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  农业资源与环境学报  2015, Vol. 32 Issue (3): 229-234

文章信息

徐聪珑, 贾丽, 张璐, 刘秋萌, 谢忠雷
XU Cong-long, JIA Li, ZHANG Lu, LIU Qiu-meng, XIE Zhong-lei
冻融作用对猪粪模拟施肥条件下东北黑土中重金属铜锌活性的影响
Effect of Freezing and Thawing on Activity of Cu and Zn in Black Soil of Northeast China Under Simulated Fertilization Using Pig Manure
农业资源与环境学报, 2015, 32(3): 229-234
Journal of Agricultural Resources and Environment, 2015, 32(3): 229-234
http://dx.doi.org/10.13254/j.jare.2014.0380

文章历史

收稿日期:2014-12-31
冻融作用对猪粪模拟施肥条件下东北黑土中重金属铜锌活性的影响
徐聪珑, 贾丽, 张璐, 刘秋萌, 谢忠雷     
吉林大学环境与资源学院, 吉林 长春 130012
摘要:随着规模化养殖场的发展和饲料添加剂中Cu和Zn的添加, 畜禽粪便中重金属Cu和Zn含量较高, 通过畜禽粪便施肥可能造成土壤重金属污染。畜禽粪便施肥和冻融作用均可能影响土壤中重金属的活性, 进而改变土壤重金属的环境效应。本文针对东北气候特点, 通过实验室模拟, 研究了猪粪施肥和冻融作用对黑土中重金属Cu和Zn活性(可交换态和碳酸盐结合态)的影响。结果表明:同未施肥的对照比, 猪粪施肥初期, Cu和Zn的可交换态含量均明显增加, 而Cu和Zn的碳酸盐结合态含量则略有下降;同低施肥量比, 高施肥量下, Cu和Zn的可交换态含量略有增加, 而Cu和Zn的碳酸盐结合态含量下降;同施肥初期比(1周), 随施肥时间延长(1个月)土壤中可交换态Cu和Zn含量下降, 而碳酸盐结合态Cu和Zn含量增加;高低不同施肥量相比, 高施肥量下可交换态Cu和Zn含量均高于低施肥量, 而碳酸盐结合态Cu和Zn含量则低于低施肥量;随冻融温度下降, 土壤中可交换态Cu和Zn含量、碳酸盐结合态Cu和Zn含量均显著增加, 且在高施肥量下的含量均大于低施肥量。由此可见, 猪粪施肥和冻融作用对黑土中Cu和Zn活性均有不同程度的影响, 总的看是随施肥量的增加和施肥时间的延长, 黑土中Cu和Zn活性不同程度地下降, 但冻融作用可以使猪粪施肥的黑土中Cu和Zn的活性增加, 且随冻融温度下降Cu和Zn活性增加的幅度增大。
关键词冻融作用     猪粪     黑土     模拟施肥     铜锌活性    
Effect of Freezing and Thawing on Activity of Cu and Zn in Black Soil of Northeast China Under Simulated Fertilization Using Pig Manure
XU Cong-long, JIA Li, ZHANG Lu, LIU Qiu-meng, XIE Zhong-lei     
College of Environment and Resources, Jilin University, Changchun 130012, China
Abstract:With the development of large-scale farms and the addition of Cu and Zn in feed additives, high Cu and Zn contents in feces of livestock and poultry occurred, and may cause soil pollution of the heavy metal especially Cu and Zn by livestock and poultry manure fertilization. Both fertilization of livestock and poultry manure and freeze-thaw action can alter the activity of heavy metals in soil, and furthermore change the environmental effect of heavy metals in soil. This paper aimed at the influence of freezing and thawing on the activities of Cu and Zn (exchangeable and carbonate) in black soil of Northeast China under pig manure fertilization according to the northeast climate characteristics through laboratory simulation. The results showed that the contents of exchangeable Cu and Zn significantly increased and that of carbonate Cu and Zn slightly decreased under pig manure fertilization initial stage comparing with the control without fertilizer. The contents of exchangeable Cu and Zn slightly increased and that of carbonate Cu and Zn decreased for the higher fertilization comparing with lower fertilization. The contents of exchangeable Cu and Zn decreased and that of carbonate Cu and Zn significantly increased with the extension of fertilization time (one month) compared with the early fertilization (one week). Moreover, the contents of exchangeable Cu and Zn under higher fertilization were all higher than that under lower fertilization, on the contrary, the contents of carbonate Cu and Zn under higher fertilization all were lower than that under lower fertilization. The contents of exchangeable and carbonate Cu and Zn all increased obviously with the freezing and thawing temperature decreased, and the contents of Cu and Zn for higher fertilization were higher than that for lower fertilization. In conclusion, the activities of Cu and Zn in black soil were disturbed by both pig manure with different fertilization amounts and fertilization culture time and freezing and thawing, there were a varying degree decreasing for the activities of Cu and Zn in black soil with the increase of fertilization amount and fertilization culture time, nevertheless, the freezing and thawing action could increase the activities of Cu and Zn in black soil under pig manure fertilization, and the amplitude of increasing Cu and Zn activity increased with the freezing and thawing temperature decreasing.
Key words: freezing and thawing     pig manure     black soil     simulating fertilization     activities of copper and zinc    

