环境科学  2021, Vol. 42 Issue (4): 1979-1988   PDF    
沼液秸秆联用对滨海围垦田土壤重金属迁移及形态变化的影响
王伟1, 周珺楠1, 汤逸帆1,2, 申建华3, 韩建刚1,2     
1. 南京林业大学生物与环境学院, 南京 210037;
2. 南京林业大学南方现代林业协同创新中心, 南京 210037;
3. 中粮肉食(江苏)有限公司, 东台 224200
摘要: 为揭示秸秆还田措施下沼液替代化学氮肥施用对土壤中重金属环境风险的影响,本文以江苏滨海典型围垦农田(稻麦轮作)为对象,设置不加沼液和不加秸秆(CK)、加沼液但不加秸秆(B)、加秸秆但不加沼液(S)和沼液秸秆联用(BS)这4个处理的田间小区试验,观测不同土层中土壤Cu、Zn、Cd和Pb的迁移及形态变化特征,并评估其环境风险.结果表明:①BS处理下稻麦田表层(0~20 cm)土壤中Zn和Pb的总量显著下降(P < 0.05).稻田土壤中4种重金属由表层向中下层(20~60 cm)相对迁移6%~11%,麦田土壤中Cu、Cd和Pb从表层向下迁移25%~33%.这表明,沼液秸秆联用加速了表层土壤中重金属的垂向下移.②BS处理下,稻田表层土壤中Cu的弱酸提取态所占质量分数下降8.8%,Zn、Cd和Pb的残渣态降低7.0%~14.2%.这表明Cu被钝化,但Zn、Cd和Pb有活化趋势.相比较而言,麦田表层土壤中Cu的残渣态降幅为弱酸提取态的2.8倍,表明Cu被活化.与此同时,Cd的残渣态升高,Pb的弱酸提取态降低,Cd和Pb被钝化.③重金属生态风险评估表明,BS处理下稻麦田土壤均未发现重金属生态风险,并且,其风险指数明显低于B和S处理(P < 0.05).因此,沼液秸秆联用有助于显著降低滨海围垦田土壤重金属污染风险.
关键词: 沼液      秸秆      稻麦两熟田      土壤      重金属     
Effects of Combined Application of Biogas Slurry and Straw on the Migration and Fractions of Soil Heavy Metals in Rice-wheat Rotation System in Coastal Reclamation Areas
WANG Wei1 , ZHOU Jun-nan1 , TANG Yi-fan1,2 , SHEN Jian-hua3 , HAN Jian-gang1,2     
1. College of Biology and Environment, Nanjing Forestry University, Nanjing 210037, China;
2. Collaborative Innovation Center of Sustainable Forestry in Southern China of Jiangsu Province, Nanjing Forestry University, Nanjing 210037, China;
3. COFCO Meat(Jiangsu) Co., Ltd., Dongtai 224200, China
Abstract: In order to reveal the impact of the application of biogas slurry instead of chemical nitrogen fertilizer on the environmental risk of heavy metals in the soil by returning straw to the field, four treatments, without biogas slurry and without straw applications (CK), biogas slurry application without straw (B), straw application without biogas slurry (S), and biogas slurry combined with straw applications (BS), were applied in a typical coastal reclaimed farmland (rice-wheat rotation) in Jiangsu province. The migration and morphological characteristics of Cu, Zn, Cd, and Pb in different soil layers were observed, and the potential environmental risks were estimated. The results showed that: ① The total amounts of Zn and Pb in the surface soils (0-20 cm) in the rice and wheat fields under the BS treatment decreased significantly (P < 0.05). The four heavy metals in the paddy soils migrated 6%-11% from the surface to the middle and lower layers (20-60 cm), and Cu, Cd, and Pb in the wheat soils migrate down from the surface by 25% to 33%. This indicated that the combined use of biogas slurry and straw accelerates the vertical downward movement of heavy metals in the surface soil. ② Under the BS treatment, the contents of the weak acid extraction of Cu in the surface soil of the paddy field decreased by 8.8%, and the residual state of Zn, Cd, and Pb decreased by 7.0% to 14.2%. This revealed that Cu was passivated, but Zn, Cd, and Pb tended to be activated. In comparison, the reduction in Cu residues in wheat field surface soil was 2.8 times that of the weak acid extraction, indicating that Cu was activated. Furthermore, the residue state of Cd increased, the weak acid extraction state of Pb decreased, and Cd and Pb were passivated. ③ The ecological risk assessment of heavy metals showed that there is no ecological risk in the soils under the BS treatment, and the risk indices were significantly lower than those of the B and S treatments (P < 0.05). Therefore, the combined use of biogas slurry and straw helps to significantly reduce the risk of heavy metal pollution in the soils in the coastal reclamation areas.
Key words: biogas slurry      straw      rice-wheat double cropping field      soil      heavy metal     

