中轻度重金属污染农田土壤的时空特征及改良

Spatio-temporal characteristics and improvement of medium and mild heavy metals contaminated farmland soil

为研究农田土壤重金属与速效养分的时空特征以及氮磷增效剂对农田土壤重金属的影响,本试验以受中、轻度污染的酸性棕壤和典型潮土为研究对象,采用田间试验、盆栽试验与室内分析相结合的方法进行研究。结果表明:农田土壤中Cd、Cu、Pb、Zn 4种重金属元素含量在0~20 cm土层显著高于深层土壤;棕壤0~20 cm土层Cd含量超标204%,潮土0~20 cm土层Cd、Zn含量分别超标104%、419%;农田土壤0~20 cm土层重金属有效态含量占比高于深层土壤,棕壤中重金属有效态含量占比高于潮土。棕壤0~20 cm土层全氮、碱解氮、铵态氮、硝态氮、有效磷和速效钾含量均显著高于深层土壤,且随土壤深度增加呈逐渐减小趋势,而潮土中仅全氮、碱解氮和有效磷含量显著高于深层土壤;农田土壤速效养分随时间波动变化,其中硝态氮和铵态氮波动幅度最大,最大变异系数分别为44.1%和47.3%。受污染农田土壤的小麦植株体内Cd、Pb、Cu主要积累在叶片,Zn主要积累在籽粒;不同重金属元素从小麦茎、叶向籽粒的迁移程度差异较大,其中Cd迁移率最小,Zn迁移率最大。氮磷增效剂能显著减少棕壤中重金属有效态含量,底肥+氢醌+双氰胺+生物炭处理的有效态Cd、Cu、Pb、Zn含量较对照(仅加底肥,不加氮磷增效剂)处理分别显著降低24.7%、19.5%、23.7%、18.1%,而在潮土中施用效果不明显。研究表明,农田土壤重金属与土壤养分之间存在一定的相关性,且在土壤垂直分布上大体一致,土壤类型是氮磷增效剂对重金属有效态产生不同影响的重要因素。

To study the spatiotemporal characteristics of heavy metals and the available nutrients in farmland soil,as well as the effects of nitrogen and phosphorus synergists on heavy metals in farmland soil,this study took acid brown soil and typical aquic soil with moderate or mild pollution as the research object and utilized field experiment,pot experiment,and laboratory analysis methods.The results showed that the contents of Cd,Cu,Pb,and Zn were significantly higher in the 0-20 cm soil layer than in the deeper soil.The Cd content in the 0-20 cm soil layer of brown soil exceeded the standard by 204%,and the Cd and Zn contents in 0-20 cm soil layer of the fluvo-aquic soil exceeded the standard by 104% and 419%,respectively.The percentage of available heavy metal content was higher in the 0-20 cm soil layer of farmland soil than in the deep soil and was higher in brown soil than in fluvo-aquic soil.The contents of total nitrogen,alkalihydrolyzable nitrogen,ammonium nitrogen,nitrate nitrogen,available phosphorus,and available potassium were also significantly higher in the 0-20 cm soil layer than in the deep layers of brown soil and gradually decreased with greater soil depth.Only the total nitrogen,alkalihydrolyzed nitrogen,and available phosphorus contents in the fluvo-aquic soil were significantly higher than those in the deep soil.The available nutrients of the farmland soil fluctuated with time,with nitrate nitrogen and ammonium nitrogen showing the maximum fluctuations.The maximum coefficients of variation were 44.1%and 47.3%,respectively.In polluted farmland soil of wheat plants,Cd,Pb,and Cu mainly accumulated in leaves,whereas Zn mainly accumulated in grains.The migration degrees of different heavy metal elements from wheat stems and leaves to grains were quite different.Among these,the migration rate of Cd was smallest and the migration rate of Zn was largest.Nitrogen and phosphorus synergists could significantly reduce the content of available heavy metals in brown soil.The contents of available Cd,Cu,Pb,and Zn in the hydroquinone+dicyandiamide+biochar treatment were significantly lower than those of the treatment without it by 24.7%,19.5%,23.7%,and 18.1%,respectively.However,the application effect was not obvious in fluvo-aquic soil.The results revealed a certain correlation between heavy metals and nutrients in farmland soil,which was similar through the vertical distribution of the soil.Soil type is an important factor modulating the different effects of nitrogen and phosphorus synergists on the available states of heavy metals.