猪粪因其富含氮磷钾等营养元素且易分解有利于形成腐殖质而成为对土壤具有改良作用的有机肥源[1, 2]。但随着现代规模化养殖场的发展和高含量Cu、Zn等重金属添加剂饲料的大量使用,过高含量重金属的畜禽粪便产生量也逐年增加[2, 3, 4],通过畜禽粪便的堆放或土地利用造成土壤重金属污染的风险也相应增加[5, 6, 7, 8]。土壤重金属污染不但影响作物产量和品质,还可通过食物链危害人体健康[9, 10]。冻融过程作为我国东北地区的季节性气候现象,不但影响畜禽粪便中重金属活性[11],也对土壤中重金属的迁移转化具有一定影响[12]。吉林省是我国的粮食主产区之一,畜禽养殖业比较发达,畜禽粪便施肥比较普遍[13],因此,针对吉林省畜禽粪便施肥及冻融过程的季节性变化,通过实验室模拟研究冻融作用对猪粪施肥条件下东北黑土中重金属铜锌活性的影响,为正确评价东北气候条件下畜禽粪便施肥后土壤重金属的潜在环境效应提供理论依据。 1 材料与方法 1.1 猪粪和土壤样品的采集及制备

于2011年4月底在吉林省长春市吉林农业大学奶牛场(43°36′00″~43°36′24″N,125°33′20″~125°33′40″E)采集猪粪和土壤样品(土壤为猪粪底土,由于猪粪中Cu、Zn含量较高,经过猪粪长时间堆放后的粪底土Cu、Zn含量也很高[5])。样品采集后于实验室自然风干,剔除杂质,分别研磨过2 mm和0.25 mm筛于塑料密封袋中保存备用。猪粪有机质含量413.9 g·kg-1、pH值为7.54,东北黑土有机质含量47.8 g·kg-1、pH值为7.51。 1.2 模拟猪粪施肥和冻融处理

将分别风干并过2 mm筛的土壤和猪粪样品装于无孔塑料盆中模拟施肥过程,每盆装土2 kg,猪粪施用量分别为0%(不添加猪粪作为对照,标记为CK)、1%和3%。将土壤和猪粪反复充分混合均匀后装盆,每个处理3个重复,培养温度为25 ℃,培养过程通过称重法保持土壤含水量为田间持水量的60%~70%,进行1周和1个月的模拟猪粪施肥培养试验。然后再取模拟猪粪施肥1个月的土壤样品(猪粪添加量分别为0%即CK、1%和3%)在不同冻结温度(0、-10、-20 ℃)进行冻融处理,冻融周期为7 d,即在0、-10、-20 ℃冷冻7 d,然后在冰箱中5~10 ℃解冻7 d。冻融后的样品于实验室自然风干,剔除杂质,分别研磨过2 mm和0.25 mm筛于塑料密封袋中保存。猪粪、原土和添加猪粪后的土壤Cu、Zn含量见表 1,经不同温度冻融后的猪粪、原土和模拟猪粪施肥土壤的pH值见表 2

表 1 模拟施肥用猪粪和土壤中重金属Cu和Zn含量(mg·kg-1 Table 1 Contents of Cu and Zn in pig manure and soil used as simulated fertilization(mg·kg-1
表 2 模拟猪粪施肥处理和不同温度冻融处理土壤的pH值 Table 2 Value of pH in soils treated by simulated fertilization with pig manure under freezing and thawing temperature
1.3 土壤和猪粪中Cu、Zn全量和活性态含量的测定

土壤和猪粪中重金属全量采用浓硝酸-高氯酸消化法:精确称取过0.25 mm筛的土壤样品0.500 g于50 mL小烧杯中,加入5.0 mL浓硝酸,静置过夜,于电热板上慢慢加热至样品分解完全,再加2.0 mL高氯酸,高温加热至白烟冒尽,稍冷后用0.5%的硝酸溶液分若干次洗入50 mL容量瓶中,定容,过滤,上清液保存于塑料瓶中,原子吸收光谱法测定Cu、Zn含量。

