Abstract: Using the dilute plate counting method and the most probable number method,populations of soil microbes were investigated in drylands under conventional film mulching,annual mulching covering two ridges,or biennial mulching covering two ridges.Results show that among the three great groups of microbes,bacteria were the highest in population and followed by actinomyces and fungi.The biennial mulching significantly incrreased the populations of the soil microbial physiological groups,except for azotobaceria.However,the population of the soil microbial physiological groups decreased with the increase in soil depth.Positive relationships were found of bacteria and actinomyces with soil microbial physiological grops(except for azotobacteria).

Key words: dryland, film mulching, soil microbe