Abstract:Alluvial sandy soil (developed from river alluvium parent materials) and purple clayey soil (developed from purple sandy shale parent materials) with similar available cadmium (Cd) content and different parent materials were selected to conduct pot experiments, and to study the difference of Cd absorption and accumulation at different growth stages of rice under Cd stress conditions in different parent material paddy soils, as well as to calculate the critical value of soil Cd environmental safety. Different concentrations of exogenous Cd (0, 0.5, 1, 2, 5 mg/kg) were added to the soils to simulate the Cd contained paddy soils. The results showed that the available Cd contents of the two soils (alluvial sandy soil and purple clayey soil) were the highest at the tillering stage. The average content of available Cd in alluvial sandy soil was 0.47 mg/kg, and that in purple clayey soil was 0.36 mg/kg. At the same level of exogenous Cd, the content of available Cd in alluvial sandy soil was higher than that in purple clayey soil. For alluvial sandy soil, with the increasing of exogenous Cd concentration, the total biomass of rice increased first and then decreased. When the concentration of exogenous Cd was 1 mg/kg, the biomass was the maximum, which was 47.11 g/pot. While the biomass of rice in purple clayey soil increased gradually, but the difference between the treatments was not significant (P>0.05). The contents of Cd in brown rice, husk, stem and leaf and root increased with the increasing of exogenous Cd concentration in the two soils, and the overall distribution characteristics were root > stem and leaf > husk > brown rice, and the Cd content of alluvial sandy soil was higher than that of purple clayey soil. The average Cd accumulation of rice in alluvial sandy soil was 51.71 g/pot, and it was 42.56 g/pot in the purple clayey soil. Compared with the tillering stage, the Cd accumulation of rice in the two soils increased by 1.45 and 1.07 times at maturation stage, respectively. Regression analysis showed that the critical Cd safety thresholds for Cd-exceeding soil were 2.03 mg/kg and 3.14 mg/kg in alluvial sandy soil and purple clayey soil, respectively. The absorption and accumulation characteristics of Cd and the critical value of soil Cd safety were significantly different among different soil parent materials.