The Effect of diazinon Application on Soil Microorganisms Frequency and Biodiversity in the laboratory condition

Application of organophosphate pesticides especially diazinon is a common phenomenon that cause pollution wide area of terrestrial and aquatic ecosystem. Therefore, an investigation of the effect of this organophosphorus pesticide on some beneficial soil microorganisms was investigated. In a laboratory research, diazinon in the concentration of 0, 4, 12, 50 mg.kg-1 was added to the soil and incubated. Then the soil sampled in different time of incubation, after preparing proper dilution, fungi, actinomycete, pseudomonas, intestinal bacteria and azotobacter cultivated in the specific medium in three replicates. The analysis was considered as completely randomized design (repeated measurement test). The effect of diazinon on biodiversity index of the cultivable microorganisms also evaluated.  In comparison to the control, after application of 4 mg.kg-1 diazinon in the soil the frequency logarithm of actinomycete and azotobacter decreased and pseudomonas increased. The frequency logarithm of intestinal bacteria and fungi were similar to untreated soil. In concentration of 12 and 50 mg.kg-1 the frequency logarithm of all the studied microorganisms reduced. Soil richness in the treatment of 4 mgkg-1 diazinon was more than control and significantly decreased in other concentrations. Biological diversity and evenness decreased in all concentrations of applied diazinon but dominance index increased in comparison with the control. Therefore, most studied soil microorganisms were incompatible with these concentrations of pesticide and this could reduce soil health and fertility.