Dynamics Analysis of Culturable Soil Microflora and Microbial Activity in Continuous and Rotation Cropping Systems of Xinjiang Cotton

Variation of culturable soil microflora and microbial activity were investigated in continuous and rotation cropping cotton field in Xinjiang.The results showed that culturable microbial population gradually decreased with long-term continuous cropping of cotton.Compared with 5 years continous cropping,the total quantity of soil microbes in 6～8 years,9～12 years and more than 13 years continuous cropping,decreased by 40.2%,46.7%,52.4%,respectively.After more than 5 years continuous cropping,the structure of the soil microbial community transformed from rich nutrition bacteria type to lower nutrition fungi type,the ratio of bacteria to fungi and actinomycetes to fungi decreased significantly.The amount of nitrogen physiological communities such as ammonifying bacteria,nitrobacteria and aerobic nitrogen-fixing bacteria decreased,while denitrifying bacteria increased.Moreover,continuous cropping resulted in soil respiration intensity and cellulolytic activity reducing.Contrary to continuous cropping,under the cotton/melilotus suavena,tomato,spring wheat or corn rotation systems were most beneficial for increasing the total quantity of soil micro-organism,improving the capability of soil microbial activity,adjusting the balance of microbial community.Also there was substantial increasement in the number of azotobacteria.The effects of different rotation modes were different,the benefits of cotton-tomato and cotton-melilotus suavena rotation were more obvious.