磷石膏、红糖等对蚯蚓改良滨海盐土的促进作用*
2017-02-23涛李素艳孙向阳王振宇张洋张乐龚小强赵秀芳谢志远宋国香
张 涛李素艳孙向阳王振宇张 洋张 乐龚小强赵秀芳谢志远宋国香
(1 北京林业大学林学院,北京 100083)
(2 天津泰达盐碱地绿化研究中心有限公司,天津 300457)
磷石膏、红糖等对蚯蚓改良滨海盐土的促进作用*
张 涛1,2李素艳1†孙向阳1王振宇2张 洋1张 乐1龚小强1赵秀芳2谢志远2宋国香2
(1 北京林业大学林学院,北京 100083)
(2 天津泰达盐碱地绿化研究中心有限公司,天津 300457)
前期研究表明,施入园林废弃物作为饵料并投放蚯蚓能够降低滨海盐土盐分。通过田间对比试验,研究同时添加磷石膏和红糖对蚯蚓改良滨海盐土的促进作用。结果表明,在每平方米施入6.5 kg园林废弃物及50条蚯蚓(平均质量0.334 g)的基础上,添加磷石膏能够显著降低土壤pH以及水溶性钠离子(Na+)和氯离子(Cl-)的含量,但同时会显著增加土壤水溶性钙离子(Ca2+)及硫酸根离子(SO42-)含量;随着磷石膏施入量的提高,土壤全盐量呈现先降低后升高的趋势。添加红糖能够间接降低盐碱土壤水溶性Na+和Cl-的含量以及全盐量,但不同红糖施入量的处理间并无显著差异。根据试验结果,推荐在施入园林废弃物作为饵料并投放蚯蚓的基础上,同时添加1 kg m-2的磷石膏及0.4 kg m-2的红糖,以取得最佳的降盐效果。
滨海盐土改良;蚯蚓;园林废弃物;磷石膏
随着我国经济和社会的快速发展,沿海城市滨海盐土的绿化改良成为亟待解决的问题。我国滨海地区盐碱地约有1.3×105km2[1],由于该区域地下水矿化度高、埋藏深度较浅,且年蒸发量高于年降雨量,容易导致土壤的盐碱化[2]。盐碱土壤的生物改良方法具有成本低、效果好、无污染的优点,但多局限于种植耐盐植物[3-5],采用土壤动物改良的方法研究较少。在改良盐碱土壤的过程中,接种蚯蚓有利于巩固盐碱地改良效果,促进盐碱地持续利用[6]。据调查,蚯蚓可以在全盐量达到11.47 g kg-1的盐碱土中生存,优势种为赤子爱胜蚓(Eisenia fetida)[7-8]。该蚯蚓品种适应性较强,自然分布于包括河北省在内的我国15个省及直辖市[9],在野外应用时可最大限度地避免由于蚯蚓入侵而可能导致的负面影响[10]。此外,赤子爱胜蚓是我国蚯蚓养殖的主要品种(商品名大平2号[11]),来源丰富,利于推广。前期研究表明,以经过腐熟发酵的园林废弃物作为饵料的条件下,投放蚯蚓能够降低滨海盐土盐分[12]。
园林废弃物是城市园林绿化过程中大量产出的有机绿化垃圾[13],其消纳处理是一项亟需解决的问题。在园林废弃物中添加一定的糖分能够促进蚯蚓活动[14],提高蚯蚓对盐碱土壤环境的适应性,并加速有机物质的分解转化,改良盐碱土壤。磷石膏是磷酸工业废渣,年产量极高,大量堆积会对自然环境造成极大的污染。作为传统盐碱土壤改良剂[15],磷石膏能够降低土壤盐分及pH[16-17],促进植物生长[18-19],为蚯蚓生存提供有利条件。本文以河北省临港经济技术开发区的滨海盐土为研究对象,探讨了在添加园林废弃物以及投放蚯蚓的前提下,同时添加磷石膏和红糖对蚯蚓改良滨海盐土的促进作用。
1 材料与方法
1.1 研究区概况
研究区位于沧州临港经济技术开发区,属暖温带半湿润大陆性季风气候,年平均气温12.1℃,1月平均气温-4.4℃,7月平均气温26.4℃,无霜期210 d。年平均降水量627 mm(其中75%集中在夏季),蒸发量为降雨量的3倍多,加之地下水矿化度大(约为4 g L-1),埋藏深度较浅(雨季地下水深度80 cm),极易造成土壤盐渍化。
试验地位于沧州临港经济技术开发区学院路南侧绿化带(38°23′ N,117°26′ E,海拔高度2 m),绿化施工时采取客土抬高地面的工程措施,用客土将试验地抬高约0.8 m,但未采取任何隔盐或排盐措施;试验于客土约半年后进行。所用绿化乔木主要有白蜡(Fraxinus chinensis)、国槐(Sophora japonica)、旱柳(Salix matsudana)和毛泡桐(Paulownia tomentosa)等。试验区原貌地土壤及绿化客土均为砂壤质典型滨海盐土,其理化性质如表1所示,各土壤取样点均未发现蚯蚓活动痕迹。
1.2 供试材料
试验用磷石膏购自山东省泰安市华蓥商贸有限公司,其pH约为2.5,主要成分为CaSO4·2H2O(占总质量的94.6%);试验用红糖购自当地供销合作联合社。试验用园林废弃物(Composted green waste,CGW)取自北京市朝阳区园林绿化废弃物消纳中心,具体堆制过程参见Zhang等[20]的二阶段堆肥方法。供试园林废弃物理化性质如表1所示。
