风干和冻干对稻田土壤镉形态分析的影响

Influence of air drying and freeze drying on cadmium fractions in paddy soils

稻田土壤样品自然风干和冷冻干燥处理,是目前稻田土壤中镉形态分析过程中广泛采用的两种前处理方法,然而,风干和冻干处理对不同施肥稻田土壤镉形态分析的影响规律及机制的影响尚不明确。本研究以长期不同施肥稻田土壤为研究对象,通过对比自然风干和冷冻干燥稻田土壤样品,探讨了两种干燥方式对稻田土壤镉形态变化和化学提取有效镉含量的影响规律及机制。结果表明:不同施肥稻田土壤冷冻干燥样品中化学提取有效态镉含量均明显低于自然风干样品,长期施用化肥和高量有机肥稻田土壤有效态镉提取量差异分别达到56.5%-69.2%和50.8%-66.3%;而长期施用常量有机肥的稻田土壤有效态镉提取量差异为16.9%-22.3%。与自然风干样品相比,冷冻干燥处理的长期施用化肥和高量有机肥稻田土壤可交换态、有机结合态和铁锰氧化物结合态镉含量变化明显,而长期施用常量有机肥稻田土壤中可交换态和碳酸盐结合态镉含量变化较明显。两种干燥方式下土壤颗粒大小分布差异对土壤有效态镉提取影响较小。相关分析表明,风干和冻干过程中土壤pH、有机质、交换态铁和水铁矿性质变化对有效态镉提取的影响较大。干燥方式可显著影响长期不同施肥稻田土壤镉的形态及化学提取有效态镉的数量,在分析稻田土壤有效态镉含量时应注意干燥方式对不同土壤和提取剂提取效果的影响。

Chemical extraction of Cd from air-dried soil samples is a commonly applied method used to analyze available Cd in paddy soils. Although during the air-drying process, a range of different physical and chemical properties will contribute to altering the fractions of different Cd species in fresh soils, the characteristics and mechanisms underlying changes in the Cd fractions of paddy soils subjected to different fertilization treatments are still incompletely understood. In this study, using natural air-drying and freeze-drying methods, we investigated the effects of drying on changes in Cd fractions and the content of chemically extractable available Cd in paddy soils that had undergone different fertilization treatments. The results revealed that the contents of chemical extractable available Cd in freeze-dried paddy soils receiving different fertilization were significantly lower than those in naturally air-dried samples. The contents of extractable available Cd in freeze-dried paddy soils that had undergone the long-term application of chemical fertilizer and high-dose organic fertilizer were reduced by 56.5%-69.2% and 50.8%-66.3%, respectively. In contrast, the amount of extractable available Cd in paddy soils with the long-term application of low-dose organic fertilizer was reduced by 16.9%-22.3%. Compared with the naturally air-dried samples, we detected significant changes in the fractions of exchangeable, organic bound, and iron-manganese oxide-bound Cd in freezedried samples with long-term application of chemical fertilizer and high-dose of organic fertilizer, whereas the fractions of exchangeable and carbonate-bound Cd showed clear changes in paddy soils that had received long-term application of low-dose organic fertilizer.Differences in the soil particle composition of air-dried and freeze-dried samples were found to have slight effects on the chemical extraction of available Cd from paddy soils. Furthermore, correlation analysis revealed that changes in soil pH and the contents of organic matter, exchangeable iron, and ferrihydrite in soils had a considerable impact on the extraction of available cadmium during air drying and freeze drying. Consequently, with respect to the extraction of available cadmium from paddy soils, attention should be paid to the differences between air-drying and freeze-drying methods.