劉小媛 高佩玲,2? 楊大明 張晴雯 張宇航
(1 山東理工大學(xué)農(nóng)業(yè)工程與食品科學(xué)學(xué)院,山東淄博 255049)
(2 山東理工大學(xué)資源與環(huán)境工程學(xué)院,山東淄博 255049)
(3 中國農(nóng)業(yè)科學(xué)院農(nóng)業(yè)環(huán)境與可持續(xù)發(fā)展研究所,北京 100086)
咸淡水間歇組合灌溉對鹽堿耕地土壤水鹽運(yùn)移特性的影響*
劉小媛1高佩玲1,2?楊大明1張晴雯3張宇航1
(1 山東理工大學(xué)農(nóng)業(yè)工程與食品科學(xué)學(xué)院,山東淄博 255049)
(2 山東理工大學(xué)資源與環(huán)境工程學(xué)院,山東淄博 255049)
(3 中國農(nóng)業(yè)科學(xué)院農(nóng)業(yè)環(huán)境與可持續(xù)發(fā)展研究所,北京 100086)
為探明土壤水鹽在咸淡水間歇組合灌溉條件下的運(yùn)移情況,采用室內(nèi)一維垂直積水入滲試驗(yàn),以全淡水和微咸水直接灌溉作為對照,設(shè)置了四種間歇時(shí)間,分別為 0、30、60、120 min,三種咸淡水組合比例,分別為 2∶1、1∶1、1∶2,進(jìn)行咸淡水間歇組合灌溉。結(jié)果表明:在同一入滲時(shí)間,間歇組合灌溉的累積入滲量大于淡水灌溉,與微咸水直接灌溉差異較??;累積入滲量(I)與濕潤鋒運(yùn)移深度(Zf)的決定系數(shù)R2均大于 0.99,I和Zf呈良好的線性關(guān)系;間歇組合灌溉的土壤含水率、灌水均勻度均遠(yuǎn)遠(yuǎn)大于淡水灌溉,但間歇組合灌溉的灌水均勻度隨著淡水所占灌水定額比例的增加而減小;在 5~45 cm作物根系密集區(qū),土壤整體脫鹽,但間歇組合灌溉土壤脫鹽率顯著高于微咸水直接灌溉,與淡水灌溉差異較小;不同間歇時(shí)間、組合比例對土壤脫鹽率的影響均達(dá)到顯著性水平。
間歇組合灌溉;灌水均勻度;一維垂直積水入滲試驗(yàn);脫鹽率
黃河三角洲地區(qū)自然資源豐富,開發(fā)前景廣闊,是我國重要的經(jīng)濟(jì)開發(fā)區(qū)[1]。該地區(qū)土地資源優(yōu)勢明顯,其未開發(fā)利用土地資源達(dá) 54.07 萬hm2[2],但土壤鹽漬化程度較高,鹽漬化土地面積高達(dá)44.29 萬hm2,占全區(qū)耕地總面積的52.5%。目前,對于鹽堿地改良已由早期的淡水漫灌洗鹽的方式逐步發(fā)展為以節(jié)約淡水資源為主的微咸水灌溉方式[3-6]。已有研究表明[7],利用微咸水進(jìn)行灌溉能夠促進(jìn)土壤顆粒的紊凝作用和團(tuán)聚性,使土壤大孔隙增加,入滲性能增強(qiáng)。但是,微咸水中含有Na+,如果土壤中 Na+含量過多,會(huì)造成土壤顆粒松散,破壞土壤結(jié)構(gòu),使土壤積鹽[8-10]。因此,合理開發(fā)利用微咸水資源,使之成為能被農(nóng)業(yè)生產(chǎn)所利用的新水源,不僅可以緩解該地區(qū)水資源供需矛盾,還可改良鹽堿耕地??沙掷m(xù)開發(fā)利用微咸水資源的關(guān)鍵是降低作物根系土層的鹽分含量,為作物提供良好的土壤水鹽環(huán)境。間歇灌溉,又稱波涌灌溉,是按照一定的時(shí)間間隔周期性供水的一種新的節(jié)水灌溉方式,具有節(jié)水、保肥、提高灌水均勻性等優(yōu)點(diǎn)[11]。國內(nèi)外學(xué)者對間歇灌溉的入滲機(jī)理進(jìn)行了廣泛的研究,邵俊昌[12]通過室內(nèi)土柱實(shí)驗(yàn),分析了微咸水間歇灌溉對土壤水鹽分布的影響,結(jié)果表明,在不同周期數(shù)、循環(huán)率的條件下,土壤入滲特性有所差異。雪靜等[13]通過室內(nèi)土柱實(shí)驗(yàn),發(fā)現(xiàn)微咸水間歇灌溉具有增加濕潤深度的特點(diǎn)。汪志榮等[14]分析了Green-Ampt 模型在連續(xù)和間歇入滲條件下的適用性,并建立了兩者的聯(lián)系,模型擬合精度較高。畢遠(yuǎn)杰等[15]通過室內(nèi)土柱實(shí)驗(yàn),研究了淡水與微咸水連續(xù)與間歇入滲特性的差異,結(jié)果表明,淡水間歇入滲減滲,微咸水間歇入滲增滲。上述研究初步揭示了間歇灌溉的理論基礎(chǔ),對于間歇灌溉的實(shí)際應(yīng)用具有重要意義。但前人的研究多集中在非鹽堿土壤在淡水或者微咸水灌溉條件下的間歇入滲機(jī)理,而對于鹽堿土壤在間歇組合灌溉條件下的入滲機(jī)理研究較少。
