Persistence of myclobutanil and its impact on soil microbial biomass C and dehydrogenase enzyme activity in tea orchard soils

Abstract

Persistence of the fungicide myclobutanil in three tea orchard soils with different cultivating ages, neighboring wasteland and forest soils, and its influence on microbial activities in 2- and 50-year-oldtea orchard soils at three rates were studied in the laboratory. Dissipation data fitted well to first-order kinetic equation, except for sterilized treatments, in which neglected dissipation of myclobutanil was observed. At 25oC, the dissipation half-lives (DT50) at level of 1mg kg-1 were in the range of 15.07-69.32 days under non-flooded condition, significantly lower than flooded condition (p < 0.05), indicating that dissipation of myclobutanil was mainly driven by soil microorganisms under aerobic condition. Dissipation rate was significantly increased at 40oC compared to those at 4oC and 25oC for all five soils (p < 0.05). Under all incubation conditions, DT50 were lowest in 50-year-old tea orchard soil (p < 0.01). Correlation analysis between DT50 in tea orchard soils and soil properties showed that soil microbial biomass carbon was negatively correlated with DT50 under 25oC and 60% water holding capacity (p < 0.05). In general, soil microbial biomass carbon and dehydrogenase activity decreased as the concentration of myclobutanil and incubation time increased except 0.1 mg kg-1 spiked soils, in which soil dehydrogenase activity was stimulated after 10 days incubation.