土壤侵蝕對坡耕地耕層質(zhì)量退化作用及其評價趨勢展望

史東梅，金慧芳，蔣光毅

土壤侵蝕對坡耕地耕層質(zhì)量退化作用及其評價趨勢展望

史東梅1，金慧芳1，蔣光毅2

（1. 西南大學(xué)資源環(huán)境學(xué)院，重慶 400715； 2. 重慶市水土保持生態(tài)環(huán)境監(jiān)測總站，重慶 401147）

土壤侵蝕是導(dǎo)致坡耕地耕層質(zhì)量退化和土壤生產(chǎn)力不穩(wěn)定的關(guān)鍵驅(qū)動因素。該文從水蝕區(qū)坡耕地侵蝕控制和生產(chǎn)功能角度，在解析地塊尺度土壤侵蝕、水土保持、農(nóng)業(yè)活動對坡耕地耕層生態(tài)過程作用特征的基礎(chǔ)上，系統(tǒng)分析了土壤侵蝕對坡耕地耕層質(zhì)量退化作用、影響效應(yīng)及作用途徑。認為：1）坡耕地耕層質(zhì)量變化由降雨侵蝕、耕作活動交互作用的生態(tài)過程決定，2種作用的時間、空間尺度不同；耕層土壤參數(shù)在坡耕地農(nóng)業(yè)生產(chǎn)中作用分為保水、保土、保肥和增產(chǎn)潛力,由地塊尺度農(nóng)作物-耕層耦合效應(yīng)決定土壤生產(chǎn)能力、坡耕地水土流失特征及耕層侵蝕性退化方向及程度。2）土壤侵蝕對坡耕地耕層質(zhì)量退化作用表現(xiàn)為土壤性質(zhì)惡化、土壤質(zhì)量劣化、土地生產(chǎn)力衰退3個方面，耕層土壤物理性質(zhì)變異程度大于化學(xué)性質(zhì)變異，徑流作用導(dǎo)致的土地生產(chǎn)力衰退大于土壤流失作用。3）坡耕地耕層質(zhì)量評價指標體系應(yīng)兼顧侵蝕下降、產(chǎn)量提升2個目標，地塊尺度診斷指標有效土層厚度、耕層厚度、土壤容重、土壤抗剪強度、土壤有機質(zhì)、土壤滲透性可作為合理耕層評價最小數(shù)據(jù)集；坡耕地合理耕層適宜性分為5級，其診斷指標分級標準宜與土壤侵蝕分級和耕地地力分級銜接。4）坡耕地合理耕層評價未來應(yīng)密切關(guān)注耕層質(zhì)量診斷指標最小數(shù)據(jù)集、坡耕地合理耕層閾值/適宜值分級標準、坡耕地水土流失阻控標準擬定3個主要方向。研究可為深入認識坡耕地侵蝕性退化機制，辨識坡耕地合理耕層調(diào)控途徑以及坡耕地合理耕層構(gòu)建技術(shù)參數(shù)提供依據(jù)。

土壤；侵蝕；有機質(zhì)；坡耕地；耕層質(zhì)量；退化作用；合理耕層；診斷指標

0 引 言

坡耕地是中國主要耕地資源類型，可占全國耕地面積35.09%；西南區(qū)是中國坡耕地分布最為集中地區(qū)，大于15°坡耕地為該地區(qū)坡耕地79.28%[1]，坡耕地在未來相當時期內(nèi)仍然是中國重要糧食和農(nóng)產(chǎn)品生產(chǎn)基地。耕層指在自然土壤基礎(chǔ)上，經(jīng)過人類長期的耕作、施肥、灌溉等活動及自然因素的持續(xù)作用形成的農(nóng)業(yè)耕作土壤，它包括耕作層（表土層）、犁底層、心土層和底土層[2]；坡耕地合理耕層指一定耕作制度下，可持續(xù)維持農(nóng)作物正常生長且能實現(xiàn)侵蝕控制雙重目標的坡耕地耕層土壤質(zhì)量基準（benchmark），采用在地塊尺度上可綜合反映土壤生產(chǎn)力過程和土壤侵蝕控制的土壤屬性（或多）指標表征[3]。國內(nèi)外對坡耕地“土壤侵蝕—土壤質(zhì)量—土地生產(chǎn)力”相關(guān)研究主要集中在坡面侵蝕土壤退化途徑及評價指標[4-5]、土壤侵蝕對土壤質(zhì)量退化影響[6-7]、土壤侵蝕與土地生產(chǎn)力及農(nóng)作物產(chǎn)量侵蝕響應(yīng)的（erosion-productivity impact calculator，EPIC）模型、土壤生產(chǎn)力指數(shù)（productivity index，PI）模型和土壤侵蝕可持續(xù)模型（an expertsystem/neural network model，ImpelERO）[8-11]等方面。美國農(nóng)業(yè)部（land evaluation and site assessment, LESA）系統(tǒng)規(guī)定，當用于耕地保護目的時，LE與SA權(quán)重比為1:2[12]；中國農(nóng)業(yè)部地力評價系統(tǒng)包括氣候、立地條件、剖面性狀、耕層理化性質(zhì)、土壤養(yǎng)分狀況、障礙因素、土壤管理7類共64項指標[13]，上述2類評價體系都包含了諸多土壤自然物理、化學(xué)指標和人為耕作活動指標。本文在水蝕區(qū)坡耕地主要生態(tài)過程分析基礎(chǔ)上，綜合分析了土壤侵蝕對坡耕地耕層土壤性質(zhì)、土壤質(zhì)量、土壤生產(chǎn)力退化作用影響，總結(jié)了侵蝕條件下坡耕地耕層質(zhì)量評價指標及方法，討論了坡耕地合理耕層評價指標及程度分級思路，從坡耕地土壤侵蝕機理、農(nóng)作物產(chǎn)量水土保持原理的視角，提出未來侵蝕條件下坡耕地合理耕層評價應(yīng)密切關(guān)注的3個問題。

1 水蝕區(qū)坡耕地主要生態(tài)過程分析

1.1 耕層及耕層質(zhì)量

農(nóng)業(yè)耕作土壤在人為熟化過程和自然因素繼續(xù)作用下所形成的層次結(jié)構(gòu)是其主要標志，在深、淺耕條件其耕層結(jié)構(gòu)與自然土壤層次發(fā)育特征如下所示（圖1a），在耕深30～40 cm條件下，活動層（0～40 cm）關(guān)系作物前期生長，穩(wěn)定層（30～40 cm）關(guān)系作物后期生長，>40～50 cm以下一般不做翻耕處理[2]。耕層是人類為了栽培作物，利用工具對土壤進行擾動的深度層，旱作土壤耕層的表土層（0～15 cm）、穩(wěn)定層（>15～35 cm）、心土層（>35～60 cm）和犁底層（耕層與心土層之間）組合特征對作物根系和產(chǎn)量具有重要意義；穩(wěn)定層也稱根系活躍層，與表土層共同組成耕層，而犁底層一般存在于耕層和心土層之間[14]。在深松條件下耕作土壤剖面構(gòu)型可分為活動層、穩(wěn)定層、保證層（圖1b），耕作層又分為表土層（0～15 cm）和犁底層（>15～20 cm），心土層（>20～40 cm）養(yǎng)分水分因素比較穩(wěn)定，可供作物后期生長的需求，而底土層（>40 cm）對農(nóng)作物產(chǎn)量形成幾乎沒有調(diào)控作用[3,14]。深松技術(shù)通過改善耕層剖面構(gòu)型、改良土壤結(jié)構(gòu)性能，實現(xiàn)耕層土壤蓄水保土保肥效應(yīng)，以獲得農(nóng)作物高產(chǎn)穩(wěn)產(chǎn)。

