水分管理联合磷酸盐施用对水稻土中镉转化的影响

为探究水分管理方式和磷酸盐对水稻土中Cd转化的影响,按磷(KH2PO4)与Cd的摩尔比为2∶1添加磷酸盐,在75%田间持水量、田间持水量、持续淹水和淹水回旱四个水分管理下,测定土壤p H值及Cd的Ca Cl2有效态含量,并采用重金属连续浸提法分析土壤中Cd的形态分布。结果表明:与对照相比,持续淹水和田间持水量处理分别使有效态Cd含量降低了37.3%和10.0%,75%田间持水量和淹水回旱处理有效态Cd含量增加了12.5%和9.5%;重金属形态分析表明,施用磷酸盐促进弱酸提取态Cd向可还原态和可氧化态转化;75%田间持水量处理中弱酸提取态Cd所占比例显著降低,更有利于Cd向稳定的形态转化,而淹水回旱处理中,弱酸提取态镉含量增加,增大了Cd浸出、迁移的风险;不同水分管理下土壤p H值随时间的变化趋势差异较大,75%田间持水量处理中土壤有效态Cd与p H值呈显著负相关关系(r=-0.861 8),而持续淹水与淹水回旱处理的淹水还原过程对Cd的有效性有较为复杂的影响。综上,水分管理与磷酸盐施用对有效态Cd的影响存在交互作用,在75%田间持水量时磷酸盐施用对镉的稳定效果较好,且水分管理是控制水稻土中Cd转化的主要影响因素。

Effects of water management and phosphate application on the transformation of Cd in paddy soil

In order to investigate the effect of water management and phosphate application on the transformation of Cd in paddy soil, incubation experiments were carried out under four water managements, namely 75% field capacity (75%FC), field capacity (FC), continuous flooding (CF) and flooding-drying (FD). KH₂PO₄ was added into the soil with the molar ratio of KH₂PO₄/Cd at 2:1. The pH values and concentrations of CaCl₂-extractable Cd in soil samples were determined, and the European Community Bureau of Reference (BCR) sequential extraction procedure was conducted to analyze the fraction distribution of Cd. The results showed that, compared to the control groups, the application of KH₂PO₄ reduced CaCl₂-extractable Cd by 10.0% and 37.3% for FC and CF treatments, respectively, whereas increased its concentration by 12.5% and 9.5% in 75%FC and FD treatments, respectively. The fraction distribution results of Cd revealed that phosphate application slightly promoted the transform of Cd from acid-soluble fraction to reducible and oxidizable fractions. The proportions of acid-soluble Cd decreased significantly in the 75%FC treatment which was benefit for the stabilization of Cd, in contrast, higher acid-soluble Cd concentrations were observed in FD treatments, suggesting a higher-risk of leaching and migrating of Cd in soil. It was observed that pH varied remarkably during the incubation period, and there was a significant negative correlation (r=-0.861 8) between CaCl₂-extractable Cd content and soil pH in 75%FC treatment. As for CF and FD treatments, the reduction process of flooding had a complicated impact on the availability of Cd. In summary, water management and phosphate application had an interaction on CaCl₂-extractable Cd, and the stabilization effect of phosphate application on Cd was better in the case of 75%FC, furthermore, water management was the main influential factor controlling the transformation of Cd in paddy soil.