不同钙质钝化剂对稻田土壤溶液中Cd浓度的影响

Effects of limestone, slaked lime and dolomite on cadmium concentration in the solution of paddy rice soils

为探讨不同钙质钝化剂对稻田土壤溶液中Cd浓度的影响,以一种Cd严重污染的农田土壤和两个水稻品种(台粳8号、Ⅱ优3301)为试验材料,采用盆栽试验法研究了三种钙质钝化剂(石灰石粉、白云石粉和消石灰)对土壤溶液Cd浓度以及相应的土壤Eh值和土壤溶液pH、Fe、Mn、TOC浓度动态变化的影响进行研究,并探讨了钙质钝化剂降低植稻土壤Cd有效性的机理。结果表明,在植稻期间,三种钝化剂均显著提高了土壤溶液的pH值,降低了土壤溶液中Cd、TOC、Fe和Mn的浓度和土壤的Eh值,降低了根表铁膜数量、铁膜Cd含量和水稻根系Cd含量。统计分析表明,土壤溶液Cd浓度与土壤Eh值、土壤溶液的TOC、Fe、Mn浓度之间均呈显著正相关,与土壤溶液pH值呈显著负相关,表明在酸性Cd污染的植稻土壤上,钙质钝化剂通过提高土壤pH值、促进土壤的还原、抑制Fe/Mn氧化物的还原溶解、减少水溶态有机物的形成等途径降低了土壤Cd的溶解性。钙质钝化剂抑制了水稻根表铁膜的形成、降低了铁膜对Cd的富集,从而也降低了水稻根系对Cd的吸收。在钝化剂种类、移栽时间和水稻品种三个外部因素中,水稻品种对土壤溶液中Cd的影响较大。在pH、Eh、TOC、水溶性Fe和Mn浓度等土壤因素中,水溶性Fe浓度成为影响水溶性Cd的主要因素(成熟期)。研究表明,三种钙质钝化剂对土壤溶液中Cd浓度的影响无显著差异,对根系Cd含量的降低效果因水稻品种而变。在提高土壤溶液pH方面,白云石粉的效果总体强于石灰石粉和消石灰。

In order to better understand the effects of limestone, slaked lime and dolomite on cadmium concentration in the solution of paddy rice soils, a pot experiment was performed using Cd contaminated soil, three amendments（limestone, slaked lime and dolomite）, and two rice varieties, Taigeng 8 and Ⅱ-You 3301, aimed to study the dynamic change in water-soluble Cd, soil Eh, pH, TOC, Fe and Mn in soil solution during rice growing period, and the mechanism of the amendments to reduce Cd availability in the soils. The results showed that the solution pH significantly increased, whereas Cd, Fe, Mn and TOC in the solution, and the amount of Fe-plaques on root surface, the Cd in the Fe-plaques and the roots were significantly decreased by the amendments. The water-soluble Cd was significantly and positively correlated with the soil Eh, TOC, Fe and Mn in the solution, while negatively correlated with the solution pH, indicating that the amendments decreased Cd solubility by increasing the soil pH, thereby, inhibiting the reduction-dissolution of Fe/Mn oxides and reduced the soluble organic matter con-tent in the soils. The amendments reduced Fe-plaques on rice roots, and the Cd content in the Fe-plaques, which also decreased Cd uptake by rice roots. The rice varieties were more important than the amendments and the growing time in affecting water-soluble Cd. Among the var-ious factors（pH, Eh, TOC, Fe and Mn contents in soil solutions）, water-soluble Fe was the most significant for water-soluble Cd（90 days transplanting）. Our results indicated that the effects of the three amendments on Cd concentration in soil solution were similar with each other whereas those on Cd contents in rice roots varied with rice varieties.