长期沼液灌溉对槟榔芋根区土壤理化性质及重金属含量的影响

目的 探究施用沼液对槟榔芋根区土壤理化性质及重金属含量的影响。方法 采集连续施用沼液6年和未施用沼液的槟榔芋种植地块土壤, 测定土壤中Cu、Zn、Pb、Cd、Cr、Hg、As共7种重金属的含量并进行污染风险评价, 同时测定土壤的基本理化指标, 分析土壤中重金属含量与土壤理化性质间的相关性。结果 长期沼液灌溉会显著增加槟榔芋根区土壤中有机质、碱解氮和速效钾含量, 但也会导致土壤中Cu、Zn、Pb、Cd、Cr显著累积, 尤其Cu和Zn含量均超出了GB 15618—2018中规定的风险筛选值。连续施用沼液增加了土壤重金属的综合污染水平和潜在生态风险, 总体呈现轻度污染等级, 具有中等水平的潜在生态风险, 其中Cu对综合污染水平的贡献率最大, Cd和Hg对综合潜在生态风险的贡献率最大。土壤中Cu、Zn、Pb、Cd、Cr之间可能存在污染同源性, 其含量基本与土壤有机质、碱解氮和速效钾呈极显著正相关, 与速效磷呈显著负相关。结论 沼液还田虽然会提高槟榔芋根区土壤整体养分状况, 但长期沼液灌溉也增加了土壤重金属的污染风险, 尤其是Cu、Cd、Hg可能引起的污染问题要引起重视。

Effects of long-term biogas slurry fertilization on soil physical and chemical properties and heavy metal content in areca taro root zone

Objective To investigate the effects of biogas slurry on soil physical and chemical properties and heavy metal content in areca taro root zone. Methods The soil of areca taro planting plots with continuous application of biogas slurry for 6 years was collected, and the soil with no application of biogas slurry was also collected as the control group. Seven metal elements (Cu, Zn, Pb, Cd, Cr, Hg and As) in the soil were determined and the pollution risk of heavy metals were assessed. Meanwhile, the soil physical-chemical properties were determined, and the correlations between the heavy metal contents and the physical-chemical properties of soil were analyzed. Results Long term biogas slurry irrigation had a significantly increase in the content of organic matter, alkali hydrolyzable nitrogen and available potassium in soil of areca taro root zone, but also could lead to metal elements (Cu, Zn, Pb, Cd and Cr) accumulated remarkably in the soil, especially Cu and Zn content exceeded the risk screening values specified in GB 15618-2018. The pollution level and potential ecological risk of heavy metals in soil were increased by continuous application of biogas slurry comprehensively, which showed a slightly pollution level and a moderate ecological risk. Among the heavy metals, Cu contributed the most to the pollution level, while Cd and Hg contributed the most to the potential ecological risks. The metal elements (Cu, Zn, Pb, Cd and Cr) in soil were highly positively related with each other, indicating that they were probably from the same pollution source. The content of these heavy metals positively correlated with the soil organic matter, alkali hydrolyzable nitrogen and available potassium, but negatively correlated with soil available phosphorus. Conclusion Although biogas slurry fertilizer application could effectively improve the overall nutrient status in soil of areca taro root zone, long-term irrigation also increases the pollution risk of heavy metals in the soil. Especially, attention should be paid to the pollution problems possibly caused by Cu, Cd and Hg elements.