)論文

2 農(nóng)田氮流失量及其影響因素

受地形地貌、土地利用、農(nóng)田管理措施等多種因素的影響,不同地區(qū)研究中的氮素流失量差別很大,同一地區(qū)不同土壤、不同種植模式之間的氮流失量也有較大差異,整體而言,世界各國(guó)氮素?fù)p失量均表現(xiàn)為隨施氮量增加而顯著增加[23- 24]。中國(guó)農(nóng)田施氮量普遍較高,由此造成的氮流失問(wèn)題也很?chē)?yán)重(表5),相對(duì)中國(guó)而言,英、美等發(fā)達(dá)國(guó)家的關(guān)于農(nóng)田氮素流失的研究中很少關(guān)注高量施氮,這可能是這些國(guó)家已經(jīng)采取了一系列措施從源頭上降低了過(guò)量施氮,較低的施氮條件下,其氮素流失量也相對(duì)較少。

相對(duì)較少,可能與這些國(guó)家較早地關(guān)注農(nóng)業(yè)面源污染,并積極采取了防控措施有關(guān),尤其是頒布的限制農(nóng)田氮素施用的法令,在減少氮流失方面效果顯著。

氮素在土壤中的殘留和累積是其流失的前提和物質(zhì)基礎(chǔ)；進(jìn)入農(nóng)田的水分溶解并攜帶土壤氮向不同方向遷移,最終將其帶出農(nóng)田或根區(qū)從而導(dǎo)致氮素流失,因此,凡是能夠改變土壤氮素累積和水分運(yùn)移的因素都會(huì)影響氮素流失的發(fā)生。農(nóng)田氮素流失發(fā)生過(guò)程受多種因素影響[41],農(nóng)田固有的特點(diǎn)如地形地貌、土壤質(zhì)地等影響氮素的本底流失,而種植模式、施肥、灌溉等管理措施是導(dǎo)致氮素流失量變化的直接原因,并且各影響因素中,只有部分農(nóng)田管理措施是可以控制調(diào)節(jié)的,固有的氣候氣象和土壤條件等是無(wú)法改變的。

降雨是產(chǎn)生氮流失的先決條件,雨強(qiáng)、時(shí)長(zhǎng)等直接決定了徑流或淋溶量的大小。通常情況下,氮素流失主要發(fā)生在降雨或灌溉集中的季節(jié),強(qiáng)降雨和較為常見(jiàn)的大水漫灌會(huì)為氮素遷移提供便利條件,是導(dǎo)致氮流失發(fā)生的重要時(shí)期[41- 42]。地形影響地表水熱條件的重新分配,尤其坡度能直接支配地表徑流,是影響土壤氮素流失最重要的地形因素。當(dāng)坡度較小時(shí),氮主要通過(guò)隨水向下滲透而淋失,隨徑流流失量較少；當(dāng)坡度較大時(shí),表層土壤易遭到侵蝕,氮主要通過(guò)隨地表水流動(dòng)遷移而發(fā)生徑流流失,向下淋失較少。在一定范圍內(nèi),坡度越大,氮素隨水土流失越嚴(yán)重[43]。此外,氮素流失量與坡度的關(guān)系還受植被覆蓋、坡長(zhǎng)、徑流時(shí)間等多種因素影響[44- 45]。

表5 國(guó)內(nèi)外典型種植模式農(nóng)田氮流失量差異

土壤質(zhì)地決定了水分的滲透性[46],土壤大孔隙是氮素遷移的主要通道,土壤質(zhì)地越粗、孔隙越多,淋溶損失越嚴(yán)重；卵石和砂礫土中氮素的流失量較大,而粘質(zhì)和粉砂質(zhì)土壤反硝化作用較強(qiáng),加之氮淋溶速度很慢,因而淋失量較小[46]。偶爾在粘質(zhì)土壤中觀(guān)測(cè)到的較大的硝態(tài)氮淋失可能也是由于大孔隙的存在造成的[46]。不同的土地利用方式導(dǎo)致不同程度的水土和養(yǎng)分流失,相同土壤類(lèi)型下,糧田的氮負(fù)荷要高于果園和林地[46],而種植蔬菜的農(nóng)田養(yǎng)分流失量明顯高于作物輪作種植模式[47]。

施氮量、氮肥種類(lèi)、施用時(shí)期等都與氮流失量密切相關(guān),施氮量與氮流失量之間存在顯著的正相關(guān)關(guān)系[48],對(duì)氮素徑流的發(fā)生起主導(dǎo)作用,正常水文年,施氮量的增加會(huì)顯著增加徑流水的氮含量[25]。適當(dāng)?shù)挠袡C(jī)肥處理與化肥處理相比可顯著減少氮素流失,緩控釋肥可以控制氮素釋放,提高氮素利用率,進(jìn)一步降低氮素流失風(fēng)險(xiǎn)[49]。氮素流失多發(fā)生在多雨季節(jié),施肥時(shí)間與產(chǎn)流時(shí)間越近,徑流硝態(tài)氮濃度越高,因此避開(kāi)雨期施肥可顯著降低氮素流失量[50],同時(shí)水肥耦合也能明顯減少氮素流失[51],優(yōu)化施肥的同時(shí)優(yōu)化灌溉更能實(shí)現(xiàn)經(jīng)濟(jì)和環(huán)境效益雙贏(yíng)[52]。

