孟天竹，朱同彬，張金波,2,3，蔡祖聰,2,3*

(1 南京師范大學(xué)地理科學(xué)學(xué)院，南京 210023；2 江蘇省物質(zhì)循環(huán)與污染控制重點實驗室，南京 210023；3 江蘇省地理信息資源開發(fā)與利用協(xié)同創(chuàng)新中心，南京 210023)

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強(qiáng)還原處理中pH對硫酸根去除效果及產(chǎn)物的影響①

孟天竹1，朱同彬1，張金波1,2,3，蔡祖聰1,2,3*

(1 南京師范大學(xué)地理科學(xué)學(xué)院，南京 210023；2 江蘇省物質(zhì)循環(huán)與污染控制重點實驗室，南京 210023；3 江蘇省地理信息資源開發(fā)與利用協(xié)同創(chuàng)新中心，南京 210023)

摘 要：強(qiáng)還原滅菌法(reductive soil disinfestation,RSD)，即淹水加有機(jī)物料創(chuàng)造強(qiáng)還原條件，可以有效修復(fù)退化土壤，但對硫酸根去除效率低。為探索RSD處理時pH對去除效果的影響，本試驗選取積累嚴(yán)重的退化蔬菜地土壤設(shè)置5個處理：淹水(CK)；淹水+紫花苜蓿(RSD0)；淹水+紫花苜蓿+石灰，調(diào)節(jié)土壤至不同pH(分別標(biāo)記為RSD1、RSD2和RSD3)。培養(yǎng)結(jié)束后CK處理中含量仍高達(dá)S 691 mg/kg，顯著高于RSD處理中含量。在RSD處理中，含量隨著pH的提高而下降，但其他形態(tài)硫含量顯著升高，且施加石灰處理的土壤中總硫含量高于不加石灰的處理。由此說明，在強(qiáng)還原處理時施用石灰生成硫酸鈣沉淀，可有效降低含量，但不利于降低總硫含量。

關(guān)鍵詞：退化土壤；RSD；石灰；

因復(fù)種指數(shù)高、受季節(jié)影響小等優(yōu)點，近30年來，我國的設(shè)施蔬菜栽培種植面積持續(xù)增長，至2013年已達(dá)到165萬hm2，占農(nóng)田面積的14.5%[1]。值得注意的是，設(shè)施蔬菜種植過程中施用大量化肥，易引起土壤酸化、鹽漬化、硝態(tài)氮及硫酸根大量積累和土傳病害的發(fā)生[2-5]，導(dǎo)致土壤退化，影響設(shè)施蔬菜種植的可持續(xù)發(fā)展。

近年來，強(qiáng)還原土壤滅菌法(reductive soil disinfestation,RSD)作為一種環(huán)境友好型修復(fù)退化土壤的方法在美國、荷蘭和日本被廣泛采用[4,6-7]，該方法包括以下步驟：①向土壤中添加易降解有機(jī)物料，如：植物秸稈和綠肥等；②淹水或灌溉至土壤水分飽和；③覆膜以隔絕土壤與大氣的氣體交換。RSD方法創(chuàng)造的強(qiáng)還原條件可以殺滅土壤中的土傳病原菌和根結(jié)線蟲[7-8]，并可有效改善土壤結(jié)構(gòu)[9-10]，去除土壤中累積的硝態(tài)氮(NO3-)，降低土壤電導(dǎo)率(EC)，提高酸化土壤的pH[5]，因而不僅是有效的土壤滅菌方法，而且也是有效地改良退化土壤理化性質(zhì)的方法[11-12]。

但是，有研究指出硫酸還原菌在pH為中性(pH = 6～8)的條件下生長速度最快且濃度顯著下降[16-19]，而在酸性條件下硫酸還原菌生長幾乎可以忽略不計[20-21]。一般情況下，退化設(shè)施蔬菜地土壤酸化嚴(yán)重(pH = 4～5)，因此，調(diào)節(jié)土壤pH至中性，可能會促進(jìn)硫酸還原菌的活性，提高的去除效率。工業(yè)廢水(如礦業(yè)、食品加工業(yè)和造紙業(yè)等)處理過程中，為提高硫酸根還原菌對的去除效率，通常會施加NaOH、Ca(OH)2或CaO提高酸性廢水pH[16,22]。施撒石灰是一種常見的提高土壤pH的農(nóng)業(yè)措施，本研究選取累積的退化設(shè)施蔬菜地土壤，采用RSD處理，同時添加石灰調(diào)節(jié)土壤至不同pH，研究pH對去除效率及其產(chǎn)物的影響。

