蔡耀輝，吳普特,※，張 林，朱德蘭,3，陳俊英,3，楊 帆

（1. 西北農(nóng)林科技大學(xué)水利與建筑工程學(xué)院，楊凌 712100；2. 西北農(nóng)林科技大學(xué)水土保持研究所，楊凌 712100；3. 西北農(nóng)林科技大學(xué)中國旱區(qū)節(jié)水農(nóng)業(yè)研究院，楊凌 712100）

設(shè)計(jì)流量和土壤質(zhì)地對(duì)微孔陶瓷灌水器入滲特性的影響

蔡耀輝1，吳普特1,2,3※，張 林2,3，朱德蘭1,3，陳俊英1,3，楊 帆1

（1. 西北農(nóng)林科技大學(xué)水利與建筑工程學(xué)院，楊凌 712100；2. 西北農(nóng)林科技大學(xué)水土保持研究所，楊凌 712100；3. 西北農(nóng)林科技大學(xué)中國旱區(qū)節(jié)水農(nóng)業(yè)研究院，楊凌 712100）

為探明微孔陶瓷灌水器土壤中入滲流量變化的原因，明確微孔陶瓷灌水器的出流原理，該研究基于土桶模擬試驗(yàn)，研究3種設(shè)計(jì)流量（0.72、1.87和4.40 L/h）的微孔陶瓷灌水器下2種土壤（黃綿土、塿土）的滲流特性。結(jié)果表明，使用不同灌水器灌溉后，短時(shí)間內(nèi)入滲流量均迅速減小，而后緩慢減小趨于穩(wěn)定。設(shè)計(jì)流量與土壤質(zhì)地均影響灌水器的出流。灌水器周圍土壤水勢的變化是造成入滲流量變化的直接原因，土壤含水率的變化是入滲流量變化的根本原因。在沒有淹沒出流的情況下，土壤含水率越高，入滲流量越小。設(shè)計(jì)流量為1.87 L/h灌水器應(yīng)用于塿土中，當(dāng)土壤含水率由13%增大至40%時(shí)，入滲流量由1.4 L/h下降至0.3 L/h左右。灌水器周圍土壤含水率對(duì)入滲流量具有反饋調(diào)節(jié)作用。采用微孔陶瓷灌水器作為灌溉系統(tǒng)的核心部件，在內(nèi)部水頭適宜（微壓或零壓）的情況下，通過灌水器入滲流量與土壤含水率的耦合作用，可實(shí)現(xiàn)土壤水分的自動(dòng)調(diào)控，達(dá)到主動(dòng)灌溉的目的。該文可為微孔陶瓷灌水器的推廣應(yīng)用提供參考。

質(zhì)地；土壤；含水率；微孔陶瓷灌水器；流量；水勢

蔡耀輝，吳普特，張 林，朱德蘭，陳俊英，楊 帆. 設(shè)計(jì)流量和土壤質(zhì)地對(duì)微孔陶瓷灌水器入滲特性的影響[J]. 農(nóng)業(yè)工程學(xué)報(bào)，2017，33(7)：100－106.doi：10.11975/j.issn.1002-6819.2017.07.013 http://www.tcsae.org

Cai Yaohui, Wu Pute, Zhang Lin, Zhu Delan, Chen Junying, Yang Fan. Effects of designed flow rate and soil texture on infiltration characteristics of porous ceramic irrigation emitters[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2017, 33(7): 100－106. (in Chinese with English abstract)doi：10.11975/j.issn.1002-6819.2017.07.013 http://www.tcsae.org

0 引 言

微孔陶瓷灌水器是一種造價(jià)低廉、性能優(yōu)良的新型灌水器，其利用微孔陶瓷作為滲水介質(zhì)對(duì)灌溉水進(jìn)行消能，直接向作物根部供水[1-4]。與常規(guī)滴灌技術(shù)相比，具有節(jié)水、節(jié)能等優(yōu)點(diǎn)，適宜在干旱和半干旱地區(qū)推廣應(yīng)用[5-6]。