江苏省滩涂总面积7 620 km2, 约占全国滩涂总面积的1/4[1].长期围垦而形成的大量农田已成为我国粮食保障的重要后备基地.然而, 作为海陆交汇区域, 土壤中重金属的环境风险备受关注[2~4].例如, 孟庆峰等[5]的研究认为盐城围垦农田土壤重金属含量偏高.姚荣江等[6]的研究显示重金属呈现不断累积的趋势.刘洋等[7]对当地作物籽粒进行测定发现存在重金属超标问题.因此, 降低围垦田重金属环境风险对提升土壤质量, 保障区域粮食安全具有重要意义.

围垦农区分布着众多大规模集约化养猪场, 沼液是其最主要的副产品.沼液富含易利用态氮素和多种生物活性物质[8, 9], 是化学氮肥替代的首选.然而, 有研究表明, 沼液施用使土壤中重金属的环境风险增加.例如, 汤逸帆等[10]的研究表明, 沼液施用5 a后, 稻麦田土壤Cu和Zn含量增加21.50%~30.35%. Duan等[11]的研究发现长期施用沼肥会显著增加土壤重金属的生物有效性.另一方面, 秸秆还田是滨海农区传统的农作措施, 可以有效提高土壤有机碳固存率和养分含量, 改善土壤结构, 促进作物生长[12~14], 而且对盐碱地改良具有很好的效果[15].有研究表明, 秸秆还田对土壤中重金属的有效性也产生显著影响.例如, 杨兰等[16]的研究发现秸秆还田使Cd的有效性下降, 但袁雪涛等[17]的研究则认为秸秆还田可能会活化重金属.尽管以往关于单一施用沼液或秸秆对重金属环境风险的研究取得了重要的进展.然而, 有关二者联用的相关影响目前还未见报道.

本文以江苏围垦农区典型稻麦两熟农田为研究对象, 设置不加沼液和不加秸秆(CK)、加沼液但不加秸秆(B)、加秸秆但不加沼液(S)和沼液秸秆联用(BS)这4个处理的田间小区试验, 采集0~20、20~40和40~60 cm土层土壤, 分析Cu、Zn、Cd和Pb的总量变化, 并采用BCR四步提取法测定土壤中重金属各形态的含量, 通过明确沼液秸秆联用对土壤重金属生态环境风险的影响, 以期为沼液合理施用及滨海围垦田土壤质量提升提供理论与实践依据.

1 材料与方法 1.1 研究区概况

研究区位于江苏省东台市黄海沼气站附近农场(32°38′23″N, 120°53′59″E), 属于亚热带和暖温带过渡区域.年日照量2100~2400 h, 年平均气温为14~15℃, 降水量为1 000~1 100 mm, 四季分明, 光热充足.农作区围垦历史在25 a以上, 耕作制度为稻麦两熟制, 同时秸秆全量还田.

1.2 土壤基本性状

研究区土壤发育为海相沉积物母质, 土壤质地为粉砂质壤土, 砂粒、粉粒和黏粒含量占比分别为37%、52%和11%, 类别为典型的滩涂盐碱地.pH为8.7, 电导率(EC)为1.3 mS·cm-1, 有机碳含量为5.1 g·kg-1.

1.3 沼液基本性状

供试沼液选自中粮肉食(江苏)有限公司为解决猪场粪污问题建立的沼气发电站, 该项目采用大型水泡粪工艺清理并收集猪舍内粪污, 由匀浆池(固体浓度控制在2.0%~3.0%)混合升温处理后进入发酵罐, 36~38℃的全混合厌氧反应器(CSTR)中发酵15~20 d.产生的沼气用来发电, 沉淀池的中上层为沼液原液, 底部为沼渣.沼液基本理化性质见表 1, 重金属含量见表 2.