1 材料與方法

1.1 試驗材料

供試土壤采自安徽省烏江鎮(zhèn)和縣郊區(qū)(31°51′N,118°45′E)退化嚴(yán)重的設(shè)施蔬菜地。該地已種植大棚作物近10年，每年種植2～3茬(辣椒、西紅柿、茄子、甜瓜和四季豆)。土壤類型為普通簡育水耕人為土。在大棚內(nèi)隨機(jī)選取10個樣地采集土樣，采樣深度為0～20 cm。剔除土壤石塊和植物根系后，將新鮮土壤混合均勻，過2 mm篩，用塑封袋密封，于4℃下保存。供試土壤pH 4.4，電導(dǎo)率0.74 mS/cm，總碳15.9 g/kg，總氮2.08 g/kg，總硫1.02 g/kg，28.9 mg/kg，147 mg/kg939 mg/kg，土壤體積質(zhì)量 1.07 g/cm3。

RSD處理以紫花苜蓿為有機(jī)物料。供試紫花苜蓿購于山東省濱州市無棣縣，60oC 烘干后粉碎，過0.25 mm篩。紫花苜?？偺己繛?49 g/kg，總氮20.3 g/kg，總硫1.63 g/kg。

1.2 試驗設(shè)計

試驗設(shè)置5個處理：對照(淹水，CK)；淹水+紫花苜蓿(RSD0)；淹水+紫花苜蓿+石灰，石灰添加量分別為1.88、3.58和5.28 g/kg干土，調(diào)節(jié)土壤pH至6.7、7.7和8.4，分別標(biāo)記為RSD1、RSD2和RSD3。紫花苜蓿添加量為4.67 g/kg干土，折合大田施用量為9.8 t/hm2，隨紫花苜蓿添加到土壤的硫為10.9 mg/kg。

稱取相當(dāng)于210 g干土重的新鮮土壤與紫花苜蓿和不同用量的石灰充分混勻后裝入PVC柱中(直徑5 cm，高15 cm)。土層厚度為10 cm，體積質(zhì)量1.07 g/cm3。按水土比1︰1(質(zhì)量比)加入蒸餾水，形成厚約為1 cm的水層。35℃ 恒溫培養(yǎng)箱中培養(yǎng)360 h。分別在第24、48、72、120、240和360 h測定土壤氧化還原電位和pH，培養(yǎng)360 h后破壞性采樣。采樣時先打開PVC柱底的閥門將柱中的自由水排出，待水排干后(約10 min)關(guān)上閥門，將柱中土壤充分混勻。其中，一部分土樣用于土壤含水量測定，剩下的土樣測pH，EC，和總硫含量。定量淋溶液的體積后，過濾，分析和濃度。

1.3 測定方法

土壤pH(水土比2.5︰1)采用pH計(Mettler S220，瑞士)測定，土壤Eh用ORP檢測器(Mettler S220，瑞士)測定，土壤EC值(水土比5︰1)采用電導(dǎo)率儀(KangYi Corp.，中國)測定，土壤總碳和總氮采用SerCon 20-22同位素質(zhì)譜儀(SerCon Ltd，Crewe，美國)測定。土壤用2 mol/L KCl(水土比5︰1)浸提，25℃、300 r/min下震蕩1 h，定量濾紙過濾，采用流動分析儀測定浸提液中的含量(Skalar，Breda，荷蘭)。土壤用0.016 mol/L KH2PO4(水土比5︰1)浸提，25℃、300 r/min下震蕩1 h，8 000 r/min離心10 min，取上清液過0.45 μm 濾膜后用液相色譜測定濾液中濃度(Thermo Dionex ICS- 1100，美國)。土壤在60℃下烘干研磨過100目篩，采用元素分析儀(Elementar，Vario MAX CNS，德國)測定總硫含量。