本文以地處黃河三角洲地區(qū)的山東省濱州市濱城區(qū)的中度鹽堿化土壤為研究對象,將間歇灌溉和先咸后淡組合灌溉相結(jié)合,在室內(nèi)進(jìn)行一維垂直積水入滲試驗(yàn),分析對比不同間歇時(shí)間、咸淡水組合比例對中度鹽堿土壤水鹽再分布規(guī)律的影響,以期為黃河三角洲地區(qū)鹽堿耕地合理利用微咸水灌溉提供理論依據(jù)和技術(shù)支撐。
試驗(yàn)用土取自山東省濱州市濱城區(qū)的小麥耕地,土壤類型為鹽化潮土。取土深度為80 cm,每隔20 cm分層取擾動(dòng)土和原狀土,原狀土取回后立即測定土壤容重和田間持水率,分別為1.39 g cm-3和 28.62%;擾動(dòng)土經(jīng)過風(fēng)干、碾壓、篩分(2 mm篩)、均勻混合后制備成室內(nèi)試驗(yàn)土樣。利用激光粒度儀(Mastersizer3000,英國)測定其土壤顆粒組成,并按照國際制土壤質(zhì)地分類標(biāo)準(zhǔn)分類,砂粒、粉粒和黏粒體積分?jǐn)?shù)分別為20.26%、76.78%和2.96%,屬于粉砂質(zhì)壤土。土壤初始含水率為2.00%,土壤全鹽量為2.381 g kg-1,屬于中度鹽堿化土壤。
試驗(yàn)用水中淡水使用的是蒸餾水,礦化度為0 g L-1;3 g L-1的微咸水根據(jù)研究區(qū)潛層地下微咸水的鹽分組成特點(diǎn),在室內(nèi)利用NaHCO3、Na2SO4、CaCl2、MgCl2和NaCl室內(nèi)配制而成,含量分別為783、602、377、644和596 mg L-1。
灌水定額M根據(jù)下式計(jì)算得:
式中,H為土壤計(jì)劃濕潤層深度,由于當(dāng)?shù)氐牡叵滤惠^高,且為鹽堿化較嚴(yán)重的地區(qū),故計(jì)劃濕潤層深度不易超過60 cm[16],故H取60 cm;θmax為土壤計(jì)劃濕潤層所允許的最大含水率(占干土重),一般為田間持水率,取28.62%;θ0為土壤計(jì)劃濕潤層初始含水率(占干土重),取2.00%;γ土、γ水分別為土壤干容重和水的密度,取1.39 g cm-3和1 g cm-3。由式(1)計(jì)算得到一次實(shí)驗(yàn)的灌水定額為22.2 cm。
試驗(yàn)裝置由試驗(yàn)土柱和馬氏瓶兩部分組成(圖1)。試驗(yàn)土柱采用內(nèi)徑為8 cm,高為90 cm的有機(jī)玻璃制成,土柱兩側(cè)每隔5 cm開一直徑為15 mm的對稱圓形取樣口(距土柱上沿10 cm以下);利用馬氏瓶供水,其截面積為50.24 cm2,高為50 cm,供水水頭控制在1.5~2.0 cm。土柱與馬氏瓶外壁標(biāo)有刻度,用于觀測馬氏瓶水位和濕潤鋒運(yùn)移深度。
圖1 試驗(yàn)裝置圖Fig. 1 Experiment device diagram
以全淡水和微咸水直接灌溉作為對照,設(shè)置了四種間歇時(shí)間,分別為0 min、30 min、60 min、120 min;三種咸淡水組合比例,分別為2∶1、1∶1、1∶2,進(jìn)行間歇組合灌溉。在試驗(yàn)過程中,將灌水定額分成兩份,第一份為微咸水,第二份為淡水,單輪入滲結(jié)束,間歇一定的時(shí)間后,進(jìn)行下一輪入滲,具體的微咸水與淡水灌溉水量如表1所示。為了保證試驗(yàn)數(shù)據(jù)的可靠性,每個(gè)處理重復(fù)三次。
試驗(yàn)土樣按土壤容重1.39 g cm-3分層(5 cm)裝,共16層。填裝完畢后,在土表放置一張與土柱內(nèi)截面積相同的帶孔濾紙以防止灌水時(shí)對表土的沖刷。在試驗(yàn)過程中用秒表計(jì)時(shí),按照先密后疏的原則記錄濕潤鋒運(yùn)移深度和馬氏瓶水位。當(dāng)灌水定額入滲結(jié)束后,立即從土表至濕潤鋒處每隔5 cm提取土樣,用烘干法測定土壤含水率,利用電導(dǎo)率儀(DDS-11A,上海)測定水土比為5∶1的土壤溶液電導(dǎo)率,并利用土壤含鹽量與土壤浸提液電導(dǎo)率之間的關(guān)系,將電導(dǎo)率轉(zhuǎn)化為含鹽量,具體的轉(zhuǎn)化公式為:
表1 間歇組合灌溉下灌溉水量試驗(yàn)方案Table 1 Experimental scheme of irrigation water amount under intermittent combined irrigation(ICI)
式中,y為土壤含鹽量,g kg-1;ED5∶1為25℃下水土比為5∶1的土壤浸提液電導(dǎo)率,mS cm-1。
采用Microsoft Office Excel 2010進(jìn)行數(shù)據(jù)整理,Origin9.0軟件繪圖,SPSS22.0進(jìn)行數(shù)據(jù)分析,采用單因素方差分析(One-way ANOVA)和最小顯著差異(LSD)法比較不同土層間和處理間土壤脫鹽率的差異。