3 氮肥施用對(duì)氮流失的影響

化肥尤其是氮肥為我國(guó)糧食持續(xù)增產(chǎn)做出了重要貢獻(xiàn)(圖2)。我國(guó)糧食產(chǎn)量由1979年的3.32億t增加到2012年的5.90億t,單產(chǎn)也從2,237 kg/hm2增加到3,608 kg/hm2。2012年,全球化肥和氮肥消費(fèi)量分別為1.70億t和1.03億t,單位播種面積用量分別為87.5 kg/hm2和52.9 kg/hm2,而我國(guó)化肥和氮肥用量分別為5839萬(wàn)t、2698萬(wàn)t,單位播種面積化肥(357.3 kg/hm2)和氮肥(165.1 kg/hm2)施用量均遠(yuǎn)高于世界平均用量。全球主要糧食作物(水稻、小麥、玉米)產(chǎn)量25.5億t,其中中國(guó)生產(chǎn)了5.41億t[53],我國(guó)以世界26%的氮肥消費(fèi)量生產(chǎn)了世界21%的糧食,較低的氮肥利用率,勢(shì)必造成資源的浪費(fèi)和潛在的環(huán)境風(fēng)險(xiǎn)。

圖2 單位農(nóng)田種植面積肥料用量和糧食產(chǎn)量(1979—2012)(中國(guó)統(tǒng)計(jì)年鑒,2013)Fig.2 Fertilizer rate and food production of per hectare farmland (1979—2102) (China Statistical Yearbook, 2013)

目前全球氮肥用量相比20世紀(jì)增加了100倍,其中60%的氮肥被用于主要糧食作物的生產(chǎn)。據(jù)估計(jì),到2050年世界人口將達(dá)到93億,對(duì)糧食的需求將增加50%—70%,如果氮肥利用率不能明顯提高,氮肥總投入量需要在目前的基礎(chǔ)上再增加1倍才能滿(mǎn)足人類(lèi)對(duì)糧食的需求[54]。中國(guó)糧食作物氮肥利用率遠(yuǎn)低于世界平均水平,有研究指出,我國(guó)小麥和玉米氮肥利用率分別為28%和26%[55],而世界平均水平為54%和63%[18,54,56]。相應(yīng)地,我國(guó)土壤氮素殘留率較高,但下茬作物對(duì)殘留的氮素利用有限[57],大多氮素最終流失出農(nóng)田,進(jìn)入環(huán)境導(dǎo)致生態(tài)系統(tǒng)功能退化。目前,農(nóng)業(yè)已成為陸地生態(tài)系統(tǒng)中重要的氮素排放源,也是大多數(shù)河流湖泊水體污染主因之一,因此,農(nóng)田氮素流失規(guī)律及防控措施研究應(yīng)受到重視[4,58]。

4 農(nóng)田氮流失防控措施

大量研究表明農(nóng)田氮素流失是目前諸多水體水質(zhì)惡化的重要原因,源頭控制和氮遷移過(guò)程攔截是控制農(nóng)田氮素流失的主要策略。優(yōu)化農(nóng)藝管理措施,在源頭上避免土壤擾動(dòng)造成的水土遷移,減少不合理灌溉造成的農(nóng)田排水,也可顯著減少氮素流失；在氮素出田至進(jìn)入水體遷移過(guò)程中,利用人工濕地、緩沖帶等工程措施,可以進(jìn)一步減少進(jìn)入水體的氮量。研究表明,合理的農(nóng)田管理措施如優(yōu)化施肥和種植結(jié)構(gòu)、保護(hù)耕地、節(jié)水灌溉等可減少15%—92%的氮素流失,而緩沖帶、人工濕地、徑流攔截等遷移過(guò)程控制措施可減少50%—77%的氮素?fù)p失(表6)。對(duì)于何種措施防控效果更好,并沒(méi)有嚴(yán)格的評(píng)價(jià)標(biāo)準(zhǔn)。氮素遷移過(guò)程控制措施大都是工程技術(shù)措施,建設(shè)難度較高,而我國(guó)農(nóng)田面積大,地形復(fù)雜,緩沖帶、人工濕地等氮素遷移過(guò)程阻斷工程建設(shè)普及難度較大[59]。因地制宜地采取合理的農(nóng)田管理措施,尤其是優(yōu)化施肥、優(yōu)化種植結(jié)構(gòu)、保護(hù)性耕作及節(jié)水灌溉[60- 62]等措施更易推廣普及。

