Objective  In order to find out the response degree of lettuce absorbing cadmium (Cd) to biochar and foliar spraying selenium, the absorption of Cd by lettuce and the forms of Cd in soil are needed to be clarified.

  Method  A pot experiment was conducted to study the effects of biochar and foliar spraying selenium on the absorption and accumulation of Cd in lettuce, the effects of combined application of biochar and foliar spraying selenium on soil physical and chemical indices (pH and organic carbon) , Cd content of different soil forms and Cd uptake were studied.

  Result  The results showed that: ① Adding biochar to soil and spraying selenium on leaves effectively reduced Cd content in edible part of lettuce, among which spraying low concentration selenium has better effect. When the amount of biochar was 30 g kg⁻¹ and the concentration of selenium sprayed on leaves was 1 mg L⁻¹, the Cd content in lettuce shoots decreased from 0.314 mg kg⁻¹ to 0.049 mg kg⁻¹, which was lower than the limit of 0.20 mg kg⁻¹ for leafy vegetables stipulated in the National Food Safety Standard (GB 2762—2017). ② Under Cd stress, the interaction between biochar and foliar sprayed selenium has a significant impact on Cd content and Cd accumulation and transportation ability of lettuce. Compared with the Cd content in lettuce roots, the effect of biochar was higher than that of foliar sprayed selenium, while the effect of foliar sprayed selenium is higher than that of biochar for the Cd content in shoot. ③ The addition of biochar reduced the proportion of acid extractable, reducible and oxidizable Cd and increase the proportion of residual Cd by changing the soil pH and organic carbon content, thus effectively reducing the Cd absorption and enrichment by lettuce.

  Conclusion  The combined application of biochar and foliar sprayed selenium can reduce the Cd content of lettuce and provide theoretical guidance for the cultivation of pollution-free vegetables.