2.1.1 對累積入滲量的影響 為了對比分析間歇組合灌溉模式對土壤累積入滲量的影響,點(diǎn)繪不同組合比例、間歇時(shí)間下土壤累積入滲量隨入滲時(shí)間的變化曲線,見圖2a、圖2b。由圖2a、圖2b 可知,入滲初期,所有處理的累積入滲量增長速度較快,入滲中后期,增幅變緩。在同一入滲歷時(shí),間歇組合灌溉的累積入滲量大于淡水,與微咸水直接灌溉差異較小。圖2a表明,在同一入滲時(shí)間下,累積入滲量隨微咸水灌水份額的增加而增加;灌溉定額入滲結(jié)束的時(shí)間隨淡水份額的增加而增加。圖2b表明,在相同入滲時(shí)間,累積入滲量大小順序依次為:間歇組合灌溉0 min > 間歇組合灌溉30 min >間歇組合灌溉60 min >間歇組合灌溉120 min。這主要由于停水時(shí)間越長,致密層形成的越充分,越穩(wěn)定,土壤導(dǎo)水率減小,累積入滲量減小。
2.1.2 對濕潤鋒運(yùn)移深度的影響 在一維垂直積水入滲過程中,水分在土體內(nèi)運(yùn)移,土壤被濕潤部分隨著入滲時(shí)間的增加而增大。對于不同的咸淡水間歇組合灌溉模式,濕潤鋒推進(jìn)速度隨入滲時(shí)間的變化不同。圖2 c、圖2d 表示不同組合比例、間歇時(shí)間濕潤鋒運(yùn)移深度的變化規(guī)律,由圖2c、圖2d可以看出,入滲初期,濕潤鋒運(yùn)移速度較快,各個(gè)處理間的曲線基本重合,隨著時(shí)間的延長,濕潤鋒運(yùn)移深度與入滲時(shí)間的變化曲線斜率發(fā)生不同程度的減小,且各個(gè)處理間的差距越來越大。對比圖2a、圖2b可知,其與累積入滲量隨入滲時(shí)間的變化規(guī)律基本一致,為了定量分析兩者的關(guān)系,利用線性方程進(jìn)行擬合:
式中,I為累積入滲量,
cm;Zf為濕潤鋒運(yùn)移深度,cm;A為擬合系數(shù)。
由表2可知,累積入滲量與濕潤鋒運(yùn)移深度的決定系數(shù)R2均大于0.99,I和Zf的線性關(guān)系成立。在同一間歇時(shí)間下,擬合系數(shù)A的變化規(guī)律表現(xiàn)為咸∶淡=2∶1>咸∶淡=1∶1>咸∶淡=1∶2。對于咸∶淡=2∶1,隨著間歇時(shí)間的增加,擬合系數(shù)A增加,而對于咸∶淡=1∶1,咸∶淡=1∶2,擬合系數(shù)A隨著間歇時(shí)間的增加呈現(xiàn)先增大后減小的趨勢。
土壤水分入滲是指水分通過地表或入滲界面進(jìn)入土壤的過程[17]。入滲結(jié)束后,農(nóng)田土壤水分分布情況決定了作物對其吸收利用的程度和土壤水分的有效性[18]。不同組合比例、間歇時(shí)間土壤含水率隨土層的變化情況見圖3。由圖3可以看出,在土壤上層(5~10 cm),淡水灌溉的土壤含水率最大;在土壤中下層(10~50 cm),間歇組合灌溉的土壤含水率遠(yuǎn)遠(yuǎn)大于淡水灌溉,與微咸水直接灌溉差異較小,說明間歇組合灌溉有利于提高中下層土壤的持水能力。由圖3a可知,在同一土層深度,土壤含水率變化規(guī)律為:咸∶淡=2∶1>咸∶淡=1∶1 >咸∶淡=1∶2,即土壤含水率與咸水所占灌溉定額比例大小呈正比。由圖3b可知,在土壤的表層和下層,土壤含水率表現(xiàn)為:間歇組合灌溉0 min>間歇組合灌溉30 min >間歇組合灌溉60 min >間歇組合灌溉120 min;而對于中層土壤,間歇組合灌溉0 min土壤含水率最低,但仍遠(yuǎn)高于淡水灌溉。故在實(shí)際灌溉中,苗期使用間歇組合灌溉0 min、生育旺期使用間歇組合灌溉30 min進(jìn)行灌溉,更有益于提高農(nóng)田水資源利用效率,使大部分水分貯存在土壤有效深度內(nèi),有利于作物的吸收利用。
表2 間歇組合灌溉模式下累積入滲量與濕潤鋒運(yùn)移深度的擬合系數(shù)Table 2 Fitted parameters of cumulative infiltration and downward depth of wetting front relative to ICI mode
圖3 間歇組合灌溉土壤含水率隨土層深度的變化規(guī)律Fig. 3 Variation of soil water content with soil depth under ICI
為了更加全面地分析間歇組合灌溉對土壤含水率的影響,引入衡量灌水質(zhì)量的重要指標(biāo)灌水均勻度Ed
[19-21],計(jì)算公式如下:
式中,Zi為各層的土壤含水率,%;Z—為土壤含水率的平均值,%;N為取樣層數(shù)。
