不同类型土壤淹水对pH、Eh、Fe及有效态Cd含量的影响

基于数据收集整理,分析了南方不同酸碱性土壤淹水后,土壤pH值、Eh值、Fe[Fe(Ⅱ)和无定型氧化铁]含量、有效态Cd含量和不同有机质土壤淹水后有效态Cd含量变化趋势,同时分析了pH、Eh、Fe变化趋势对有效态Cd含量的影响。结果表明:不同酸碱性土壤长时间淹水后,pH均趋于中性、Eh下降、Fe含量增加;有效态Cd含量在酸性和中性土壤中呈持续下降趋势,分别降低了42%和38%;在碱性土壤中降低了27%,其中淹水前15 d呈增加趋势,淹水15 d后逐渐减少。不同有机质含量土壤淹水后,有效态Cd含量在中高(≥20 g·kg~(-1))有机质土壤中降低78%,且为持续降低趋势;在中低(≤20 g·kg~(-1))有机质土壤中降低了52%,在淹水15~30 d增加,且淹水15 d有效态Cd含量要低于淹水60 d有效态Cd含量。土壤有效态Cd含量随着pH值增大而降低,且变化速率一致,即pH值增加速率大时,有效态Cd含量降低速率也大,反之亦然;土壤有效态Cd含量在淹水前15 d随Fe含量的增加而增加,淹水15 d后随着Fe含量增加而降低;整个淹水期间,土壤有效态Cd含量随着Eh值降低而降低。综上,酸性土壤和中高有机质土壤淹水后可有效降低土壤有效态Cd含量,碱性土壤淹水时间不低于30 d、中低有机质土壤淹水不超过15 d才能达到有效降低土壤有效态Cd含量之目的。

Effects of pH,Eh,Fe,and flooded time on available-Cd content after flooding of different kinds of soil

Based on collected and arranged data, the following variables were assessed after flooding:the trend in the change of soil pH val-ues, Eh values, Fe(Fe(Ⅱ)and amorphous iron oxide)content, and available Cd content under different pH values in southern soil; the trend in the change of available Cd content in soil with different organic matter contents;and the effect of the trend in the change of pH, Eh, and Fe on the content of available Cd in soils. Several conclusions were drawn based on these analyses. All pH values tended to be neutral, the Eh decreased, and the Fe content increased in three kinds of soil with different pH values after 60 days of flooding. The content of avail-able Cd in acid and neutral soils showed a continuous decreasing trend, decreasing 42%and 38%, respectively. In alkaline soil, it decreased 27%, and it increased on the first 15 days of flooding and then decreased gradually. In soil with different organic matter content after flood-ing, the content of available Cd in the soil with medium-high organic matter(≥20 g·kg-1)showed a continuous decreasing trend and de-creased 78%. In the soil with medium-low organic matter(≤20 g·kg-1), it decreased 52%and increased on the flooded 15~30 days;the content of available Cd in the soil with the 15-day flooded treatment was lower than that for the 60-day treatment. After flooding, the content of available Cd in soil decreased with the increase in pH value, and the change rate was consistent;when the increase rate of the pH value increased, the decrease rate of the content of available Cd also increased, and vice versa. The content of available Cd in soil increased with the increase in the Fe content on the first 15 days of flooding, and then decreased with increase in Fe content. The content of available Cd de-creased with the decrease in the Eh value during the flooding. In conclusion, the content of available Cd in soil could be effectively reduced in acid soil and medium-high organic soil after flooding. In alkaline soil, the available Cd content could only be reduced by flooding of not less than 30 days. In the medium-low organic soil, flooding should be conducted for less than 15 days in order to reduce the content of available Cd in soil.