作為一種新型的地下灌水器，有關(guān)微孔陶瓷灌水器土壤中滲流特性的研究較少[7-11]。徐增輝等[12]研究發(fā)現(xiàn)，2 m工作水頭下，免燒微孔陶瓷灌水器在黏壤土中的入滲流量隨著灌水歷時(shí)的增加逐漸趨于穩(wěn)定。任改萍等[13-14]研究發(fā)現(xiàn)，供水水頭越大，微孔陶瓷滲灌初始階段的入滲流量越大，相同時(shí)間的累計(jì)入滲量也越大。Gupta等[15]研究發(fā)現(xiàn)，土壤質(zhì)地對(duì)多孔黏土管的入滲流量影響較為顯著，土壤的飽和導(dǎo)水系數(shù)越大，多孔黏土管的入滲流量較空氣中設(shè)計(jì)流量增長幅度越大；同時(shí)在低水頭下，土壤毛細(xì)管力對(duì)多孔黏土管的入滲流量影響較大，但在高水頭下影響可以忽略不計(jì)。谷川寅彥等[16]研究發(fā)現(xiàn)，在砂質(zhì)黏壤土中、0.2 m工作水頭下，多孔素?zé)艿耐杆禂?shù)（設(shè)計(jì)流量）越大，累計(jì)灌水量越大；一定灌水量情況下，透水系數(shù)大可有效降低系統(tǒng)的工作水頭，同時(shí)可以發(fā)揮灌溉系統(tǒng)的自調(diào)節(jié)作用。上述研究分別對(duì)不同條件下陶瓷灌水裝置在土壤中的滲流特性進(jìn)行了分析，但對(duì)影響陶瓷灌水裝置入滲流量的主要原因分析不透徹。因此本研究的目的在于通過研究不同條件下微孔陶瓷灌水器的滲流規(guī)律，分析微孔陶瓷灌水器入滲流量變化的主要原因，進(jìn)而明確微孔陶瓷灌水器工作原理。

本研究基于室內(nèi)定容重土桶模擬試驗(yàn)，研究 3種設(shè)計(jì)流量（灌水器在空氣中設(shè)計(jì)水頭下的流量）的微孔陶瓷灌水器在 2種土壤中的滲流特性，分析灌水器入滲流量和周圍土壤含水率隨時(shí)間的變化規(guī)律，并通過灌水器周圍土壤水勢變化對(duì)灌水器入滲流量和含水率變化規(guī)律進(jìn)行解釋，旨在為微孔陶瓷灌水器的推廣應(yīng)用奠定基礎(chǔ)。

1 材料與方法

1.1 試驗(yàn)裝置與土樣

試驗(yàn)在西北農(nóng)林科技大學(xué)中國旱區(qū)節(jié)水農(nóng)業(yè)研究院灌溉水力學(xué)試驗(yàn)大廳進(jìn)行。試驗(yàn)裝置由土桶、馬氏瓶、排氣穩(wěn)壓管、灌水器和土壤水分傳感器組成（圖 1a）。土桶規(guī)格為37 cm×29 cm×42 cm（上直徑×下直徑×高）。土桶上有直徑為 20 mm的對(duì)稱小孔（距離土桶上邊緣16 cm）用以通過進(jìn)水管。供水裝置為馬氏瓶，其直徑為15 cm，高為66 cm。灌水器通過聚氯乙烯三通與輸水管道相連接，垂直埋置于土桶中，埋深為20 cm。灌水器采用西北農(nóng)林科技大學(xué)中國旱區(qū)節(jié)水農(nóng)業(yè)研究院研制的砂基微孔陶瓷灌水器（圖1b）。灌水器為圓柱形腔體結(jié)構(gòu)，以石英砂、滑石粉、糊精和硅溶膠為主要原料燒結(jié)而成，灌水器陶瓷材料內(nèi)部均勻分布著孔徑為10～100 μm的微孔，可實(shí)現(xiàn)灌溉水的消能與運(yùn)移。灌水器的結(jié)構(gòu)參數(shù)與性能參數(shù)如表1所示。設(shè)計(jì)流量為空氣中0.2 m水頭下的測定值。

圖1 試驗(yàn)裝置與微孔陶瓷灌水器示意圖Fig.1 Schematic of experimental device and porous ceramic irrigation emitter

