Degradation of the Fungicides, Azoxystrobin and Difenoconazole in Soil and their Influence on Soil Microbial Activity

The non-target effects of Amistar (azoxystrobin) and Score (difenoconazole) were studied in terms of changes in the soil microbial populations, soil respiration and activity of soil enzymes. Both the fungicides significantly reduced the fungal population in the soils even at the lowest concentration used (0.44 g. (a.i.) g soil) and totally eliminated it at the recommended dose for field application (2.2 g. (a.i.) g soil). On the other hand, the populations of bacteria and actinomycetes in the treated soil increased with increasing concentrations of the fungicides. Soil respiration decreased significantly with increasing concentrations of Azoxystrobin and Difenoconazole. However, there was an increase in the rate of soil respiration when up to 0.44 g. (a.i.) g soil of Difenoconazole was applied. The activities of soil enzymes cellulase, xylanase and protease increased with increasing concentrations of the fungicides Azoxystrobin and Difenoconazole. On the other hand, the activities of urease and acid phosphatase decreased with the application of these fungicides. Both the rate of soil respiration and the activities of the tested soil enzymes reached the same level as controls after prolonged incubation. Degradation of Azoxystrobin and Difenoconazole in two different soils was estimated using HPLC. Azoxystrobin was degraded by 95% in a period of 96 hours in the slightly alkaline Coimbatore soil, whereas in the acidic Valparai soil, the degradation was only 70% during the same period. Difenoconazole, however, was quickly degraded in both Coimbatore (95%) and Valparai (97%) soils after 96 hours. _____________________________________________________________________________________________________________