禾豆間作氮素高效利用機(jī)理及農(nóng)藝調(diào)控途徑研究進(jìn)展*

柴 強(qiáng),胡發(fā)龍,陳桂平

(甘肅省干旱生境作物學(xué)重點(diǎn)實(shí)驗(yàn)室/甘肅農(nóng)業(yè)大學(xué)農(nóng)學(xué)院 蘭州 730070)

禾豆間作氮素高效利用機(jī)理及農(nóng)藝調(diào)控途徑研究進(jìn)展*

柴 強(qiáng),胡發(fā)龍,陳桂平

(甘肅省干旱生境作物學(xué)重點(diǎn)實(shí)驗(yàn)室/甘肅農(nóng)業(yè)大學(xué)農(nóng)學(xué)院 蘭州 730070)

為保障糧食安全,農(nóng)業(yè)生產(chǎn)中化肥使用極為普遍,但過(guò)量使用,往往引起地下水污染、溫室效應(yīng)加劇、生物多樣性降低等多種環(huán)境和生態(tài)問(wèn)題。禾豆間作系統(tǒng)由于不同作物生物學(xué)特性和氮素利用存在差異,進(jìn)行合理調(diào)控可充分發(fā)揮生物固氮優(yōu)點(diǎn),從而減少化肥投入,提高生產(chǎn)效益,是一種穩(wěn)產(chǎn)、高產(chǎn)、高效可持續(xù)的種植體系。該系統(tǒng)中“氮轉(zhuǎn)移”、“氮阻遏”消減和氮素時(shí)空分異是目前研究的熱點(diǎn),也是促進(jìn)豆科作物固氮、減少化肥投入的有效途徑,可實(shí)現(xiàn)禾、豆兩種作物對(duì)氮素的高效利用。特別是該系統(tǒng)中作物品種、施氮制度、空間布局以及種植密度等農(nóng)藝措施是對(duì)種間關(guān)系進(jìn)行調(diào)控的必要手段,合理優(yōu)化可有效促進(jìn)禾/豆間作競(jìng)爭(zhēng)與互補(bǔ)協(xié)同作用,增強(qiáng)氮素協(xié)調(diào)利用,從而挖掘兩種作物對(duì)氮素高效利用的生物學(xué)潛力。為此,本文基于前人研究成果和農(nóng)業(yè)可持續(xù)發(fā)展觀點(diǎn),重點(diǎn)綜述了國(guó)內(nèi)外有關(guān)禾豆間作氮素高效利用主要機(jī)理及相關(guān)農(nóng)藝調(diào)控途徑的研究現(xiàn)狀,旨在為構(gòu)建簡(jiǎn)易、高產(chǎn)、高效、氮肥節(jié)約型禾豆間作模式提供有力的科學(xué)依據(jù)和理論支撐。

禾豆間作;氮轉(zhuǎn)移;氮阻遏;種間關(guān)系;氮素高效利用

為保障糧食安全,農(nóng)業(yè)生產(chǎn)中普遍使用化肥,但化肥的過(guò)量使用,往往會(huì)造成嚴(yán)重的環(huán)境和生態(tài)問(wèn)題,如地下水污染、水體富營(yíng)養(yǎng)化、溫室效應(yīng)加劇、生物多樣性和生態(tài)系統(tǒng)穩(wěn)定性降低、農(nóng)作物病蟲(chóng)害加重等[1-5]。禾豆間作具有保護(hù)土壤[6]、控制雜草和病害[7]、增產(chǎn)[8]等諸多優(yōu)點(diǎn),并在熱帶和雨養(yǎng)農(nóng)業(yè)地區(qū)廣泛應(yīng)用[9-10]。近年來(lái),隨種植業(yè)對(duì)化肥依賴性的增大,以及大量施用化肥帶來(lái)的環(huán)境污染和農(nóng)業(yè)可持續(xù)性下降等問(wèn)題加劇,禾豆間作能夠提高養(yǎng)分利用效率、減少種植業(yè)對(duì)化肥的依賴性等優(yōu)點(diǎn)受到了諸多研究者的高度關(guān)注[11-12],其穩(wěn)產(chǎn)、高產(chǎn)和高效可持續(xù)[13]的特性被認(rèn)為是未來(lái)有機(jī)農(nóng)業(yè)和高效替代農(nóng)業(yè)的重要模式[14]。禾豆間作群體中,豆科作物的生物固氮是眾所關(guān)注的焦點(diǎn),發(fā)揮禾豆間作優(yōu)勢(shì),提高豆科作物的生物固氮潛力至關(guān)重要[15]。大多數(shù)研究表明,間作禾本科作物可以提高豆科作物的固氮能力[16-17],增加氮素轉(zhuǎn)移,產(chǎn)生“氮阻遏”消減作用,并實(shí)現(xiàn)氮素高效利用。本文綜述了國(guó)內(nèi)外有關(guān)禾豆間作氮素高效利用的主要機(jī)理,重點(diǎn)解析了通過(guò)優(yōu)化施氮制度、空間布局、密度等農(nóng)藝調(diào)控措施來(lái)改善禾豆間作體系種間關(guān)系,從而增強(qiáng)間作氮素協(xié)調(diào)利用的重要原理,將對(duì)構(gòu)建簡(jiǎn)易、高產(chǎn)、高效、氮肥節(jié)約型禾豆間作模式提供有力的理論和實(shí)踐支撐。