表1 試驗(yàn)用灌水器特征參數(shù)Table1 Characteristic parameter of emitters used in experiment

試驗(yàn)選擇塿土和黃綿土 2種不同類型的土壤。塿土取自陜西渭河三級(jí)階地小麥田，黃綿土取自陜西省榆林市清澗縣店則溝鎮(zhèn)紅棗林地；取土深度均為30 cm，將取得的試驗(yàn)土壤風(fēng)干、碾壓、混合后過2 mm篩網(wǎng)分別留樣。土壤顆粒組成采用激光粒度分析儀（MS2000型，馬爾文，英國）測定，土壤飽和導(dǎo)水率利用土壤顆粒組成和容重，采用RETC軟件進(jìn)行估算，結(jié)果如表2所示。土壤水分特征曲線采用高速冰凍離心機(jī)（CR21G PF型，日立，日本）測定，結(jié)果如圖2所示。

表2 試驗(yàn)所用土壤的物理性能指標(biāo)Table2 Summary of physical properties for tested soils

圖2 塿土與黃綿土水分特征曲線Fig.2 Soil water characteristic curves of lou soil and loessial soil

1.2 試驗(yàn)方法與測定內(nèi)容

本試驗(yàn)包括灌水器設(shè)計(jì)流量和土壤質(zhì)地 2個(gè)因素。應(yīng)用3種不同設(shè)計(jì)流量的灌水器（S型、M型、B型）分別在 2種土壤（塿土、黃綿土）中進(jìn)行入滲試驗(yàn)，試驗(yàn)共6個(gè)處理，各處理重復(fù)3次，共進(jìn)行18組試驗(yàn)。將試驗(yàn)土樣（容重為1.35 g/cm3；填土?xí)r風(fēng)干塿土含水率為7%左右，風(fēng)干黃綿土含水率為5%左右）分層（每層5 cm）裝入土桶，分層界面處打毛，使土壤顆粒充分接觸。試驗(yàn)裝土深度為40 cm。土桶表面采用0.5 mm塑料薄膜覆蓋，以減小土壤水分蒸發(fā)損失對(duì)試驗(yàn)的影響。灌水器工作水頭通過馬氏瓶出口與灌水器中心點(diǎn)處高差決定，為0.2 m。試驗(yàn)裝置充滿水后，立刻采用秒表記錄灌水時(shí)間，同時(shí)記錄灌水開始時(shí)刻（北京時(shí)間，與土壤水分傳感器時(shí)刻一致）；按照先2 min后10 min的原則，記錄不同時(shí)刻馬氏瓶的水位線。灌水時(shí)間達(dá)到5 h時(shí)停止供水，灌水器的入滲流量根據(jù)單位時(shí)間馬氏瓶刻度和橫截面積乘積計(jì)算，試驗(yàn)數(shù)據(jù)取3次重復(fù)的平均值，L/h。同時(shí)在灌水器中心點(diǎn)周圍4 cm處均勻布置3個(gè)標(biāo)定后的土壤水分傳感器探頭（EC-5型，Decagon，美國），間隔1 min測定土壤含水率，試驗(yàn)數(shù)據(jù)取3個(gè)探頭所測得數(shù)據(jù)的平均值。

2 結(jié)果與分析

2.1 不同灌水器對(duì)土壤入滲的影響

圖3為不同灌水器設(shè)計(jì)流量和土質(zhì)條件下土壤累計(jì)入滲量與入滲流量在5 h內(nèi)隨時(shí)間的變化過程。從圖3可以看出，不同處理下土壤累計(jì)入滲量隨時(shí)間的變化較為類似。累計(jì)入滲量均隨灌水時(shí)間增加而逐漸增大。相同灌水時(shí)間下同類型灌水器在黃綿土的累計(jì)入滲量明顯大于塿土。相同灌水時(shí)間下，B型灌水器的累計(jì)入滲量最大，在5 h時(shí)黃綿土中為12.2 L，塿土中為8.8 L；M型灌水器的累計(jì)入滲量最小，在5 h時(shí)黃綿土中為3.65 L，塿土中為1.75 L。不同處理下灌水器入滲流量隨時(shí)間的變化也較為類似。灌水器入滲流量隨時(shí)間的變化趨勢可分為 2個(gè)階段：1）初始階段（灌水0.5 h左右），灌水器的入滲流量隨灌水時(shí)間的增加迅速減??；2）穩(wěn)定階段，隨著灌水時(shí)間的繼續(xù)增加，灌水器的入滲流量緩慢減小趨于穩(wěn)定。但B型灌水器在黃綿土中的出流規(guī)律略有不同，在灌溉4 h后，灌水器的累計(jì)入滲量為10.4 L，造成土桶中灌水器下部已經(jīng)完全飽和，進(jìn)而淹沒灌水器，此時(shí)灌水器相當(dāng)于淹沒出流，灌水器的累計(jì)入滲量越大，其周圍的水位越高，因此在4 h后其入滲流量會(huì)出現(xiàn)明顯的降低。

