施用石灰降低污染稻田上双季稻镉积累的效果

【目的】研究在不同镉（Cd）污染程度稻田上施用石灰（CaO）的效果以及双季稻稻米Cd积累的差异,为早、晚稻季下不同污染程度稻田上的稻米安全生产提供参考。【方法】在湖南省选取43个县（区）的典型Cd污染稻田作为试验点,以常规栽培作为对照,研究施用石灰（1 200 kg·hm^-2）后,轻度污染（土壤有效镉≤0.2 mg·kg^-1）、中度污染（0.2 mg·kg^-1土壤有效镉≤0.4 mg·kg^-1）、重度污染（0.4 mg·kg^-1土壤有效镉≤0.6 mg·kg^-1）和严重污染（土壤有效镉>0.6 mg·kg^-1）稻田土壤pH、土壤有效镉含量、稻米Cd含量以及稻米富集系数的变化。【结果】（1）从Cd污染稻田整体的角度分析,相比常规栽培,施用石灰能够极显著降低早、晚稻米Cd含量均值,降幅分别为31.0%和28.6%。（2）从不同稻季下不同污染程度稻田的角度分析,相比常规栽培,施用石灰能够降低早稻季中度、重度和严重污染稻田的稻米Cd含量均值,降幅分别为37.0%、38.7%（P＜0.05）和22.6%;施用石灰能够降低晚稻季轻度、中度、重度和严重污染稻田的稻米Cd含量均值,降幅分别为2.0%、31.3%（P＜0.05）、31.8%和22.9%。不同污染程度稻田施用石灰后能够提高土壤pH,降低土壤有效镉含量,使稻米Cd富集系数明显下降,实现对稻米Cd含量的调控。【结论】施用石灰能够有效调控早稻季的轻度、中度、重度以及晚稻季的轻度Cd污染稻田的稻米Cd含量均值,降至限量标准（0.2 mg·kg^-1）以下。因此,以石灰施用为基础,结合其他降Cd措施,实施“分稻季分污染程度”和“晚稻优先于早稻”的治理思路,能提高大田生产上稻米Cd含量调控的稳定性并降低治理成本。

Effects of Lime on Cadmium Accumulation of Double-Season Rice in Paddy Fields with Different Cadmium Pollution Degrees

【Objective】The purpose of this study was to explore the effects of applicating liming in the double-season rice in paddy fields with varying degrees of cadmium pollution, and then to provide a reference for rice safety production in different polluted paddy fields with early and late rice seasons.【Method】43 typical cadmium polluted paddy fields in counties (districts) of Hunan province were used as experimental sites, and the lime was applied according to the standard of 1 200 kg·hm^-2, to explore the change of four values such as soil pH, soil available Cd content, rice Cd content and rice enrichment coefficient, that were respectively researched in lightly polluted paddy fields (soil available Cd≤0.2 mg·kg^-1), moderately polluted paddy fields (0.2 mg·kg^-1soil available Cd≤0.4 mg·kg^-1), severely polluted paddy fields (0.4 mg·kg^-1soil available Cd≤0.6 mg·kg^-1), and super severely polluted paddy fields (soil available Cd>0.6 mg·kg^-1). The conventional cultivation was used as control.【Result】The multi-point experiment results showed that: (1) From the perspective of integral Cd polluted paddy fields, compared with conventional cultivation, the average Cd content in early and late rice was significantly reduced by applying lime, with a decrease of 31.0% and 28.6%, respectively. (2) From the perspective of different rice seasons in diverse pollution levels rice fields, the mean rice Cd content in paddy fields with moderately, severely, and seriously polluted rice fields in early rice seasons was decreased by 37.0%, 38.7% (P＜0.05) and 22.6%, respectively, compared with that in conventional cultivation. Application of lime could also reduce the mean Cd content of rice in lightly, moderately, severely and super severely polluted paddy fields in late rice season by 2.0% ,31.3% (P＜0.05), 31.8% and 22.9%, respectively. The lime could regulate Cd content in rice, because it could lower the Cd enrichment coefficient of rice in paddy fields with different degrees of pollution and the available Cd content in soil, ,and increase the soil pH. 【Conclusion】The application of lime could effectively control the mean Cd content of rice in the paddy fields polluted by light, moderate and severe Cd in early rice season and lightly Cd polluted paddy fields in late rice season to below the limit standard (0.2 mg·kg^-1). Therefore, on the basis of lime application and in combination with other measures to reduce Cd as the main ideas of “separating the degree of pollution in rice season” and “ late rice is prior to early rice” could improve the stability of controlling rice Cd content in field production and the economy of governance costs.