圖1 耕層土壤剖面構(gòu)型分析

根據(jù)以上分析，坡耕地耕層質(zhì)量指沿土壤剖面農(nóng)作物80%～90%根系活動層及其下層的土壤質(zhì)量特性、垂直組合狀況及其坡面立地條件，耕層質(zhì)量與土壤質(zhì)量內(nèi)涵有重合之處；而從農(nóng)學(xué)角度土壤質(zhì)量被定義為土壤生產(chǎn)力，包括土壤供作物生長內(nèi)在能力以及受土地利用類型和土壤管理措施影響的土壤質(zhì)量動態(tài)2個方面，土壤生產(chǎn)力和適宜性是土壤質(zhì)量主要內(nèi)容[15]。由此可見，耕層質(zhì)量指沿土壤剖面農(nóng)作物根系活動層及其下層的土壤質(zhì)量特性、垂直組合狀況及其坡面立地條件，坡耕地耕層剖面構(gòu)型指土壤質(zhì)地、容重、孔隙度、機械阻力在土壤垂直層次分布特征，對于特定耕層構(gòu)型而言，耕層厚度、土壤容重、土壤有機質(zhì)、土壤有效厚度等土壤屬性參數(shù)的垂直分布及組合特征是影響耕層質(zhì)量、水分庫、養(yǎng)分庫容量的關(guān)鍵因素。

1.2 坡耕地耕層生態(tài)過程

水蝕區(qū)坡耕地耕層生產(chǎn)能力是在自然因素和人為因素綜合作用下形成，根據(jù)生產(chǎn)力形成要素來源，分為自然因素（降雨、光熱、母質(zhì)）和人為因素（種植制度、耕作活動、土壤管理）；根據(jù)調(diào)控程度，分為可調(diào)控管理因素（種植制度、土壤管理等）和不可調(diào)控自然因素（降雨、光熱、母質(zhì)等），在地塊尺度，各種自然因素和管理因素對坡耕地“農(nóng)作物—土壤”系統(tǒng)的作用表現(xiàn)如圖2。由圖可見，在水蝕區(qū)土壤侵蝕對坡耕地地塊具有off-site和on-site 2種效應(yīng)，前者表現(xiàn)為坡耕地土壤侵蝕量、徑流損失和面源污染現(xiàn)象由地塊-集水區(qū)-小流域逐級匯流現(xiàn)象，對周邊生態(tài)環(huán)境安全造成潛在威脅；而后者則表現(xiàn)為耕層土壤侵蝕性退化和土地生產(chǎn)力下降現(xiàn)象，直接影響農(nóng)作物產(chǎn)量、品質(zhì)及區(qū)域糧食安全。坡耕地農(nóng)業(yè)耕作活動具有周期性特點，根據(jù)典型種植制度農(nóng)作物生長過程，采用耕作機械對地塊土壤進行播種、中耕、除草、施肥、收獲等農(nóng)業(yè)活動，對土壤擾動深度在5~30 cm不等[3]；同時農(nóng)作物收獲會使得坡耕地地面覆蓋度發(fā)生急劇變化，在侵蝕性次降雨條件下，則是中、強度土壤侵蝕發(fā)生的潛在危險期，因此構(gòu)建坡耕地合理耕層，應(yīng)著重從加深耕層恢復(fù)地力、蓄水保墑防止徑流和保護土壤提高產(chǎn)量角度進行調(diào)控[16]。

圖2 地塊尺度農(nóng)業(yè)活動對坡耕地耕層生態(tài)的影響過程

根據(jù)圖2對水蝕區(qū)坡耕地在年內(nèi)（農(nóng)業(yè)周期內(nèi)）自然因素和人為因素作用過程綜合分析可知，坡耕地耕層生態(tài)過程具有具有以下特征：

1）坡耕地耕層生態(tài)過程發(fā)生在農(nóng)作物-土壤下墊面及耕層土體內(nèi)部，由地塊尺度農(nóng)作物-耕層耦合效應(yīng)決定土壤生產(chǎn)能力、坡耕地水土流失特征及耕層侵蝕性退化方向及程度。農(nóng)作物-土壤下墊面表層生態(tài)過程主要有次降雨引起的自然干濕交替過程、地表覆蓋快速變化過程以及地表徑流沖刷過程，耕層土體內(nèi)部生態(tài)過程主要有成土過程、根系生長過程及固土抗蝕過程，上述坡耕地生態(tài)過程的自然影響因素有降雨量、微地形（坡度、坡長、坡向、坡型）、土壤抗侵蝕性能，人為因素有坡面水系分布、地塊破碎化程度、耕作活動方式等，而對三峽庫區(qū)紫色土坡地而言，人類耕作措施不當和種植制度不合理是其坡耕地土壤退化主要驅(qū)動力[17]。

2）坡耕地耕層生態(tài)過程具有時空尺度特征。坡耕地耕層厚度及其土壤屬性變化由降雨侵蝕、耕作過程、成土過程綜合作用的生態(tài)過程決定，耕作活動時間尺度為農(nóng)作物種植周期，空間尺度為地塊；水蝕過程的時間尺度為次降雨，在空間尺度上存在由地塊—集水區(qū)逐級匯流匯沙現(xiàn)象；坡耕地耕層質(zhì)量變化具有明顯的水蝕對耕作擾動的累積效應(yīng)南方坡耕地水土保持以“保土排水”原理布置工程措施、耕作措施，而北方坡耕地以“保土保水”原理布置各項水土保持措施。

3）從坡耕地水土流失阻控角度，一年多熟制的坡耕地農(nóng)業(yè)生產(chǎn)可分為侵蝕期和非侵蝕期2個階段，侵蝕期耕層調(diào)控目標兼顧土壤抗侵蝕性能和土壤生產(chǎn)性能，非侵蝕期耕層調(diào)控目標以土壤生產(chǎn)性能為主導(dǎo)。在坡耕地水土資源承載力前提下，調(diào)整坡耕地一元種植模式為糧經(jīng)二元種植模式，增加多年生農(nóng)作物種植比例，主動選擇可避開降雨侵蝕力集中分布期的典型種植制度，均是水土保持效應(yīng)明顯的坡耕地持續(xù)利用模式。

4）在地塊尺度，農(nóng)戶（農(nóng)場）水土保持行為對坡耕地耕層生態(tài)過程影響很大。單位土壤侵蝕厚度引起的土壤生產(chǎn)力下降水平，是引導(dǎo)農(nóng)民實施土壤管理措施的主要驅(qū)動力[3]，可調(diào)控的人為因素有耕作措施、土壤管理措施，坡面徑流調(diào)控工程，農(nóng)作物產(chǎn)量、品質(zhì)和市場價格將決定農(nóng)戶采取水土保持措施種類及水平，進而對坡耕地耕層質(zhì)量保持年限和水平造成影響。

2 土壤侵蝕對坡耕地耕層質(zhì)量退化驅(qū)動作用及評價

坡耕地耕層質(zhì)量涉及耕層結(jié)構(gòu)及功能2個方面，前者指耕層土壤理化性質(zhì)、剖面構(gòu)型與土壤質(zhì)量指數(shù)關(guān)系，后者指土壤理化性質(zhì)與作物產(chǎn)量及土壤生產(chǎn)力指數(shù)關(guān)系。國內(nèi)外對坡耕地侵蝕土壤退化類型及過程、土壤生產(chǎn)力與侵蝕土壤理化性質(zhì)關(guān)系都進行了大量研究，土壤侵蝕對土壤性質(zhì)及土壤質(zhì)量劣化作用最為深入，而土壤侵蝕對土壤性質(zhì)與土壤生產(chǎn)力衰退作用也有大量工作。