1 禾豆間作氮素高效利用主要機(jī)理

間作群體中,作物的競(jìng)爭(zhēng)與互補(bǔ)提高了產(chǎn)量和養(yǎng)分利用效率,主要原因包括間作作物顯著的根間作用對(duì)養(yǎng)分吸收的促進(jìn)、作物產(chǎn)量形成的競(jìng)爭(zhēng)-恢復(fù)效應(yīng)、養(yǎng)分高效利用以及對(duì)非高效作物養(yǎng)分的有效化等[18]。對(duì)豆科作物與非固氮類作物間作而言,Willey[19]提出禾豆間作潛在的優(yōu)勢(shì)在于:通過(guò)提高土地當(dāng)量比提高總產(chǎn)量,通過(guò)增加土壤中的有效氮含量和氮轉(zhuǎn)移減少對(duì)化學(xué)氮肥的需求量,提高水分和其他有效養(yǎng)分的利用效率;通過(guò)作物多樣化降低作物生產(chǎn)風(fēng)險(xiǎn)和市場(chǎng)風(fēng)險(xiǎn),并減少害蟲(chóng)危害。最新研究表明,間作的豆科作物可產(chǎn)生直接或間接的氮素轉(zhuǎn)移供給禾本科作物,而禾本科作物可以減緩化學(xué)氮肥對(duì)豆科作物的“氮阻遏”[20],從而促進(jìn)豆科作物結(jié)瘤,增加固氮量;另外,不同作物對(duì)氮素吸收具有明顯的時(shí)空分異特性,禾豆間作能顯著提高復(fù)合群體對(duì)不同時(shí)間及空間生態(tài)位上氮素的吸收和利用。

1.1 豆科作物結(jié)瘤與固氮的促進(jìn)

土壤水分含量影響豆科植物的結(jié)瘤數(shù)、瘤重、固氮酶活性和固氮量[23],干旱和過(guò)高的土壤水分都不利于豆科植物氮素利用效率的提高。土壤溫度同樣影響豆科植物的生物固氮水平,一般認(rèn)為豆科作物最適宜結(jié)瘤和固氮的溫度為20～22℃,溫度的高低會(huì)對(duì)共生體系的發(fā)育和功能產(chǎn)生影響,過(guò)低的溫度會(huì)導(dǎo)致豆科植物結(jié)瘤和固氮能力下降,生物量降低[6]。此外,土壤pH和微生物種群結(jié)構(gòu)對(duì)豆科植物的固氮水平具有顯著影響[24],在未種植豆科作物且缺乏根瘤菌的土壤上種植豆科作物,接種根瘤菌可顯著提高豆科作物產(chǎn)量[25]。優(yōu)化土壤水分含量、溫度和土壤微生物種群結(jié)構(gòu)、接種根瘤菌是提高豆科植物結(jié)瘤固氮及氮肥利用效率的可行途徑。