表6 氮素流失防控措施

優(yōu)化農(nóng)田施氮量可從源頭上減少氮隨水流失的發(fā)生機(jī)率[64,69],是眾多防控措施之中最節(jié)約成本、節(jié)省勞力、最易被農(nóng)民接受的方法[70]我國(guó)農(nóng)田面積大而單戶(hù)農(nóng)田面積較小,受氣候、地形、種植模式、政策等諸多因素的影響,基于不同目的確定田塊尺度適宜施氮量的方法多種多樣(表7)。以滿(mǎn)足作物生長(zhǎng)發(fā)育過(guò)程中氮素需求為目的方法,包括利用葉綠素儀監(jiān)測(cè)作物長(zhǎng)勢(shì)、根據(jù)土壤無(wú)機(jī)氮含量進(jìn)行氮素實(shí)時(shí)監(jiān)測(cè)調(diào)控、借助長(zhǎng)期定位監(jiān)測(cè)建立經(jīng)驗(yàn)施肥模型等,此類(lèi)方法的特點(diǎn)是可以指導(dǎo)何時(shí)施氮,確定經(jīng)驗(yàn)施氮量,間接緩解了環(huán)境污染風(fēng)險(xiǎn),但是這一方法是以滿(mǎn)足作物養(yǎng)分需求為主,并不直接考慮環(huán)境效應(yīng)。以獲得最高產(chǎn)量或經(jīng)濟(jì)效益為目的的方法,包括測(cè)土配方施肥、建立氮肥-產(chǎn)量或氮肥-經(jīng)濟(jì)效益效應(yīng)曲線(xiàn)等,其特點(diǎn)是可以通過(guò)明顯的突變點(diǎn)確定基于作物最高產(chǎn)量或經(jīng)濟(jì)效益的施氮量。以氮肥環(huán)境風(fēng)險(xiǎn)估算為目的的方法,包括氮淋失潛力估算、各種氮素?fù)p失風(fēng)險(xiǎn)估算模型等,其中采取表觀(guān)平衡法核算農(nóng)田氮素投入與支出比例,減少土壤氮素盈余是目前最常用的確定適宜施氮量的方法[23,71],其特點(diǎn)是沒(méi)有明顯的突變點(diǎn),僅局限于風(fēng)險(xiǎn)評(píng)估,也就是環(huán)境風(fēng)險(xiǎn)之間的相互比較,不能直接確定造成環(huán)境污染突變的施氮臨界值。以執(zhí)行相關(guān)規(guī)章制度為目的方法,包括執(zhí)行相關(guān)環(huán)境保護(hù)規(guī)章、根據(jù)環(huán)保法規(guī)限定施氮量及施氮時(shí)期[72- 73]等,但這一方法是建立在對(duì)某一環(huán)境指標(biāo)有明確的限制性規(guī)定基礎(chǔ)上的,如歐盟實(shí)施已久的《硝酸鹽法案》中規(guī)定有機(jī)肥氮用量不能高于170 kg/hm2,這也是農(nóng)田施氮與環(huán)境目標(biāo)聯(lián)系最為密切的確定施氮臨界值方法,但這一方法多用于后期監(jiān)測(cè)調(diào)整管理措施。以上各種方法均是在田塊尺度確定的適宜施氮量,然而在區(qū)域尺度上仍然缺乏較統(tǒng)一的施氮量,中國(guó)科學(xué)院南京土壤研究所的朱兆良院士首先提出了區(qū)域平均適宜施氮量的概念[74],并實(shí)地驗(yàn)證了區(qū)域平均適宜施氮量的合理性和可行性[75],這為區(qū)域尺度氮肥管理提供了參考。

表7 農(nóng)田適宜施氮量的確定方法

5 問(wèn)題與展望

現(xiàn)有研究中所闡述的農(nóng)田氮素流失量多數(shù)為出田氮量,而對(duì)于流失出田的氮素如何遷移進(jìn)入水體以及這一遷移過(guò)程中的氮形態(tài)變化特征仍不清楚；此外,淋失出根區(qū)或徑流出農(nóng)田的氮素雖然并未直接進(jìn)入環(huán)境,但這些氮素難以再被利用而成為嚴(yán)重的污染源,因此,今后的研究除了要精確量化農(nóng)田氮素出田外,還要進(jìn)一步闡明氮素在出田至目標(biāo)水體這一階段內(nèi)的變化特征,并積極探索消除農(nóng)田氮流失環(huán)境風(fēng)險(xiǎn)的有效措施。

農(nóng)田氮流失的發(fā)生及其流失量受多種因素影響,分析當(dāng)前氮肥施用現(xiàn)狀,揭示氮素向水體的遷移規(guī)律,有助于制定合理、有效的針對(duì)性氮流失防控措施。諸多農(nóng)田管理措施中,施氮量是最直接、最易控制的關(guān)鍵管理措施,在保證一定糧食產(chǎn)量的基礎(chǔ)上,確定基于環(huán)境安全尤其是水質(zhì)保護(hù)的合理農(nóng)田施氮量是可行的,也是平衡產(chǎn)量需求與環(huán)境污染之間矛盾的有效措施。然而,當(dāng)前種植業(yè)面源污染愈加嚴(yán)重,為防治由此造成的水體水質(zhì)持續(xù)惡化,迫切需要制定以水質(zhì)保護(hù)為目標(biāo)的農(nóng)田氮肥施用閾值(造成水質(zhì)污染的施氮臨界值),全國(guó)各大高校及科研院所也都為實(shí)現(xiàn)這一目標(biāo)不斷努力,但是目前在這一研究方向上并無(wú)突破。