1.4 數(shù)據(jù)處理

C(N)= V × L(N)/ w + C(N)R

采用SPSS 17.0軟件中Pearson相關(guān)系數(shù)進(jìn)行相關(guān)性分析，采用方差分析和Duncan法進(jìn)行處理間差異顯著性檢驗(α = 0.05)。

2 結(jié)果與分析

2.1 土壤pH、EC 和Eh變化

培養(yǎng)結(jié)束后，各處理土壤的pH均顯著高于土壤初始pH(4.38)(P＜0.05，表1)。不同處理的土壤pH在處理過程中的變化趨勢不同(圖1)。CK和RSD0處理的土壤pH分別升高至4.91和5.85，但RSD1、RSD2和RSD3處理pH分別降至6.55、7.07和7.43，各處理間pH差異顯著(P＜0.05)。同時，各處理土壤EC值顯著下降，CK、RSD0、RSD1、RSD2和RSD3處理EC值由初始的0.74 mS/cm分別降至0.53、0.39、0.31、0.29和0.27 mS/cm。

在培養(yǎng)過程中各處理的土壤Eh均下降，但下降模式和速率不同(圖2)，表現(xiàn)為pH越高，Eh下降速率越快。CK處理的土壤Eh緩慢下降，培養(yǎng)結(jié)束時僅從初期的412 mV下降到340 mV，RSD0處理的土壤Eh下降到 -100 mV以下需要240 h，而RSD+石灰處理僅需48 h，而后基本維持在 -100 mV以下(圖 2)。培養(yǎng)結(jié)束時的土壤Eh與土壤pH呈顯著負(fù)相關(guān)關(guān)系(r = -0.85，P＜0.01)，與EC呈顯著正相關(guān)關(guān)系(r = 0.93，P＜0.01，表 2)。

表1　培養(yǎng)結(jié)束后不同處理的土壤理化性質(zhì)Table 1 Soil properties under different treatments at the end of incubation

圖1　淹水條件下不同處理土壤pH的變化Fig.1 Changes in soil pH values under different treatments during 360 h incubation period

圖2　淹水條件下不同處理土壤Eh的變化Fig.2 Changes in soil Eh values under different treatments during 360 h incubation period

表2　培養(yǎng)結(jié)束時不同土壤理化性質(zhì)之間的相關(guān)系數(shù)Table 2 Correlation coefficients between different soil properties at the end of incubation

2.2 土壤氮、硫含量的變化

淹水添加紫花苜?？梢杂行コ寥乐欣鄯e的硝態(tài)氮。培養(yǎng)360 h后，CK處理中含量從初始的147 mg/kg下降至30.3 mg/kg，而RSD處理均降至1 mg/kg以下(表1)。含量變化與相反，培養(yǎng)結(jié)束后CK、RSD0、RSD1、RSD2和RSD3處理中含量分別升至56.5、50.4、55.9、72.4和81.0 mg/kg，比初始值28.9 mg/kg均有顯著提高(P＜0.05，表1)。

3 討論

與過去的研究結(jié)果相一致[5]，本試驗中RSD處理快速降低土壤Eh且完全消除了土壤中累積的單獨淹水處理(CK)土壤Eh下降非常緩慢(圖1)，硝態(tài)氮也未能完全去除(表1)，可能與供試土壤易降解有機(jī)碳不足有關(guān)，因而不能有效還原硝態(tài)氮及其他氧化物質(zhì)。淹水條件下添加苜蓿，提供了大量的易降解有機(jī)物，刺激了土壤微生物活性，造成了Eh的快速下降和有效去除。由于和其他氧化物質(zhì)還原消耗大量H+，使土壤pH顯著上升(表1)，因此RSD可以有效地提高酸化土壤的pH。在RSD處理過程中，由于有機(jī)氮的礦化和硝態(tài)氮異化還原為銨[23-24]，土壤中含量顯著升高(表1)。文獻(xiàn)資料表明，導(dǎo)致設(shè)施蔬菜地土壤次生鹽漬化的鹽主要為硫酸鹽和硝酸鹽[3]。RSD處理幾乎全部去除了硝酸根，大幅度降低了硫酸根含量，所以，經(jīng)RSD處理后土壤的次生鹽漬化程度下降，表現(xiàn)為EC值的降低(表1)。