1.2 禾豆間作體系中氮素的轉(zhuǎn)移

研究表明,蠶豆(Vicia faba)與大麥(Hordeum vulgare)間作時(shí),蠶豆的固氮量明顯增大[26],而與大麥間作的豌豆(Pisum sativum),其氮累積量中生物固氮量也明顯高于單作豌豆[27];玉米(Zea mays)與飯豆(Lablab purpureus)間作增加了系統(tǒng)中固定空氣氮的比例,在飯豆與玉米的種植比例達(dá)75︰25時(shí),1季作物固氮量可達(dá)81kg·hm-2,而單作時(shí)僅固定49kg·hm-2[28],這些研究證明禾豆間作群體對(duì)生物固氮具有促進(jìn)作用。通過(guò)15N標(biāo)記法研究證明禾豆間作群體中存在氮素從豆科作物向禾本科作物的直接轉(zhuǎn)移。Kessel等[29]利用15N標(biāo)記土壤在大豆(Glycine max)中富集方法的分根試驗(yàn)證明了從大豆向玉米根間發(fā)生了“氮轉(zhuǎn)移”;Ledgard[30]通過(guò)葉片喂飼15N的方法對(duì)氮素轉(zhuǎn)移的定量研究作了新的嘗試,發(fā)現(xiàn)三葉草(Trifolium repens)中有2.2%的氮向黑麥草(Lolium perenne)發(fā)生了直接轉(zhuǎn)移。另?yè)?jù)報(bào)道,與菜豆(Phaseolus vulgaris)間作的玉米吸氮量中20%～30%來(lái)自于菜豆,占菜豆固氮量的10%～15%[31]。一般認(rèn)為豆科作物向非豆科作物進(jìn)行氮素轉(zhuǎn)移途徑有3種,即:1)間作組分根系相互接觸時(shí)發(fā)生的直接轉(zhuǎn)移;2)殘留于土壤中的氮素被當(dāng)季非豆科作物后期利用的間接轉(zhuǎn)移;3)殘留氮素被下一季作物吸收利用的間接轉(zhuǎn)移。然而,當(dāng)間作群體中的作物類型、空間布局、栽培土壤的本底特性不同時(shí),禾豆間作群體通過(guò)直接或者間接的“氮轉(zhuǎn)移”作用產(chǎn)生的氮素高效利用效應(yīng)不同。因此,在搭配作物確定的情況下,調(diào)控主栽作物在空間上的布局以及土壤中養(yǎng)分的豐缺程度,對(duì)挖掘“氮轉(zhuǎn)移”效應(yīng)均存在較大可能性。

1.3 禾本科作物對(duì)豆科作物“氮阻遏”的減緩效應(yīng)

在豆科植物生長(zhǎng)初期,過(guò)低的土壤氮水平形成的“氮饑餓”會(huì)降低結(jié)瘤能力和固氮量[32],其主要原因是作物根系尚未發(fā)育完善,結(jié)瘤和固氮過(guò)程尚未啟動(dòng),在苗期施用少量的“啟動(dòng)氮”即可削除缺氮癥狀[33]。作物生長(zhǎng)期間,施氮將導(dǎo)致豆科作物結(jié)瘤數(shù)量和生物固氮量的下降[34],這種現(xiàn)象被視為“氮阻遏”。王樹(shù)起等[35]研究發(fā)現(xiàn),施氮對(duì)大豆根瘤形成、生長(zhǎng)和固氮能力有顯著影響,隨著氮用量的增加,根瘤干重、根瘤數(shù)量均呈現(xiàn)先增加而后降低的趨勢(shì),而固氮酶活性和豆血紅蛋白含量則表現(xiàn)為持續(xù)下降的趨勢(shì),即產(chǎn)生了“氮阻遏”。而適量施氮?jiǎng)t對(duì)根瘤生長(zhǎng)具有促進(jìn)作用。大豆單作時(shí),施25kg·hm-2的“啟動(dòng)氮”,并在開(kāi)花期或種子形成初期追施50kg·hm-2氮,可獲得最高的氮吸收總量和固氮總量[33]。持續(xù)供氮和非持續(xù)供氮對(duì)大豆生長(zhǎng)影響不同,非持續(xù)供氮對(duì)苗期大豆生長(zhǎng)有較大促進(jìn)作用,而持續(xù)供氮對(duì)花期以后大豆生長(zhǎng)有較大促進(jìn)作用,但氮肥的持續(xù)施用對(duì)大豆根瘤形成和生長(zhǎng)均有抑制作用,使其固氮效率降低。因此,“啟動(dòng)氮”、適宜施氮水平和施氮方式是決定豆科作物固氮潛力和消減“氮阻遏”的重要調(diào)控途徑。

與禾本科作物間作時(shí),由于禾本科作物大量吸收硝酸鹽使土壤礦質(zhì)氮維持在較低水平,通過(guò)降低土壤礦質(zhì)氮來(lái)減小對(duì)豆科固氮的抑制[36],這種作用可視為禾本科作物對(duì)豆科作物“氮阻遏”的減緩效應(yīng)。事實(shí)上,大量研究表明,禾本科作物能夠刺激豆科作物的結(jié)瘤量和固氮量,其可能原因是禾本科作物競(jìng)爭(zhēng)利用了豆科作物根際的硝態(tài)氮或者銨態(tài)氮[37]。此外,Li等[38]在中國(guó)西北地區(qū)設(shè)計(jì)了不同供氮水平下的玉米間作蠶豆試驗(yàn),探討了玉米對(duì)間作蠶豆“氮阻遏”的減緩作用,結(jié)果發(fā)現(xiàn)在75kg·hm-2、150kg·hm-2、225kg·hm-2和300kg·hm-24個(gè)施氮水平下,玉米減緩氮肥對(duì)蠶豆瘤重抑制作用的百分比(Ca%)分別為9.7%、-10%、15.2%和10%,減緩氮肥對(duì)蠶豆固氮量占總氮吸收量的百分比(Cis%)分別為20.3%、-0.5%、17.4%和3.9%,充分證明了通過(guò)間作禾本科作物緩解施氮對(duì)豆科作物結(jié)瘤和固氮抑制作用的可行性,同時(shí)為禾豆間作群體選擇合理的施氮水平提供了理論依據(jù)。

