Abstract: The experimental results showed that in sterilized soils,the degradation rate of 50 mg穔g^-1,500 mg穔g^-1 and 5 000 g穔g^-1 chlopyrifos was very slow (only 20% after 60 d),and in soils which previously treated with chlopyrifos,the degradation rate of 50 mg穔g^-1,500 mg穔g^-1 and 5 000 mg穔g^-1 chlopyrifos was 100%,90% and 80%,respectively.However,in un-sterilized and untreated soils,the degradation rate was at the medium of the rates mentioned-above,indicating that soil microorganisms played an important role in chlopyrifos degradation,and using chlopyrifos could induce the chlopyrifos degrading ability of soil microorganisms.Compared to the soils untreated with chlopyrifos,the soils treated with 50 mg穔g^-1 and 500 mg穔g^-1 chlopyrifos had somewhat increased bacteria and fungi during a short period of treatment,which recovered to normal level after 60 days.But,when treated with 5 000 mg穔g^-1 chlopyrifos,the bacteria and fungi were inhibited,and couldn't recover after 60 days.Under the same treatment condition,the number of bacteria and fungi was not different between soils previously treated and untreated with chlopyrifos,which indicated that enhanced degradation of chlopyrifos was not decided by the numbers of bacteria and fungi,but by their ability of enhanced degradation.

Key words: Chlopyrifos, Microorganism, Degradation