试验用蚯蚓(E. fetida)购自北京市顺义区大环顺鑫有机肥料厂,购回后将蚯蚓置于装有盐碱土壤的塑料桶中,并在表面覆盖1 cm厚的园林废弃物;保持桶内物料湿度在25%(±1%,W/W)左右并保持凉爽,以使蚯蚓适应试验环境。待蚯蚓适应试验环境约1个月后,选取环带清晰,反应灵敏,个体大小与体重基本相同的蚯蚓进行试验。
表1 试验区土壤及园林废弃物理化性质Table 1 Physico-chemical properties of the saline soil in the experiment field site and the composted green waste applied to the saline soil
1.3 试验设计
试验于试验地盐碱水平相同的区域进行,共设置2个因素,分别为磷石膏(Phosphogypsum,Pg)和红糖(Brown sugar,BS);每个因素设置4个水平,其中磷石膏施用量为0 kg m-2、1 kg m-2、2 kg m-2、3 kg m-2(即Pg-0、Pg-1、Pg-2、Pg-3),红糖施用量为0 kg m-2、0.2 kg m-2、0.4 kg m-2、0.6 kg m-2(即BS-0、BS-0.2、BS-0.4、BS-0.6);各因素的不同水平间两两组合,共计16个处理,其中Pg-0、BS-0处理组合为只添加园林废弃物并投放蚯蚓,而未添加磷石膏或红糖的处理。各处理在试验区内随机分布,每个处理小区面积为12 m2,包含3棵毛泡桐(P. tomentosa),试验重复3次。根据前期试验的结果,各处理均添加6.5 kg m-2的园林废弃物及50 条 m-2(约16.7 g)的蚯蚓[12]。磷石膏按照不同处理要求的用量直接撒入土壤;红糖按不同处理要求的用量,用水溶解后掺入园林废弃物中混匀,再撒入土壤。由于蚯蚓对土壤改良的效果集中在土壤表层[21],故在本试验中将施入的磷石膏及掺有红糖的园林废弃物与0~20 cm的表层土壤搅拌混匀。虽然试验所用蚯蚓仅对表层土壤产生作用,但由于盐碱土壤盐分也多聚积在土壤表层[22-23],因此采取蚯蚓改良盐碱土壤仍具有积极意义。
为防止磷石膏酸性过强毒害蚯蚓,磷石膏于2014年6月施入土壤,蚯蚓随掺有红糖的园林废弃物于1个月后投放于土壤中;该1个月时间用于前文提到的蚯蚓适应试验环境的过程。此外,保留未进行任何处理,仅对0~20 cm表层土壤进行搅拌混匀的区域作为对照(CK)。试验期间,各处理采取相同的养护措施。
1.4 样品采集与分析
土壤样品于2015年7月进行采集,于每个处理中随机选取3个点采集表层土壤(0~20 cm)。由于大田试验条件限制,试验结束后各处理的蚯蚓数目未进行统计,但在取样时各处理均可发现存活的蚯蚓或新鲜的蚯蚓粪,说明蚯蚓能够适应试验地条件并自然越冬。
采回的土壤样品经自然风干后,碾碎过筛(1 mm),并以水土比5∶1制备土壤水溶液以进行指标测定。其中,土壤pH使用通用型pH计(OHAUS Starter 3C,美国)测定;土壤的水溶性盐分离子中,碳酸根离子(CO32-)和碳酸氢根离子(HCO3-)采用双指示剂—中和滴定法测定;氯离子(Cl-)采用硝酸银滴定法(莫尔法)测定;钙离子(Ca2+)和镁离子(Mg2+)采用乙二胺四乙酸(EDTA)滴定法测定;硫酸根离子(SO42-)采用EDTA间接络合滴定法测定;钾离子(K+)和钠离子(Na+)采用火焰光度法测定;全盐量为上述八种离子含量之和[24]。
1.5 数据处理
全部数据采用Excel 2010及SPSS 18进行统计分析。采用单因素方差分析(one-way ANOVA)比较不同处理间的差异;多重比较采用邓肯(Duncan)法检验在方差分析中有差异的变量间的差异显著性。
2 结果与讨论
2.1 蚯蚓与改良剂施入后土壤pH变化
在施入园林废弃物并投放蚯蚓的基础上,添加磷石膏能够有效降低盐碱土壤的pH,如图1所示。与未施入磷石膏的处理(Pg-0)相比,施入磷石膏能够显著降低土壤的pH,但不同磷石膏用量的处理间无显著差异。磷石膏能够降低盐碱土壤pH的结果与刘易等[17]的研究相符,这可能由两个原因造成:首先,磷石膏是在制取磷肥时用硫酸处理磷矿而产生的固体废渣,有部分硫酸残留,使得磷石膏本身pH较低(本试验中所用磷石膏pH约为2.5),这能够直接影响到盐碱土壤的pH;其次,磷石膏中的CaSO4与土壤溶液中HCO3-和CO32-反应生成Ca(HCO3)2和难溶性的CaCO3,以及溶解度小于NaCl的Na2SO4[25],从而固定HCO3-和CO32-并促进Na+的淋洗,间接降低土壤的pH[26]。而不同磷石膏用量的处理间无显著差异,可能是由于土壤本身具有一定的缓冲性造成的。
本试验中,施入红糖对蚯蚓活动的促进作用并未间接改变盐碱土壤的pH。虽然蚯蚓活动能够改善土壤pH,使之趋向于中性[27],但其主要是依靠蚯蚓粪中具有一定酸性和缓冲性的腐殖酸类物质对土壤pH进行调节[28],因此,短时间内难以产生显著影响。
