Control locations confuse evaluation of passivation effects of iron-based biochar and selenium applications on wheat grain cadmium accumulation in a Cd-contaminated weakly alkaline soil

Abstract

Inhibiting cadmium (Cd) accumulation in wheat grains could reduce the risk of human exposure to Cd. This study conducted a field experiment and evaluated the effects of iron (Fe)-based biochar and selenium (Se) applications alone or in combination on Cd accumulation in wheat grains in a Cd-contaminated weakly alkaline soil of rice-wheat rotation farmland. Considering soil Cd heterogeneity in the field, we set up 22 replicates of control (CK) and three replicates of each Fe-based biochar and/or Se treatment. Results clearly showed that the CK locations could greatly affect the evaluation of whether the difference in the wheat grain Cd concentration between treatments and CK was significant. There was an insignificant difference in the wheat grain Cd concentration between the treatment and the adjacent CK replicates. Although soil Se application at 2 mg kg⁻¹ and foliar Se application at 4 mg L⁻¹ significantly increased the grain Se concentration as compared with the adjacent CK replicates, they still could not reduce the Cd concentration in wheat grains. However, when compared to the CK replicates that had the highest grain Cd concentration, foliar and soil applications of Se could significantly reduce the wheat grain Cd concentration by 47.7% and 41.3%–46.1%, respectively. No matter which CK replicates were selected, the application of Fe-based biochar had no significant impact on Cd accumulation in wheat grains, and there was no significant difference in diethylenetriaminepentaacetic acid-Cd concentration between the Fe-based biochar treatment and adjacent CK replicates. In conclusion, applying Fe-based biochar and Se in the field could not reduce the Cd accumulation in wheat grains in Cd-contaminated weakly alkaline soils.