[Effects and mechanism of amendments on remediation of Cd-Zn contaminated paddy soil].

Amendments are widely applied in agricultural soils to improve soil quality and crop yield. Effects of three amendments, lime, manure, and sepiolite on cadmium (Cd) and zinc (Zn) bioavailability in contaminated paddy soils were studied by pot experiment with cultivating rape. There were eight treatments, including lime, manure, and sepiolite separately applied and combined with others in contaminated soil. The biomass yield of rape was investigated after harvest. The amounts of absorbed Cd and Zn in harvested rape with application amendments were determined. Besides soil pH, different forms of Cd and Zn in the conducted soils were also measured. Results showed that the yield of rape increased after amendments application. The treatment of lime and manure co-application showed the highest increasing yield by more than 170% comparing with no amendments application in the eight treatments. The amount of absorbed Cd and Zn in rape decreased after the three amendments application. Lime application showed the best effect to decrease the heavy metal content in rape when amendments were separately applied. However, sepiolite could hardly decrease the content in rape after separately applied in contaminated soil. It was mainly due to the decrease of exchangeable Cd and Zn, which was available for rape, after lime application. Soil pH in these treatments increased in response. Accordingly, the carbonate combined and the Fe-Mn oxide fractions, which were unavailable in soil for rape, increased greatly. The uptake coefficient of Cd was higher than that of Zn. It indicated that Cd was more movable in soil and lime application could obviously decrease the uptake coefficient. The remediation efficiency was significantly improved in the treatment of co-application with lime and manure in Cd-Zn contaminated paddy soil. Compared with control (CK), it increased 13.5 times for Cd and 2.4 times for Zn, respectively.