试验结果表明,施用磷石膏能够显著降低滨海盐碱土壤的pH,但当磷石膏的用量大于1 kg m-2(Pg-1)时,其对盐碱土壤pH的降低作用不再显著。因此,综合考虑磷石膏本身较高的盐分和较低的pH对园林绿化植物可能产生的负面作用,以及降低改良成本的目的,推荐采用1 kg m-2的用量进行改良。
2.2 蚯蚓与改良剂施入后土壤Ca2+及SO24-含量变化
由于磷石膏中的主要成分为CaSO4,因此土壤中的Ca2+及SO42-含量均随磷石膏施入量的增加而增加,如图2所示;施入红糖对Ca2+及SO42-含量无显著影响。土壤中增加的Ca2+能够代换土壤胶体上的Na+,形成钙胶体,从而促进土壤团粒结构的形成,加速土壤盐分自然淋洗的过程[29],有利于盐碱土壤的改良。应注意的是,SO42-含量基本随Ca2+含量同步增长;虽然SO24-对植物的毒害作用低于Cl-,但其含量过高时仍会对植物产生盐胁迫(中国内陆的盐碱土类型多为硫酸盐型),造成危害。因此,磷石膏的施入量不宜过高。
图1 不同处理土壤pH变化Fig 1 pH of the soil as affected by treatment
2.3 蚯蚓与改良剂施入后土壤Na+及Cl-含量变化
在未施入磷石膏的处理中(Pg-0),随着红糖添加量的提高,表层土壤(0~20 cm)中的Na+含量显著降低;而在施入磷石膏的处理中,添加红糖虽然能够显著降低表层土壤Na+含量,但不随红糖添加量的提高而改变(图3)。Cl-含量变化与Na+相类似,在未施入磷石膏的处理中,添加红糖能够显著降低表层土壤中的Cl-含量;随着磷石膏施入量的提高,添加红糖对Cl-含量的降低作用趋于不显著(图3)。
图2 不同处理土壤Ca2+及SO24-含量变化Fig 2 Ca2+and SO24-contents in the soil as affected by treatment
添加红糖可以降低表层盐碱土壤Na+及Cl-含量的原因,可以归结为蚯蚓活动以及微生物活性提高的影响。由于蚯蚓喜食富含糖分的有机物质[30],在饵料(即园林废弃物)中添加红糖可以促进蚯蚓活动,增加土壤中由于蚯蚓活动而产生的孔洞以及具有一定水稳性的团粒状蚯蚓粪,从而改善土壤物理性质,加强了土壤盐分自然淋洗的过程[31];蚯蚓活动还能够打断土壤毛细管通路,切断土层之间水吸力的连贯性,从而能够缓解表层土壤的盐分积累程度。此外,蚯蚓能够加速园林废弃物的分解,将其转化为具有较高阳离子吸附能力的腐殖酸类物质[32],并与Ca2+结合为较为稳定的腐殖酸钙,促进土壤团粒结构的生成[33],从而间接促进了土壤盐分自然淋洗的过程;蚯蚓活动还能够提高盐碱土壤微生物数量[34],促进土壤微生物群落的年轻化[35],提高土壤微生物活性[36],而添加红糖本身也可以提高微生物的活性,加速园林废弃物的腐熟分解[20],从而促进了腐殖酸类物质的形成,增强了盐碱土壤的改良效果。
图3 不同处理土壤Na+及Cl-含量变化Fig 3 Na+and Cl-contents in the soil as affected by treatment
随着磷石膏施入量的提高,一方面,其自身所含的盐分以及较强的酸性,可能会对蚯蚓以及土壤微生物群落产生越来越大的毒害作用,降低蚯蚓以及土壤微生物的活性,从而减弱了其对盐碱土壤的改良作用;另一方面,前文提到磷石膏中的Ca2+能够将Na+从土壤胶体上代换出来,生成钙胶体并促进土壤团聚体的形成,改善土壤物理性质,在加强土壤盐分自然淋洗作用的同时抑制表层土壤返盐,从而降低土壤中Na+及Cl-的含量,减小了不同红糖添加量处理间的差距,对方差分析的结果产生影响。因此,随着磷石膏施入量的提高,添加红糖降低Na+及Cl-含量的效果趋于不显著。
2.4 蚯蚓与改良剂施入后土壤全盐量变化
与Na+及Cl-含量类似,在施入园林废弃物并投放蚯蚓的基础上,未施入磷石膏的处理(Pg-0)随着红糖施入量的提高,表层土壤全盐量显著下降;而在施入磷石膏的处理中,随着磷石膏施入量的提高,施入红糖对表层土壤全盐量的降低作用趋向不显著,尤其是Pg-2和Pg-3处理,施入红糖未对土壤盐分造成显著影响(图4)。造成该结果的原因可能有两点,首先,由于施入过多磷石膏抑制了蚯蚓活动,从而降低了其对盐碱土壤的改良作用;其次,随着磷石膏施入量的提高而引入的大量Ca2+及SO42-会对表层土壤全盐量产生显著影响,而蚯蚓活动并不能抑制施入磷石膏造成的Ca2+及SO42-含量的提高,因此可能会对表层土壤全盐量方差分析的结果产生影响。
虽然前人大量研究均发现磷石膏能够降低土壤全盐量[37-39],但并未提及磷石膏施入量高于一定程度后,土壤全盐量会发生反弹。当磷石膏施入量为1 kg m-2时(Pg-1),表层土壤全盐量与未施入磷石膏的处理(Pg-0)相比有显著的降低;随着磷石膏施入量的提高,表层土壤全盐量有回升的趋势,尤其是红糖施入量为0.4 kg m-2和0.6 kg m-2的处理(BS-0.4、BS-0.6);当磷石膏施入量达到3 kg m-2时(Pg-3),表层土壤全盐量反而显著高于未施入磷石膏的处理(Pg-0),这是由于施入红糖可促进蚯蚓以及微生物对盐碱土壤的改良作用,使未施入磷石膏的处理(Pg-0)全盐量降低造成的。虽然表层土壤中的Na+及Cl-的含量随着磷石膏施入量的提高而减小(图3),但Ca2+及SO42-含量会提高(图2),因此,表层土壤全盐量发生反弹的结果是很容易发生的。
