Effects of successive metalaxyl application on soil microorganisms and the residue dynamics

Abstract

Metalaxyl, a chiral fungicide, was widely used to control mold fungi and oomycetes in many plants. However, studies are insufficient on the effects of successive metalaxyl applications on soil microorganisms and the residue dynamics. In the present study, metalaxyl was applied in field at two different doses (the recommended field rate, and twice of the recommended field rate) for 2 and 3 times, respectively. The soil samples were collected on days 0, 1, 3, 7, 14, 28 and 45 after the second and third treatment to determine the residue dynamics and were collected on days 7, 14, 28 and 56 to assess the effects of successive metalaxyl application on soil cultivable microbial populations and microbial community structure. The results revealed the degradation rate slightly accelerated with the increasing applied times of metalaxyl. The second application of metalaxyl increased soil bacteria populations, inhibited soil fungi, and had a transient stimulated effect on actinomycetes. No distinct differences were observed in soil bacterial, actinomycic and fungal populations except for fungi population on day 14 after the third treatment. The analysis of terminal restriction fragment length polymorphism (T-RFLP) and denaturing gradient gel electrophoresis (DGGE) revealed soil microbial community structure could be affected by metalaxyl at all experimental doses. These obtained results could provide basic data for evaluating the ecological toxicity of metalaxyl.