1.4 不同作物需氮的時(shí)空分異特性

間作中不同組分作物由于其遺傳特性及形態(tài)特征,各自占有的生態(tài)位具有較大差異,因此好的間作系統(tǒng)能有效削弱種間競(jìng)爭(zhēng),促進(jìn)彼此對(duì)有限資源的互補(bǔ)利用。一方面,間作系統(tǒng)中不同作物對(duì)養(yǎng)分的敏感程度具有較大差異,養(yǎng)分吸收的峰值在時(shí)間上有明顯分異,由此保證了不同作物養(yǎng)分最大效率期可得到充足養(yǎng)分供應(yīng)[39]。此外,間作系統(tǒng)中涉及組分作物往往播種和收獲時(shí)期分開(kāi),早播作物在資源利用上具有一定優(yōu)勢(shì),可競(jìng)爭(zhēng)利用晚播作物盈余養(yǎng)分,而后播作物恢復(fù)生長(zhǎng)時(shí)根系能直接分布于相鄰作物帶吸收養(yǎng)分[8]。特別是當(dāng)同一資源成為限制因子時(shí),間作中兩種作物對(duì)某種資源在利用時(shí)間上不同,養(yǎng)分吸收量在時(shí)間上分開(kāi),可保證養(yǎng)分需求在某一時(shí)段不超過(guò)養(yǎng)分供應(yīng)速率[40]。另一方面,不同作物根系生物學(xué)特性存在較大差異,扎根深度以及根系分布范圍明顯不同,從而能吸收利用不同土壤層次、區(qū)域和不同形態(tài)的養(yǎng)分,由此促進(jìn)間作根際養(yǎng)分利用優(yōu)勢(shì)的形成[41]。

另外,不同類型植物對(duì)氮素形態(tài)的反應(yīng)不同。與硝態(tài)氮抑制豆科作物結(jié)瘤和固氮能力不同,硝態(tài)氮對(duì)小麥(Triticum aestivum)、玉米等作物的生長(zhǎng)多具有促進(jìn)作用。Li等[20]發(fā)現(xiàn),小麥偏好硝態(tài)氮,在采用硝態(tài)氮為唯一氮源或氮肥中硝態(tài)氮所占比重較高時(shí),小麥生長(zhǎng)較好,與此相似玉米也具有偏好硝態(tài)氮的趨勢(shì),且在氮素用量較低的情況下更為明顯。但是,從化學(xué)氮肥的生產(chǎn)成本和未來(lái)發(fā)展趨勢(shì)分析,銨態(tài)氮肥由于其在節(jié)約能源等方面的優(yōu)勢(shì),必然成為未來(lái)氮肥的主流,作物生產(chǎn)過(guò)程中大量應(yīng)用硝態(tài)氮肥的可行性相對(duì)較小,禾本科作物對(duì)硝態(tài)氮肥的偏好只能通過(guò)銨態(tài)氮的高效硝化加以解決。在由禾本科和豆科作物組成的間、套復(fù)合群體中,兩種組分對(duì)氮素高效利用生物學(xué)特性的差異必將形成氮肥精準(zhǔn)施用的難點(diǎn),只有科學(xué)設(shè)計(jì)施氮制度,同時(shí)促進(jìn)個(gè)體生長(zhǎng)和兩種作物的氮素補(bǔ)償利用,才可能實(shí)現(xiàn)間作群體的經(jīng)濟(jì)施氮。

2 禾豆間作氮素高效利用的農(nóng)藝調(diào)控途徑

相關(guān)研究證明,間作資源高效利用的前提是科學(xué)調(diào)控種間競(jìng)爭(zhēng)、充分挖掘種間互補(bǔ)[42-43]。間作氮素高效利用的調(diào)控因子主要包括作物品種[44]、水肥管理[45]、作物空間布局以及種植密度等[46]。優(yōu)化不同調(diào)控因子可促進(jìn)禾豆間作競(jìng)爭(zhēng)與互補(bǔ)協(xié)同作用,提高氮肥利用效率。