2.1 土壤侵蝕對坡耕地土壤質(zhì)量劣化作用

水蝕區(qū)土壤侵蝕是造成坡耕地耕層質(zhì)量退化的主要驅(qū)動因素，由于自然侵蝕條件不可控性及坡耕地農(nóng)業(yè)生產(chǎn)長周期性特點，鏟土侵蝕模擬法廣泛地應(yīng)用于坡耕地土壤性質(zhì)及土壤質(zhì)量與土地生產(chǎn)力衰退作用中。國內(nèi)外土壤侵蝕與土壤質(zhì)量相關(guān)研究主要集中在：1）土壤侵蝕對坡耕地退化影響直接表現(xiàn)在坡面耕層變薄、土壤物理、化學(xué)及生物性質(zhì)惡化和土地產(chǎn)力下降等，而土壤物理性質(zhì)和結(jié)構(gòu)性質(zhì)變化與侵蝕程度最為密切。土壤物理性質(zhì)退化增加了其水蝕敏感性，對水蝕抗性較高土壤集中表現(xiàn)為較低土壤滲透阻力、體積密度、砂粒含量以及較高抗剪強度、液壓電導(dǎo)率、滲透率、有機質(zhì)含量和黏粒含量等[18]；而加拿大、中國和德國對比研究表明，土壤團聚體結(jié)構(gòu)、大小是直觀診斷可靠指標，土壤物理性質(zhì)與產(chǎn)量和土壤團聚體診斷值高度相關(guān)但有明顯區(qū)域性差異，不利土壤結(jié)構(gòu)表現(xiàn)為較高土壤干容重、土壤強度及較低入滲率[19]。2）侵蝕土壤退化形式與類型，楊艷生認為[20]退化形式表現(xiàn)為土壤環(huán)境劣化、土壤剖面形態(tài)毀損、各肥力要素間調(diào)節(jié)功能減弱并最終造成生產(chǎn)力下降或自然肥力消失過程；何毓蓉認為[21]四川盆地紫色土退化類型分為土壤物理性退化、土壤構(gòu)造性退化和土壤營養(yǎng)性退化，退化紫色土具有粗骨性、易蝕性、易旱性特征；土壤侵蝕退化機理可分為土壤薄層化過程、土壤養(yǎng)分循環(huán)失衡、土壤性質(zhì)劣化和貧瘠化、土壤砂質(zhì)化和礫質(zhì)化4個方面[22]。3）侵蝕土壤退化驅(qū)動力及調(diào)控，史志華等認為[23]土地利用方式及管理措施是影響紅壤土壤質(zhì)量演變方向和強度的關(guān)鍵因素，有效土層厚度、耕層土壤質(zhì)地、土壤剖面構(gòu)型等可用于表征鄂南紅壤土壤質(zhì)量變化；施用生物炭可增加紫色土坡耕地耕層土壤有效持水量、提高土壤導(dǎo)水率，有利于作物抗旱和水分入滲，減少地表徑流和侵蝕發(fā)生[24]；添加1%生物炭對黃綿土耕層土壤可產(chǎn)生減流減沙作用，提高土壤入滲能力和持水性能，改善土壤可蝕性[25]；在以色列對2種易蝕性土壤的生物炭試驗表明，生物炭通過降低土壤容重、增加持水能力和土壤滲透率而減少徑流和土壤侵蝕，是土壤保持有效途徑[26]。

2.2 土壤侵蝕對坡耕地土地生產(chǎn)力衰退作用

坡耕地土地生產(chǎn)力多采用農(nóng)作物產(chǎn)量高低表示，也有采用土壤生產(chǎn)力指數(shù)表示，前者側(cè)重侵蝕條件下農(nóng)作物產(chǎn)量與影響因素關(guān)系，后者側(cè)重坡耕地地塊對農(nóng)作物根系生長適宜程度；目前坡耕地土壤侵蝕與土地生產(chǎn)力研究中，多側(cè)重在不同侵蝕程度和恢復(fù)措施下農(nóng)作物減產(chǎn)速率、產(chǎn)量變化趨勢以及定量分析不同因素對產(chǎn)量變化貢獻率，集中在：

1）對于農(nóng)作物產(chǎn)量衰退試驗研究表明，土壤侵蝕可使土壤水分有效性下降而導(dǎo)致農(nóng)作物產(chǎn)量降低且當降雨量低于平均水平年時，對重度侵蝕水平土地生產(chǎn)力影響較大[27]；Francis等[28]在加拿大采取鏟土0、5、10、15、20 cm以及施N+P肥、覆蓋表土等恢復(fù)措施的侵蝕模擬法定量研究了土壤侵蝕對土壤質(zhì)量、土壤生產(chǎn)力的影響，Oyedele等[29]在尼日利亞采取人為鏟土0～20 cm方法模擬在不同侵蝕程度條件下，侵蝕土壤理化性質(zhì)對作物產(chǎn)量影響的貢獻率。中國則采用鏟土侵蝕模擬小區(qū)或侵蝕模擬盆栽法，在不同區(qū)域開展了土壤侵蝕對作物產(chǎn)量影響定量研究，如陳奇伯等[30]采用侵蝕模擬小區(qū)法對比研究了黃土高原區(qū)和干熱河谷區(qū)土壤侵蝕對坡耕地土地生產(chǎn)力衰退影響；王志強等[31]在黑土區(qū)研究了模擬侵蝕0、10、20、30、40、50、60、70 cm小區(qū)條件下，坡耕地在施肥、不施肥條件下土壤侵蝕對土地生產(chǎn)力影響；Zhao等[32]采用侵蝕模擬小區(qū)和盆栽試驗，發(fā)現(xiàn)紫色丘陵區(qū)農(nóng)作物產(chǎn)量下降速率與鏟土厚度（侵蝕程度）關(guān)系；劉慧等[33]基于人為剝離表土模擬不同侵蝕程度的耕層土壤的盆栽試驗，分析土壤侵蝕厚度對土壤理化性質(zhì)、大豆生物性狀和水分利用效率等的影響。

2）在土壤生產(chǎn)力衰退模型研究方面，土壤侵蝕與土地生產(chǎn)力模型（EPIC）基于作物生理參數(shù)和USLE模型表征土壤侵蝕與作物產(chǎn)量復(fù)雜關(guān)系，但在應(yīng)用時需要大量前期資料，否則準確性較差[34]；Pierce等[35]采用PI模型重點分析土壤持水量、容重與pH值等土壤指標對作物根系生長適應(yīng)性，在世界各地土壤生產(chǎn)力評價[36]、侵蝕對土壤脆弱性及土壤生產(chǎn)力影響評價[37-38]方面廣泛應(yīng)用，也有基于人工剝離熟土層模擬不同侵蝕程度的盆栽試驗結(jié)果，采用 PI模型對比了施肥、表土覆蓋對侵蝕土壤生產(chǎn)力恢復(fù)水平[39]。

3）對于水蝕-農(nóng)作物-土壤生境系統(tǒng)分析，土壤脆弱性對作物生長及環(huán)境影響極為重要，土壤侵蝕通過影響土壤性質(zhì)和土壤厚度而造成土壤生產(chǎn)力下降，PI可作為土壤允許流失量標準，與土壤侵蝕風(fēng)險指數(shù)（erosion risk index，ERI）共同用于土壤保護；而基于土壤生產(chǎn)力或基于環(huán)境保護，可辨識出隨耕作、肥料、水分管理而變化的敏感指標集，為防止土壤質(zhì)量惡化提供預(yù)警；ImpelERO可用于評價土壤侵蝕脆弱性（敏感性）并分析流失土層厚度對作物產(chǎn)量影響[40-42]。紫色土坡耕地作物產(chǎn)量隨侵蝕土壤厚度（侵蝕程度）呈指數(shù)增加且單位侵蝕厚度（10 cm）作物產(chǎn)量下降率最大可達10.5%，60 cm土層厚度可作為紫色土坡地生產(chǎn)力臨界土層厚度[43]；紫色土坡耕地農(nóng)作物與耕層適宜性存在協(xié)調(diào)發(fā)展類和失調(diào)衰退類兩種狀態(tài)和同步型、滯后型、損益型、共損型4種表現(xiàn)；在同樣地力條件下，農(nóng)作物產(chǎn)量較坡耕地耕層質(zhì)量更為敏感，衰退表現(xiàn)更加明顯[44]。綜合以上分析可知，土壤厚度、土壤黏粒含量和有機質(zhì)臨界水平是引起坡耕地土壤生產(chǎn)力變化的關(guān)鍵因素，土壤滲透性與土壤侵蝕敏感性直接關(guān)系到坡耕地生產(chǎn)力持續(xù)、穩(wěn)定。