表 1 供试沼液基本理化性质 Table 1 Basic physical and chemical properties of the biogas slurry

表 2 供试沼液重金属浓度/mg·L-1 Table 2 Concentration of heavy metals in the biogas slurry/mg·L-1

1.4 试验设计

设置4个处理, 包括不加沼液和不加秸秆(CK)、加沼液但不加秸秆(B)、加秸秆但不加沼液(S)和沼液秸秆联用(BS).重复3次, 共12个试验小区.每个小区面积为60 m2(6 m×10 m), 各小区随机排布, 小区间用防渗布隔开.秸秆还田按当地传统做法全量还田, 利用翻耕机粉碎翻耕15 cm左右.

水稻和小麦种植所需总氮量分别为225 kg·hm-2和150 kg·hm-2.通过沼液或尿素态氮肥使每个处理各作物种植季施加的总氮量相等.稻田沼液和尿素施用总量分别为204.5 m3·hm-2和484.9 kg·hm-2, 分基肥、分蘖肥和穗肥按2∶1∶2比例施用; 麦田沼液和尿素施用总量分别为136.4 m3·hm-2和323.3 kg·hm-2, 分基肥和追肥按1∶1比例施用.具体施肥量见表 3.

表 3 各处理施肥量 Table 3 Amount of fertilizer applied in each treatment

灌溉水pH为7左右, 灌水时间按当地耕作习惯, 沼液与水配比为1∶4, 各处理总灌水量相同, 避免灌溉对不同处理重金属的积累迁移造成影响.其它田间管理均按照当地耕作传统.小麦和水稻种植周期分别为2017年11月4日~2018年6月10日和2018年6月10日~2018年11月16日, 作物品种为淮稻5号和扬麦16号.

1.5 样品采集与重金属测定

样品采集与前处理分别于2018年6月(小麦收获期)和11月(水稻收获期)进行田间采样.采样用梅花形布点, 使用20 cm土钻垂直采样, 每个小区分0~20、20~40和40~60 cm这3个土层, 每层取3个点混匀为1个样品.稻田和麦田各采集36个样品.土样经自然风干后, 研磨过100目(0.149 mm)尼龙筛, 备用.

土壤各重金属总量根据HJ766-2015国家标准方法进行测定.将土壤样品置于HNO3-HF-HClO4体系中消煮[18, 19], 利用电感耦合等离子体质谱仪(ICP-MS, NexION 300X型, 美国)测定Cu、Zn、Cd和Pb的总量.

土壤中重金属各形态含量采用BCR四步提取法[20], 根据赋存形态将重金属分为4种:F1, 弱酸提取态(可交换态和碳酸盐结合态, 生物直接利用效率高); F2, 可还原态(铁锰氧化物结合态, 在还原条件下可被利用, 为潜在生物有效组分); F3, 可氧化态(有机物及硫化物结合态, 在强氧化条件下可被利用, 为潜在生物有效组分); F4, 残渣态(存在于矿物晶格中, 性质稳定, 生物不可利用).本试验以标准土壤GBW-07451进行质量控制, 所有试验设置空白对照和平行试验, 回收率85.3%~112.2%.

1.6 不同土层重金属累积总量

为了反映重金属在不同土层间的垂直迁移特征, 本文定义了土壤中重金属累积总量[Mi, 式(1)]:

(1)

式中, Mi为第i土层中重金属的累积量, kg·hm-2; Ci为第i土层中单位土壤重金属实测总量, mg·kg-1; ρi为第i土层土壤容重, 0~20、20~40和40~60 cm土层土壤平均容重分别为1.56、1.71和1.79 g·cm-3; d为土层深度, 20 cm; 10为单位转换系数.

1.7 土壤重金属生态风险评价

采用Håkanson提出的潜在生态风险指数法[21] [式(2)]:

(2)

式中, RI为滨海稻麦两熟田土壤中重金属潜在生态风险指数; Eri为单个重金属元素的潜在风险系数; Tri为单个重金属元素毒性响应系数, 根据文献[22]将重金属Cu、Zn、Cd和Pb毒性响应系数分别定为5、1、30和5; Cfi为单个重金属元素污染系数; Ci为单个重金属元素总量实测值; CBi为重金属元素参比值, Cu、Zn、Cd和Pb的自然背景值分别为35、100、0.2和35 mg·kg-1[23].RI值越大, 生态风险越高.评价分级标准参照文献[24]和表 4.