由表3可知,間歇組合灌溉的灌水均勻度均高于全淡水灌溉。在間歇組合灌溉模式下,灌水均勻度與間歇時(shí)間的關(guān)系不明顯,如在組合比例為1∶1條件下,間歇時(shí)間由0 min提高至30 min、60 min、120 min時(shí),均勻度基本穩(wěn)定在0.96左右。灌水均勻度隨著淡水所占灌水定額比例的增加而減小,造成這種現(xiàn)象的原因可能是,利用微咸水進(jìn)行灌溉能改善土壤結(jié)構(gòu),增強(qiáng)土壤持水能力,但當(dāng)微咸水入滲量減小時(shí),土壤結(jié)構(gòu)形成不充分,故對土壤含水率的分布情況影響不明顯。
為了進(jìn)一步研究間歇組合灌溉對土壤鹽分的淋洗效果,引入土壤脫鹽率來進(jìn)行說明。土壤脫鹽率的計(jì)算方法如下:
表3 間歇組合灌溉土壤灌水均勻度Table 3 Irrigation uniformity under ICI
式中,S1為土壤初始含鹽量,g kg-1;S2為灌后土壤含鹽量,g kg-1。不同間歇組合灌溉模式土壤各層次的脫鹽率如表4所示。
由表4可知,對于所有處理,在5~45 cm作物根系密集區(qū),土壤整體脫鹽,但間歇組合灌溉土壤脫鹽率顯著高于微咸水直接灌溉,與淡水灌溉差異較小。咸淡水組合比例對土壤脫鹽率的影響差異較顯著,淡水所占灌水定額比例越高,脫鹽效果越好,越有利于為作物提供良好的土壤水鹽環(huán)境。間歇組合灌溉對各土層土壤脫鹽率的顯著性分析結(jié)果表明,不同間歇時(shí)間、組合比例對土壤脫鹽率的影響均達(dá)到顯著水平,說明間歇組合灌溉參數(shù)對土壤鹽分的運(yùn)移具有重要影響。由土壤脫鹽率平均值顯著性分析結(jié)果可知,在間歇時(shí)間為0 min、120 min時(shí),組合比例1∶1與1∶2之間的差異不顯著,1∶2與2∶1間差異較顯著;在間歇時(shí)間為30 min、60 min時(shí),所有處理之間的差異均不顯著;微咸水直接灌溉條件下土壤脫鹽率平均值顯著低于其他處理。
表4 間歇組合灌溉模式下的土壤各層次脫鹽率Table 4 Soil desalinization rate of different depth relative to ICI mode(%)
利用微咸水灌溉不僅可以使作物增產(chǎn),而且可改良鹽堿土壤[22-24]?;诖?,有學(xué)者提出了集咸淡水組合灌溉模式、間歇灌溉方式、作物輪作等一體化的微咸水灌溉調(diào)控技術(shù)。咸淡水組合灌溉應(yīng)用于輕度鹽堿化土壤能夠有效提高土壤脫鹽效果,但淡咸咸組合灌溉模式是最合理的入滲模式[25]。在非鹽堿化土壤,淡淡咸組合灌溉模式有利于土壤脫鹽,而咸淡淡能夠有效地淋洗小麥主根區(qū)的土壤鹽分[26]。在濱海鹽土區(qū),由于土壤含鹽量較高、有機(jī)質(zhì)和速效養(yǎng)分含量較低,先用咸水灌溉達(dá)到穩(wěn)定狀態(tài),再采用淡水灌溉方式淋洗,效果最好,其脫鹽速度最快,脫鹽率最高[27],與本試驗(yàn)結(jié)果基本一致。但本試驗(yàn)結(jié)果與吳忠東等[25]、米迎賓等[26]研究結(jié)果區(qū)別較大,產(chǎn)生這種差異的原因可能主要是:與非鹽堿化土壤相比,鹽堿化土壤中離子含量豐富,與微咸水中的離子發(fā)生交換吸附作用,使土壤結(jié)構(gòu)發(fā)生改變,改善了土壤的入滲性能。
間歇灌溉是一項(xiàng)新型的田間節(jié)水灌溉技術(shù),主要包括周期數(shù)、間歇時(shí)間等技術(shù)參數(shù)。畢遠(yuǎn)杰等[15]探究了微咸水與淡水間歇入滲特性的差異,結(jié)果表明,隨著間歇時(shí)間的增加,微咸水間歇灌溉的增滲效果變強(qiáng)。劉靜妍等[28]研究表明,與連續(xù)灌溉相比,間歇灌溉土壤水分分布更均勻,且間歇灌溉未從本質(zhì)上改變濕潤鋒運(yùn)移深度與累積入滲量的線性函數(shù)關(guān)系,與本試驗(yàn)結(jié)果基本一致。產(chǎn)生這種現(xiàn)象的主要原因可能是:①在間歇灌溉中,灌水是間斷式的,土壤經(jīng)受灌水濕潤與停水落干的交替過程,土壤顆粒重分布,土壤表層的物理結(jié)構(gòu)、性狀發(fā)生改變,使土壤糙率減小,創(chuàng)造了新的水流界面,提高了灌水均勻性;②表層土壤容重增加,使地表形成致密層,土壤孔隙減少,導(dǎo)水率減小,入滲速率降低,這為節(jié)水、提高灌水效率和改善灌水質(zhì)量起到了重要作用。
