| Summary: | 碩士 === 國立臺灣大學 === 農業化學研究所 === 99 === For reducing the cost on pesticide application, mixed or sequential pesticides application were often used in field. It makes insecticides, herbicides, and fungicides frequently simultaneous presence in soil. Tea is the most important economic agricultural products in Taiwan. For keeping the highest quality and quantity of tea, many pesticides were used to control weeds, diseases, and insect on tea field. In this study, the effect of mix application of three fungicides, benomyl, tebuconazole and triadimefon, with herbicide, diuron, on persistent of these pesticides on soil was investigated. Meanwhile, the impact of mixed application on soil bacterial communities was also monitored. From the result, diuron degraded more slowly in sterilized soil than in unsterilized soil, it can prove that diuron degraded by biodegradation in tea field soil. In 10-fold field rate of herbicide and fungicides application treatments, diuron DT50 are 125 (D), 141 (B+D), 127 (Te+D) and 122 day (Tr+D). Diuron degradation rate decreased in B+D treatment slightly. In 50-fold field rate application treatments, diuron DT50 are 167 (D), 231 (B+D), 189 (Te+D) and 238 day (Tr+D). Diuron degradation rate decreased significantly in B+D and Tr+D treatments. The diuron metabolite N’-[3,4-dichlorophenyl]-N,N-methylurea (DCPMU) was detected in 10-fold field rate treatments, DCPMU and N’-3,4-dichloro- phenylurea (DCPU) were detected in 50-fold field rate in experimental period. The metabolites produced amount weren’t equal to the diuron degraded amount. The result indicated that diuron may degrade to other metabolites in experimental period. Benomyl may inhibit the degradation of diuron, therefor the amount of DCPMU product in B+D treatment is less than other treatment in 50-fold field rate. The DGGE fingerprint and cluster analysis result indicated that D, Te+D and Tr+D treatments applied in tea field might increase the bacterial community richness, and B+D might impact on the bacterial community in 10-fold field rate. Tr+D and B+D impacted on the bacterial comunity in 50-fold field rate. The impact on bacterial community may inhibit the degradation of diuron and therefore increase the persistence of diuron in environment. Thus there are assessments when appling diuron with fungicides benomyl and triadimefon simultaneously in tea field soil.
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