Abstract:In-situ passivation is one of the important methods for the remediation of cadmium-contaminated paddy soil, and the selection of passivation agent is critical for efficient remediation. This paper studied the inactivation effect of cadmium in paddy soil by applying limestone and main conditioning agents with three field trials and comparative investigations in demonstration plots, and the effective technical measures was discussed. The results showed that sufficient amount of limestone (≥3.75 t/hm2, experiment I), calcium-magnesium phosphate fertilizer (3.75 t/hm2, experiment III) and biomass charcoal (9.00 t/hm2, test II; 7.50 t/hm2, test III)), lime (3.00 t/hm2, test III) and other alkaline conditioners can significantly increase soil pH and reduce soil Cd extraction rate (P<0.05); application of diatomaceous earth (8.25 t/hm2) and hydroxyapatite stone (3.75 t/hm2) can also reduce the soil Cd extraction rate. Among them, the application of limestone 11.25 t/hm2 could reduce the Cd extraction rate by 21%; the application of diatomaceous earth 8.25 t/hm2 (experiment II) and biomass charcoal 9.00 t/hm2 (experiment II) could significantly reduce the soil Cd extraction rate (P<0.05) by 10% and 19% respectively; compared with the control in Experiment III, the pH of the soil treated with lime 3.00 t/hm2, calcium magnesium phosphate fertilizer 3.75 t/hm2, and biomass charcoal 7.50 t/hm2 increased significantly (P<0.05). The Cd extraction rate of soil treated with lime, calcium magnesium phosphate, biomass charcoal, and hydroxyapatite 3.75 t/hm2 was significantly reduced (P<0.05), and it was found that the pH value of soil treated with lime was significantly higher than that of calcium magnesium phosphate fertilizer, biomass charcoal, hydroxyapatite, and other three treatments, while the soil Cd extraction rate was significantly less than the latter three. Correlation analysis results based on comparative investigations showed that the extraction rate of Cd was significantly negatively correlated with pH, and was significantly positively correlated with effective Cd content (P<0.05). The cluster analysis showed that the passivation effects of different conditioners on soil cadmium can be divided into five categories. The most passivation effects were lime 6.00, 9.00 t/hm2 and GSA-4 6.00, 9.00 t/hm2, which can be used first. For the actual passivation repair, the sepiolite 4.50 t/hm2, zeolite 4.50 t/hm2, humus 4.50 t/hm2, and hydroxyapatite 3.00 t/hm2 with insignificant effects are not recommended.