表 4 潜在生态风险评价法等级划分 Table 4 Classification of potential ecological risk assessment method

1.8 数据处理与分析

运用Excel 2019和Origin 2017对数据进行整理、分析和绘图, 采用SPSS 19.0统计分析软件进行单因素方差分析(one-way ANOVA), 利用Duncan新复极差法来分析稻麦田不同处理下0~20、20~40和40~60 cm土层土壤中重金属总量的差异显著性(P<0.05).

2 结果与分析 2.1 土壤中重金属的积累分布 2.1.1 稻田土壤重金属总量分布特征

S和BS处理下, 稻田土壤中Zn在0~20 cm土层的总量显著低于CK和B处理(P<0.05); 20~40 cm土层中B处理显著高于CK和BS, 但三者均显著高于S处理(图 1).B处理下, 0~20 cm和20~40 cm土层中Cd的总量显著高于S和BS处理.相比较而言, CK和BS处理下, 40~60 cm土层中Cd的总量显著高于S.在0~20 cm土层中, BS处理下Pb的总量显著低于CK和S, 同时B和S处理显著低于CK(P<0.05); 20~40 cm和40~60 cm土层中S、BS处理显著低于CK, 但高于B处理.Cu的总量在各土层中4个处理间差异不显著.

图 1 稻田各处理不同土层土壤中重金属总量 Fig. 1 Total amount of heavy metals in different soil layers of the paddy field

2.1.2 麦田土壤重金属总量分布特征

麦田0~20 cm土壤Cu、Zn和Cd的总量按高低依次为B>CK>S>BS(图 2).S处理下, 20~40 cm土层中Cu和Cd的总量显著低于其它3个处理, B处理下Zn的总量显著高于其它处理.CK和S处理下, 40~60 cm土层中Cu、Zn和Cd的总量显著低于B和BS处理, B处理下Cd的总量显著高于BS.BS处理下, Pb的总量在0~20 cm土层土壤中显著低于B和S处理, 但二者均显著低于CK; 在20~40 cm土层中B和S处理显著低于CK和BS; 40~60 cm土层中B处理显著低于CK和S, 同时显著低于BS.

图 2 麦田各处理不同土层土壤中重金属总量 Fig. 2 Total amount of heavy metals in different soil layers of the wheat soil

2.2 重金属在土层间的迁移

BS处理下, 稻田土壤中Cu、Zn、Cd和Pb在中下层(20~60 cm)积累量的占比分别高出表层(0~20 cm)6%、10%、8%和11%(表 5); Zn在B和S处理下中下层比表层分别高出5%和8%; Cu、Cd和Pb在B和S处理下土层间的差异均小于5%.表 6可见, 麦田土壤中Cu、Cd和Pb在BS处理下中下层积累量占比较表层分别高出25%、33%和25%; 其他变化均小于5%(除S处理Cd增加8%).

表 5 稻田各处理下重金属在不同土层土壤中的质量分数/% Table 5 Proportion of heavy metal accumulation in three soil layers under different treatments in the paddy field/%

表 6 麦田各处理下重金属在不同土层土壤中的质量分数/% Table 6 Proportion of heavy metal accumulation in three soil layers under different treatments in the wheat field/%

2.3 土壤重金属形态的变化 2.3.1 稻田土壤重金属形态变化特征

稻田0~20 cm土层土壤中, 与CK相比, BS处理下Cu的弱酸提取态质量分数降低8.8%, Zn、Cd和Pb的残渣态分别降低7.0%、8.9%和14.2%(图 3).B和S处理下, Pb的残渣态分别降低8.1%和6.8%, 可还原态和可氧化态(F2+F3态)相应升高, 但Cu、Zn和Cd各形态质量分数无明显变化.中下层(20~60 cm)土壤中, BS处理下Cu和Cd的残渣态分别降低12.6%和5.9%.B处理Cu的F2+F3态升高27.8%, 残渣态降低.S处理下Pb的残渣态降低7.4%, 转化成F2+F3态.

