Abstract: Plastic mulching is widely used in commercial vegetable production in the world.The technique changes soil hydrothermal properties significantly and eventually bioavailability of heavy metals in the soil.Field experiments were conducted to study effect of plastic mulching on translocation characteristics of copper and zinc in the soil-Chinese cabbage(Brassica chinensis L.)system.Results show that plastic mulching promoted growth of cabbage,while changing physicochemical properties of the soil.Compared with un-mulched field,the mulched field was 12.77% and 33.90% lower in soil pH and SO2-4 contents,respectively,showing a significant level of difference(P<0.05).Plastic mulching didn’t have significant effect on the distribution and translocation characteristic of Cu,while it affected those of Zn.The concentration of each fraction of zinc extracted by BCR(community bureau of reference)three-stage sequential extraction procedure,in mulched field decreased by 25.87%,35.80% and 28.17%,respectively.The concentrations of Zn in Chinese cabbage in mulched field increased by 130.9% and 13.6% in root and leaf,respectively,but deceased by 23.7% in shoot.Plastic mulching activated Zn somewhat in the soil,releasing Zn,of which most was absorbed by Chinese cabbage root.So Zn absorption by Chinese cabbage root in mulched field was far larger than that in un-mulched field.

Key words: plastic mulching, bioavailability, vegetable soil, Chinese cabbage, copper, zinc