目前,確定田塊尺度適宜施氮量的方法較多,但在區(qū)域尺度上,隨著農(nóng)田面源氮污染問(wèn)題日益突出,控制區(qū)域氮肥用量越來(lái)越重要,而要解決這一問(wèn)題,應(yīng)當(dāng)建立區(qū)域乃至全國(guó)范圍內(nèi)的農(nóng)業(yè)面源污染監(jiān)測(cè)網(wǎng)絡(luò),在長(zhǎng)期定位監(jiān)測(cè)基礎(chǔ)上,創(chuàng)建合理的面源氮污染核算方法,測(cè)算出種植業(yè)源污染物產(chǎn)生與排放系數(shù),并明確農(nóng)田氮肥施用與水體水質(zhì)的關(guān)系,最終確定導(dǎo)致水體污染的氮肥施用臨界值。

致謝：中國(guó)科學(xué)院文獻(xiàn)情報(bào)中心在文獻(xiàn)檢索和數(shù)據(jù)分析過(guò)程中給予幫助,彭皓老師幫助寫(xiě)作，特此致謝。

[1] Erisman J W, Sutton M A, Galloway J, Klimont Z, Winiwarter W. How a century of ammonia synthesis changed the world. Nature Geoscience, 2008, 1(10): 636- 639.

[2] Malhi S S, Grant C A, Johnston A M, Gill K S. Nitrogen fertilization management for no-till cereal production in the Canadian Great Plains: a review. Soil & Tillage Research, 2001, 60(3/4): 101- 122.

[3] Li S X, Wang Z H, Hu T T, Gao Y J, Stewart B A. Nitrogen in dryland soils of china and its management//Sparks D L, ed. Advances in Agronomy. New York: Academic Press, 2009: 123- 181.

[4] Cameron K C, Di H J, Moir J L. Nitrogen losses from the soil/plant system: a review. Annals of Applied Biology, 2013, 162(2): 145- 173.

[5] Vitousek P M, Naylor R, Crews T, David M B, Drinkwater L E, Holland E, Johnes P J, Katzenberger J, Martinelli L A, Matson P A, Nziguheba G, Ojima D, Palm C A, Robertson G P, Sanchez P A, Townsend A R, Zhang F S. Nutrient imbalances in agricultural development. Science, 2009, 324(5934): 1519- 1520.

[6] Cui Z L, Chen X P, Zhang F S. Current nitrogen management status and measures to improve the intensive wheat-maize system in China. AMBIO, 2010, 39(5/6): 376- 384.

[7] Ju X T, Xing G X, Chen X P, Zhang S L, Zhang L J, Liu X J, Cui Z L, Yin B, Christie P, Zhu Z L, Zhang F S. Reducing environmental risk by improving N management in intensive Chinese agricultural systems. Proceedings of the National Academy of Sciences of the United States of America, 2009, 106(9): 3041- 3046.

[8] Howarth R W. An assessment of human influences on fluxes of nitrogen from the terrestrial landscape to the estuaries and continental shelves of the North Atlantic Ocean. Nutrient Cycling in Agroecosystems, 1998, 52(2/3): 213- 223.

[9] Zhang W L, Tian Z X, Zhang N, Li X Q. Nitrate pollution of groundwater in northern China. Agriculture, Ecosystems & Environment, 1996, 59(3): 223- 231.

[10] Spiertz J H J. Nitrogen, sustainable agriculture and food security. A review. Agronomy for Sustainable Development, 2010, 30(1): 43- 55.

[11] Liu X J, Zhang L, Hong S. Global biodiversity research during 1900- 2009: a bibliometric analysis. Biodiversity and Conservation, 2011, 20(4): 807- 826.

[12] Li J F, Wang M H, Ho Y S. Trends in research on global climate change: A science citation index expanded-based analysis. Global and Planetary Change, 2011, 77(1/2): 13- 20.

[13] Wang M H, Li J F, Ho Y S. Research articles published in water resources journals: A bibliometric analysis. Desalination and Water Treatment, 2011, 28(1/3): 353- 365.

[14] Huang W L, Zhang B G, Feng C P, Li M, Zhang J. Research trends on nitrate removal: a bibliometric analysis. Desalination and Water Treatment, 2012, 50(1/3): 67- 77.

[15] Monge-Nájera J, Ho Y S. Costa rica publications in the science citation index expanded: a bibliometric analysis for 1981- 2010. Revista de Biologia Tropical, 2012, 60(4): 1649- 1661.

