Rice whole-plant removal to improve safe utilization of cadmium-contaminated rice fields
In order to explore pathways toward safe rice production in paddy fields with moderate to light Cd contamination,this study investigated the specific depletion of crop-available Cd by different rice cultivars which was then complemented by measures for soil liming and silicon(Si)supplement.We aimed to identify the effect of this synergistic strategy coupling Cd depletion with follow-up immobilization on mitigating rice Cd accumulation.In the field experiment in 2021,two high Cd-accumulating cultivars,ie.hybrid rice(TaoyouXiangzhan)and conventional rice(Yuzhenxiang),were planted under saturated moisture condition with no visible floodwater for soil Cd extraction.In the following field experiment next year,local edible hybrid rice(Y liangyou 9918)was cultivated under conventional water management,with calcium oxide(CaO)alone or combined CaO and rice husk ash(CaO+RHA)applied to further secure rice production by raising soil pH and enhancing effective Si level.The results showed that:①under moisture water management,TaoyouXiangzhan and Yuzhenxiang exerted a significantly distinct impact on soil Cd fraction.In specific,Yuzhenxiang depleted Cd from readily available(exchangeable+carbonate-bound)and more stable(iron-manganese oxide bound+organically bound+residual)fractions by 11%and 14%,respectively,as compared to 2%and 29%by TaoyouXiangzhan.②Compared with the unextracted soil,grain Cd of edible Y-liangyou 9918 decreased by 10%～18%from 1.02 mg·kg-1 to 0.85～0.92 mg·kg-1 in the post-extracted fields with the whole rice plants removed.In the post-extracted soil,grain Cd content was reduced by 73%～82%with CaO alone,which was further diminished by 26%～71%under the treatment of CaO+RHA.Particularly,with synergistic application of either CaO or CaO+RHA,grain Cd level in the fields subjected to phytoextraction with TaoyouXiangzhan fell within the national food safety standards.Therefore,to achieve safe utilization of strictly controlled acidic paddy soils,phytoextraction with Taoyouxiangzhan rice cultivars under saturated moisture condition followed by whole plant removal is recommended for reduction of soil available Cd content in this area.For post-extracted fields,soil amendments such as liming is suggested as essential measures to strengthen the mitgation of grain Cd accumulation and,hence,ensure safe rice production.
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