2.1 選育氮高效品種

作物氮素高效利用的生理機(jī)制是一個(gè)復(fù)雜的代謝過(guò)程,不僅取決于作物自身的基因型,還與其生理代謝密切相關(guān)[47]。明確植物營(yíng)養(yǎng)生長(zhǎng)和生殖生長(zhǎng)兩個(gè)重要時(shí)期的養(yǎng)分需求特征以及養(yǎng)分再循環(huán)代謝和遺傳調(diào)控機(jī)理是提高作物氮素高效利用的重要途徑,新的育種目標(biāo)應(yīng)該是培育適應(yīng)低氮投入的新型作物品種。研究表明,作物品種在礦質(zhì)營(yíng)養(yǎng)的吸收和利用上存在著明顯的遺傳多樣性,不同作物如小麥、玉米、大豆、水稻(Oryza sativa)等因品種類型不同在氮效率上存在著明顯的基因型差異。在低氮或氮脅迫條件下,作物不同生育時(shí)期的株高、葉面積指數(shù)、群體干物重以及各生育階段群體生長(zhǎng)率、凈同化率和光合勢(shì)均以氮高效品種最高[48]。然而,現(xiàn)有關(guān)于選育新品種提高氮素利用效率的研究主要集中在氮高效品種篩選和氮效率的評(píng)價(jià)指標(biāo)等方面,且多為單作模式,但對(duì)于間作系統(tǒng)中不同氮效率作物在不同生育時(shí)期的氮素吸收和利用特征,特別是作物之間氮素協(xié)調(diào)利用的相互關(guān)系以及內(nèi)在生理機(jī)制研究尚不深入。因此,通過(guò)組配不同氮高效作物或作物品種發(fā)揮間作優(yōu)勢(shì)來(lái)達(dá)到生理氮素高效利用具有廣闊的研究空間。

2.2 優(yōu)化施氮制度

施氮水平影響間作組分在復(fù)合群體中的主導(dǎo)地位,并對(duì)混合產(chǎn)量和組分產(chǎn)量具有一定影響。研究發(fā)現(xiàn),在大麥間作豌豆中,大麥?zhǔn)歉?jìng)爭(zhēng)優(yōu)勢(shì)種,間作大麥的產(chǎn)量和氮吸收量與單作相似,但由于競(jìng)爭(zhēng)作用的存在,間作豌豆的單株地上干物重和氮累積量比單作顯著降低;施氮可增大間作大麥的相對(duì)競(jìng)爭(zhēng)力,并使間作豌豆對(duì)復(fù)合群體混合產(chǎn)量的貢獻(xiàn)下降[4]。與此相似,Corre-Hellou等[49]研究發(fā)現(xiàn),大麥與豌豆間作時(shí),大麥在營(yíng)養(yǎng)生長(zhǎng)階段根系的快速生長(zhǎng)使其獲得了比豌豆更多的土壤氮素,但這種競(jìng)爭(zhēng)優(yōu)勢(shì)僅存在于營(yíng)養(yǎng)生長(zhǎng)階段,對(duì)最終產(chǎn)量的不利影響也只有在土壤氮供給量較低時(shí)發(fā)生;在高供氮情況下,大麥和豌豆對(duì)土壤氮素的分享不受兩種作物根系相互穿插深度的影響。因此,禾豆間作中施氮制度的制定需同時(shí)兼顧兩種作物的需氮特征。減量施氮或氮肥后移充分考慮了禾豆間作不同作物對(duì)氮素的反應(yīng)差異,能協(xié)同促進(jìn)兩種組分對(duì)氮素的有效吸收和高效利用。劉文鈺等[50]研究發(fā)現(xiàn),玉米大豆套作模式下減量施氮可顯著提高大豆R5期的單株根瘤數(shù)、根瘤干重、根瘤固氮潛力及R8期的總吸氮量。在該模式下減量施氮還能顯著降低氮肥殘留量、損失量和氨揮發(fā),提高氮肥表觀利用率[51]。氮肥后移一方面消減了前期施氮對(duì)豆科固氮的阻遏作用,另一方面還促進(jìn)了禾本科作物花后干物質(zhì)積累和向籽粒中的轉(zhuǎn)運(yùn),增大干物質(zhì)最大增長(zhǎng)速率,提高籽粒產(chǎn)量和氮肥利用率[52]。

間套復(fù)合群體中,適度的競(jìng)爭(zhēng)可在系統(tǒng)水平上提高復(fù)合群體的產(chǎn)量和資源利用效率,但當(dāng)間作作物組分間的競(jìng)爭(zhēng)作用過(guò)大時(shí),互補(bǔ)性必然下降。已有研究證明,施氮量對(duì)間作禾本科、豆科作物的競(jìng)爭(zhēng)力有重要影響,說(shuō)明通過(guò)優(yōu)化施氮可實(shí)現(xiàn)間作作物種間互補(bǔ)作用的提高。而問(wèn)題的關(guān)鍵在于,只有量化不同生育期兩作物間的競(jìng)爭(zhēng)力與目標(biāo)產(chǎn)量的相關(guān)關(guān)系,才能制定精細(xì)的氮肥管理制度。

