镉在不同质地水稻土剖面中的分布特征及与作物吸收的关系

通过野外定点采集土壤和作物植株、籽粒样品, 利用石墨炉(novAA400)原子吸收法, 研究了成都平原稻麦轮作下水稻土剖面中镉的分布特征及其与水稻、小麦吸收镉的相关性。结果表明，土壤剖面中的镉主要集中在0～15 cm的耕层土壤，总体表现为“向根层富集”的特征，土壤全镉和有效态镉均随土层深度的增加而逐渐降低，30～45 cm土层的全镉和有效态镉含量平均值分别为表层的47.60%和39.49%。不同质地土壤中的镉向下迁移量大小顺序为砂壤>重壤>中壤，以15～30 cm土层的迁移量差异最大。土壤pH与0～15 cm土层的有效态镉含量间相关性不显著(r=-0.46)，与15～30 cm和30～45 cm土层有效态镉含量间呈显著的负相关(r=-0.78*～-0.86**)。水稻、小麦秸秆和籽粒镉含量与0～15 cm和30～45 cm土层的全镉含量间相关性不大(r=-0.092～-0.383, 0.174～0.424)，但与0～15 cm和15～30 cm土层的有效态镉含量呈显著正相关(r=0.766*～0.953**)，与30～45 cm土层的有效态镉含量相关性不显著(r=0.526～0.584)。因此，土壤有效态镉含量比全镉含量更适合作为农作物产品安全的土壤镉污染评价指标。

Distribution Characteristics of Soil Cadmium in Different Textured Paddy Soil Profiles and Its Relevance with Cadmium Uptake by Crops

Adopting atomic absorption spectrometry (novAA400), the present study investigated the distribution characteristics of soil cadmium (Cd) in different textured paddy soil profiles under rice-wheat rotation and its correlation with Cd uptake by rice and wheat in Chengdu Plain through repeatedly taking soil and plant samples at the fixed sites in the field. The results revealed that Cd in the paddy soil profiles was mainly concentrated at the plough layer (0～15 cm) that obviously featured ‘Cd accumulates towards the rooting layer’. Soil total Cd and available Cd (1 mol·L-1 MgCl₂ extraction) in the profile declined with soil depths and its average values at 30～45 cm only accounted for 47.60% and 39.49% of those at 0～15 cm. The potential downward movement of Cd in the different textured soil profiles was observed as sandy loam>heavy loam>loam. There was no significant correlation between soil pH and available Cd(r=-0.46) at 0～15 cm soil depth, while significantly negative correlations between soil pH and available Cd were observed at 15～30 cm (r=-0.78) and 30～45 cm (r=-0.86). The results further demonstrated that the Cd contents in either grain or straw of rice and wheat were not well correlated with soil total Cd at any soil depth (r=-0.092～0.383 for rice and r=0.174～0.424 for wheat), but significantly correlated with soil available Cd at 0～15 cm and at 15～30 cm (r=0.766*～0.953**) despite insignificant correlation at 30～45 cm (r=0.526～0.584). It is strongly suggested that the soil available Cd can be used as a better criterion than the total soil Cd to rate Cd contaminated soils in relation to safety of agricultural products.