华北地区有机种植和常规种植模式下土壤重金属含量及污染评价

Assessment of heavy metal content and pollution in organic and conventional farming soils in North China

为探讨有机种植与常规种植两种不同种植方式对土壤重金属含量和污染特性的影响,本文在华北5个地区选取典型的有机蔬菜和有机小麦种植基地及附近相似条件的常规种植地块,比较了土壤中Cu、Zn、Pb、Cr、Cd、As共6种重金属含量的差异,并采用不同评价方法对不同种植方式下土壤中重金属的污染程度进行了评价。结果表明:与常规种植相比,有机种植减轻了土壤酸化和盐渍化,提高了土壤有机质含量和阳离子交换量,在一定程度上有利于降低土壤中重金属的生物有效性。与土壤背景值相比,所有调查地区的土壤重金属均有不同程度的增加和积累。与常规种植相比,有机种植模式能有效降低土壤中Cd、Cr含量,有机小麦种植地块因长期施用大量有机肥导致土壤中Cu、Zn、As大量富集;而常规温室菜田同时施用大量的有机肥、化肥及农药,土壤中Cu、Zn、As富集的风险比有机种植模式高;露天蔬菜有机种植地块土壤中Cu、Zn、As含量与常规地块差异不明显。综合污染指数评价结果显示,调查地区土壤均属于轻污染程度,主要贡献因子为Cd、Cu、Zn,有机种植降低了土壤中重金属的综合污染水平;地累积指数法评价结果表明,调查地区处于无污染到中等污染水平,最明显的污染元素是Cd,有机种植降低了土壤中重金属污染的程度和风险;潜在生态危害指数评价结果表明,所调查地块存在轻微潜在生态风险,其中产生较大生态危害的是Cd,表现出轻微生态危害程度。本研究表明,有机种植减轻了土壤中重金属综合污染水平和污染风险,并减轻了土壤重金属的潜在生态危害。

To study the effects of conventional and organic farming systems on soil heavy metals contents and heavy metals pollution degree, an experiment was conducted in typical organic and conventional vegetable and wheat fields in five regions of North China（Suning, Quzhou of Hebei Province; Feicheng, Gaotang, and Cao County of Shandong Province）. The contents of Cu, Zn, Pb, Cr, Cd and As in 0-20 cm soils under conventional and organic cropping systems of greenhouse vegetable, open-air vegetable and wheat were measured in the five regions. The pollution degrees of heavy metals under different cropping systems were assessed by using single and comprehensive pollution indexes, geo-accumulation index, and potential ecological hazard coefficient and potential ecological risk index. The results showed that compared with conventional farming, organic farming balanced soil p H, alleviated soil salinization, significantly increased soil organic matter content and cation exchange capacity（CEC） and reduced biological effectiveness of heavy metals in soils in different regions. Also compared with background values, soil contents of heavy metals increased and accumulated to different degrees in five regions. Compared with conventional farming, organic farming effectively reduced con-tents Cr and Cd in soil. There was obvious enrichment and accumulation of Cu, Zn and As in organic wheat fields because of long-term application of large amounts of organic manure. The use of large quantities of organic manure, chemical fertilizers and pesticides in conventional greenhouse vegetable fields increased the accumulation of Cu, Zn and As in soil than in organic greenhouse vegetation fields. The contents of Cu, As and Zn in open-air organic vegetable fields were not significantly different from those in conventional vegetable fields. The comprehensive pollution index evaluation showed that soils in different investigated regions were lightly polluted and the main contributors were Cd, Cu and Zn. The geo-accumulation index evaluation showed no-pollution to moderate pollution levels in the investigated fields of different regions. Cd is the most obvious pollution heavy metal. Potential ecological hazard index assessment showed a slight potential of ecological risk in the investigated regions and that Cd had a higher ecological risk and showed a slight ecological damage. The research results showed that compared with conventional farming, organic farming comprehensively reduced pollution levels and pollution risks of heavy metals and alleviated ecological hazards of heavy metal in soils in the investigated regions.