Selenium treated foliage and biochar treated soil for improved lettuce (Lactuca sativa L.) growth in Cd-polluted soil

Cadmium (Cd) pollution in farmland soils is a serious concern due to its devastating effects on living organisms. This requires developing effective strategies to inhibit the Cd absorption and accumulation by vegetables. In this study, the influence of soil applied biochar (BC) (10 and 30 g kg⁻¹) and foliage applied selenium (Se) fertilizer (1 and 3 mg L⁻¹) on the absorption and accumulation of Cd and growth of lettuce under Cd stress (1 and 3 mg/kg) was evaluated. In Cd-contaminated soil, the application of BC and Se significantly increased lettuce biomass and chlorophyll contents by 74% and 100%, respectively, compared to control in lettuce. The combined application of BC and Se at (B 30 g kg⁻¹, Se 3 mg L⁻¹) was effective in reducing the accumulation of Cd by lettuce shoot by 73.41% than control. Co-application of BC and Se enhanced the activities of antioxidant enzymes catalase, superoxide dismutase by 77 and 96%, respectively, and reduced the malondialdehyde contents by 56% than control. Application of biochar (30 g kg⁻¹) significantly increased the soil electrical conductivity and soil organic carbon of soil by 48 and 41%, respectively as compared to control. The combination of BC and Se (B 30 g kg⁻¹, Se 3 mg L⁻¹) reduced the Cd contents in lettuce shoots from 0.79 mg kg⁻¹ to 0.08 mg kg⁻¹ below the national food safety standard threshold (0.2 mg kg⁻¹ Cd). Overall, this study revealed that the integrated application of BC (30 g kg⁻¹) and Se (3 mg L⁻¹) can help prevent the absorption of Cd by lettuce. However, the effectiveness of BC in remediating trace metals may decrease with time due to the aging factor and leaching alkalinity of BC, so long-term field experiments are needed to enhance the understanding of BC efficiency and an appropriate Se concentration for specific green soil remediation goals.