2.3 合理布局空間結(jié)構(gòu)

間作作物的空間布局主要指不同作物在復(fù)合群體中的占地比、株行距以及兩種作物共生期的長(zhǎng)短而產(chǎn)生的空間占有量大小。Hauggaard-Nielsen等[34]設(shè)計(jì)的大麥間作豌豆試驗(yàn)證明,大麥和豌豆各占100cm、各占50cm、大麥占50cm豌豆占100cm3種模式總吸氮量顯著大于單作,說(shuō)明兩種作物間存在補(bǔ)償作用,這種補(bǔ)償作用主要?dú)w因于間作大麥大量吸氮迫使豌豆對(duì)生物固氮的依賴性增大,但這種補(bǔ)償作用在3種模式間差異并不明顯。玉米與豌豆間作時(shí),帶型的不同能引起間作體系吸氮總量和籽粒產(chǎn)量的差異,與2︰4間作模式相比,3︰4間作模式能顯著提高氮肥利用率[53]。玉米與大豆間作時(shí)4行玉米間作6行大豆具有最大土地當(dāng)量比和植株吸氮量[54]。另?yè)?jù)Davis等[55]研究,玉米與大豆窄行套作可顯著提高產(chǎn)量,但兩種作物同時(shí)播種形成的復(fù)合群體產(chǎn)量略有降低,而適當(dāng)擴(kuò)大同時(shí)播種作物的行距,即可明顯降低競(jìng)爭(zhēng)作用,協(xié)調(diào)復(fù)合群體氮素利用,實(shí)現(xiàn)增產(chǎn)。

帶狀間套作中,兩種作物的相鄰帶是資源競(jìng)爭(zhēng)與互補(bǔ)的焦點(diǎn)區(qū)域,傳統(tǒng)的間作空間結(jié)構(gòu)設(shè)計(jì)原則是“擠中間、空兩邊”,即在設(shè)計(jì)的密度范圍內(nèi)盡量減小同種作物的行距而擴(kuò)大相鄰帶的距離(間距),但這種理念是否合理,特別在養(yǎng)分互補(bǔ)性較高的禾豆間作體系中是否適用,對(duì)“氮轉(zhuǎn)移”以及“氮阻遏”消減效應(yīng)有何影響缺乏系統(tǒng)研究,是否會(huì)使間作生產(chǎn)者可能喪失通過(guò)縮小間距來(lái)提高氮素利用效率的機(jī)會(huì),這些都是需要進(jìn)一步探討的問(wèn)題。

2.4 密植與競(jìng)爭(zhēng)補(bǔ)償

間作作物種植密度對(duì)競(jìng)爭(zhēng)和補(bǔ)償?shù)挠绊懼饕Q于生長(zhǎng)資源的豐缺和作物的物候?qū)W特征。在降水和溫度適宜時(shí),燕麥(Avena sativa)間作豌豆在高密度下的產(chǎn)量較高,但在干旱和高溫天氣下低密度處理的產(chǎn)量較高,說(shuō)明資源充足時(shí),間作作物的競(jìng)爭(zhēng)相對(duì)較小而補(bǔ)償效應(yīng)較大,而資源量不足時(shí),間作作物的競(jìng)爭(zhēng)加劇而補(bǔ)償弱化[56]。燕麥間作豌豆中,燕麥?zhǔn)歉?jìng)爭(zhēng)優(yōu)勢(shì)種,密度可作為類似于氮素的種間競(jìng)爭(zhēng)調(diào)控因子[42]。Hauggaard-Nielsen等[46]研究發(fā)現(xiàn),大麥與豌豆間作時(shí),由于大麥出苗較早表現(xiàn)出一定的競(jìng)爭(zhēng)優(yōu)勢(shì),但豌豆在苗期后的競(jìng)爭(zhēng)優(yōu)勢(shì)較大,這種競(jìng)爭(zhēng)優(yōu)勢(shì)的逆轉(zhuǎn)主要取決于兩種作物的物候?qū)W特征;間作大麥的生長(zhǎng)與后期的密度呈顯著負(fù)相關(guān),在豌豆占競(jìng)爭(zhēng)優(yōu)勢(shì)的間作群體中更為明顯。高密度可增大豌豆產(chǎn)量的比重,但間作并未增大豌豆對(duì)大氣固氮量的依賴,并且豌豆占地比對(duì)間作群體吸氮量的影響遠(yuǎn)大于密度影響[57]。玉米豌豆間作群體中,密植能促進(jìn)植株與土壤中碳氮的協(xié)同利用,提高氮肥利用率[58]。而玉米與大豆間作時(shí),密植則增強(qiáng)了間作大豆“氮阻遏”消減作用,實(shí)現(xiàn)了種間促進(jìn)和氮素互補(bǔ)利用[59]。

