Objective In response to the issues of low pH, poor structure, and combined pollution of cadmium (Cd) and lead（Pb）in red soil, this study investigated the remediation and amendment effects of various conditioning agents on Cd and Pb contaminated red soil, with the aim of providing a scientific basis for the management of Cd and Pb polluted soils in red soil regions.

Method Soil samples were collected from the strictly controlled area of Youxi Meixian Town in Sanming to conduct a pot experiment. A total of six treatments were set up, including a control group (CK) without any amendment and five amendment treatments: T1 (organic fertilizers of pig manure), T2 (oyster shells powder), T3 (calcined oyster shells), T4 (soybean straw charcoal), and T5 (soybean straw biochar modified by oyster shells). The amendments were incorporated into the soil samples at equal proportions, followed by indoor incubation. After the incubation period, soil samples were collected from the pots for analysis of various soil properties.

Result ①The utilization of soil conditioners markedly elevated the soil pH, exhibiting a rise of 0.45 - 1.66 units relative to the control group. Notably, treatments T2, T3, T4 and T5 demonstrate a more pronounced enhancement in soil pH levels. ②Different soil conditioners can enhance soil water retention, cation exchange capacity, electrical conductivity, soil mechanical stability aggregate (5 - 2 mm, 1 - 0.25 mm and < 0.25 mm), as well as the content of organic carbon, total nitrogen, total potassium, and available nutrient content to a certain extent, reduce soil bulk density, and have minimal impact on the total phosphorus content and soil water stability aggregate of the soil. ④After the application of different soil conditioners, Cd in the soil primarily exists in the forms of carbonate-bound and Fe-Mn oxide-bound fractions, constituting 55.95% - 74.09% of the total Cd content. This is followed by the exchangeable fraction, ranging from 15.36% - 30.92%, and the residual fraction, which varied between 2.81% and 12.43% of the total Cd content. The predominant speciation of Pb was the Fe-Mn oxide-bound form, with a distribution range of 56.16% - 62.50%, followed by the less mobile residual form, which constitutes 21.19% - 28.76%. The application of soil conditioners can promote the transformation of Cd and Pb from the exchangeable fraction to the carbonate-bound and Fe-Mn oxide-bound fraction.

Conclusion Evaluation of soil fertility enhancement, Cd and Pb pollution remediation capacity, and acidic soil amelioration indicated that T1 (organic fertilizer of pig manure) and T5 (soybean straw biochar modified by oyster shells) were more appropriate for the remediation of agricultural soils.