Utilization and Remediation of Heavily Cadmium-Contaminated Agricultural Soils by Two Crop Rotation Patterns After Lime and Sepiolite Passivation

Abstract

In order to safely utilize and remediate the heavily cadmium-contaminated farmland in a mining area and ensure that the crops meet the feed safety standards, two rotation patterns (maize-alfalfa and maize-ryegrass) were tested after passivation with different ratios of lime and sepiolite as passivating agents, and the best ratio of passivating agent and matching crop rotation patterns were selected through comprehensive analysis and comparison. The field test was conducted to determine the physical and chemical properties of the soil, the content of the effective state of the heavy metal Cd, and the content and biomass of Cd in crops. We also studied the changes in heavy metal morphology before and after soil passivation using the BCR morphology classification test and comprehensively analyzed and evaluated its remediation effect. ① The results showed that the soil pH, organic matter, and CEC could be increased to different degrees by the application of lime and sepiolite. ② The recommended application amount of LS1 (lime 6.6 t·hm-2+sepiolite 9.9 t·hm-2) significantly reduced the content of heavy metal Cd in maize roots, stems, leaves, and seeds by 70.27%, 61.54%, 46.51%, and 44.23%, respectively, compared with those of CK. The Cd above ground in alfalfa was significantly reduced by 78.47%, whereas the Cd above ground in ryegrass was significantly reduced by 65.79%. The effective state Cd passivation rate of the soil was 51.37%, 69.58%, and 77.83% in the corn season, alfalfa growing area, and ryegrass growing area, respectively. The heavy metals in the soil were converted from the weak acid extracted state with high activity to the residual state with low activity. ③ The recommended crop rotation pattern of supporting maize-alfalfa under the applied amount of LS1 can significantly increase alfalfa yield while slightly increasing maize yield compared with those of CK, and the forageable parts can meet the feed standard[GB 13078-2017, ω(Cd) ≤ 1 mg·kg-1], achieving safe cultivation with the lowest restoration cost.