[16] Valkama E, Salo T, Esala M, Turtola E. Nitrogen balances and yields of spring cereals as affected by nitrogen fertilization in northern conditions: A meta-analysis. Agriculture, Ecosystems & Environment, 2013, 164: 1- 13.

[17] Carpenter S R, Caraco N F, Correll D L, Howarth R W, Sharpley A N, Smith V H. Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecological Applications, 1998, 8(3): 559- 568.

[18] Sebilo M, Mayer B, Nicolardot B, Pinay G, Mariotti A. Long-term fate of nitrate fertilizer in agricultural soils. Proceedings of the National Academy of Sciences of the United States of America, 2013, 110(45): 18185- 18189.

[19] Fungaroli A A, Steiner R L, Remson I. Design of A Sanitary Landfill Laboratory Lysimeter. 1900.

[20] Peierls B L, Caraco N F, Pace M L, Cole J J. Human influence on river nitrogen. Nature, 1991, 350(6317): 386- 387.

[21] Smith R A, Alexander R B, Wolman M G. Water-quality trends in the nation′s rivers. Science, 1987, 235(4796): 1607- 1615.

[22] Lin K F, Xiang Y L, Liu X F, Pastore G. Loss of nitrogen, phosphorus, and potassium through crop harvests in agroecosystems of Qianjiang, Hubei province, PR China. Critical Reviews in Plant Sciences, 1999, 18(3): 393- 401.

[23] Song X Z, Zhao C X, Wang X L, Li J. Study of nitrate leaching and nitrogen fate under intensive vegetable production pattern in northern China. Comptes Rendus Biologies, 2009, 332(4): 385- 392.

[24] Sogbedji J M, Van Es H M, Yang C L, Geohring L D, Magdoff F R. Nitrate leaching and nitrogen budget as affected by maize nitrogen rate and soil type. Journal of Environmental Quality, 2000, 29(6): 1813- 1820.

[25] Tian Y H, Yin B, Yang L Z, Yin S X, Zhu Z L. Nitrogen runoff and leaching losses during rice-wheat rotations in Taihu Lake Region, China. Pedosphere, 2007, 17(4): 445- 456.

[26] Yu Y L, Xue L H, Yang L Z. Winter legumes in rice crop rotations reduces nitrogen loss, and improves rice yield and soil nitrogen supply. Agronomy for Sustainable Development, 2014, 34(3): 633- 640.

[27] Fang Q X, Yu Q, Wang E L, Chen Y H, Zhang G L, Wang J, Li L H. Soil nitrate accumulation, leaching and crop nitrogen use as influenced by fertilization and irrigation in an intensive wheat-maize double cropping system in the North China Plain. Plant and Soil, 2006, 284(1/2): 335- 350.

[28] Huang M X, Liang T, Ouyang Z, Wang L Q, Zhang C S, Zhou C H. Leaching losses of nitrate nitrogen and dissolved organic nitrogen from a yearly two crops system, wheat-maize, under monsoon situations. Nutrient Cycling in Agroecosystems, 2011, 91(1): 77- 89.

[29] Liang X Q, Xu L, Li H, He M M, Qian Y C, Liu J, Nie Z Y, Ye Y S, Chen Y X. Influence of N fertilization rates, rainfall, and temperature on nitrate leaching from a rainfed winter wheat field in Taihu watershed. Physics and Chemistry of the Earth, Parts A/B/C, 2011, 36(9/11): 395- 400.

[30] Wang T, Zhu B, Kuang F H. Reducing interflow nitrogen loss from hillslope cropland in a purple soil hilly region in southwestern China. Nutrient Cycling in Agroecosystems, 2012, 93(3): 285- 295.

[31] Shepherd M A, Lord E I. Nitrate leaching from a sandy soil: The effect of previous crop and post-harvest soil management in an arable rotation. The Journal of Agricultural Science, 1996, 127(2): 215- 229.

[32] Readman R J, Beckwith C P, Kettlewell P S. Effects of spray application of urea fertilizer at stem extension on winter wheat: N recovery and nitrate leaching. The Journal of Agricultural Science, 2002, 139(1): 11- 25.

[33] Catt J A, Howse K R, Christian D G, Lane P W, Harris G L, Goss M J. Strategies to decrease nitrate leaching in the Brimstone Farm Experiment, Oxfordshire, UK, 1988- 1993: The effects of winter cover crops and unfertilised grass leys. Plant and Soil, 1998, 203(1): 57- 69.

[34] Bjorneberg D L, Kanwar R S, Melvin S W. Seasonal changes in flow and nitrate-N loss from subsurface drains. Transactions of the ASABE, 1996, 39(3): 961- 967.

[35] Baker J L, Timmons D R. Fertilizer management effects on leaching of labeled nitrogen for no-till corn in field lysimeters. Journal of Environmental Quality, 1994, 23(2): 305- 310.

[36] Bakhsh A, Kanwar R S, Baker J L. N-application methods and precipitation pattern effects on subsurface drainage nitrate losses and crop yields. Water, Air, & Soil Pollution, 2010, 212(1/4): 65- 76.