RSD處理后，土壤回復(fù)到落干狀態(tài)，厭氧條件下轉(zhuǎn)化生成的有機(jī)硫和硫化物可能會再次礦化或氧化生成土壤再次酸化后硫酸鈣會解離成所以，RSD處理時，添加石灰對的轉(zhuǎn)化產(chǎn)物的長期影響還需要進(jìn)一步試驗驗證。添加石灰有利于增加和提高微生物的數(shù)量和活性，從而消耗更多的氧氣，促進(jìn)了RSD處理土壤Eh的下降(圖2)?？焖購?qiáng)還原條件可以有效殺滅病原菌菌絲及孢子，有利于增強(qiáng)RSD的殺菌效果[34-36]。此外，RSD處理時添加石灰提高了處理后的pH，為有益微生物的生長提供了更好的環(huán)境條件，不利于偏好酸性環(huán)境的病原菌的生長。然而，有機(jī)物料厭氧降解產(chǎn)生有機(jī)酸是RSD方法殺滅病原菌的一個重要機(jī)制[37-39]，只有未電離狀態(tài)的有機(jī)酸可穿透細(xì)胞膜，具有殺菌作用，而未電離狀態(tài)的有機(jī)酸含量和土壤pH呈負(fù)相關(guān)關(guān)系[40]，施加石灰會降低未電離狀態(tài)的有機(jī)酸。因此，施加石灰是否可以增強(qiáng)RSD方法的滅菌效果需要進(jìn)一步研究。由于添加石灰的正反效應(yīng)可能同時發(fā)生，RSD處理時添加石灰的實際效果需要田間試驗的驗證。

4 結(jié)論

RSD處理時施加石灰進(jìn)一步地改善土壤酸化和鹽漬化。同時，施加石灰可以有效降低土壤濃度，但減少的大部分并未從土壤中脫除而是轉(zhuǎn)化為其他硫形態(tài)繼續(xù)殘留在土壤中。施加石灰對強(qiáng)還原方法修復(fù)退化土壤的實際效果需要田間試驗的驗證。

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Effects of Liming on Sulfate Removal and Transformation in Degraded Vegetable Soil Treated by Reductive Soil Disinfestation(RSD)

MENG Tianzhu1,ZHU Tongbin1,ZHANG Jinbo1,2,3,CAI Zucong1,2,3*
(1 School of Geography Sciences,Nanjing Normal University,Nanjing 210023,China; 2 Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control,Nanjing 210023,China; 3 Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application,Nanjing 210023,China)

Abstract:Reductive soil disinfestations(RSD),namely amending organic materials and mulching or flooding to create strong reductive status,has been widely applied to improve degraded soils,but the removal efficiency of sulfatein RSD is low.To investigate the effect of liming onremoval during RSD treatment,aaccumulated(939 mg/kg)vegetable soil was treated by five treatments:control(flooding only,noted as CK),flooding + alfalfa(RSD0)and RSD0+ lime at three application rates,which adjusted soil pH to 6.7,7.7 and 8.4,noted as RSD1,RSD2and RSD3,respectively.The results showed thatcontent in CK treatment was as high as 691 mg/kg,and was significant higher than those in RSD treatments after the incubation.In RSD treatments,contents decreased with the increase of pH.But,other sulfur(S)forms increased significantly,which indicated that disappearedwas mainly transformed into other S forms.Total S contents in RSD+liming treatments were higher than that in RSD0treatment.The results indicates that liming stimulates the conversion ofinto calcium sulfate,which effectively decreasescontent but cannot decrease total S content.

Key words:Degraded soil; RSD; Lime;

作者簡介：孟天竹(1988—)，女，江蘇南京人，博士研究生，主要從事修復(fù)退化土壤方面的研究。E-mail:zmeng09@163.com

* 通訊作者(zccai@njnu.edu.cn)

基金項目：①江蘇省自然科學(xué)基金項目(BK20140062)、國家自然科學(xué)基金項目(41301313，41330744)和江蘇高校優(yōu)勢學(xué)科建設(shè)工程項目(PAPD，164320H116)資助。

DOI:10.13758/j.cnki.tr.2016.01.018

中圖分類號：S156