2.3 侵蝕條件下坡耕地土壤質(zhì)量評價

土壤質(zhì)量評價多以土壤功能維護與保持為目標篩選評價指標，在耕地質(zhì)量評價中多以作物產(chǎn)量或作物適宜性為目標，采用主成分分析、加權(quán)和法、加權(quán)綜合法等數(shù)學(xué)方法篩選關(guān)鍵指標并構(gòu)建土壤質(zhì)量指數(shù)。集中在：1）由土壤功能導(dǎo)向的土壤質(zhì)量評價指標選擇，冷疏影[45]提出采用包含土壤質(zhì)地、酸堿度、氮、磷、鉀、有機質(zhì)含量、侵蝕狀況、鹽漬化程度在內(nèi)的土壤有效系數(shù)反映農(nóng)地土壤農(nóng)業(yè)生產(chǎn)潛力；國外研究表明，與侵蝕最為相關(guān)的土壤物理指標有土壤滲透、水力傳導(dǎo)、切變強度和團聚體穩(wěn)定性[46]；土壤肥力低、碎石含量高、有效土層淺是尼日利亞耕地主要限制因素[47]；基于土壤根系發(fā)育、蓄水和養(yǎng)分供應(yīng)3個功能的土壤質(zhì)量評價可很好指導(dǎo)巴西向日葵種植[48]，土壤貫入阻力、土壤容重、土壤透氣性及最小水分限制范圍對作物生長很重要，可據(jù)此確定蘇格蘭耕作適宜性下限范圍[49]；土壤有機碳、粉粒+黏粒含量、pH、土壤陽離子交換量（cation exchange content，CEC）、土壤厚度和坡度作為德國農(nóng)地土壤恢復(fù)性指標[50]。2）在侵蝕土壤質(zhì)量評價方面，史德明等[5]提出采用土壤屬性評估法可很好地反映南方侵蝕土壤退化現(xiàn)狀、過程及其對土地生產(chǎn)力影響，退化指標必須準確地反映土壤剖面被剝蝕厚度或殘留厚度；在黃土高原，許明祥等[51-52]認為土壤有機質(zhì)、土壤抗沖性8項指標可很好反映侵蝕土壤質(zhì)量，加權(quán)綜合法可敏感地反映出土地利用變化對侵蝕土壤質(zhì)量影響；鄭粉莉等[53]采用土壤有機碳、毛管孔隙度、物理性黏粒等8個指標定量評價子午嶺近100 a來侵蝕環(huán)境下農(nóng)地土壤質(zhì)量退化過程；基于“壓力—狀態(tài)—響應(yīng)（pressure-status-response，PSR）”模式，在地塊和小流域尺度建立了針對土壤侵蝕退化的土地質(zhì)量評價指標體系[54]；因子分析法和判別分析可以識別對土壤侵蝕和土地利用最為敏感的土壤質(zhì)量指標[55]。3）土壤質(zhì)量評價最小數(shù)據(jù)集提出，可解決由于土壤理化性質(zhì)時空變異性大所致的土壤指標指示作用穩(wěn)定性變差、數(shù)據(jù)獲取成本高的問題，Mohammad等[56]以愛爾蘭耕地和草場樣地進行對比，分析土壤結(jié)構(gòu)對總體土壤質(zhì)量的貢獻率，采用主成分分析確定土壤質(zhì)量評價最小數(shù)據(jù)集minimum dataset，MDS）；李桂林等[57]利用多元方差分析、主成分定量評價了土地利用方式和種植年限對土壤質(zhì)量影響程度，確定了城市周邊2種土壤類型的MDS。Bram等[58]基于長期耕作、殘茬和輪作管理評價建立了墨西哥土壤質(zhì)量評價最小數(shù)據(jù)集，物理指標有團聚體穩(wěn)定性、永久萎蔫點、土壤滲透性等，化學(xué)指標有土壤有機質(zhì)、N、P等，認為優(yōu)良土壤質(zhì)量代表高持續(xù)性生產(chǎn)力和無明顯土壤或環(huán)境退化現(xiàn)象；而1個包括土壤主要功能作用（土壤水分入滲、儲存和供應(yīng)能力，養(yǎng)分儲存、供應(yīng)和循環(huán)能力，持續(xù)生物活性）的最小指標集可為土地管理提供有價值土壤質(zhì)量信息[59]。

侵蝕土壤質(zhì)量評價多采用土壤屬性評價法、土壤生產(chǎn)力評價、農(nóng)作物-土壤耦合度評價，評價尺度有地塊、小流域和區(qū)域尺度，指標篩選手段也由定性邏輯分析到定量數(shù)理化取舍。診斷指標最小數(shù)據(jù)集是土壤質(zhì)量特征評價、措施調(diào)控的科學(xué)方法。從坡耕地水土流失阻控及坡耕地農(nóng)業(yè)生產(chǎn)過程來看，坡耕地坡度、土壤層厚度、土壤有機質(zhì)可作為侵蝕條件下耕層質(zhì)量診斷的關(guān)鍵指標，土壤容重、土壤飽和導(dǎo)水率可作為診斷輔助指標；土壤層厚度可分為流失厚度、耕層厚度、有效土層厚度3個指標，分別反映了坡耕地土壤侵蝕程度、農(nóng)作物水分庫、養(yǎng)分庫容量特征。根據(jù)坡耕地耕層質(zhì)量相關(guān)研究[3,20,31,33,36,43,50,52,60-65]，建立了坡耕地耕層質(zhì)量診斷指標中耕層厚度、有效土層厚度、有機質(zhì)的侵蝕、生產(chǎn)性能對應(yīng)表（表1）。

表1 侵蝕條件下坡耕地耕層質(zhì)量診斷指標分級

注：流失厚度指標按土壤容重1.35 g·cm-3計算。侵蝕程度分級參考文獻[60]。

Note: Erosion thickness is calculated based on soil bulk density of 1.35 g·cm-3. Degree of erosion is classified base on reference[60].

