种植模式对南方旱地重金属含量及其迁移规律的影响

Effects of Different Planting Patterns on Concentrations and Migration of Soil Heavy Metals in Dryland in Southern China

以玉米和大豆为试验材料,研究了单种、套种对土壤重金属含量及迁移转化规律的影响。试验结果表明,试验区土壤中Pb、Cd和Zn含量均超过土壤环境质量二级标准(GB 1518—2008)。套种时,非根系和根系土壤中Pb、Zn、Cu、Cd、Fe和Mn含量呈下降趋势,但与单种无显著性差异,种植模式对土壤重金属形态影响显著不同,且根系土壤与非根系土壤差异显著。根系土壤和非根系土壤中Zn、Cu、Fe和Mn以残渣态为主,占50%以上,而Pb以铁锰结合态为主,非根系土壤中铁锰结合态Pb的比例约为40%,而根系土壤约为50%。根系土壤中可交换态和碳酸盐结合态Cd的比例分别占土壤中Cd总量的14.01%~15.82%和9.56%~9.90%,与根系土壤相比,非根系土壤中可交换态Cd和碳酸盐结合态Cd的比例分别高0.63~0.85倍和1.38~1.48倍。研究还发现,大豆和玉米对Pb、Zn、Cu、Cd、Fe和Mn吸收富集能力显著不同,且种植模式对植物吸收富集重金属能力也有显著性影响。在试验区土壤中种植大豆和玉米,重金属在土壤-植物系统中的迁移率都比较高,从而使作物可食部分重金属含量较高,大豆中Pb和Cd含量分别超标48.0~53.5倍和24.8~30.8倍,玉米中Pb和Cd含量分别超标47.2~51.8倍和9.7~15.8。所有试验结果显示,在试验区种植粮食作物存在较大的健康风险,且水改旱不能实现试验区土壤重金属污染治理的目的。

Plant species have different impacts on forms and transformation of heavy metals in soil. Here an experiment was performed to investigate the effects of single and inter-planting of soybean and maize on content, forms and migration of soil heavy metals in dryland in Southern China. Results showed that the content of Pb, Cd and Zn exceeded the second grade levels of the National Soil Environmental Quality Standard(GB 1518—2008). Compared to the soil with single planting, Pb, Zn, Cu, Cd, Fe and Mn concentrations under the inter-planting tended to decrease in both rhizospheric and non-rhizospheric soils. However, plating patterns had significant effects on forms of soil heavy metals. The forms of soil heavy metals were significantly different between rhizospheric and non-rhizospheric soils. Residual form was the main fraction of Zn, Cu, Fe and Mn in both rhizospheric and non-rhizospheric soils, accounting for more than fifty percent. The forms of Pb and Cd were significantly different from those of Zn, Cu, Fe and Mn. Oxide bound Pb was the major fraction in both rhizospheric and non-rhizospheric soils, constituting about forty percent in non-rhizospheric soil and about fifty percent in rhizospheric soil. Percentages of exchangeable and carbonate bound Cd were respectively 14.01% ~15.82% and 9.56% ~9.90% in rhizospheric soil, while 0.63 ~0.85 and1.38~1.48 times more in non-rhizospheric soil. The content of Pb, Zn, Cu, Cd, Fe and Mn was significantly different between soybean and maize, and influenced by planting patterns. Lead and Cd in edible part of soybean were 37.95~43.45 and 50.5~52.6 times higher, while in maize 47.2~56.8 and 9.7~15.8 times more than the limits for pollution standard in food(GB 2762—2012), respectively. These results show that food crops planted in the tested field had high health risks and that changing from paddy field to dry land is not an option for remediation of soil contaminated with heavy metals