图 3 稻田不同处理土壤中重金属各形态分布 Fig. 3 Distribution of four forms of heavy metals in the paddy soil under different treatments

2.3.2 麦田土壤重金属形态变化特征

麦田0~20 cm土层中, BS处理下Cu的F2+F3态质量分数升高47.7%, 而弱酸提取态和残渣态分别降低12.6%和35.1%; Cd的残渣态升高7.1%; Pb的弱酸提取态质量分数降低9.2%, 转化成F2+F3态(图 4).B处理下Cu、Zn和Cd的残渣态质量分数分别升高19.4%、13.7%和21.7%.S处理Cu的弱酸提取态和残渣态分别降低14.7%和16.0%, F2+F3态升高; Zn的残渣态降低10.5%; Cd的残渣态上升9.8%.中下层土壤中BS处理下4种重金属残渣态质量分数上升5.6%~17.8%.B处理各重金属残渣态含量也均增加.S处理Cu的F2+F3态降低19.9%, 而残渣态上升, Cd则相反.

图 4 麦田不同处理土壤中重金属各形态分布 Fig. 4 Distribution of four forms of heavy metals in the wheat soil under different treatments

2.4 土壤重金属生态风险评价

表 7可见, 除稻田B处理Cd超过1级标准8.3%, 其它处理土壤中重金属的Eri值均小于30, 整体处于轻微程度.相比于CK, 稻田和麦田土壤BS处理下4种重金属的潜在生态风险系数分别降低16.67%~37.61%和52.24%~73.11%.稻田B处理Cd的潜在生态风险系数增加17.60%, Pb降低31.19%; 但麦田Cu、Zn、Cd的风险系数增加21.55%~43.24%.稻田和麦田S处理4种重金属的潜在生态风险系数降幅分别为11.98%~22.02%和20.69%~32.84%.稻田和麦田RI的范围分别为24.34~35.72和4.02~16.66, 均无生态风险.RI值大小按各处理排序为:B>CK>S>BS.

表 7 不同处理下围垦田土壤重金属潜在生态风险系数和指数 Table 7 Potential ecological risk factor and index of heavy metals in the coastal farmland soil

3 讨论

沼液施用会显著增加土壤中重金属的累积量, 原因可能与畜禽养殖饲料中有不同程度重金属的添加有关[25].宋三多等[26]在成都平原施用沼肥发现高量沼肥(稻麦季施肥量分别为1.7×105 kg·hm-2和1.3×105 kg·hm-2)显著增加了稻麦田0~20 cm土壤Cu、Zn和Pb的含量, 麦田土壤Cd含量显著增加, 但稻田降低.赖星等[27]的研究表明, 连续3 a施用沼液会显著增加土壤中重金属的累积量, 并且随着沼液用量增加, 土壤重金属的累积量也随之增大.本研究发现麦田单施沼液处理表层土壤中Cu、Zn和Cd的含量显著增加.这与以往研究结论相似.此外, 本研究表明秸秆还田措施也会对土壤重金属含量产生显著影响.曹阳等[28]的研究认为水稻秸秆还田显著降低耕作层土壤Pb和Cd的含量, 与不还田处理相比分别下降8.96%和11.08%.但郑顺安等[29]的研究发现, 秸秆还田会增加表层土壤中的Cd累积量, 并且4~5 a后土壤重金属含量显著高于不还田处理.本文单施秸秆处理显著降低表层土壤中Zn和Pb的总量, 但Cu和Cd的总量无显著变化.该变化的原因可能在于不同试验涉及的秸秆还田量和施用年限存在差异.前一研究采用150%秸秆还田经过2 a处理, 而后者采用上季作物秸秆全量还田经过5~9 a田间试验.沼液秸秆联用下, 稻田Zn、Pb和麦田Cu、Zn、Cd、Pb在表层(0~20 cm)土壤的总量均显著降低.这表明, 沼液与秸秆联用可显著降低稻麦田表层土壤中重金属总量, 比单一施加沼液或秸杆的作用效果更好.