3 趨勢展望

目前在土壤侵蝕對坡面理化性質(zhì)及土地生產(chǎn)力影響、耕地土壤質(zhì)量評價方面已有完善評價體系，但集合土壤侵蝕視角和土壤生產(chǎn)維持功能視角的量化評價仍需探索。坡耕地既是山區(qū)丘陵區(qū)主要農(nóng)業(yè)生產(chǎn)單元，也是嚴重水土流失單元；因此從坡耕地水土流失有效防治目標看[3,5,11,14,36,42,61,66-67]，坡耕地耕層質(zhì)量評價應(yīng)密切關(guān)注耕層土壤抗侵蝕性能和土壤生產(chǎn)性能2個功能，從“土壤侵蝕-質(zhì)量退化-改善恢復(fù)”系統(tǒng)性角度及坡耕地農(nóng)業(yè)生產(chǎn)關(guān)鍵生態(tài)過程（圖2），未來水蝕區(qū)坡耕地耕層質(zhì)量可在以下3個方面加強和突破（圖3）。

注：MDS為最小數(shù)據(jù)集。

1）坡耕地耕層質(zhì)量診斷指標最小數(shù)據(jù)集：針對不同水蝕區(qū)坡耕地典型耕作制度，整合或建立現(xiàn)有坡耕地侵蝕序列定位及模擬研究中耕層土壤理化性質(zhì)變化為基本數(shù)據(jù)源，深入分析表征坡耕地耕層侵蝕性能與生產(chǎn)性能指標的生態(tài)過程/驅(qū)動機制，揭示侵蝕條件下坡耕地耕層質(zhì)量主控過程、退化機理；基于坡耕地侵蝕控制和生產(chǎn)功能雙重目標，篩選耕層土壤理化性質(zhì)與剖面特征參數(shù)，確定能夠科學(xué)反映土壤生產(chǎn)力形成和侵蝕風(fēng)險控制的坡耕地耕層質(zhì)量診斷最小數(shù)據(jù)集是坡耕地合理耕層指標體系建立的重要方向。

2）坡耕地合理耕層閾值分析/適宜值：坡耕地合理耕層診斷宜在地塊尺度、耕作制度種植年、以耕層土壤指標及其立地條件為原則；以坡耕地中產(chǎn)穩(wěn)產(chǎn)的產(chǎn)量為依據(jù)，從坡耕地典型耕作制度在侵蝕條件下土壤生產(chǎn)力形成主要限制因素及其臨界水平，定量確定紫色土坡耕地合理耕層標準、閾值；建立坡耕地侵蝕等級和地力等級對應(yīng)關(guān)系，以侵蝕控制和農(nóng)作物根系適宜土層深度劃分合理耕層等級；根據(jù)降雨侵蝕危險期和農(nóng)作物生長周期性，坡耕地耕層質(zhì)量最小數(shù)據(jù)集診斷指標閾值/適宜值應(yīng)充分考慮其時間響應(yīng)特征。

3）基于MDS的坡耕地水土流失阻控標準擬定：在坡耕地“壓力（土壤侵蝕）—狀態(tài)（耕層質(zhì)量）—響應(yīng)（土壤管理）”框架下，分析坡耕地耕層質(zhì)量主控過程、障礙因素及恢復(fù)機制，揭示水蝕和土壤管理措施對坡耕地耕層質(zhì)量的交互作用、調(diào)控機制和優(yōu)先序；在坡耕地水土流失防治的土壤流失量、徑流系數(shù)、土壤允許流失量指標基礎(chǔ)上，增加坡耕地耕層質(zhì)量診斷MDS指標（如土壤有機質(zhì)、土壤入滲性、土壤黏粒含量），為坡耕地區(qū)域性治理標準擬訂提供量化預(yù)警監(jiān)測，實現(xiàn)水蝕區(qū)坡耕地水土資源高效利用、糧食安全及生態(tài)安全。

4 結(jié) 論

1）坡耕地耕層生態(tài)過程發(fā)生在農(nóng)作物-土壤下墊面及耕層土體剖面，耕層生態(tài)過程具有時空尺度特征；坡耕地耕層厚度及其土壤屬性變化由降雨侵蝕、耕作過程、成土過程綜合作用的生態(tài)過程決定，由地塊尺度農(nóng)作物-耕層耦合效應(yīng)決定土壤生產(chǎn)能力、坡耕地水土流失特征及耕層侵蝕性退化方向及程度。

2）耕層質(zhì)量指沿土壤剖面農(nóng)作物根系活動層及其下層的土壤質(zhì)量特性、垂直組合狀況及其坡面立地條件，坡耕地耕層剖面構(gòu)型指土壤質(zhì)地、容重、孔隙度、機械阻力在土壤垂直層次分布特征，坡耕地耕層質(zhì)量變化具有明顯的水蝕對耕作擾動的累積效應(yīng)。

3）土壤侵蝕對坡耕地退化影響直接表現(xiàn)在坡面耕層變薄、土壤物理化性質(zhì)及生物性質(zhì)惡化和土地產(chǎn)力下降等，而土壤物理性質(zhì)和結(jié)構(gòu)性質(zhì)變化與侵蝕程度關(guān)系最為密切；土壤厚度、土壤黏粒含量和有機質(zhì)臨界水平是引起坡耕地土壤生產(chǎn)力變化的關(guān)鍵因素，土壤滲透性與土壤侵蝕敏感性直接關(guān)系到坡耕地生產(chǎn)力持續(xù)、穩(wěn)定。

4）在中國主要水蝕區(qū)，應(yīng)針對典型坡耕地土壤類型及耕作制度，建立統(tǒng)一的坡耕地耕層質(zhì)量評價最小數(shù)據(jù)集；從坡耕地水土流失有效阻控及坡耕地農(nóng)業(yè)生產(chǎn)持續(xù)穩(wěn)定來看，坡耕地坡度、土壤層厚度、土壤有機質(zhì)可作為侵蝕條件下耕層質(zhì)量診斷的關(guān)鍵指標，土壤容重、土壤飽和導(dǎo)水率可作為診斷輔助指標。

[1] 謝俊齊，唐程杰，李憲文，等. 中國坡耕地[M]. 北京：中國大地出版社，2005.

[2] 陳恩風(fēng). 農(nóng)業(yè)土壤的成因、熟化、耕翻深度與層次發(fā)育[J].中國農(nóng)業(yè)科學(xué)，1961(12)：1－6.

Chen Enfeng. Causes of maturation and development of tilling depth and gradation of agricultural soil[J]. Scientia Agricultura Sinica, 1961(12): 1－6. (in Chinese with English abstract)

[3] 史東梅，蔣光毅，蔣平，等. 土壤侵蝕因素對紫色丘陵區(qū)坡耕地耕層質(zhì)量影響[J]. 農(nóng)業(yè)工程學(xué)報，2017，33(13)：270－279.

Shi Dongmei, Jiang Guangyi, Jiang Ping, et al. Effects of soil erosion factors on cultivated-layer quality of slope farmland in purple hilly area[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2017, 33(13): 270－279. (in Chinese with English abstract)

[4] National Soil Erosion-Soil Productivity Research Planning Committee. Soil erosion effects on soil productivity: A research perspective[J]. Journal of Soil and Water Conservation, 1981, 36(2): 82－90.

[5] 史德明，韋啟潘，梁音，等. 中國南方侵蝕土壤退化指標體系研究[J]. 水土保持學(xué)報，2000，14(3)：1－9.

Shi Deming, Wei Qipan, Liang Yin, et al. Study on degradation index system of eroded soils in Southern China[J]. Journal of Soil and Water Conservation, 2000, 14(3): 1－9. (in Chinese with English abstract)

[6] 史衍璽. 人為開墾加速侵蝕下土壤質(zhì)量演變及其機理研究[D]. 楊凌：中國科學(xué)院西北水土保持研究所，1998.

[7] Lal R, Ahmandi M, Bajracharya R M. Erosional impacts on soil properties and corn yield on alfisols in central Ohio[J]. Land Degradation & development, 2000, 11: 575－585.

[8] Williams J R, Renard K G, Dyke P T. EPIC: A new method for assessing erosion effects on soil productivity[J]. Journal of Soil and Water Conservation,1983, 38(5): 381－383.

[9] 李軍，邵明安，張興昌，等. 黃土高原地區(qū)EPIC模型數(shù)據(jù)庫組建[J]. 西北農(nóng)林科技大學(xué)學(xué)報：自然科學(xué)版，2004，32(8)：21－26.

Li Jun, Shao Ming'an, Zhang Xingchang, et al. Database construction for the EPIC model on the Loess Plateau region[J]. Journal of Northwest Sci-Tech University of Agriculture and Forestry, 2004, 32(8): 21－26. (in Chinese with English abstract)

[10] Neill L L. An Evaluation of Soil Productivity Based on Root Growth and Water Depletion[D]. Columbia:University of Missouri, 1979.