采用Tessier等[14]提出的对土壤中重金属可交换态和碳酸盐结合态的提取方法,并参照畜禽粪便中Zn的活性判断方法[11],将土壤中Cu、Zn可交换态和碳酸盐结合态作为模拟施肥土壤中Cu、Zn的活性态,土壤中Cu、Zn的活性态含量即为Cu、Zn的可交换态和碳酸盐结合态之和,其余形态为非活性态。提取后的溶液保存于塑料瓶中,用原子吸收光谱法测定Cu、Zn含量。 1.4 数据处理方法

不同施肥及冻融处理土壤中重金属含量均为3个重复处理样品测定结果的平均值;采用t检验确定不同施肥处理及不同温度冻融处理的两组数据(2个样本平均数)之间的差异显著性关系,采用Microsoft Office Excel 2007进行t检验的数据统计计算。 2 结果与分析 2.1 猪粪施肥对土壤Cu和Zn活性的影响

表 3是模拟猪粪施肥土壤中Cu、Zn的可交换态和碳酸盐结合态含量及活性态含量在总量中所占比例。由表 3可见,同未施肥的对照比,猪粪施肥初期(1周),Cu和Zn的可交换态含量均显著增加,而Cu和Zn的碳酸盐结合态含量则略有下降;同低施肥量比,高施肥量下,Cu和Zn的可交换态含量显著增加,而Cu和Zn的碳酸盐结合态含量变化不显著;同施肥初期(1周)比,随施肥时间延长(1个月),土壤中可交换态Cu和Zn含量显著下降,而碳酸盐结合态Cu和Zn含量呈增加趋势;同低施肥量比,在高施肥量下可交换态Cu和Zn含量显著高于低施肥量,而碳酸盐结合态Cu和Zn含量变化不显著。由表 3可见,模拟猪粪施肥后,土壤中Cu、Zn活性态比例随施肥量增加而增加,非活性态所占比例相应下降,但随施肥时间延长,土壤中Cu、Zn活性态比例下降,且Zn的活性态比例下降幅度更大。由此说明,猪粪施肥可以增加土壤重金属Cu和Zn的活性,且随施肥量的增加活性也相应增加,但随施肥时间延长,土壤Cu和Zn的活性降低。张学政等[7]研究发现猪粪经过堆肥处理对Cu和Zn的活性影响有差异,对Cu稳定化具有明显作用,但是对猪粪中Zn则有活化作用,这说明猪粪堆肥和施肥处理对重金属的活性影响是有差异的。徐秋桐等[8]研究表明,猪粪施肥后茶园土壤中积累的Cu主要向有机质结合态和交换态转化,而Zn主要向交换态、有机质结合态和氧化铁结合态转化,这可能是猪粪施肥对土壤中Cu和Zn活性影响有差异的原因之一。

表 3 模拟猪粪施肥土壤中Cu、Zn的可交换态和碳酸盐结合态含量及活性态含量在总量中所占比例 Table 3 Contents of exchangeable and carbonate Cu, Zn and percentage of active form accounting for total content in soils treated by simulated fertilization using pig manure
2.2 冻融对猪粪施肥条件下土壤Cu和Zn活性的影响

表 4为模拟猪粪施肥土壤经不同温度冻融作用后Cu和Zn的可交换态和碳酸盐结合态含量及活性态含量在总量中所占比例。由表 4可见,随冻融温度的下降,土壤中可交换态Cu和碳酸盐结合态Cu含量均显著增加,且在高施肥量条件下均显著高于低施肥量。同时,土壤中Cu的活性态比例亦随冻融温度下降和施肥量增加而增加,与Cu相似,随冻融温度的下降,土壤中可交换态Zn和碳酸盐结合态Zn含量均显著增加,且在高施肥量条件下一般都显著高于低施肥量,同时,土壤中Zn的活性态比例亦随冻融温度下降和施肥量增加而总体增加。根据活性态Cu、Zn在总量中所占比例,随冻融温度下降,Zn的活性增加比例明显高于Cu。由此可见,随冻融温度下降,猪粪施肥后的土壤中可交换态Cu和Zn含量、碳酸盐结合态Cu和Zn含量均显著增加,土壤中的Cu和Zn被活化,且在高施肥量下Cu和Zn的活性大于低施肥量。郭平等[12]研究结果表明,冻融作用降低了土壤对Pb和Cd的固持能力,增加了土壤中Pb和Cd的生态风险;李悦铭等[15]也发现在外源可溶性有机质条件下冻融作用使土壤中Pb的溶出释放量增加;党秀丽[16]的研究结果也表明冻融过程具有促进土壤中结合牢固态镉向不稳定的离子态镉转化的作用,冻融过程有利于镉的释放。