施用有机肥有利于农田土壤重金属向下层迁移.何梦媛等[30]通过连续4 a在麦田施用猪粪发现, Cu可迁移至15~30 cm土层中, 但Cd、Pb迁移较弱.孙娜等[31]的研究也表明, Cu可迁移至15~30 cm土层, Zn则迁移至60~90 cm土层土壤中.本研究中沼液与秸秆联用下, 稻田4种重金属从表层向中下层(20~60 cm)土壤相对迁移6%~11%, 麦田Cu、Cd和Pb达到25%~33%, 相比较来说, 单施沼液或秸秆处理下, 重金属向中下土层相对迁移量均小于BS.王琼瑶等[32]研究猪粪和秸秆配施时发现除水稻季表层土壤中的Cu含量略低于下层土壤, Zn并没有发生显著下移.该变化的原因可能在于, 土壤质地显著影响重金属的迁移.土壤中黏粒多会对重金属的迁移产生阻滞作用, 从而减缓重金属向下运移[33, 34].同时, 表层土壤中的有机质高于底层, 这使得重金属在表层形成稳定的有机质-重金属络合物, 向下迁移的能力减弱[35, 36].沼液与秸秆联用下, 重金属发生明显垂向下移原因可能在于, 二者共存时沼液中的小分子有机酸和官能团与秸秆腐解后产生游离腐植酸[37], 提高重金属迁移活性.此外, 沼液中大量的盐基离子可占据秸秆或其腐解产物上的吸附位点, 通过竞争降低了其对重金属的吸附, 进而增加重金属的迁移性[38, 39].另一方面, 沼液施用后碱性土壤pH下降[40], 这可能使吸附于土壤上的重金属易于解吸[41], 有利于重金属向下层土壤垂直迁移.值得关注的是, 麦田沼液秸秆联用下Cd仅有12%残留在表层土壤, 其他均迁移至中下层, 这可能与Cd的水合离子半径小, 迁移速度快有关[42].

重金属的环境效应不仅由重金属的总量决定, 同时也取决于其在土壤环境中的赋存形态[43].沼液秸秆联用下, 稻田表层土壤中Cu的弱酸提取态所占质量分数降低, 这表明沼液与秸秆联用降低了稻田土壤中Cu的生物活性.相比较而言, 麦田Cu的F4残渣态降幅为F1弱酸提取态的2.8倍, 麦田土壤Cu被活化.稻田单施沼液或秸秆处理Cu的弱酸提取态均有下降趋势, 但降低幅度均低于BS.该变化的原因可能与沼液中的小分子有机酸及秸秆腐解产生的胡敏酸(HA)和富里酸(FA)有关.邱勇等[44]的研究发现HA可与土壤中的Cu通过络合、氢键结合、离子交换以及物理吸附等方式结合, 抑制其活性.罗梅等[45]的研究认为腐植酸能作为电子传递体影响重金属的氧化还原过程, 从而改变重金属的形态及生物有效性.此外, 沼液与秸秆联用加快了稻田表层土壤Zn、Cd和Pb活化, 但麦田Cd和Pb被钝化.胡青青等[46]的研究认为随着土壤中有机质和阳离子交换量的增加, 重金属的生物有效性增加, 但这种作用对中下层土壤影响较小.

表层土壤重金属与作物安全和人体健康紧密相关[47, 48].本研究对滨海围垦农田表层土壤进行重金属生态风险评估, 结果显示除稻田单施沼液处理土壤中Cd存在轻微超标风险, 其它重金属的潜在生态风险系数均显示稻麦围垦田土壤无生态风险水平.从RI值来看, 单施沼液会显著增加稻麦田土壤潜在生态风险指数, 而单施秸秆则会有效降低生态风险, 二者联用下比单一施用秸秆降低生态风险的效果更好.由此, 在沼液替代化学氮肥背景下, 农田消纳沼液与秸秆联用值得推荐.相比较而言, 沼液与秸秆联用下, 稻田土壤的潜在生态风险指数比麦田高出5倍.该变化与谢沂希等[49]的研究结论一致.原因可能在于, 一方面稻田处于厌氧环境中, 氧化还原电位低[50, 51]; 另一方面可能与稻田沼液施肥量大于麦田有关.因此, 水稻种植时, 适当降低沼液的施用量有望进一步降低重金属污染风险.

4 结论

(1) 沼液秸秆联用加速了表层(0~20 cm)土壤中Cu、Zn、Cd和Pb向中下层(20~60 cm)迁移, 稻田土壤重金属向中下层相对迁移6%~11%, 麦田Cu、Cd和Pb下移25%~33%.

(2) 沼液与秸秆联用下, 稻田表层土壤中Cu的有效性降低, Zn、Cd和Pb增加; 麦田表层土壤中Cu被活化, 但Cd和Pb被钝化.

(3) 沼液与秸秆联用下稻麦田土壤均未发现重金属生态风险, 二者联用是降低滨海围垦田土壤重金属污染风险的有效措施.

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