Relationship between changes of soil microbial biomass content and imazamox and benfluralin degradation

The present research was carried out to determine the relationship between the soil microbial biomass content and the persistence of imazamox and benfluralin in three different soils, incubated in the laboratory under different conditions. The half-life values varied between 17.1 and 92.4 days for imazamox and 11.4 and 37.9 days for benfluralin depending on initial concentration, temperature, soil moisture and soil type. Significant decreases in microbial biomass-C content compared to untreated soil were observed initially, not exceeding 25.0% for imazamox and reaching 64.7% for benfluralin. The microbial biomass-C content then returned to initial values at varying times depending on incubation conditions. The relationship between herbicide persistence and microbial biomass-C content gave parabolic curves (P<0.001 in all cases) under all conditions tested. At the time of maximum microbial biomass decrease, the concentration of imazamox was generally about 50% of the initial dose (except for at 10°C for imazamox, when the biomass began to recover as early as the point when the pesticide concentration was at 60-65% of its initial dose). The final equation proposed could be useful to deduce the decrease in soil microbial biomass in relation to the herbicide level.