[37] Basso B, Ritchie J T. Impact of compost, manure and inorganic fertilizer on nitrate leaching and yield for a 6-year maize-alfalfa rotation in Michigan. Agriculture, Ecosystems & Environment, 2005, 108(4): 329- 341.

[38] Gehl R J, Schmidt J P, Stone L R, Schlegel A J, Clark G A. In situ measurements of nitrate leaching implicate poor nitrogen and irrigation management on sandy soils. Journal of Environmental Quality, 2005, 34(6): 2243- 2254.

[39] Li C S, Farahbakhshazad N, Jaynes D B, Dinnes D L, Salas W, McLaughlin D. Modeling nitrate leaching with a biogeochemical model modified based on observations in a row-crop field in Iowa. Ecological Modelling, 2006, 196(1/2): 116- 130.

[40] Akkal-Corfini N, Morvan T, Menasseri-Aubry S, Bissuel-Bélaygue C, Poulain D, Orsini F, Leterme P. Nitrogen mineralization, plant uptake and nitrate leaching following the incorporation of (15N)-labeled cauliflower crop residues (Brassicaoleracea) into the soil: a 3-year lysimeter study. Plant and Soil, 2010, 328(1/2): 17- 26.

[41] Kakuturu S, Chopra M, Hardin M, Wanielista M. Total nitrogen losses from fertilized turfs on simulated highway slopes in Florida. Journal of Environmental Engineering-ASCE, 2013, 139(6): 829- 837.

[42] Di H J, Cameron K C, Moore S, Smith N P. Nitrate leaching and pasture yields following the application of dairy shed effluent or ammonium fertilizer under spray or flood irrigation: results of a lysimeter study. Soil Use and Management, 1998, 14(4): 209- 214.

[43] Wang H X, Shi Y, Ma J, Lu C Y, Chen X. Characteristics of non-point source N export via surface runoff from sloping croplands in Northeast China. Advanced Materials Research, 2011, 347- 353: 2302- 2307.

[44] Dorofki M, Elshafie A H, Jaafar O, Karim O A, Abdullah S M S. A GIS-ANN-based approach for enhancing the effect of slope in the modified green-ampt model. Water Resources Management, 2014, 28(2): 391- 406.

[45] Xu L, Marinova D. Resilience thinking: a bibliometric analysis of socio-ecological research. Scientometrics, 2013, 96(3): 911- 927.

[46] Witheetrirong Y, Tripathi N K, Tipdecho T, Parkpian P. Estimation of the effect of soil texture on nitrate-nitrogen content in groundwater using optical remote sensing. International Journal of Environmental Research and Public Health, 2011, 8(8): 3416- 3436.

[47] Karcher S C, VanBriesen J M, Nietch C T. Alternative land-use method for spatially informed watershed management decision making using swaT. Journal of Environmental Engineering, 2013, 139(12): 1413- 1423.

[48] Kim J S, Oh S Y, Oh K Y. Nutrient runoff from a Korean rice paddy watershed during multiple storm events in the growing season. Journal of Hydrology, 2006, 327(1/2): 128- 139.

[49] Clark M J, Zheng Y B. Plant nutrition requirements for an installed sedum-vegetated green roof module system: effects of fertilizer rate and type on plant growth and leachate nutrient content. HortScience, 2013, 48(9): 1173- 1180.

[50] Torbert H A, Gerik T J, Harman W L, Williams J R, Magre M. EPIC Evaluation of the Impact of Poultry Litter Application Timing on Nutrient Losses. Communications in Soil Science and Plant Analysis, 2008, 39(19- 20): 3002- 3031.

[51] Qian X Y, Shen G X, Gu H R, Pugliese M, Gullino M L. Effects of drip fertigation management on nutrient losses and pear production at Chongming Dongtan in Yangtze River Estuary, China. Advanced Materials Research, 2011, 396- 398: 1716- 1724.

[52] Zhang X, Huang G, Bian X, Zhao Q. Effects of root interaction and nitrogen fertilization on the chlorophyll content, root activity, photosynthetic characteristics of intercropped soybean and microbial quantity in the rhizosphere. Plant, Soil and Environment, 2013, 59(2): 80- 88.

[53] FAO. FAOSATA. http://faostat.fao.org/site/339/default.aspx. 2014.

[54] Ladha J K, Pathak H, Krupnik T J, Six J, Van Kessel C. Efficiency of fertilizer nitrogen in cereal production: Retrospects and prospects. Advances in Agronomy, 2005, 87: 85- 156.

[55] 張福鎖, 王激清, 張衛(wèi)峰, 崔振嶺, 馬文奇, 陳新平, 江榮風(fēng). 中國(guó)主要糧食作物肥料利用率現(xiàn)狀與提高途徑. 土壤學(xué)報(bào), 2008, 45(5): 915- 924.

