Abstract: Cypermethrin(CYP),an insecticide,is extensively used on horticultural crops to control sucking insects.However,it is widely believed that the residue of CYP joins with Cd²⁺ pollution of the farmland in affecting soil environment quality.To explore combined effect of Cd²⁺ -CYP pollution upon the soil quality,an indoor simulation experiment was carried out.The effects of single CYP pollution(5,20 and 50 mg·kg^-1),single Cd²⁺ pollution and Cd²⁺ -CYP complex pollution on soil microbial biomass(M_C and M_N) and soil enzyme(protease,sucrase,urease) were analyzed.Results show that both complex pollution and mere Cd²⁺ pollution reduced the value of M_C and M_N,showing an inhibiting effect, whereas the mere CYP pollution displayed an activating effect,which was in a significant positive correlation with CYP concentration.The effects of CYP on soil enzymes varied,being little on protease,inhibitive first and promotive later on sucrase and just the reverse on urease.Complex pollution,when low in concentration [(5+5) mg·kg^-1],did not affect much soil enzymes as compared to CK,but when high in concentration [(20+20) mg·kg^-1],it effectively activated sucrase and inhibited urease.The use of complex pollution index(P_d) to express interaction between Cd²⁺ and CYP indicated that the effect of the complex pollution was an additive effect on soil quality. 

Key words: cypermethrin, cadmium, soil microbial biomass, soil enzyme, single pollution, complex pollution