Soil samples were collected from apple orchards 5,15,20,30,and 45 years old,and one adjacent forest soil was used as reference to investigate the free Cu2+ion activity in soil solution and the soil Cu fractionation in the solid phase following long-term application of copper fungicide,Bordeaux mixture,in apple orchards and to investigate the relationships among soil free Cu2+ions,Cu fractionation and soil microbial parameters.The total Cu concentration in the orchard soils varied from 21.8 to 141 mg kg-1,increasing with the orchard age,and the value for the reference soil was 12.5 mg kg-1.The free Cu2+ion concentrations in the soil solutions extracted by 0.01 mol L-1 KNO3 ranged from 3.13×10-8(reference)to 4.08×10-6 mol L-1(45 years-old orchard).The concentration of Cu complexed in the fulvic fraction increased with orchard age from 5.16 to 52.5 mg kg-1.This was also the case for other soil Cu fractions except the residual one.The residual soil Cu remained practically constant,ranging from 4.28 to 5.66 mg kg-1,suggesting that anthropogenic soil Cu mainly existed in the more labile active fractions.Regression analyses revealed that both the free Cu2+ions in the soil solution and the humic acid-complexed Cu fraction in the solid phase were strongly related with soil microbial parameters.