[56] Goulding K W T, Poulton P R, Webster C P, Howe M T. Nitrate leaching from the Broadbalk Wheat Experiment, Rothamsted, UK, as influenced by fertilizer and manure inputs and the weather. Soil Use and Management, 2000, 16(4): 244- 250.

[57] Liang B, Zhao W, Yang X Y, Zhou J B. Fate of nitrogen- 15 as influenced by soil and nutrient management history in a 19-year wheat-maize experiment. Field Crops Research, 2013, 144: 126- 134.

[58] Birgand F, Skaggs R W, Chescheir G M, Gilliam J W. Nitrogen removal in streams of agricultural catchments-A literature review. Critical Reviews in Environmental Science and Technology, 2007, 37(5): 381- 487.

[59] Kuusemets V, Mander ü. Ecotechnological measures to control nutrient losses from catchments. Water Science and Technology, 1999, 40(10): 195- 202.

[60] Wang Q, Li F R, Zhao L, Zhang E H, Shi S L, Zhao W Z, Song W X, Vance M M. Effects of irrigation and nitrogen application rates on nitrate nitrogen distribution and fertilizer nitrogen loss, wheat yield and nitrogen uptake on a recently reclaimed sandy farmland. Plant and Soil, 2010, 337(1/2): 325- 339.

[61] Shan N, Ruan X H, Xu J, Pan Z R. Estimating the optimal width of buffer strip for nonpoint source pollution control in the Three Gorges Reservoir Area, China. Ecological Modelling, 2014, 276: 51- 63.

[62] Cui F, Zheng X H, Liu C Y, Wang K, Zhou Z X, Deng J. Assessing biogeochemical effects and best management practice for a wheat-maize cropping system using the DNDC model. Biogeosciences, 2014, 11(1): 91- 107.

[63] Pappa V A, Rees R M, Walker R L, Baddeley J A, Watson C A. Nitrous oxide emissions and nitrate leaching in an arable rotation resulting from the presence of an intercrop. Agriculture, Ecosystems & Environment, 2011, 141(1/2): 153- 161.

[64] Ruidisch M, Bartsch S, Kettering J, Huwe B, Frei S. The effect of fertilizer best management practices on nitrate leaching in a plastic mulched ridge cultivation system. Agriculture, Ecosystems & Environment, 2013, 169: 21- 32.

[65] Kurothe R S, Kumar G, Singh R, Singh H B, Tiwari S P, Vishwakarma A K, Sena D R, Pande V C. Effect of tillage and cropping systems on runoff, soil loss and crop yields under semiarid rainfed agriculture in India. Soil & Tillage Research, 2014, 140: 126- 134.

[66] Wang L M, Duggin J A, Nie D P. Nitrate-nitrogen reduction by established tree and pasture buffer strips associated with a cattle feedlot effluent disposal area near Armidale, NSW Australia. Journal of Environmental Management, 2012, 99: 1- 9.

[67] Abbassi B, Al-Zboon K, Radaideh J, Wahbeh A. Using constructed wetlands to improve drainage water quality from hydroponics farms. Irrigation and Drainage, 2011, 60(3): 370- 380.

[68] Kovacic D A, David M B, Gentry L E, Starks K M, Cooke R A. Effectiveness of constructed wetlands in reducing nitrogen and phosphorus export from agricultural tile drainage. Journal of Environmental Quality, 2000, 29(4): 1262- 1274.

[69] Min J, Zhang H L, Shi W M. Optimizing nitrogen input to reduce nitrate leaching loss in greenhouse vegetable production. Agricultural Water Management, 2012, 111: 53- 59.

[70] Wang W N, Lu J W, Ren T, Li X K, Su W, Lu M X. Evaluating regional mean optimal nitrogen rates in combination with indigenous nitrogen supply for rice production. Field Crops Research, 2012, 137: 37- 48.

[71] Min J, Zhao X, Shi W M, Xing G X, Zhu Z L. Nitrogen balance and loss in a greenhouse vegetable system in southeastern China. Pedosphere, 2011, 21(4): 464- 472.

[72] Schr?der J J, Neeteson J J. Nutrient management regulations in The Netherlands. Geoderma, 2008, 144(3/4): 418- 425.

[73] Nevens F, Reheul D. Agronomical and environmental evaluation of a long-term experiment with cattle slurry and supplemental inorganic N applications in silage maize. European Journal of Agronomy, 2005, 22(3): 349- 361.

[74] 朱兆良, 張紹林, 徐銀華. 平均適宜施氮量的含義. 土壤, 1986, 18(6): 316- 317.

[75] 晏娟. 太湖地區(qū)稻麥輪作體系氮肥適宜用量及提高其利用效率的研究[D]. 南京: 南京農(nóng)業(yè)大學(xué), 2009.

[76] Hou P, Gao Q, Xie R Z, Li S K, Meng Q F, Kirkby E A, R?mheld V, Müller T, Zhang F S, Cui Z L, Chen X P. Grain yields in relation to N requirement: Optimizing nitrogen management for spring maize grown in China. Field Crops Research, 2012, 129: 1- 6.

