Effects of Rice-Vegetable Rotation Regime on the Form Distribution and Bioavailability of Soil Cd
Rice-Vegetable Rotation regime(RVRr), which has been proposed by Guangdong Academy of Agricultural Sciences, was a highly effective farming model and advance soil environment. We carried out a field experiment in Dongguan to explore the impacts of RVRr on heavy metal cadmium(Cd)in farmland soil. In comparison with Vegetable Continuous Cropping regime(VCCr)and Rice Continuous Cropping regime(RCCr), we aimed to get the distributional characteristics and migration rules of various Cd occurrence modes in soil, as well as accumulative laws of Cd in edible parts of crops under RVRr. The results showed that RVRr and VCCr had no significant influence on the contents of total Cd and its various occurrence modes. However, RCCr could significantly reduce the contents of exchangeable, oxidizable, residual form and the total Cd in soil. Cd was dominated in the high activity fractions in soil, and followed the order of exchangeable reducible oxidizable residual. Additionally, reducible form could transform with oxidizable and residual form. Rice had more cumulative capacity of Cd than vegetables, so that the risk of excessive Cd in rice should be carefully considered before extending RVRr.