圖3 不同灌水器設(shè)計(jì)流量和土壤類型條件下累計(jì)入滲量與入滲流量隨時(shí)間的變化過程Fig.3 Cumulative infiltration and infiltration rate as function of time at emitter with different designed flow rate and soil type

表3為土壤平均入滲流量（0.5 h、5 h平均值）與灌水器設(shè)計(jì)流量。從表中看出，土壤類型會(huì)對(duì)入滲流量造成影響，黃綿土的入滲流量均大于塿土。設(shè)計(jì)流量對(duì)灌水器的實(shí)際出流有顯著影響（P＜0.05）。隨著灌水器設(shè)計(jì)流量增大，灌水器在塿土中的平均入滲流量出現(xiàn)先減小后增大。

表3 灌水器設(shè)計(jì)流量與不同時(shí)段土壤入滲流量Table3 Designed flow rate of emitters and infiltration rate in soil at different time

2.2 微孔陶瓷灌水器周圍土壤水勢估算

谷川寅彥等[16]研究發(fā)現(xiàn)，灌水器入滲流量變化是灌水器內(nèi)、外部水勢差和微孔陶瓷滲透系數(shù)共同作用的結(jié)果。因此由Darcy定律可得[17]

式中Q為灌水器的入滲流量，L/h；k為微孔陶瓷的滲透系數(shù)，cm/h；H為灌水器內(nèi)、外部水勢差，m；A為灌水器的滲流面積，cm2；L為灌水器的滲流路徑長度，cm；K為與灌水器結(jié)構(gòu)尺寸、滲透系數(shù)有關(guān)的常數(shù)，稱為流量系數(shù)，m2/h；H′為灌水器工作水頭，m；φ為灌水器外部土壤水勢，m。

因?yàn)榱髁肯禂?shù)K僅與灌水器結(jié)構(gòu)尺寸、滲透系數(shù)有關(guān)，因此空氣中和土壤中的流量系數(shù)保持不變。本研究中灌水器工作水頭H′均為0.2 m。根據(jù)圖3和式（1）計(jì)算得灌水器周圍土壤水勢如圖4所示。由圖4可以看出，灌水初期，灌水器周圍的土壤水勢迅速增大，隨著灌水進(jìn)行，土壤水勢逐漸趨于穩(wěn)定。土壤質(zhì)地不同會(huì)對(duì)灌水器周圍土壤水勢造成影響。隨著灌水器設(shè)計(jì)流量增大，灌水器周圍的土壤水勢出現(xiàn)先增大后減小的趨勢。

圖4 不同設(shè)計(jì)流量和土質(zhì)條件下灌水器周圍土壤水勢隨時(shí)間的變化過程Fig.4 Soil water potential as a function of time at emitters with different design flow rates and soil types

結(jié)合表3可以看出，在2種土壤中，B型、M型灌水器的平均流量均小于灌水器的設(shè)計(jì)流量。這是由于 B型、M 型灌水器設(shè)計(jì)流量較大，在灌水器周圍形成正壓區(qū)[18-21]，阻礙灌水器的出流，使得灌水器的入滲流量降低。由于 S型微孔陶瓷灌水器的設(shè)計(jì)流量較小，其設(shè)計(jì)流量接近于塿土的飽和導(dǎo)水率，小于黃綿土的飽和導(dǎo)水率。因此在塿土中，土壤對(duì)其出流的阻礙作用較小，因而其入滲流量與設(shè)計(jì)流量較為接近。但在黃綿土中，S型微孔陶瓷灌水器的入滲流量小于黃綿土的飽和導(dǎo)水率，微孔陶瓷灌水器周圍逐漸濕潤，土壤對(duì)灌水器出流的抑制作用尚不明顯，因此其入滲流量稍大于設(shè)計(jì)流量。

