The effect of Chlorpyrifos on frequency of some microorganisms in soil in the laboratory condition

Chlorpyrifos is one of the most widely used pesticides in agriculture and may have a detrimental effect on soil microorganisms. In a laboratory research, the effect of different concentrations of chlorpyrifos (0, 4, 12, 50 mg/kg) on the log frequency of fungi, actinomycete, pseudomonas, intestinal bacteria and azotobacter during 2, 4, 7, 18, 30 and 40 days was considered as a repeated measures ANOVA. The effect of the organophosphorus pesticide also evaluated on biodiversity of the microorganisms. Result showed that after application of 4 mg/kg chlorpyrifos in the soil, the frequency of actinomycete and azotobacter decreased but pseudomonas frequency increased compared to control. Frequency of intestinal bacteria and fungi were similar to control. The log frequency of the most studied microorganisms decreased after 12 and 50 mg/kg chlorpyrifos application. In concentrations of 4 and 50 mg/kg chlorpyrifos, richness of the studied microorganism increased and decreased respectively, compared to the control. In 4 and 12 mg/kg chlorpyrifos concentrations, biological diversity and evenness decreased but dominance index increased in comparison with control treatment. Therefore, application of chlorpyrifos, especially more than the recommended dose, had inhibitory effect on the frequency and diversity of soil microorganisms, in the period of 40 days after application.