摘要
为探究硫肥与磷肥联用对稻田土壤中镉(Cd)的钝化效果,采用土壤培养试验,研究了2种硫肥(硫磺和硫酸钠)与钙镁磷肥联用对稻田土壤中Cd有效性变化规律和Cd形态转化的影响,共设置6种处理:对照(CK)、钙镁磷肥(P)、硫磺(S1)、硫酸钠(S2)、钙镁磷肥+硫磺(PS1)及钙镁磷肥+硫酸钠(PS2),并分析了土壤Cd有效性与有效硫、有效磷、pH及Eh的关系。研究结果显示,在土壤中施用不同钝化材料后,土壤有效Cd含量均明显降低,其中PS1处理有效Cd含量最低,较CK降低了49.8%;钙镁磷肥能够提高土壤pH值,较CK升高了0.39;硫磺能显著降低土壤Eh值,较CK降低了23.2%,并促进了SO
镉(Cd)是稻田中典型的无机污染物,具有较强的迁移能力和生物有效性,容易被作物吸收并储存,并通过食物链传递到人
Cd污染土壤的修复技术主要有物理法、化学法及农艺调控
目前,关于硫肥和磷肥联用对水稻土Cd有效性和形态转化的影响研究较少见报道。本研究针对安徽省铜陵矿区周边被重金属Cd污染的土壤,选用2种硫肥(硫磺和硫酸钠)与钙镁磷肥联用作为钝化剂,探讨了硫磷联用对稻田土壤Cd有效性和形态转化的影响,土壤硫和磷有效性与土壤性质的相互作用,以及对稻田土壤Cd形态转化的影响因子之间的相互作用,旨在为中轻度Cd污染稻田低成本、高效原位修复措施提供科学依据。
供试土壤采自安徽省铜陵市义安区某废弃矿区的周边农田。土壤类型为水稻土,亚类为潜育型水稻土,成土母质为砂质洪冲沉积物。土壤总Cd含量为1.96 mg/kg,碱解氮、有效磷、速效钾、有机质、有效硫含量分别为124.13 mg/kg、34.66 mg/kg、111.67 mg/kg、27.92 g/kg、30.34 mg/kg,土壤pH 6.55。取样深度为0~20 cm。采集后剔除石块、植物残体等杂质,在室温下自然风干,研磨过筛(孔径2 mm),保存备用。供试钙镁磷肥购自广西鹿寨化肥有限责任公司,其中P2O5的含量≥17%。供试硫磺和硫酸钠购自西陇化工股份有限公司。
以干基土壤计,分别添加200 mg/kg钙镁磷肥(P)和100 mg/kg硫磺(S1)或硫酸钠(S2)组合至供试土壤中,试验共设置6个处理,包括:不添加钝化剂的对照组(CK)、钙镁磷肥(P)、硫磺(S1)、硫酸钠(S2)、钙镁磷肥+硫磺(PS1)及钙镁磷肥+硫酸钠(PS2),每个处理重复3次。
本试验采用室内恒温恒湿培养的方法,将各处理添加到1 kg土壤中并混匀装盆,培养试验过程中,每日对各处理塑料盆称质量,并以去离子水补足至恒质量,保证土壤始终淹水2~3 cm,在25 ℃恒温条件下培养60 d。在1、3、7、15、30、45和60 d时采集土壤样本。所取样品自然风干后,研磨过筛后装袋,待测。
土壤pH值按照水土质量比2.5∶1,加入去二氧化碳的超纯水,震荡后,静置0.5 h,用pH计(TARTER 2100,美国奥豪斯)测定。
土壤Eh值的测定:用便携式ORP测定仪(PH 200,美国科霖)测定。
土壤有效硫含量的测定:磷酸二氢钙浸提-硫酸钡比浊法测定。
土壤有效磷含量的测定:碳酸氢钠浸提-钼锑抗比色法测定。
土壤有效Cd含量的测定:0.05 mol/L乙二胺四乙酸二钠盐(EDTA)浸提,原子吸收分光光度计(zeenith 700 p,德国耶拿)测定。
土壤Cd形态测定采用Tessier
培养60 d后,不同钝化剂处理对土壤Eh的影响显著(P<0.05)(