[11] Ddela R, Moreno J A, Mayol F, et al. Assessment of soil erosion vulnerability in western Europe and potential impact on crop productivity due to loss of soil depth using the ImpelERO model[J]. Agriculture Ecosystems & Environment, 2000, 81(3): 179－190.

[12] James R Pease, Robert E Coughlin. Land Evaluation and Site Assessment: A guidebook for Rating Agricultural Lands, Second Edition[M]. Ankeny, Iowa: Soil and Water Conservation Society, 2000.

[13] 全國農(nóng)業(yè)技術(shù)推廣服務(wù)中心. 耕地地力評價指南[M]. 北京：中國農(nóng)業(yè)科學(xué)技術(shù)出版社，2006：14－18

[14] 韓曉增，鄒文秀，陸欣春，等. 旱作土壤耕層及其肥力培育途徑[J]. 土壤與作物，2015，4(4)：145－150.

Han Xiaozeng, Zou Wenxiu, Lu Xinchun, et al. The soil cultivated layer in dryland and technical patterns in cultivating soil fertility[J]. Soil and Crop, 2015, 4(4): 145－150. (in Chinese with English abstract)

[15] 劉世梁，傅伯杰，劉國華，等. 我國土壤質(zhì)量及其評價研究的進展[J]. 土壤通報，2006，37(1)：137－143.

Liu Shiliang, Fu Bojie, Liu Guohua, et al. Research review of quantitative evaluation of soil quality in China[J]. Chinese Journal of Soil Science, 2006, 37(1): 137－143. (in Chinese with English abstract)

[16] 鄭洪兵，齊華，劉武仁，等. 玉米農(nóng)田耕層現(xiàn)狀、存在問題及合理耕層構(gòu)建探討[J]. 耕作與栽培，2014，52(5)：39－42.

Zheng Hongbing, Qi Hua, Liu Wuren, et al. Present and problem of tillage layer of maize cropland and discussion of optimum tillage layer[J]. Tillage and Cultivation, 2014, 52(5): 39－42. (in Chinese with English abstract)

[17] 董杰，段藝芳，許玉鳳，等. 三峽庫區(qū)紫色土坡地土壤退化程度評價及驅(qū)動機制[J]. 水土保持通報，2009，29(4)：51－56.

Dong Jie, Duan Yifang, Xu Yufeng, et al. Evaluation and driving mechanism of land degradation in a sloping field of Purple soil in Three Gorges reservoir area[J]. Bulletin of Soil and Water Conservation, 2009, 29(4): 51－56. (in Chinese with English abstract)

[18] Ilan Stavi, Rattan Lal. Variability of soil physical quality and erodibility in a water-eroded cropland[J]. Catena, 2011, 84: 148－155.

[19] Lothar Mueller, Bev D Kay, Chunsheng Huc, et al. Visual assessment of soil structure: Evaluation of methodologies on sites in Canada, China and Germany Part I: Comparing visual methods and linking them with soil physical data and grain yield of cereals[J]. Soil & Tillage Research, 2009, 103: 178－187.

[20] 楊艷生. 第四紀紅粘土區(qū)侵蝕土壤退化機理研究[J]. 水土保持研究，1997，4(1)：100－108.

Yang Yansheng. Research on soil degradation mechanism in the quaternary red clay area[J]. Research of Soil and Water Conservation | Res Soil Water Conserv, 1997, 4(1): 100－108. (in Chinese with English abstract)

[21] 何毓蓉.中國紫色土：II[M]. 北京：科學(xué)出版社，2003：2－11，43－45，398－404.

[22] 程冬兵，蔡崇法，左長清. 土壤侵蝕退化研究[J]. 水土保護研究，2006，13(5)：252－254.

Cheng Dongbing, Cai Chongfa, Zuo Changqing, et al. Advances in research of soil degradation by erosion[J]. Soil and Water Conservation Research, 2006, 13(5): 252－254. (in Chinese with English abstract)

[23] 史志華，蔡崇法，王天巍，等. 紅壤丘陵區(qū)土地利用變化對土壤質(zhì)量影響[J]. 長江流域資源與環(huán)境，2001，10(6)：537－543.

Shi Zhihua, Cai Chongfa, Wang Tianwei, et al. In flueece of land use changes on soil quality in hilly region of red soil[J]. Resourceses and Environment in the Yangtze Basin, 2001, 10(6): 537－543. (in Chinese with English abstract)

[24] 王紅蘭，唐翔宇，張維，等. 施用生物炭對紫色土坡耕地耕層土壤水力學(xué)性質(zhì)的影響[J]. 農(nóng)業(yè)工程學(xué)報，2015，31(4)：107－112.

Wang Honglan, Tang Xiangyu, Zhang Wei, et al. Effects of biochar application on tilth soil hydraulic properties of slope cropland of purple soil[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2015, 31(4): 107－112. (in Chinese with English abstract）

[25] 吳媛媛，楊明義，張風(fēng)寶，等. 添加生物炭對黃綿土耕層土壤可蝕性的影響[J]. 土壤學(xué)報，2016，53(1)：77－88.

Wu Yuanyuan, Yang Mingyi, Zhang Fengbao, et al. Effect of biochar addition on erodibility of loess soil[J]. Acta Pedologica Sinica, 2016, 53(1): 77－88. (in Chinese with English abstract)

[26] Vikas Abrol, Meni Ben-Hur, Frank G A. Verheijen, et al. Biochar effects on soil water infiltration and erosion under seal formation conditions: Rainfall simulation experiment[J]. J Soils Sediments, 2016, 16: 2709－2719.

[27] Arriaga F J, Lowery B. Corn production on an eroded soil: Effects of total rainfall and soil water storage[J]. Soil & Tillage Research, 2003, 71: 87－93.

[28] Francis J Larney， Henry H Janzen，Barry M Olson，et al. Soil quality and productivity responses to simulated erosion and restorative amendments[J].Canadian Journal of Soil Science, 2000, 80: 515－522.

[29] Oyedele D J, Aina P O. Response of soil properties and maize yield to simulated erosion by artificial topsoil removal[J]. Plant and Soil, 2006, 284: 375－384.

[30] 陳奇伯，王克勤，齊實，等. 不同生態(tài)脆弱區(qū)土壤侵蝕對土地生產(chǎn)力影響對比研究[J]. 水土保持通報，2005，25(3)：29－32.

Chen Qibo, Wang Keqin, Qi Shi, et al. Soil erosion and its relations to slope field productivity in hilly gully area of loess plateau and dry-hot valley of Jinshajiang river[J]. Bulletin of Soil and Water Conservation, 2005, 25(3): 29－32. (in Chinese with English abstract)

[31] 王志強，劉寶元，王旭艷，等. 東北黑土區(qū)土壤侵蝕對土地生產(chǎn)力影響試驗研究[J]. 中國科學(xué)D輯：地球科學(xué)，2009，39(10)：1397－1412.

Wang Zhiqiang, Liu Baoyuan, Wang Xuyan, et al. Erosion effect on the productivity of black soil in Northeast China[J]. Sci China Ser D-Earth Sci, 2009, 39(10): 1397－1412. (in Chinese with English abstract)

[32] Zhao Li, Jin Jie, Du Shuhan, et al. A quantification of the effects of erosion on the productivity of purple soils[J]. Journal of Mountain Science, 2012, 9: 96－104.

[33] 劉慧，魏永霞. 黑土區(qū)土壤侵蝕厚度對土地生產(chǎn)力的影響及其評價[J]. 農(nóng)業(yè)工程學(xué)報，2014，30(20)：288－296..