结合施入磷石膏及红糖对盐碱土壤的pH、Ca2+、SO24-、Na+和Cl-含量的影响(各处理对土壤中其他离子的影响较小),以及全盐量等因素,建议磷石膏采取1 kg m-2的施用量(Pg-1);此时为获得更显著的改良效果,红糖采取0.4 kg m-2的施用量(BS-0.4)。
图4 不同处理土壤全盐量变化Fig 4 Content of total salt in the soil as affected by treatment
2.5 改良效果及成本
如图5所示,与同期未采取任何措施的对照处理(CK)相比,仅添加园林废弃物作为饵料并投放蚯蚓、而未添加磷石膏或红糖的措施(Pg-0、BS-0处理组合,T0)可以在一定程度上减缓土壤的次生盐渍化,防止其退化至原貌地(Original soil,OS)的土壤盐分水平;而采取上述推荐用量的措施(Pg-1、BS-0.4处理组合,Tbest)能够进一步抑制土壤的次生盐渍化,促使表层土壤盐分保持在与绿化客土(Alien soil for greening,AS)相近的水平,此时土壤改良成本约为每平方米10.60元(表2)。
图5 不同处理对滨海盐土改良效果Fig 5 Amelioration effects of saline soil as affected by treatment
表2 推荐措施下的土壤改良成本Table 2 Cost of saline soil amelioration using the recommended measures
试验结果表明,若不采取一定措施,回填的客土会很快退化成为盐化土壤,造成大量直接或间接的经济损失,如重新更换客土、补植苗木的材料费及其产生的运输、人工费用等。本研究推荐的土壤改良方式成本较低(目前常用的布设排盐暗管等工程改良措施,施工成本约为每平方米70元),且配合栽植绿化植物,其产生的枯落物可为蚯蚓持续提供饵料,无需后续投入;而蚯蚓对土壤的改良作用会促进植物生长,从而产生更多的枯落物为蚯蚓提供饵料,形成良性循环。在条件允许的情况下,若园林废弃物能够就地取材进行堆制,则可进一步降低土壤改良成本;此外,本方案中的红糖可以采用制糖工业的副产品代替,如甜菜渣(1 920 Yuan t-1)、甘蔗渣(700 Yuan t-1)、糖蜜(1 200 Yuan t-1)等,也可降低改良成本。
3 结 论
本研究提出了一项采用废弃资源改良滨海盐碱土壤的方法,即在向每平方米土壤中添加6.5 kg园林废弃物作为饵料并投放50条蚯蚓的基础上,额外施用1 kg m-2的磷石膏和0.4 kg m-2的红糖,以进一步抑制表层土壤的返盐,巩固滨海盐土改良效果,降低土壤次生盐渍化造成的损失。与常见的工程改良措施相比,该改良方法成本较低,利于推广,并具有一定的可持续性。此外,本改良方法为磷石膏及园林废弃物的资源化再利用提供了可行的方案,利于循环经济的发展。在后期研究中,还可以考虑使用制糖工业的副产品代替本方案中的红糖,可进一步降低改良成本并提高废弃资源的利用率。
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Effect of Amendments of Phosphogypsum and Brown Sugar on Earthworms Ameliorating Coastal Saline Soil
ZHANG Tao1,2LI Suyan1†SUN Xiangyang1WANG Zhenyu2ZHANG Yang1ZHANG Le1GONG Xiaoqiang1ZHAO Xiufang2XIE Zhiyuan2SONG Guoxiang2
(1 College of Forestry,Beijing Forestry University,Beijing 100083,China)
(2 Tianjin TEDA Saline Green Research Center Co.,Ltd.,Tianjin 300457,China)
