| The differences in physical and chemical properties of different parent soils can affect the occurrence state and environmental behavior of Cd,as well as its environmental capacity.It is of great scientific significance to clarify the environmental behaviors and influencing factors of different soil Cd and propose soil Cd control measures.Therefore,it can provide a scientific basis by studying the responses and differences of exogenous cadmium(Cd)stress and soil conditioners in different parent soils for the security of using contaminated cultivated land.Pot experiments were conducted to study the effects of Cd on the Cd uptake and accumulation of rice in typical paddy soils(alluvial sandy soil and purple clayey soil)under the condition of Cd stress,and the soil environmental safety threshold was calculated.The effects of two soil conditioners(lime,silicon-calcium-magnesium fertilizer)were studied on the Cd contaminated paddy fields.The main results are shown as follows:(1)Under the condition of Cd stress,the content of available Cd in the two soils and the concentration of Cd in the soil solution were decreased with the extension of the growth period of rice,the average content of available Cd in alluvial sandy soil was 0.47 mg·kg-1 and the average content of Cd in purple clayey soil was 0.36 ma·kg-1.In the whole growth period of rice,the concentration of Cd in soil sediments of alluvial sandy soil and purple clayey soil was 0.08?0.49?g·L-1,0.03?0.44?g·L-1,respectively,and with an average of 0.29?g·L-1 and 0.18?g·L-1.Under the condition of Cd stress,the content of Cd in brown rice,husk,stem and leaf and root all increased with the increase of exogenous Cd concentration in the two soils,the characteristics of the whole distribution were root>stem and leaf>husk>brown rice,and under the same level of exogenous Cd,the Cd content of all parts of alluvial sandy soil was higher than purple clayey soil.Compared with no application of Cd,the Cd content of brown rice in alluvial sandy soil increased by 5.91 times and the Cd content in purple clayey soil increased by 5.24 times under the high level stress of Cd.Compared with the tillering stage,the Cd content of rice roots increased by 2.1%?13.7%,18.5%?33.1%,and the Cd content of stems and leaves decreased by 15.0%-24.2%and 10.5%-35.3%,respectively on the mature stage.(2)The application of lime and silica-calcium-magnesium could reduce the content of Cd in the soil exchangeable state and TCLP extracted state,and the Cd content of exchangeable state in the alluvial sandy soil was reduced by 27.2%?31.2%,21.1%?28.2%,and the content of Cd in the TCLP extracted state was reduced by 8.7%?14.4%and 13.3%?18.4%,respectively.The content of exchangeable Cd in purple clayey soil decreased by 5.9%?12.7%,11.4%?16.5%,and the content of TCLP extracted Cd in soil decreased by 32.2%-37.0%,11.0%-27.4%,respectively.The decrease was increased with the increase of the amount of conditioner applied.The application of these two kinds of soil conditioners(lime,silicon-calcium-magnesium fertilizer)significantly increased the pH value of alluvial sandy soil,which increased by 0.62 to 0.79 units and 0.35 to 0.46 units,respectively.The application of soil conditioner could change the soil Cd fraction.For the alluvial sandy soil,the application of lime reduced the content of acid extractable fraction of Cd in alluvial sandy soil,and it had a highest decline in S3.0 treatment;while the application of silicon-calcium-magnesium fertilizer significantly decreased acid extractable fraction of Cd in the purple clayey soil.(3)The application of silicon-calcium-magnesium fertilizer could reduce the content of Cd in brown rice in the two kinds of soils(alluvial sandy soil and purple clayey soil),which were reduced by 9.5%-21.9%and 23.5%-34.1%,respectively.The application of lime could significantly reduce the content of Cd in brown rice in alluvial sandy soil,which decreased by 23.5%?35.9%,but had no significant effect on purple clayey soil.Comparing different application rates of the same soil conditioner,the effect of high application rate on the reduction of Cd in rice was better.According to the study,the safety threshold of Cd is 2.03 mg kg-1 in alluvial sandy soil and 3.14 mg kg-1 in purple clayey soil,so different parent soil has different environmental thresholds for Cd.The effects are different in the two soils which lime and silica-calcium-magnesium fertilizer are added to control rice cadmium.Therefore,the environmental quality standards and treatment measures of different parent materials should also be different,and it is suggested that differentiated control should be implemented in the cadmium contaminated soil according to different soil types. |
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