图1 不同处理下土壤Eh(A)和pH(B)的动态变化
Fig.1 Dynamic variation of soil Eh(A) and pH(B) in different treatments
CK:无钝化剂对照;P:添加钙镁磷肥;S1:添加硫磺;S2:添加硫酸钠;PS1:添加钙镁磷肥和硫磺;PS2:添加钙镁磷肥和硫酸钠。不同小写字母表示不同处理之间差异显著(P<0.05),ns表示不显著,下同。CK:No passivation agent control; P:Adding calcium magnesium phosphate fertilizer; S1:Adding sulfur; S2:Adding sodium sulfate; PS1:Adding calcium magnesium phosphate fertilizer and sulfur; PS2:Adding calcium magnesium phosphate fertilizer and sodium sulfate. Different lowercase letters indicate significant difference among treatments (P<0.05), ns indicate P>0.05, the same as below.
施用不同钝化剂处理的土壤pH值如
各处理土壤有效磷含量呈现先大幅上升后逐渐减少的趋势,大小依次为:PS1≈PS2>P>S1>S2≈CK(

图2 不同处理土壤有效磷含量的变化
Fig.2 Variation of the content of available phosphorus in different treated soils
土壤中有效硫包括水溶性硫、吸附态硫和部分有机态硫,主要以SO

图3 不同处理土壤有效硫含量的变化
Fig.3 Variation of the content of available sulfur in different treated soils
磷、硫的施用对土壤中有效Cd含量有显著(P<0.05)影响(

图4 不同处理土壤有效态Cd含量的变化
Fig.4 Variation of the content of available Cd in different treated soils

图5 不同处理下土壤Cd赋存形态占比
Fig.5 Fractions of Cd in soil under different treatments
不同小写字母表示不同处理之间差异显著 (P<0.05)。Different lowercase letters above the bars indicate significant difference among treatments (P<0.05).
土壤Cd形态与其他检测指标的相关性分析如
指标 Indicators | EXC | CAR | OX | OM | RES | 有效磷 Available phosphorus | 有效硫 Available sulfur | pH | Eh |
---|---|---|---|---|---|---|---|---|---|
EXC | 1.000 | ||||||||
CAR | 0.165 | 1.000 | |||||||
OX | -0.042 | -0.185 | 1.000 | ||||||
OM | 0.327 | 0.050 |
0.62 | 1.000 | |||||
RES |
-0.93 | -0.342 | -0.193 |
-0.55 | 1.000 | ||||
有效磷 Available phosphorus |
-0.57 | 0.307 | -0.122 |
-0.50 |
0.53 | 1.000 | |||
有效硫 Available sulfur |
-0.69 | -0.415 |
0.57 | -0.036 |
0.57 | 0.237 | 1.000 | ||
pH | 0.084 | 0.350 |
-0.61 | -0.409 | 0.024 | 0.379 |
-0.56 | 1.000 | |
Eh |
0.80 | 0.257 | -0.140 | 0.104 |
-0.74 |
-0.52 |
-0.72 | 0.281 | 1.000 |
注: *表示差异显著(P<0.05);**表示差异极显著(P<0.01)。Note: * indicates significant correlation(P<0.05); ** indicates extremely significant correlation(P<0.01).
通过相关性分析进一步得出:硫肥和磷肥的联用可通过对Eh、有效硫和有效磷的改变,进而影响土壤可交换态Cd向残渣态Cd的转换。
培养第60天时,PS1处理的Eh值最低,降低至-221 mV。当Eh下降到-100 mV时,硫酸盐还原菌(SRB)会将SO
pH是影响土壤中Cd有效性的重要因素,与CK处理相比,P处理的pH值提高了0.39个单位,显著提高了土壤pH值,此结果与Luo
本研究中,PS1和PS2处理的有效磷含量显著高于其他处理,且PS1处理的有效磷含量最高。一方面是因为钙镁磷肥本身含有大量的磷酸根,施入土壤后会溶解在土壤中。另一方面是因为SO
本研究中,PS1处理的有效Cd含量最低,钝化效果最好,分析其原因包括:①硫磺和钙镁磷肥联用处理的Eh值最低,显著提高了土壤的还原作用,促进了CdS沉淀的生成。②硫磺和钙镁磷肥联用提高了土壤的pH值,增强了土壤对C
土壤中Cd的不同赋存形态在一定程度上反映了Cd的溶解迁移能力和生物有效性。本研究中,硫肥的施用促进了土壤可交换态Cd向残渣态Cd的转化,这是由于
相关性分析表明,硫肥和磷肥的联合施用通过对Eh、有效硫和有效磷的影响,进而促进土壤可交换态Cd向残渣态Cd的转换。结果表明,在Cd污染稻田土壤里,相比硫酸钠和钙镁磷肥联用,硫磺和钙镁磷肥联用更能促进土壤可交换态Cd向残渣态Cd的转换。
综上所述,硫磺和钙镁磷肥联合施用的稻田土壤有效Cd含量降幅最大,钝化效果最好,为矿区周边Cd污染稻田的治理提供了新方法。但需要进一步研究以评估其稳定性及对作物吸收重金属污染物的影响。
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