Liu Hui, Wei Yongxia. Influence of soil erosion thickness on soil productivity of black soil and its evaluation[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2014, 30(20): 288－296. (in Chinese with English abstract)

[34] Lothar Mueller, Bev D Kay, Bill Deen, et al. Visual assessment of soil structure: Part II. Implications of tillage, rotation and traffic on sites in Canada, China and Germany[J]. Soil & Tillage Research, 2009, 103(1): 188－196.

[35] Pierce F C, Larson W E, Dowdy R H, et al. Graham. 1983. Productivity of soils: Assessing long-term changes due to erosion[J]. Journal of Soil and Water Conservation. 1983, 38: 39－44.

[36] 孫振寧，謝云，段興武. 生產(chǎn)力指數(shù)模型PI在北方土壤生產(chǎn)力評價中的應(yīng)用[J]. 自然資源學(xué)報，2009，24(4)：708－718.

Sun Zhenning, Xie Yun, Duan Xingwu. Applied productivity index model(PI) in soil productivity assessment of northern China[J]. Journal of Natural Resources, 2009, 24(4): 708－718. (in Chinese with English abstract)

[37] Martha M. Bakker, Gerard Goversb, Mark D A. Rounsevella. The crop productivity-erosion relationship: An analysis based on experimental work[J]. Catena, 2004, 57: 55－76.

[38] Duan Xingwu, Xie Yun, Ou Tinghai, et al. Effects of soil erosion on long-term soil productivity in the black soil region of northeastern China[J]. Catena, 2011, 87: 268－275.

[39] 成婧，吳光艷，云峰，等. 渭北旱塬侵蝕退化土壤生產(chǎn)力的恢復(fù)與評價[J]. 中國水土保持科學(xué)，2013，11(3)：6－11.

Cheng Xie, Wu Guangyan, Yun Feng, et al. Soil productivity restoration and evaluation of erosion degradation in Weibei dry highland[J]. Science of Soil and Water Conservation, 2013, 11(3): 6－11. (in Chinese with English abstract)

[40] Deyanira Lobo，Zenaida Lozano，F(xiàn)ernando Delgado. Water erosion risk assessment and impact on productivity of a Venezuelan soil[J]. Catena, 2005, 64: 297－306.

[41] Debarati Bhaduri, Purakayastha T J. Long-term tillage, water and nutrient management in rice-wheat cropping system: Assessment and response of soil quality[J]. Soil & Tillage Research, 2014, 144(12): 83－95.

[42] de la Rosa D, Moreno J A, Mayol F, et al. Assessment of soil erosion vulnerability in western Europe and potential impact on crop productivity due to loss of soil depth using the ImpelERO model[J]. Agriculture, Ecosystems and Environment, 2000, 81: 179－190.

[43] 朱波，況福虹，高美榮，等. 土層厚度對紫色土坡地生產(chǎn)力的影響[J]. 山地學(xué)報，2009，27(6)：735－739.

Zhu Bo, Kuan Fuhong, Gao Meirong, et al. Effects of soil thicknesson productivity of sloping cropland of purple soil[J]. Journal of Mountain Science, 2009, 27(6): 735－739. (in Chinese with English abstract)

[44] 婁義寶，史東梅，金慧芳，等. 西南紫色土坡耕地農(nóng)作物-耕層質(zhì)量適宜性的耦合度診斷[J]. 中國農(nóng)業(yè)科學(xué)，2019，52(4)：661－675.

Lou Yibao, Shi Dongmei, Jin Huifang, et al. Coupling degree diagnosis on suitability evaluation of cultivated-layer quality for slope farmland in purple hilly region of south-western China[J]. Scientia Agricultura Sinica, 2019, 52(4): 661－675. (in Chinese with English abstract)

[45] 冷疏影. 地理信息系統(tǒng)支持下的中國農(nóng)業(yè)生產(chǎn)潛力研究[J]. 自然資源學(xué)報，1992，7(1)：71－79.

Leng Shuying. Research on the potential agricultural productivity of China with the help of GIS[J]. Journal of Natural Resources, 1992, 7(1): 71－79. (in Chinese with English abstract)

[46] Karlen D L, Eash N S, Unger P W. Soil and crop management effects on soil quality indicators[J]. American Journal of Alternative Agriculture, 1992, 7(7): 48－55.

[47] Oluwatosin G A, Adeyolanu O D, Ogunkunle A O, et al. From land capability classification to soil quality: An assessment[J]. Tropical and Subtropical Agroecosystems, 2006, 6: 49－55.

[48] Jairo Costa Fernandes, Carlos Antonio Gamero, Jose′ Guilherme Lanca Rodrigues, et al. Determination of the quality index of a Paleudult under sunflower culture and different management systems[J]. Soil & Tillage Research, 2011, 112: 167－174.

[49] Rachel Muylaert Locks Guimara, Bruce C Ball, Cassio Antonio Tormena, et al. Relating visual evaluation of soil structure to other physical properties in soils of contrasting texture and management[J]. Soil & Tillage Research, 2013, 127: 92－99.

[50] Jasmin Schiefera, Georg J Laira, Winfried E H. Blum. Indicators for the definition of land quality as a basis for the sustainable intensification of agricultural production[J]. International Soil and Water Conservation Research, 2015, 3: 42－49.

[51] 許明祥，劉國彬，趙允格.黃土丘陵區(qū)侵蝕土壤質(zhì)量評價[J].植物營養(yǎng)與肥料學(xué)報，2005，11(3)：285－293.

Xu Mingxiang, Liu Guobin, Zhao Yunge. Quality assessment of erosion soil on hilly Loess Plateau[J]. Plant Nutrition and Fertilizer Science, 2005, 11(3): 285－293. (in Chinese with English abstract)

[52] Xu M, Qiang L, Wilson G. Degradation of soil physicochemical quality by ephemeral gully erosion on sloping cropland of the hilly Loess Plateau, China[J]. Soil & Tillage Research, 2016, 155: 9－18.

[53] 鄭粉莉，張鋒，王彬. 近100年植被破壞侵蝕環(huán)境下土壤質(zhì)量退化過程的定量評價[J]. 生態(tài)學(xué)報，2010，30(22)：6044－6051.

Zheng Fenli, Zhang Feng, Wang Bin. Quantifying soil quality degradation over 100 years after deforestation under erosional environments[J]. Acta Ecologica Sinica, 2010, 30(22): 6044－6051. (in Chinese with English abstract)

[54] 郭旭東，邱揚，連綱，等. 基于PSR框架，針對土壤侵蝕小流域的土地質(zhì)量評價[J]. 生態(tài)學(xué)報，2004，24(9)：1884－1894.

Guo Xudong, Qiu Yang, Liang Gang, et al. Land quality indictors based on “Press-State-Response” framework at catchment for soil degradation by water erosion[J]. Acta Ecologica Sinica, 2004, 24(9): 1884－1894. (in Chinese with English abstract)

[55] Kazem Nosrati. Assessing soil quality indicator under different land use and soil erosion using multivariate statistical techniques[J]. Environmental Monitoring & Assessment, 2013, 185(4): 2895－2907.

[56] Mohammad Sadegh Askari, Junfang Cui, Sharon M O’Rourke, et al. Evaluation of soil structural quality using VIS-NIR spectra[J]. Soil & Tillage Research, 2015, 146: 108－117.

[57] 李桂林，陳杰，檀滿枝，等. 基于土地利用變化建立土壤質(zhì)量評價最小數(shù)據(jù)集[J]. 土壤學(xué)報，2008，45(1)：16－25.

Li Guilin, Chen Jie, Tan Manzhi, et al. Establishment of a minimum dataset for soil quality assessment based on land use change[J]. Acta Pedologica Sinica, 2008, 45(1): 16－25. (in Chinese with English abstract)

[58] Bram Govaerts, Ken D Sayre, Jozef Deckers. A minimum data set for soil quality assessment of wheat and maize cropping in the highlands of Mexico[J]. Soil & Tillage Research, 2006, 87: 163－174.

