稻菜轮作制下土壤有效态汞提取剂和提取条件研究

Extractants and Extraction Conditions for Available Hg in Soil of a Rice-Vegetable Rotation System

选择长三角地区代表性人为耕作土——青紫泥为研究对象,通过网室盆栽和室内试验,选用CaCl2,HCl,DTPA(二乙烯三胺五乙酸)和NH4OAc共4种提取剂,研究了水稻—小白菜—萝卜作物轮作系统中土壤有效态汞提取剂的选择与提取条件的优化问题。结果表明,不同提取剂提取的有效态汞含量随提取时间的延长而逐渐增加,30min可作为提取剂提取土壤有效态汞的最佳平衡时间;随土水比的减小,提取剂提取的土壤有效态汞量明显提高,1∶5为较适宜的土水比;不同提取剂的提取能力不同,对供试土壤,提取剂提取能力的大小顺序为:CaCl2>HCl>NH4OAc>DTPA。提取剂提取的土壤有效态汞量之间存在显著正相关,其中CaCl2和NH4OAc之间相关性最高;在土壤—水稻系统和土壤—萝卜系统中作物可食部位汞含量与提取剂提取的土壤有效态汞含量之间存在显著正相关关系,但在土壤—小白菜系统中相关性不强。综合分析,确定CaCl2为供试土壤汞有效态的最佳化学提取剂。

The soil locally referred to as a purplish clayey soil（PCS）, which was sampled in Deqing County, Zhejiang Province. Both laboratory and greenhouse pot experiments were conducted to investigate availability of soil Hg to crop plants in a rice--cabbage--radish rotation system. Four extractants including 0.1 M hy- drochloric acid（HC1）, 1 M ammonium acetate（NH4OAc, pH=7.0）, 0. 005 M Diethylenetriaminepentaacetic acid（DTPA）, and 0.1 M calcium chloride（CaC12, pH=5.0） were compared for their adequacy in estimating mercury（Hg） availability to crop plants. The results show that the amounts of Hg extracted by each of the four procedures increased with extraction time. The optimal time required for extraction of soil Hg was ap- proximately 30 min~ the time, however, varied slightly among the four extractants. The amounts of extrac- ted Hg increased with decreasing soil/solution ratio, and a soil/solution ratio of 1 ~ 5 appeared to be adequate for soil Hg availability tests. The amounts of extracted Hg decreased in the order of used extraetants as CaC12 ~HCI^NH4OAc^DTPA. Extractable soil Hg determined using the four extractants were correlated with each other positively significantly, especially between CaC12 and NH4OAc. Significant correlations were also found between extractable Hg in the soil and total Hg concentrations in edible tissues of rice and radish, except for cabbage. Overall, the 0.1 M CaC12 extraction provided the best estimation of available Hg in the soil and could be used to estimate phytoavailability of Hg in the rice--cabbage--radish rotation system.