三種殺菌劑於茶園土壤中對除草劑達有龍之降解及土壤菌相的影響

Abstract

現代農業為減少人力成本常混合施用農藥，因此田間常有除草劑及殺菌劑同時存在的可能。茶葉為臺灣的經濟作物之一，為了維持茶葉的產量常使用大量的農藥於雜草及病蟲害的防治。達有龍為苯尿素系的除草劑，生物降解為主要之降解途徑；殺菌劑的施用可能會衝擊土壤微生物族群，而影響除草劑的降解速率與在環境中的流布。本研究為探討茶園土壤中施用三種殺菌劑，得克利 (Tebuconazole, Te) 、三泰芬 (Triadimefon, Tr) 及免賴得 (Benomyl, B) 對除草劑達有龍 (Diuron, D) 消散的影響及利用變性梯度凝膠電泳 (Denaturing gradient gel electrophoresis, DGGE) 探討農藥對土壤菌相之影響。達有龍在滅菌土壤中的降解速率比未滅菌土壤慢，顯示達有龍於本試驗土壤是以生物性降解為主。殺菌劑及除草劑 10 倍推薦施用量之處理達有龍之 DT50 (Half-degradation time) 分別為 125 (D), 141 (B+D), 127 (Te+D) 及 122 天 (Tr+D)，在 B+D 處理中，達有龍的持久性略微增加。殺菌劑及除草劑 50 倍推薦施用量之處理中，達有龍 DT50 為 167 (D), 231 (B+D), 189 (Te+D) 及 238天 (Tr+D)，三種殺菌劑在 50 倍推薦施用量下均會增加達有龍的殘留時間，且在 B+D 及 Tr+D 處理中，顯著的使達有龍在土壤中的持久性增長。10 倍推薦施用量處理中，在試驗期間僅偵測到達有龍之代謝產物 N’-[3,4-dichlorophenyl]- N,N-methylurea (DCPMU) ，在 50 倍推薦施用量處理中，偵測到 DCPMU 及 N’-3,4-dichloro-phenylure (DCPU)，然代謝產物產量與達有龍降解量未達質量平衡，推測在茶園土壤中達有龍之降解還會產生其他代謝產物。混合施用50 倍推薦施用量 B+D 的處理結果顯示，免賴得施加於土壤中明顯的抑制 DCPMU 的生成，進而造成達有龍降解速率趨緩。DGGE 圖譜及聚類分析結果顯示在 10 倍推薦施用量情況下，達有龍、得克利+達有龍及三泰芬+達有龍可以促進土壤中細菌族群的豐富度。免賴得+達有龍處理相較其他三種處理來說，對土壤菌相的衝擊較大。高劑量處理中，於試驗末期可以看出免賴得+達有龍及三泰芬+達有龍對菌相的衝擊是比較大的，進而推論達有龍於免賴得+達有龍及三泰芬+達有龍處理中降解速率趨緩的原因為高劑量的殺菌劑影響菌相族群結構而導致達有龍於土壤中的生物性降解受到抑制所造成。綜合以上結果，達有龍在土壤中與殺菌劑共同存在所產生的相互作用，可能會導致達有龍在土壤中的持久性增長。因此在施用達有龍的茶園土壤中，應審慎評估達有龍與殺菌劑間的效應，而避免達有龍於環境中的殘留。

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.