【Objective】Coastal soils in North China are extremely susceptible to salinization because of the geographical and meteorological conditions of these areas. Nowadays,soil bioremediation has proved to be an effective and economical way to ameliorate saline soils and hence been extensively applied. However,researches in this aspect are mostly focused on phytoremediation by planting salt-tolerant plants,and little has been done on use of earthworms or other soil animals. The first phase of this study demonstrates that the introduction of earthworms Eisenia fetida using composted green waste as its food source could help lower salinity of the coastal saline soil in North China. 【Method】 In order to improve the efficiency of using E. fetida and composted green waste to ameliorate saline soil,a field experiment was conducted on addition of phosphogypsum,the conventional soil amendment,and brown sugar in an attempt to determine whether they may help improve the efficiency of the bioremediation. The experimental site was located on a tract of typical coastal saline soil in the Lingang Economic and Technological Development Zone of Cangzhou,Hebei,China. The field was divided into plots. Each plot,covering an area of 12 m2,was amended with 6.5 kg m-2of composted green waste and earthworms at 50 individuals per m2(average weight 0.334 g). In addition,the plots were applied with 0 kg m-2,1 kg m-2,2 kg m-2,or 3 kg m-2of phosphogypsum,along with 0 kg m-2,0.2 kg m-2,0.4 kg m-2,or 0.6 kg m-2of brown sugar,separately. 【Result】 The experiment went on forone year,with results showing that the addition of phosphogypsum could significantly decrease pH of the soil in the treatments applied with the same rate of brown sugar,however,the effect did not vary much with the amendment rate of phosphogypsum. As Ca2+and SO42-are the major component of phosphogypsum,application of the substance significantly increased the content of soluble Ca2+and SO24-in the soils the same in brown sugar treatment. The Ca2+in phosphogypsum helped formation of soil structure and promoted desalination of the saline soil,while reducing the content of soluble Na+and Cl-significantly;the amendment of brown sugar stimulated activities of the earthworms,thus facilitating formation of soil