Chlorpyrifos, Chlorothalonil, Butachlor On Soil Microbes And Soil Enzymes,

Greenhouse production of vegetables has been developed rapidly in China during the past decades. Compared to field conditions, greenhouse provides more favorable climate for fast reproduction of pests and diseases that result in extensive application of pesticides. On the other hand, hermetic environment in greenhouse alters dissipation behavior of pesticides in crops and soil. Thus, there is an increasing concern on the effects of pesticide application in greenhouse on soil microorganisms and soil enzyme activities. The influence of three pesticides (chlorpyrifos, chlorothalonil and butachlor) on the soil microorganisms and soil enzyme activities were investigated in this study. The results were summarized as follows.The effect of chlorpyrifos at rates of 2.0 mg/kg and 4.0 mg/kg on soil microbes is temporal and disappears within a few days. However, chlorpyrifos at high rate of 10.0 mg/kg inhibited soil microbes significantly. The activities of acid phosphatase, alkaline phosphatase, urease, catalase and invertase in soil treated with chlorpyrifos were almost all inhibited during the first periods after treatments. The inhibitory effect disappeared gradually with time, and enzyme activities recovered to the levels of the control without chlorpyrifos.The data showed that the soil bacteria were inhibited significantly after the application of chlorothalonil, and then recovered at 21d. The effect of chlorothalonil on actinomycetes in soil was less than that on bacteria, and the populations of actinomycetes recovered after 14 d. However, no significant inhibition on fungi caused by the fungicide was observed. The activities of acid phosphatase, alkaline phosphatase and urease in soil treated with chlorothalonil were all inhibited in the first time intervals after chlorothalonil treatments, and subsequently recovered to the similar levels of the controls without chlorothalonil. Invertase was resistant to chlorothalonil at the low concentrations. The impact of chlorothalonil on catalase differed to those on above soil enzymes. The activities of catalase in soil treated with chlorothalonil was inhibited in first stages of the treatment and enhanced subsequently.The effect of butachlor at rates of 2.0 mg/kg and 4.0 mg/kg on soil microbial population is a temporal phenomena and disappears within a few days. However,butachlor at high rate of 10.0 mg/kg inhibited soil microbial population significantly till 21 days after treatments. The activities of acid phosphatase, alkaline phosphatase, urease and invertase in soil treated with butachlor were all inhibited. The inhibitory effect disappeared gradually with time, and enzyme activities recovered to the levels of the control without butachlor. The influence of butachlor on catalase was different from acid phosphatase, alkaline phosphatase, urease and invertase, an enhancement effect was observed.The degradation rate of chlorothalonil in soil was rapidly with half-live of 5.6d. Soil bacteria and actinomycetes populations were inhibited by the first treatment of chlorothalonil, whereas fungi population was stimulated by the treatment. The inhibitory effects on soil microorganisms were increased by second addition of chlorothalonil, and after that no negetive effect was observed in the following chlorothalonil treatments. The effects of repeated chlorothalonil treatments on soil enzyme activities were similar to those on soil microbes.Three bacteria strains (Yl, W2 and W3) were isolated from the soil. Chlorothalonil (10.0 mg/kg) was degraded by the isolated strain Y1, and 53.4% of chlorothalonil was removed at 7d.