土壤鹽分的分布易受土壤含水率、土壤結(jié)構(gòu)、灌溉水質(zhì)等多種因素的影響,咸淡水間歇灌溉可以改善土壤水鹽環(huán)境,對作物的生長產(chǎn)生影響。嚴(yán)亞龍等[29]研究發(fā)現(xiàn),周期數(shù)對土壤鹽分含量分布有一定影響,間歇時(shí)間對土壤鹽分含量無顯著影響,而本研究發(fā)現(xiàn),在間歇組合灌溉條件下,間歇時(shí)間對土壤脫鹽率的影響均達(dá)到顯著水平。吳忠東和王全九[30]研究表明,與連續(xù)灌溉相比,間歇灌溉有效降低了土壤鹽分局部累積的發(fā)生,保證了土壤的可持續(xù)利用,與本研究結(jié)果基本一致。本研究還發(fā)現(xiàn),間歇組合灌溉對作物根系密集區(qū)(0~45 cm)的鹽分具有淋洗作用,形成低鹽區(qū),不會(huì)對作物產(chǎn)生鹽害。同時(shí),咸淡水組合比例對土壤脫鹽率具有重要影響,淡水所占灌水定額比例越高,脫鹽效果越好,越有利于為作物提供良好的土壤水鹽環(huán)境。故在實(shí)際灌溉中,應(yīng)根據(jù)作物的耐鹽度和作物根系活動(dòng)層選擇合適的間歇組合灌溉參數(shù),將土壤鹽分對作物的脅迫損害降至最低。
綜上所述,利用咸淡水間歇組合灌溉模式,更有利于為作物提供良好的土壤水鹽環(huán)境。由于時(shí)間與條件所限,本試驗(yàn)僅在室內(nèi)條件下進(jìn)行,所得結(jié)論有一定的局限性,需要大田試驗(yàn)驗(yàn)證。為了獲得鹽堿地作物高產(chǎn)優(yōu)質(zhì)效果,今后應(yīng)綜合考慮土壤鹽分、pH及土壤鹽分離子等重要參考指標(biāo),全面系統(tǒng)地研究它們對作物產(chǎn)量和品質(zhì)的影響。
室內(nèi)土柱試驗(yàn)下,在同一入滲歷時(shí),間歇組合灌溉累積入滲量、濕潤鋒運(yùn)移深度均大于淡水灌溉,與微咸水灌溉差異較小,且在間歇組合灌溉條件下,累積入滲量、濕潤鋒運(yùn)移深度均隨淡水份額的增加、間歇時(shí)間的減小而增大。在整個(gè)入滲過程中,濕潤鋒運(yùn)移深度與累積入滲量呈線性關(guān)系。間歇組合灌溉能夠顯著提高每層土壤的含水率,且土壤含水率分布更均勻。在5~45 cm作物根系密集區(qū),間歇組合灌溉脫鹽效果更好,更能為作物提供良好的生長環(huán)境。
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(責(zé)任編輯:陳榮府)
Effects of Intermittent Combined Irrigation on the Characteristics of Soil Water and Salt Movement in Farm Land of Salt-affected Soil
LIU Xiaoyuan1GAO Peiling1,2?YANG Daming1ZHANG Qingwen3ZHANG Yuhang1
(1 Institute of Agriculture Engineering and Food Science,Shandong University of Technology,Zibo,Shandong 255049,China)
(2 Institute of Resources and Environment Engineering,Shandong University of Technology,Zibo,Shandong 255049,China)
(3 Institute of Environment and Sustainable Development in Agriculture,Chinese Academy of Agricultural Sciences,Beijing 100086,China)
【Objective】Researchers in the Salt Soil Laboratory of the USA(United States Department of Agriculture,1954)and ASCE(American Society of Civil Engineers,1990)have brought forth a series of advice aiming at ameliorating salt-affected soils. Amelioration of salt-affected soils requires for the first priority removal of excessive soluble salt. However,in actual productive application,the only method available for reducing soluble salt content in the root zone of the crop is to wash the salt off the soil with fresh water. Owing to shortage of fresh water resources,the use of