農藥이 土壤 微生物의 相變化에 끼치는 影響을 究明하기 위하여 湛水土壤 狀態下 水稻를 移秧한 區와 移秧하지 않은 區에 殺蟲劑인 carbofuran, 除草劑 pyrazolate 및 pyrazolate+pretilachlor 合劑를 處理한 後 pH 變化와 總細菌, 그람 陰性菌, 絲狀菌등의 數를 경시적으로 調査分析한 結果는 다음과 같다. 1. pH 變化는 水稻栽培 藥劑 處理後 時日이 經過함에 따라 若干 낮아지다 6週째에는 다시 上昇하였고, 水稻를 栽培한지 않은 境遇 藥劑處理後의 pH는 거의 變化가 없었다. 2. 供試藥劑 모두 水稻栽培 有無에 關係없이 藥劑處理 後의 總細菌數는 對照區에 비하여 적었고 處理藥量이 增加함에 따라 減少되었으나 時日이 經過함에 따라 增加되었다. 3. 農藥處理後 6週째까지 그람 陰性菌의 數는 對照區보다 적었고 時日이 經過함에 따라 carbofuran處理區의 그람 陰性菌의 數는 減少되었으나 pyrazolate 및 合劑處理의 그람 陰性菌 數는 增加되는 傾向이었다. 4. 藥劑處理區의 嫌氣性 細菌의 數도 對照區보다도 적었으나 時日이 經過하면서 增加되었다. 5. 絲狀菌의 數는 carbofuran 處理의 境遇 對照區와 비슷하였으나 pyrazolate와 그 合劑處理區의 境遇는 處理濃度가 增加하면서 4-5週째 까지는 더욱 減少되다가 6週째 까지는 더욱 減少되다가 6週째에는 增加한는 傾向이었다.

This study was conducted to estimate influences of pesticides such as carbofuran[2,3-dihydro-2,2-dimethylbenzofuran-7-yl methyl carbamate] as an insecticide, and pyrazolate [4-(2,4-dichlorobenzolyl)-1,3-dimethyl-5-pyrazolyl-1,3-dimethyl-5-pyrazolyl-p-toluensulfonate], pyrazolate+pretilachlor [2-chlor-2,6-diethyl-N-(n-propoxyethyl) acetanilied] as herbicides on change in numbers of soil microorganisms and pH in planted and unplanted flooded rice paddy soils. The results of weekly investigated change of pH and populations of total bacteria, gram negative bacteria, anaerobic bacteria and fungi after treatments of pesticides were as follows : The change of pH in rice-planted soil gradually decreased in a matter of weeks after treatment with pesticide and the pH increased again from the sixth week, but no change of pH could be observed in nonplanted soil. The total numer of bacteria in the treated plots were slightly less than in the control plot, and the numbers decreased with increasing application rates of pesticides. But the microbial population increased in a matter of days after treatment with pesticide. Number of the gram negative bacteria until the sixth week after treatment of pesticide were fewer than control. The number in the carbofuran-treated plot decreased after a weeks after treatment, but numbers in plots treated with pyrazolate and pyrazolate+pretilachlor increased. The number of anaerobic bacteria in the treated plots were few by comparison with the untreated control, but the number increased after a weeks after treatment with pesticides. The populations of fungi in the carbofuran-treated plot were similar by comparison with the untreated control. The populations in the plots treated with pyrazolate and pyrazolate+pretilachlor decreased in 4 to 5 weeks with increase of application rate, but afterwards increased.