Effects of Passivator Amendment on Rhizospheric Soil Cd Activity and Cd Bioconcentration and Translocation in Rice Plants for 5 Continuous Years

Objective This study aimed to explore the cumulative influences of 5-year continuous chicken manure, quicklime, and Si-Ca-Mg mineral amendments on rhizospheric soil Cd mobility, Cd bioconcentration and translocation factor in rice tissues.

Method The moderately Cd-contaminated acidic purple mud paddy was selected. Three passivators were applied separately and biannually in field-paired trials since 2015. Soil and plant samples were collected at late rice ripening stage in 2019, and the Cd concentration of rhizosphere soil and rice parts was determined. The responses of rhizosphere soil Cd activities and the Cd bioconcentration and translocation in different rice organs were analyzed with the application of passivator for 5 consecutive years.

Result The Cd concentrations in brown rice (Cd_R), stem and leaf, and root were significantly reduced by 60%-75%, 40%-77%, and 17%-48%, respectively, after the continuous organic fertilizer, quicklime, and Si-Ca-Mg mineral amendments (P < 0.05). Particularly, the Cd_R was lowered down to < 0.2 mg kg⁻¹ and met the food safety standard set by China after the continuous quicklime and Si-Ca-Mg mineral amendments. Continuous passivator amendments significantly reduced the translocation factors of Cd from root to stem and leaf as well as from stem and leaf to brown rice by 26%-38% and 29%-58%, respectively. Also, they reduced the concentration of DTPA-extractable Cd in rhizospheric soils by 13%-33%, whereas elevated the pH value in rhizospheric soils by 0.2-0.9 units. The labile organic C and available nutrient contents in rhizospheric soils exhibited an increasing trend (P < 0.05). The Cd_R was mainly related to the Cd translocation factor in rice tissues, soil pH, DTPA-extractable Cd, exchangeable Ca, and complexed Fe contents.

Conclusion The Cd_R could meet the food safety standard after 5 years continuous quicklime and Si-Ca-Mg mineral amendments in moderately Cd-contaminated acidic purple mud paddy. The Cd_R-reduction was related to the reduction in rhizospheric soil Cd activity and the Cd bioconcentration and translocation capacity in rice tissues.