brackish water as replacement has aroused extensive attention. Reasonable exploitation of brackish water can not only improve crop production,but also ameliorate salt-affected soils. To explore characteristics of soil and water movement in the fields under intermittent combined irrigation(ICI),a lab experiment was conducted in an attempt to provide certain theoretical basis and technical support for reasonable use of brackish water in moderately salt-affected soil.【Method】The experimental system consisted of soil columns and Mariotte bottles. The latter was used to supply water with a constant water head of 1.5~2 cm. The one-dimension vertical water infiltration experiment was designed to have four treatments in terms of interval in intermittent irrigation,i.e. 0 min,30 min,60 min and 120 min and five treatments in terms of combination of the irrigation water,i.e. simple fresh water(F),simple brackish water(B),2∶1(brackish and fresh water),1∶1(brackish and fresh water)and 1∶2(brackish and fresh water). During the experiment,wetting front movement and cumulative infiltration was monitored. At the end of the experiment,soil samples were extracted at the soil extraction port as quickly as possible to avoid the effect of water redistribution inside the cylinder,and soil water content was measured with the oven-drying method and electrical conductivity of the soil solution with a conductivity meter.【Result】Cumulative infiltration was relatively high during the initial stage of infiltration,and dropped drastically with the experiment going on. Measurements done at the same time show that the treatments of ICI were all higher than Treatments F,but differed slightly from Treatment B in cumulative infiltration,and among the treatments of ICI,the same in quantity of water supply,cumulative infiltration increased with the ratio of brackish water. And the infiltration lasted longer when the ratio of fresh water was higher. Cumulative infiltration was in good linear relationship with wetting front movement(R2>0.99). Determination of soil water content at the same