2.3 微孔陶瓷灌水器周圍土壤含水率隨時(shí)間變化規(guī)律

圖5為不同設(shè)計(jì)流量和土質(zhì)條件下灌水器周圍土壤含水率在300 min內(nèi)隨時(shí)間的變化過程。不同處理灌水器周圍土壤含水率隨時(shí)間的變化規(guī)律基本一致，略有差異。灌水器周圍土壤含水率在短時(shí)間內(nèi)迅速增加，接近飽和，B型灌水器周圍土壤含水率增加速率最快，M型次之，S型最慢。灌水300 min時(shí)灌水器周圍土壤含水率均接近于土壤飽和含水率。

圖5 不同設(shè)計(jì)流量和土質(zhì)條件下灌水器周圍土壤含水率隨時(shí)間的變化過程Fig.5 Soil water contents around emitters as a function of time at emitters with different designed flow rates and soil types

結(jié)合圖3～圖5可以看出，初始階段，灌溉水經(jīng)由灌水器消能進(jìn)入土壤，灌水器周圍的土壤含水率由 10%以下迅速增長，導(dǎo)致灌水器周圍土壤水勢迅速由負(fù)壓轉(zhuǎn)變?yōu)榱銐汉驼龎?，因此土壤?duì)灌水器的出流由促進(jìn)作用迅速轉(zhuǎn)變?yōu)橐种谱饔茫沟霉嗨魅霛B流量隨時(shí)間迅速減小。穩(wěn)定階段，灌水器周圍的土壤含水率趨于飽和，土壤水勢變化較小，土壤水分?jǐn)U散達(dá)到穩(wěn)定階段，灌水器的入滲流量基本維持穩(wěn)定。

2.4 微孔陶瓷灌水器周圍土壤水勢與入滲流量的關(guān)系

灌水器周圍土壤水勢（150～300 min的平均值）與灌水器設(shè)計(jì)流量關(guān)系如圖 6所示。隨著設(shè)計(jì)流量增大，灌水器外部土壤水勢逐漸向零壓和正壓轉(zhuǎn)變，而后正壓值出現(xiàn)先增大后減小的趨勢。當(dāng)灌水器的設(shè)計(jì)流量小于土壤的飽和導(dǎo)水率時(shí)，土壤對(duì)于灌水器的出流有促進(jìn)作用，灌水器周圍則以負(fù)壓為主。當(dāng)設(shè)計(jì)流量等于土壤的飽和導(dǎo)水率時(shí)，土壤對(duì)灌水器的出流無抑制作用，灌水器周圍則以零壓為主。當(dāng)設(shè)計(jì)流量大于土壤的飽和導(dǎo)水率時(shí)，土壤對(duì)灌水器的出流有抑制作用，灌水器周圍則以正壓為主。當(dāng)灌水器的設(shè)計(jì)流量遠(yuǎn)遠(yuǎn)大于土壤的飽和導(dǎo)水率時(shí)，灌水器周圍的土壤水勢仍為正壓，但較為復(fù)雜。本研究預(yù)試驗(yàn)表明，當(dāng)灌水器設(shè)計(jì)流量遠(yuǎn)遠(yuǎn)大于土壤的飽和導(dǎo)水率時(shí)，出流過程中，土壤水分會(huì)優(yōu)先在大孔隙中形成通道，灌水器周圍的土壤結(jié)構(gòu)可能就會(huì)受到破壞，形成空穴，滲流通道等。此時(shí)若滲流通道與地表連通，則灌水器周圍的正壓就下降到與此處的重力勢相等。若形成空穴，則灌水器周圍的正壓就與空穴內(nèi)部自由水面與灌水器中心點(diǎn)的高差有關(guān)，稱為積水深度[22]。