[77] Xu X P, He P, Qiu S J, Pampolino M F, Zhao S C, Johnston A M, Zhou W. Estimating a new approach of fertilizer recommendation across small-holder farms in China. Field Crops Research, 2014, 163: 10- 17.

[78] Cui Z L, Chen X P, Zhang F S. Development of regional nitrogen rate guidelines for intensive cropping systems in China. Agronomy Journal, 2013, 105(5): 1411- 1416.

[79] Xia Y Q, Yan X Y. Ecologically optimal nitrogen application rates for rice cropping in the Taihu Lake region of China. Sustainability Science, 2012, 7(1): 33- 44.

[80] Deng J, Zhou Z, Zhu B, Zheng X, Li C, Wang X, Jian Z. Modeling nitrogen loading in a small watershed in southwest China using a DNDC model with hydrological enhancements. Biogeosciences, 2011, 8(10): 2999- 3009.

[81] Aveline A, Rousseau M L, Guichard L, Laurent M, Bockstaller C. Evaluating an environmental indicator: Case study of MERLIN, a method for assessing the risk of nitrate leaching. Agricultural Systems, 2009, 100(1/3): 22- 30.

ZHANG Yitao1, LIU Hongbin1, WANG Hongyuan1, ZHAI Limei1, LIU Shen1, LEI Qiuliang1, REN Tianzhi2,*

1MinistryofAgricultureKeyLaboratoryofNonpointSourcePollutionControl/InstituteofAgriculturalResourcesandRegionalPlanning,ChineseAcademyofAgriculturalSciences,Beijing100081,China

2Agro-EnvironmentalProtectionInstitute,MinistryofAgriculture,Tianjin300191,China

A bibliometric analysis method was used to identify the developmental trend of international research on nitrogen losses in farmlands as affected by nitrogen applications, based on peer-reviewed studies available in the ISI Web of Science since 1957. We also reviewed control and prevention measures for farmland nitrogen loss, with the same method. The bibliometric analysis showed that the current focus of research regarding nitrogen losses worldwide involved assessing and monitoring of the effects of nitrogen fertilization on water pollution and quality. Keywords included Groundwater, Water quality, Surface water, Nitrate pollution, Eutrophication, Contamination, Nonpoint source pollution, Lysimeter, Runoff, and Subsurface drainage, etc. Research institutions that contributed to a large number of research findings are mainly resided in large agricultural countries, including China, United States, and Canada, and the mainstream journals that included most relevant papers are published in the Netherlands, United States, and China. Literature analysis showed that nitrogen losses are site-specific because it can be influenced by precipitation, topography, soil properties, and forms, rates, timing and placement of fertilizers, as well as other management practices. Nitrogen losses in China (13.7—347 kg/hm2) was significantly higher than that of countries in Europe and North America (4—107 kg/hm2). On average, the fertilizer use is 357.3 kg/ hm2and nitrogen rate is 165.1 kg/hm2in China, which was much higher than the world average application rates (fertilizer rate: 87.5 kg/hm2; nitrogen rate: 52.9 kg/hm2). As a result, nitrogen use efficiency during one crop growth period in China (17%) was significantly lower than the world average (58%). These results indicated that excessive fertilizer application and underutilization of nitrogen were main reasons for nitrogen losses to surface and ground water. By comprehensively analyzing prevention and control measures for farmland nitrogen losses, we found that reducing nitrogen losses from the source was the most effective measure. Optimizing agronomic management practices and intercepting nitrogen migration could reduce nitrogen losses by 15% to 82%. Among a large diversity of studies, the largest group of studies focused on optimizing nitrogen applications. However, faced with resource shortage, water quality deterioration, and food production pressure, future research focus should shift from nitrogen balance to study of the nitrogen cycle in the entire farmland ecosystem. Further, there is an urgent need to determine nitrogen fertilization thresholds (critical nitrogen levels resulting in risk of pollution) for water quality protection. Effective prevention and control measures for nitrogen losses will provide theoretical and technical supports to balance the conflicts among food demand, resource conservation, and environmental protection.

farmland nitrogen; Web of Science; water quality; N loss; prevent and control measures; critical nitrogen rate

公益性行業(yè)(農(nóng)業(yè))科研專(zhuān)項(xiàng)(201303089, 201003014)

2015- 04- 14;

日期:2016- 01- 22

10.5846/stxb201504140764

*通訊作者Corresponding author.E-mail: rentianzhi@caas.cn

張亦濤,劉宏斌,王洪媛,翟麗梅,劉申,雷秋良,任天志.農(nóng)田施氮對(duì)水質(zhì)和氮素流失的影響.生態(tài)學(xué)報(bào),2016,36(20):6664- 6676.

Zhang Y T, Liu H B, Wang H Y, Zhai L M, Liu S, Lei Q L, Ren T Z.A bibliometric analysis of status and trend of international research on field nitrogen application effects on nitrogen losses and water quality.Acta Ecologica Sinica,2016,36(20):6664- 6676.