表 4 模拟猪粪施肥土壤经不同温度冻融作用后Cu和Zn的可交换态和碳酸盐结合态含量及活性态含量在总量中所占比例 Table 4 Contents of exchangeable and carbonate Cu, Zn and percentage of active form accounting for total content in soils treated by simulated fertilization using pig manure under freezing and thawing temperature
3 讨论

虽然规模化养殖场猪粪中Cu、Zn含量较高,但主要以活性较低的形态存在[11],猪粪施肥不但能增加土壤有机质含量,也能增加土壤重金属含量[17],猪粪施肥后可在物理化学与微生物作用下完成一个复杂的动态好氧发酵过程,有机物分解,逐步形成腐殖质类物质,芳构化程度不断增强[18],这些物质能够与重金属元素发生螯合反应,使土壤中的活性重金属被有效地结合和固定[19]。猪粪施肥腐解后,与猪粪中大分子有机物结合的Cu、Zn被释放,并可重新与土壤组分结合或与猪粪的腐解产物结合;同时,猪粪腐解可使土壤理化性状如pH值和有机质组成结构发生变化[17, 20],因此,猪粪施肥后土壤中Cu和Zn含量和形态也相应发生改变。猪粪施肥量增加,猪粪的腐解矿化作用使土壤可交换态和碳酸盐结合态Cu、Zn含量相应增加,而随施肥时间延长猪粪的腐解作用产生的腐殖质与Cu、Zn发生螯合作用又对Cu、Zn有固定作用而使非活性态Cu、Zn含量有所增加。

冻融作用可通过改变土壤的颗粒物结构、生物活性和矿化作用以及土壤理化性质而影响重金属的活性[21]。土壤被冻结时土壤颗粒孔隙中冰晶的膨胀可以打破颗粒之间的联结而释放出易于分解矿化的物质[22],随冻融温度下降和猪粪施肥量的增加这种作用可能更强烈;冻融作用可以杀死土壤中的一些微生物而刺激残余微生物的活动,增加土壤有机质中的有效养分[23],导致土壤中由猪粪腐解产生的腐殖物质的矿化作用增强[24]。因此,经过冻融作用后,畜禽粪便施肥的土壤中难以分解矿化的有机质可转变为易分解矿化的有机质,在微生物的作用下有机质进一步分解矿化,使有机结合态Zn和Cu释放而变为游离态Zn和Cu,而增加了土壤中Zn和Cu的活性;同时,有机质的分解和矿化可以产生如疏水性酸和亲水性酸等可溶性有机质,使畜禽粪便施肥后的土壤pH值经冻融作用后有不同程度的下降(表 2),进一步使残渣态Zn和Cu溶解而增加了畜禽粪便中Zn和Cu的活性。根据表 3表 4非活性态在总量中所占比例,施肥和冻融条件下Zn的活性均大于Cu,这可能主要与Cu比Zn更易于与有机质结合形成有机结合态的Cu有关[25]4 结论

本文通过实验室模拟,研究了猪粪土壤施肥和模拟冻融作用对东北黑土中重金属Cu、Zn活性的影响,初步得到如下结论:

猪粪施肥可以增加土壤重金属Cu和Zn的活性,且随施肥量的增加活性也相应增加,但同施肥初期(1周)比,施肥1个月后,土壤Cu和Zn的活性降低。冻融作用可以使猪粪施肥的黑土中Cu和Zn的活性增加,随冻融温度下降,黑土中可交换态Cu和Zn含量、碳酸盐结合态Cu和Zn含量均显著增加,且在高施肥量下的Cu、Zn活性态含量均大于低施肥量。

虽然冻融作用使模拟猪粪施肥黑土中Cu、Zn活性态含量增加,但活性态中的大部分是以碳酸盐结合态存在的,而碳酸盐结合态Cu、Zn只有在土壤酸化时才可能溶出,产生环境效应。因此,猪粪施肥的东北黑土经冻融作用后对Cu、Zn环境效应的影响只是一种潜在的,而东北黑土一旦酸化则可能增加猪粪施肥土壤中重金属的环境污染风险。同时,有必要进一步研究冻融作用对模拟猪粪施肥的东北黑中重金属活性的影响机制。

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