Effects of Continuous Tobacco on Soil Microbial Diversity and Enzyme Activities

Soil samples were collected from continuous cropping 1a- 8a( except 7 year) tobacco fields in Xiangcheng county,and the amount of soil microbial,bacteria diversity,activities of sucrase,amylase,pectase cellulase were determined. Results showed that with the increasing of continuous cropping year,the number of soil bacteria and actinomycetes was going down,while the number of soil fungus kept the trend ofup- down- up- down. The bacterial diversity index as estimated by DGGE banding patterns,e. g. Shannon,Simpson and McIntosh index had the same trend of falling down,but had a slight rise in the fifth continuous cropping year that consistenting with the results of soil bacteria isolation. The changes of invertase and amylase activity revealed increased at the begaining and reached a peak in second continuous cropping year and then decreased. When the continuous cropping year is greater than 3 years,the invertase and amylase activities changed a little and then kept at a lower level. Meanwhile,the cellulase activity declined violently within 1- 3continuous cropping years,and kept at a lower levels when the continuous cropping term more than 2 years. The impact of tobacco continuous cropping on soil microbial diversity and soil enzyme activities csused the disadvantage of healthy soil ecosystem development.