已有研究成果提供了高效調(diào)控間作群體的實(shí)踐依據(jù),但深入到通過(guò)優(yōu)化施氮制度、作物空間布局和密植,進(jìn)而促進(jìn)禾豆間作體系氮素高效利用的理論研究十分薄弱,使得禾豆間作氮素互補(bǔ)利用的生物學(xué)潛力遠(yuǎn)未挖掘出來(lái)。因此,在集成應(yīng)用農(nóng)藝調(diào)控措施的基礎(chǔ)上,探討不同調(diào)控措施與間作體系“氮轉(zhuǎn)移”和“氮阻遏”消減效應(yīng)的關(guān)系,將對(duì)深化禾豆間作氮素高效利用機(jī)理、構(gòu)建高效調(diào)控技術(shù)產(chǎn)生重要推動(dòng)。

3 典型禾豆間作模式——玉米間作豌豆的發(fā)展現(xiàn)狀及存在問(wèn)題

以大豆、蠶豆作為豆科組分的間作模式在我國(guó)應(yīng)用面積大、歷史長(zhǎng),但眾多研究者認(rèn)為豌豆是有機(jī)農(nóng)作模式的理想組成作物之一[60],特別是在歐盟其豌豆產(chǎn)量更是占到了粒用豆的80%以上。加之豌豆良好的固氮特性、與其他作物間作的高效兼容性,已形成大麥間作豌豆[34,46]、燕麥間作豌豆[56]、小麥間作豌豆[61]等多種模式。玉米間作豌豆是近年來(lái)我國(guó)甘肅省河西走廊區(qū)興起的新型種植模式,應(yīng)用面積已突破2萬(wàn)hm2。我國(guó)的西北內(nèi)陸灌區(qū)光資源豐富、土質(zhì)良好、熱量一熟有余兩熟不足,適宜發(fā)展間作套種,但受水資源不足矛盾的日益加劇,傳統(tǒng)的小麥間作玉米、小麥間作大豆等模式已不適應(yīng)生產(chǎn)實(shí)踐需求。2005年以來(lái),玉米間作豌豆因其顯著的節(jié)水、高效和推進(jìn)農(nóng)牧結(jié)合的潛力而得到迅速推廣。然而現(xiàn)有生產(chǎn)規(guī)范中,玉米間作豌豆按單作玉米的施肥制度、灌溉制度進(jìn)行管理,作物空間布局、玉米密度均參照小麥間作玉米設(shè)計(jì),這種管理技術(shù)既忽視了禾豆間作的氮素補(bǔ)償效應(yīng),又忽略了不同作物組合時(shí)潛在的密植和競(jìng)爭(zhēng)效應(yīng)以及密植、競(jìng)爭(zhēng)對(duì)“氮轉(zhuǎn)移”以及“氮阻遏”消減效應(yīng)的影響,使得該模式在限量供水條件下提高氮肥利用效率、作物產(chǎn)量和土地利用效率等方面的優(yōu)勢(shì)未能充分發(fā)揮出來(lái)。因此,研究并配制合理的空間布局以及科學(xué)的水氮管理制度對(duì)充分挖掘玉米間作豌豆氮素互補(bǔ)高效利用的生物學(xué)潛力具有重要意義。

4 結(jié)語(yǔ)

協(xié)調(diào)氮素供應(yīng)形態(tài),優(yōu)化土壤水分、溫度和微生物種群結(jié)構(gòu)以及接種根瘤菌是促進(jìn)豆科作物結(jié)瘤固氮的重要措施。在禾豆間作系統(tǒng)中,不同作物生物學(xué)特性和氮素利用特征存在較大差異,合理調(diào)控并協(xié)同配對(duì)作物的種間關(guān)系能有效促進(jìn)禾豆競(jìng)爭(zhēng)與互補(bǔ)作用,增強(qiáng)氮素協(xié)調(diào)利用,特別是對(duì)氮轉(zhuǎn)移的促進(jìn)和“氮阻遏”的消減具有重要作用。間作系統(tǒng)中作物品種、水肥管理、作物空間布局以及種植密度等是科學(xué)調(diào)控種間競(jìng)爭(zhēng)、充分挖掘種間互補(bǔ)的重要農(nóng)藝途徑,合理優(yōu)化可實(shí)現(xiàn)禾、豆兩種作物對(duì)氮素的高效利用。綜觀禾豆間作氮肥高效利用研究成果不難發(fā)現(xiàn),針對(duì)氮素轉(zhuǎn)移、“氮阻遏”消減與施氮水平、間作群體資源利用特點(diǎn)及作物組合、帶型設(shè)計(jì)等領(lǐng)域的成果比較豐富,但有關(guān)禾本科作物在不同施氮方式、種植密度下對(duì)間作豆科作物“氮阻遏”消減效應(yīng)的影響,以及通過(guò)調(diào)控間作作物空間布局增強(qiáng)禾本科作物對(duì)豆科作物氮素協(xié)同促進(jìn),進(jìn)而提高氮素高效利用的研究十分薄弱。目前,玉米間作豌豆在我國(guó)不同地區(qū)已有較大規(guī)模應(yīng)用,且呈快速增大趨勢(shì),但已有研究中,針對(duì)玉米間作豌豆氮素高效利用的理論和技術(shù)研究十分少見(jiàn),特別是旨在服務(wù)于提高生物固氮量且可操作性強(qiáng)、簡(jiǎn)易的農(nóng)藝調(diào)控技術(shù)機(jī)理研究鮮見(jiàn)報(bào)道,造成了進(jìn)一步高效開(kāi)發(fā)利用該模式的理論和技術(shù)短板。因此,以玉米間作豌豆為主要模式的高效生產(chǎn)理論和技術(shù)研究亟待進(jìn)一步開(kāi)展。