圖6 灌水器設(shè)計(jì)流量與土壤水勢關(guān)系Fig.6 Relationship between designed flow rate of emitter and soil water potential

國內(nèi)外學(xué)者[23-27]對(duì)地下滴灌的研究中發(fā)現(xiàn)，地下滴灌灌水器周圍的土壤水勢一般高達(dá)0.5～4.0 m。這是因?yàn)榈叵碌喂嗨捎霉嗨骶鶠辄c(diǎn)源入滲，灌溉水經(jīng)過灌水器消能后由灌水器出口進(jìn)入土壤，水分主要在灌水器出口處聚集，因而會(huì)使得灌水器出口處出現(xiàn)較高的正壓。這與本研究中灌水器周圍土壤水勢均未超過 0.2 m有顯著區(qū)別。張書函等[28]在滲灌管的研究中，滲灌管的設(shè)計(jì)流量為0.79 L/(h·m)，其入滲流量僅為0.06 L/h，該種情況下滲灌管周圍土壤水勢為負(fù)壓。滲灌管可類比為7 cm長的微孔陶瓷灌水器，微孔陶瓷灌水器與滲灌管類似，均為非點(diǎn)源入滲，而是面源入滲。灌溉水經(jīng)由灌水器中微孔消能后在整個(gè)灌水器外表面上與土壤接觸，相對(duì)于地下滴灌，即使是設(shè)計(jì)流量較大的陶瓷灌水器（B型）在單點(diǎn)處流量也較小，因此形成正壓比較低。而對(duì)于設(shè)計(jì)流量較小的陶瓷灌水器，灌水器周圍土壤水勢則為零壓或負(fù)壓。

綜上，土壤水勢的變化是灌水器入滲流量變化的直接原因。隨著設(shè)計(jì)流量增大，土壤對(duì)灌水器的出流由促進(jìn)逐漸轉(zhuǎn)變?yōu)橐种疲种颇芰t會(huì)出現(xiàn)先增大后減小的趨勢。因此，在同一土壤中，隨著設(shè)計(jì)流量增大，由于土壤水勢的作用，灌水器在土壤中的平均流量會(huì)出現(xiàn)先減小后增大的趨勢。

2.5 微孔陶瓷灌水器入滲流量與土壤含水率的耦合關(guān)系

圖7為不同處理下灌水器周圍含水率與入滲流量的關(guān)系曲線。從圖中可以看出，各處理灌水器入滲流量均隨著含水率的增大而減小。以塿土中M型灌水器為例，當(dāng)土壤含水率由13%增大至40%時(shí)，灌水器入滲流量由1.4 L/h下降至0.3 L/h左右，土壤含水率的增加使得土壤水勢由負(fù)壓逐漸轉(zhuǎn)變?yōu)檎龎?，因而?duì)灌水器出流也由促進(jìn)轉(zhuǎn)變?yōu)橐种疲沟霉嗨鞯娜霛B流量逐漸降低。在沒有淹沒出流的情況下（如黃綿土中B型灌水器 240 min后），土壤含水率越高，灌水器的入滲流量也就越小。灌水器周圍土壤含水率對(duì)灌水器入滲流量具有反作用。

圖7 不同灌水器在土壤中的入滲流量與周圍含水率關(guān)系Fig.7 Relationships between flow rate of different emitters in soil and soil water content around emitters

灌水器土壤中入滲流量發(fā)生變化的直接原因是土壤水勢的變化，但根本原因在于土壤含水率的變化。雷廷武等[29-32]利用陶土頭進(jìn)行負(fù)壓灌溉的試驗(yàn)結(jié)果表明，只需要灌水器內(nèi)部水頭大于外部水勢，灌溉水即可由灌水器流入土壤；灌水器停止出流的條件為內(nèi)部水頭等于外部水勢。在負(fù)水頭條件下，該工況較易出現(xiàn)。當(dāng)灌水器內(nèi)部工作水頭為正，灌水器外部土壤水勢為正壓；或者當(dāng)灌水器內(nèi)部工作水頭為0，灌水器外部土壤水勢為0，均可使灌水器停止出流。本研究中，當(dāng) S型灌水器內(nèi)部水頭為0，隨著灌溉進(jìn)行，灌水器周圍土壤達(dá)到飽和，土壤水勢為0，此時(shí)灌水器就會(huì)停止出流。當(dāng)M型灌水器內(nèi)部水頭為小于0.2 m的某一正值，隨著灌溉進(jìn)行，灌水器周圍土壤達(dá)到飽和，土壤水勢為正值，此時(shí)灌水器也會(huì)停止出流。因此采用微孔陶瓷灌水器作為灌溉系統(tǒng)的核心部件，在內(nèi)部水頭適宜（低壓或零壓）的情況下，通過灌水器入滲流量與土壤含水率的耦合作用，即可實(shí)現(xiàn)土壤水分的自動(dòng)調(diào)控，達(dá)到主動(dòng)灌溉的目的。

