Effects Of Limestone,Slaked Lime And Dolomite On Cadmium Concentration In The Solution Of Paddy Rice Soils

In order to better understand the effects of limestone,slaked lime and dolomite on cadmium(Cd)concentration in soil solutions of paddy soils,a pot experiment was performed using a Cd-contaminated soil,three amendments(limestone,slaked lime and dolomite),and two rice varieties,Taigeng 8 and II-You 3301,aimed to study the dynamic change in the concentration of pH,Cd,Pb,TOC,Fe and Mn in soil solution,and soil Eh during rice-growing period,and the mechanism of the amendments to reduce Cd and Pb availability in the soils.The main results are as follows.1.The solution pH was significantly increased whereas the concentrations of Cd,Pb,Fe,Mn and TOC in soil solutions,and soil Eh were significantly decreased by the three amendments.The amount of Feplaques on root surface,the Cd and Pb in the Fe-plaques and the roots were also decreased by the amendments.2.The water-soluble Cd and Pb was significantly and positively correlated with the soil Eh,TOC,Fe and Mn in the solution while was negatively correlated with the solution pH,indicating that the amendments decreased the solubility of Cd and Pb in the soils by increasing the soil pH,promoting soil reduction,inhibiting the reductiondissolution of Fe/Mn oxides,and reducing TOC in the soils.3.The amendments reduced Fe-plaques on rice roots,and the accumulation of Cd and Pb in the Fe-plaques,which also decreased the uptake of Cd and Pb by rice roots.4.Rice variety was more important in influencing water-soluble Cd than amendment type and the growing period of rice.The amendment type was more important than rice variety and the growing period of rice in affecting waer-soluble Pb.Among the various soil factors(pH,Eh,the content of TOC,Fe and Mn in soil solutions),water-soluble Fe was the most important factor for influencing water-soluble Cd(90 days transplanting)and water-soluble Fe,Mn(30 days and 60 days transplanting)and Eh(90 days transplanting)were the most significant for affecting water-soluble Pb.5.There were no significant difference in the effects on reducing soil Eh,and the contents of Cd,Fe,Mn,TOC in the soil solutions among the three amendments.The solution pH was more significantly increased by limestone and slaked lime as compared to dolomite.The Pb content in brown rice of the two rice varieties were both reduced to below the national limit(0.2 mg.kg-1)whereas the Cd content in the brown rice was not significantly affected by the amendments.