soil depth shows that the treatments of ICI exhibited an order of ICI 2∶1(Brackish water :Fresh water)> ICI 1∶1 > ICI 1∶2,indicating that soil water content was positively related proportional to ratio of brackish water. Treatments ICI were all higher than Treatment F in irrigation uniformity,which was negatively related to ratio of fresh water. In the 5~45 cm crop root zone,soil desalinization rate was significantly higher in Treatments ICI than in Treatment B,and varied sharply between the treatments. The higher the proportion of fresh water,the higher the soil desalinization rate,the more favorable the salt-water environment for the crop to grow in. Significance tests of the effects of Treatments ICI on soil desalinization rate show that all the treatments reached significant levels,regardless of combination ratio and length of interval,indicating that the parameters of ICI have important on soil salt movement.【Conclusion】Intermittent combined irrigation is more conducive than other irrigation modes to the formation of a good soil water-salt environment for crops to grow. In actual productive application,a proper combination(fresh water and brackish water ratio and interval)should be designed and used in the light of crop salt tolerance and depth of the main root system active zone,so as to minimize damage of salt stress to crops.
Intermittent combined irrigation;Irrigation uniformity;One-dimension vertical water infiltration experiments;Soil desalinization rate
S275.8
A
10.11766/trxb201705090207
* 國家水體污染控制與治理科技重大專項(xiàng)(2015ZX07203-007)、國家自然科學(xué)基金項(xiàng)目(41402208)和山東省自然科學(xué)基金項(xiàng)目(ZR2016EEM34)資助 Supported by the National Major Science and Technology Program for Water Pollution Control and Treatment(No.2015ZX07203-007),the National Natural Science Foundation of China(No.41402208)and the Natural Science Foundation of Shandong Province(No.ZR2016EEM34)
? 通訊作者 Corresponding author,E-mail:gaoplxj@163.com
劉小媛(1991—),女,山東青島人,碩士,主要從事農(nóng)業(yè)水土工程研究。E-mail:402983329@qq.com
2017-05-09;
2017-07-23;優(yōu)先數(shù)字出版日期(www.cnki.net):2017-08-18