Abstract: Studies on the soil microbial population and biological activity in a brown earth continuously planted with corn and covered with plastic film show that after long-term mulching, the numbers of bacteria, actinomyces and fungi in the topsoil increased 22.6%, 29.3% and 19.7 %, respectively.At seedling stage, bacteria increased by 21.4%; at elongating and ripening stages, actinomyces increased by 22.4% and 24.4%, respectively; and within the whole growth period, fungi increased 12.2～14.6%.In addition, the dominant facultative anaerobial populations of bacteria tended to be increased, but those of fungi were not to be changed.Soil respiration rate was also enhanced by mulching in all sites with different fertility, but soil urease activity only increased obviously in the site with high fertility.

Key words: Mulching with plastic film, Soil microorganism, Biological activity