3 結(jié) 論

灌溉開始后短時(shí)間內(nèi)，灌水器入滲流量迅速減小，而后緩慢減小趨于穩(wěn)定。相同灌水時(shí)間下黃綿土中灌水器入滲流量均大于塿土中；隨著設(shè)計(jì)流量增大，灌水器在土壤中的平均流量出現(xiàn)先減小后增大的趨勢。

灌水器周圍土壤水勢變化是引起灌水器入滲流量變化的直接原因。當(dāng)灌水器的設(shè)計(jì)流量小于土壤的飽和導(dǎo)水率時(shí)，土壤對(duì)于灌水器的出流有促進(jìn)作用；灌水器周圍則以負(fù)壓為主；當(dāng)設(shè)計(jì)流量等于土壤的飽和導(dǎo)水率時(shí)，土壤對(duì)灌水器的出流無抑制作用，灌水器周圍則以零壓為主；當(dāng)設(shè)計(jì)流量大于土壤的飽和導(dǎo)水率時(shí)，土壤對(duì)灌水器的出流有抑制作用，灌水器周圍則以正壓為主。

土壤含水率的變化是引起灌水器入滲流量變化的根本原因。灌水開始后，灌水器周圍土壤含水率在短時(shí)間內(nèi)迅速增加，接近飽和。在沒有淹沒出流的情況下，土壤含水率越高，灌水器的入滲流量越小。對(duì)于設(shè)計(jì)流量為1.87 L/h灌水器，當(dāng)塿土土壤含水率由13%增大至40%時(shí)，灌水器入滲流量由1.4 L/h下降至0.3 L/h左右。灌水器周圍土壤含水率對(duì)灌水器入滲流量具有反饋調(diào)節(jié)作用。采用微孔陶瓷灌水器作為灌溉系統(tǒng)的核心部件，在內(nèi)部水頭適宜（微壓或零壓）的情況下，通過灌水器入滲流量與土壤含水率（水勢）的耦合作用，即可實(shí)現(xiàn)土壤水分的自動(dòng)調(diào)控，達(dá)到主動(dòng)灌溉的目的。

灌溉水、灌水器和土壤是一個(gè)相互關(guān)聯(lián)的系統(tǒng)，該研究只是初步對(duì)于 2種不同條件下灌水器出流規(guī)律進(jìn)行了研究，在后續(xù)工作中應(yīng)當(dāng)對(duì)工作水頭、設(shè)計(jì)流量與土壤導(dǎo)水能力加以綜合考慮，以期得出更為普遍定量的規(guī)律。

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Effects of designed flow rate and soil texture on infiltration characteristics of porous ceramic irrigation emitters

Cai Yaohui1, Wu Pute1,2,3※, Zhang Lin2,3, Zhu Delan1,3, Chen Junying1,3, Yang Fan1
(1. College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling 712100, China; 2. Institute of Soil and Water Conservation, Northwest A&F University, Yangling 712100, China; 3. Institute of Water Saving Agriculture in Arid Areas of China, Northwest A&F University, Yangling 712100, China)