[59] Lima A C R, Brussaard L, Totolac M R, et al. A functional evaluation of three indicator sets for assessing soil quality[J]. Applied Soil Ecology, 2013, 64: 194－200.

[60] 中華人民共和國水利部. 土壤侵蝕分類分級標準：SL 190－2007[S]. 北京：中國標準出版社，2008.

[61] 蘇正安，張建輝，聶小軍. 紫色土坡耕地土壤物理性質(zhì)空間變異對土壤侵蝕的響應(yīng)[J]. 農(nóng)業(yè)工程學(xué)報，2009，25(5)：54－60.

Su Zheng'an, Zhang Jianhui, Nie Xiaojun. Response of spatial variability of soil physical properties to soil erosion in purple soil slope farmland[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2009, 25(5): 54－60. (in Chinese with English abstract)

[62] Munkholm L J. Soil friability: A review of the concept, assessment and effects of soil properties and management[J]. Geoderma, 2011, 167/168(8): 236－246.

[63] Adélia N Nunes, António C de Almeida, Celeste O A Coelho. Impacts of land use and cover type on runoff and soil erosion in a marginal area of Portugal[J]. Applied Geography, 2011, 31: 687－699.

[64] 金慧芳，史東梅，陳正發(fā)，等. 基于聚類及PCA分析的紅壤坡耕地耕層土壤質(zhì)量評價指標[J]. 農(nóng)業(yè)工程學(xué)報，2018，34(7)：155－164.

Jin Huifang, Shi Dongmei, Chen Zhengfa, et al. Evaluation indicators of cultivated layer soil quality for red soil slope farmland based on cluster and PCA analysis[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2018, 34(7): 155－164. (in Chinese with English abstract)

[65] 馬芊紅，張光輝，耿韌，等我國水蝕區(qū)坡耕地土壤肥力現(xiàn)狀分析[J]. 水土保持學(xué)報，2018，34(7)：155－164.

Ma Qianhong, Zhang Guanghui, Gen Ren, et al. Present condition analysis of sloping farmland and soil fertility in the water erosion zone of China[J]. Journal of Soil and Water Conservation, 2018, 34(7): 155－164. (in Chinese with English abstract)

[66] Liu Gangcai, Li Lan, Wu Laosheng. Determination of Soil loss tolerance of an entisol in Southwest China[J/OL]. Soil Science Society of America Journal, 2009,73(2):412. DOI: 10.2136/sssaj2008.015

[67] Duan Xingguo, Shi Xiaoning, Li Yanbo, et al. A new method to calculate soil loss tolerance for sustainable soil productivity in farmland[J]. Agronomy for Sustainable Development, 2017, 37(1): 2.DOI: 10.1007/s13593-016-0409-3

Degradation effect of soil erosion on tillage-layer quality of slope farmland and its evaluation trend

Shi Dongmei1, Jin Huifang1, Jiang Guangyi2

(1.,,400715; 2.,401147,)

Soil erosion is the key driving force that causes tillage-layer quality degradation gradually and soil productivity variation precariously in sloping farmland. According to 2 functions of tillage-layer, erosion control and soil productivity, in this paper, we firstly focused on the ecological processes occurring in tillage-layer of farmland under the comprehensive interactions among soil erosion, soil and water conservation practices and agricultural activities at plot scale, and further summarized its influencing roads of soil erosion on tillage-layer qualityResults showed that: 1) Tillage-layer quality of sloping farmland was determined by the 2 ecological interaction process, rainfall erosion and tillage activities, and the temporal and spatial scales of these interaction on tillage-layer quality were very different. Soil properties functions indicating tillage-layer quality of slope farmland could be divided into such 4 types as water conservation, soil conservation, fertilizer conservation and production potential during a total agricultural production process. Crop-tillage coupling coordination could determine such characteristics of slope farmland as soil productivity, soil and water loss and the degradation direction & degree of tillage-layer caused by water erosion. 2) Tillage-layer quality was the characteristics of soil quality, its vertical combination along the active layer of crop root-system and underlying layer along the soil profile and the site conditions of sloping farmland. Tillage profile configuration of sloping farmland was the vertical distribution characteristics of soil texture, soil bulk density, soil porosity and soil mechanical resistance, so did its combination characteristics. The changes of tillage-layer quality of sloping farmland had obvious cumulative effects of water erosion on tillage disturbance. Degradation effects by water erosion on tillage-layer quality of sloping farmland were manifested in 3 aspects: deterioration of soil properties, deterioration of soil quality and decline of land productivity. The variation degree of soil physical properties was greater than that of chemical properties, and the decline of land productivity caused by runoff was greater than that caused by soil erosion. The change of crop yield had a significant hysteresis effect compared with soil quality degradation, meanwhile, soil permeability and soil erosion sensitivity had a direct correlation to the sustainable and stable productivity of sloping farmland. 3) In primary water erosion areas of China, an unified minimum data set of tillage-layer quality evaluation of sloping farmland should be set up aimed at the typical soil types and farming systems, which paid more close attention to the 2 functions of tillage-layer on erosion reduction and yield increase simultaneously. Such soil parameters as effective soil layer thickness, tillage layer thickness, soil bulk density, soil shear strength, soil organic matter and soil permeability could be included into the minimum data set for rational tillage-layer evaluation at plot scale. The time response characteristics of the minimum data set of tillage-layer quality should be fully taken into account in determining the threshold/suitable value. Rational tillage suitability of sloping farmland was divided into 5 grades, which were connected with soil erosion classification and cultivated land fertility classification. 4) Tillage-layer evaluation of slope farmland should focus on 3 aspects in the future, minimum data set of diagnosis index for tillage-layer quality, classification criteria of rational tillage threshold/suitable value and criterion of soil erosion control on sloping farmland. Accompanied by such normal indicators as soil erosion modulus, runoff coefficient and soil loss tolerance for protection of sloping farmland, the minimum data set index for diagnosing tillage-layer quality, as soil organic matter, soil infiltration, soil clay content could provide quantitatively a regional early-warning standards, which would benefit to more efficient soil and water loss control and realize sustainable utilization of sloping farmland These viewpoints were helpful in understanding the mechanism of degradation process caused by erosion of sloping farmland, and identifying quantitatively regulation approaches for rational cultivated-layer of sloping farmland, and also could provide some technical parameters for constructing rational tillage layer of slope farmland in water erosion area.

soils; erosion; organic matter;sloping farmland; tillage-layer quality; degradation effect; rational tillage-layer; diagnostic indicator

史東梅，金慧芳，蔣光毅. 土壤侵蝕對坡耕地耕層質(zhì)量退化作用及其評價趨勢展望[J]. 農(nóng)業(yè)工程學(xué)報，2019，35(18)：118－126.doi：10.11975/j.issn.1002-6819.2019.18.015 http://www.tcsae.org

Shi Dongmei, Jin Huifang, Jiang Guangyi. Degradation effect of soil erosion on tillage-layer quality of slope farmland and its evaluation trend[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2019, 35(18): 118－126. (in Chinese with English abstract) doi：10.11975/j.issn.1002-6819.2019.18.015 http://www.tcsae.org

2019-07-19

2019-08-10

國家自然科學(xué)基金（41771310）；公益性行業(yè)（農(nóng)業(yè)）科研專項（201503119-01-01）

史東梅，博士，教授，博士生導(dǎo)師，主要從事水土生態(tài)工程、土壤侵蝕與水土保持研究。Email：shidm_1970@126.com

10.11975/j.issn.1002-6819.2019.18.015

S157.1

A

1002-6819(2019)-18-0118-09