Abstract: he objectives of this work were to clarify the effects of biochar addition on microbial biomass and enzyme activities in continuous cropping soil and to provide scientific basis for alleviating soil continuous cropping obstacles. There were six rates of biochar application (0, 5, 10, 20, 30, and 40 t·hm^-2, designated as CK, C₁, C₂, C₃, C₄ and C₅, respectively). Soil samples from 0 to 20 cm layer were collected in the third season of cucumber ripening to measure soil microbial biomass and enzyme activities. The results showed that microbial biomass C and N increased at first and then decreased with the increases of biochar addition rate. C₂ and C₃ treatments significantly increased microbial biomass C by 70.62% and 81.09% (P<0.01). Meanwhile, significant increases in microbial biomass N were observed in C₂ and C₃ treatments (P<0.01). Soil enzyme activity was increased first and then decreased with increasing biochar application rates. C₂, C₃ and C₄ treatments significantly increased the catalase activity. Meanwhile, C₄ treatment significantly increased the urease activity by 84.08%. The alkaline phosphatase activities in C₃, C₄ and C₅ treatments showed significant increases. Results from the cluster analysis revealed that the six treatments could be classified into four distinct groups (CK, C₁, C₂-C₃, and C₄-C₅) when the Eudidean distance was 1.01. Furthermore, the highest values of microbial biomass C and N, catalase, and urease and alkaline phosphatase activities were obtained when the application rates of biochar were 20, 20, and 30 t·hm^-2, respectively.

Key words: forest fragmentation, landscape mosaic indicator, Markov model.