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Research advance in the mechanism and agronomic regulation of high-efficient use of nitrogen in cereal-legume intercropping

CHAI Qiang,HU Falong,CHEN Guiping
(Gansu Provincial Key Laboratory of Arid Land Crop Science /Faculty of Agronomy,Gansu Agricultural University,Lanzhou 730070,China)

Chemical fertilizer use is very common in agriculture for sustainable food production and food security.However,the excessive use of N fertilizer has often caused severe environmental and ecological problems.The existing issues regarding the over use of N fertilizers include groundwater pollution,greenhouse effect,biodiversity loss,etc.Cereal-legume intercropping is a yield-stable,high-efficient and sustainable cropping system compared to any monoculture.A favorable model of cereal-legume intercropping allows two distinct crops with different biological characteristics and nitrogen demand to grow together in the same field.With consideration of reasonable regulation of the differences between two crops,improvements can be achieved by taking advantage of biological N2fixation to reduce the use of chemical fertilizers and increase crop productivity.It is presently a hot research area to address issues on N transfer,alleviation of inhibitory effect on nodulation and N2fixation,and temporal-special distribution of N in cereal-legume intercropping systems.Addressing these topics will improve N2fixation in legume crops and reduce the heavy dependence of crop production on chemical fertilizers.Furthermore,clarifying the underlying mechanisms of the three issues will greatly enhance high-efficient use of N by the two distinct crops.Crop variety,N fertilizer management,special layout and planting density are the vital regulation measures of the interrelations between cereals and legumes.The optimization of the above measures will improve synergistic effect of competition and recovery,and enhance coordination of nitrogen use in cereal-legume intercropping systems,and thereby promote biological potential on high-efficient use of N.This paper summarized research advances in the major mechanisms of high-efficient use of N and the relevant regulatory factors in cereal-legume intercropping systems.The summary of the paper was based on the results of previous studies and the approaches of sustainable agricultural development.The objective was to provide scientific and theoretical basis for establishing a simple,high-yield,efficient and N-saving model for cereal-legume intercropping systems.

Cereal-legume intercropping;N transfer;Inhibitory effect of N application on N2fixation;Interspecific relationship;High-efficient use of N

,CHAI Qiang,E-mail:Chaiq@gsau.edu.cn

S344.2

:A

:1671-3990(2017)01-0019-08

10.13930/j.cnki.cjea.160603

柴強(qiáng),胡發(fā)龍,陳桂平.禾豆間作氮素高效利用機(jī)理及農(nóng)藝調(diào)控途徑研究進(jìn)展[J].中國(guó)生態(tài)農(nóng)業(yè)學(xué)報(bào),2017,25(1):19-26

Chai Q,Hu F L,Chen G P.Research advance in the mechanism and agronomic regulation of high-efficient use of nitrogen in cereal-legume intercropping[J].Chinese Journal of Eco-Agriculture,2017,25(1):19-26

* 國(guó)家科技支撐計(jì)劃(2012BAD14B10)、國(guó)家自然科學(xué)基金項(xiàng)目(31360323)和公益性行業(yè)(農(nóng)業(yè))專項(xiàng)課題(201503125)資助

柴強(qiáng),研究方向?yàn)槎嗍旆N植、節(jié)水農(nóng)業(yè)和循環(huán)農(nóng)業(yè)。E-mail:chaiq@gsau.edu.cn

2016-07-06接受日期:2016-09-07

* This work was supported by the National Key Technology R&D Program of China (2012BAD14B10),the National Natural Science Foundation of China (31360323) and the Special Fund for Agro-scientific Research in the Public Interest of China (201503125).

Received Jul.6,2016;accepted Sep.7,2016