Abstract: It has been observed from a 12-year fixed site field trial in Jilin Province that potassium chloride(KCl) application has a significant positive influence on corn stalk rot incidence.Incubation experiment was conducted to study the effects of KCl and soil extracts on the growth of Fusarium graminearum,the most common stalk rot fungi in this area and population changes in rhizosphere fungi,bacteria and actinomyces at the different growth stages of corn.The results showed that KCl addition to the PDA medium could not directly suppress Fusarium graminearum development.Soil extracts from soil samples which taken from the field plots with and without KCl application affected Fusarium graminearum development,with soil extracts with KCl treatments suppressed Fusarium graminearum development more significantly,compared with that from no KCl supply.These results indicated that soil extracts played a role in the interaction between corn and Fusarium graminearum.Long-term KCl application increased the populations of rhizosphere fungi and actinomyces in the early growth stages,nevertheless there was no significant difference existed in rhizosphere bacteria number among the treatments.And the populations of rhizosphere fungi were correlated negatively with stalk rot incidence in the early grown stages of corn.The sensitive infection stages of pathogen to corn were consisted with the stages when the significant difference in rhizosphere fungi and actinomyces populations was found.Consequently,the change in rhizosphere microbe population(especially fungi) is one of the mechanisms of potassium chloride suppressing corn stalk rot.