Subsurface irrigation has been achieved by using pitchers, pots and ceramic tubes, which has gained a certain degree of interest in arid regions due to its high-water use efficiency. Porous ceramic irrigation emitter is an improved version of the traditional method of subsurface irrigation, and it has good performance and low cost. In order to minimize evaporation losses and deep percolation, a proper design for an irrigation system with ceramic emitters as the core component is required. In this study, we investigated the effects of designed flow rate and soil type on seepage characteristics of soil water content under the irrigation system with ceramic emitter. Soil tank laboratory experiments were conducted with 2 different soil types and 3 designed flow rates. The designed flow rates were 0.72, 1.87 and 4.40 L/h for the 2 soil types (Lou soil and Loessial soil). The Marriote bottle with 15 cm in diameter and 66 cm in height was used to supply water for the ceramic emitter during the experiment, the designed working pressure was 20 cm. The cumulative infiltration was measured by different water levels in Markov bottle. Porous ceramic emitter was prepared by a sintering and compression molding technology using silica, talc and silica sol as raw materials. The discharge coefficient of ceramic emitter was 4.23, 11.71, and 22.85, respectively. When the soil tank was filled with soil, the soil moisture sensors were installed around the ceramic emitter to record the changes of soil water content. The variations of cumulative infiltration, infiltration rate, soil water content, and soil water potential around emitters in the 6 different treatments were analyzed. The results showed that: 1) Infiltration rate of ceramic emitter in the soil decreased gradually with time and finally stabilized. On the contrary, the soil water content around the emitter increased rapidly, tending to approach saturation; 2) Soil texture had a great influence on the infiltration rate. The infiltration rate in lou soil was smaller than that in the loessial soil under the same designed flow rate. Designed flow rate had a great effect on the emitter flow rate in the soil. The average emitter flow rate increased at first then decreased with increase of the designed flow rate; 3) The change of soil water potential was the direct cause for changing of infiltration rate. When the designed flow rate higher than soil saturated hydraulic conductivity, a saturated zone formed around the emitter and a certain positive pressure was generated. Therefore, the infiltration rate was less than the designed flow rate. On the contrary, when the designed flow rate was smaller than soil saturated hydraulic conductivity, the soil water potential around the emitter would be negative pressure and promoted the outflow of emitter, and the infiltration rate would be bigger than designed flow rate; 4) When experiment started, soil water content around the emitter increased rapidly and reached closely to the saturated water content. For the emitter with designed flow rate of 1.87 L/h, the infiltration rate in lou soil decreased from 1.4 to 0.3 L/h when the soil water content increased from 13% to 40%. The higher the soil water content was, the smaller the infiltration rate was. Soil water content around emitters had an appreciable negative effect on emitter infiltration rate in the soil. There was a feedback regulation relationship between the water content and emitter flow rate. If a porous ceramic emitter with an appropriate designed flow rate, which working pressure head was extremely low or zero, the soil water content can be automatically controlled and the emitter would take the initiative to irrigate. Irrigation system is an interrelated subsurface system of irrigation water, ceramic emitter and soil, therefore, in the future, more factors such as working pressure, designed flow rate and soil saturated hydraulic conductivity should be comprehensive/y considered in studying the seepage characteristics of ceramic emitter.

texture; soils; water content; porous ceramic irrigation emitter; flow rate; soil water potential

10.11975/j.issn.1002-6819.2017.07.013

S275.6

A

1002-6819(2017)-07-0100-07

2016-07-18

2017-03-10

國家科技支撐計(jì)劃資助項(xiàng)目（2015BAD22B01-02）；高等學(xué)校學(xué)科創(chuàng)新引智計(jì)劃（111計(jì)劃）資助項(xiàng)目（B12007）；西北農(nóng)林科技大學(xué)基本科研業(yè)務(wù)專項(xiàng)資金資助項(xiàng)目（2014YB061）

蔡耀輝，男，陜西岐山人，博士生，主要從事節(jié)水灌溉新技術(shù)研究。楊凌 西北農(nóng)林科技大學(xué)水利與建筑工程學(xué)院，712100。

Email：yaohui_cai@163.com

※通信作者：吳普特，男，陜西武功人，研究員，博士生導(dǎo)師，主要從事節(jié)水農(nóng)業(yè)與水土保持方面的研究。楊凌 西北農(nóng)林科技大學(xué)中國旱區(qū)節(jié)水農(nóng)業(yè)研究院，712100。

Email：gjzwpt@vip.sina.com