aggregates and hence leaching of salts,and eventually intensifying the effect of bioremediation. So in the treatments the same in phosphogypsum amendment rate,addition of brown sugar significantly lowered the content of soluble Na+and Cl-in the soil. As affected by the contents of soluble Ca2+,SO24-,Na+and Cl-in the soil,in the treatments amended with 0 kg m-2or 1 kg m-2of phosphogypsum,addition of brown sugar significantly lowered the content of total salt,but the effect did not vary with its amendment rate;however,in the treatments the same in the amendment rate of brown sugar,the content of total salt in the soil increased rather than decreased if too much phosphogypsum was used. 【Conclusion】 Aiming at lowering the content of total salt,it is recommended that in addition to 6.5 kg m-2of composted green waste and 50 individuals per m2of E. fetida,1 kg m-2of phosphogypsum and 0.4 kg m-2of brown sugar should be amended in bioremediation of the coastal saline soil in North China. Compared with CK(nothing amended),the amendment of composted green waste and E. fetida significantly decreased the content of total salt,and the effect was further enhanced when phosphogypsum and brown sugar was added at a recommended rate. The cost of soil amelioration with the above-described method is only 10.60 Yuan per m2,and it would be lowered if brown sugar is replaced by some by-products from the sugar industry,such as beet pulp,bagasse,and molasses.
Coastal saline soil amelioration;Earthworm;Composted green waste;Phosphogypsum
S156.4+2
A
10.11766/trxb201603170607
(责任编辑:陈荣府)
* 公益性行业(林业)科研专项经费项目(201504205)和北京市教育委员会科学研究与研究生培养共建项目(BLCXY201603,BLCXY201604)共同资助 Supported by the Special Fund for Forest Scientific Research in the Public Welfare (No. 201504205)and the Graduate Training and Development Program of Beijing Municipal Commission of Education of China (Nos. BLCXY201603 and BLCXY201604)
† 通讯作者 Corresponding author,E-mail:lisuyan@bjfu.edu.cn
张 涛(1988―),男,天津人,博士,主要从事滨海盐土改良研究。E-mail:zhangtao5291@126.com
2016-03-17;
2016-09-22;优先数字出版日期(www.cnki.net):2016-10-17