Abstract: To clarify the residue behavior of imazapic，imazethapyr，carfentrazone‑ethyl，and terbacil in alfalfa（Medicago sativa L.），a quantitative analytical method was established using LC‑MS/MS.Field trials were conducted during the spring and summer of 2023 to characterize the degradation kinetics and final residues of these four herbicides in alfalfa. Results demonstrated that the method achieved limits of detection（LODs）ranging from 0. 01 to 0. 1 mg/kg for imazapic，imazethapyr，carfentrazone‑ethyl，and terbacil in alfalfa. The average recovery rate fell within 83. 8%—113. 2%，with relative standard deviations（RSDs）all below 4.81%.These parameters confirmed the method’s accuracy，precision，and suitability for pesticide residue analysis. The degradation of imazapic，imazethapyr，carfentrazone‑ethyl，and terbacil in alfalfa followed first‑order kinetics，with half‑lives of 1.37—1.62，2.57—2.86，2.09—3.18，and 8.66—9.36 d，respectively. At harvest，residues were detected only in summer trials treated with imazethapyr at 150 g/ha（1.5×recommended high dosage），and terbacil at 432 g/ha（1.5×recommended high dosage）.However，the detected residue levels for both compounds were below the corresponding United States Maximum Residue Limits（US MRLs）.These findings indicate that imazapic，imazethapyr，carfentrazone‑ethyl，and terbacil are readily degradable herbicides in alfalfa.Their application at normal rates is considered safe with respect to the residue levels at harvest.

Key words: Alfalfa, Herbicide, Degradation dynamics, Residues, Imazapic, Imazethapyr, Carfentrazone?ethyl, Terbacil

摘要： 为了明确甲咪唑烟酸、咪唑乙烟酸、唑草酮和特草定在紫花苜蓿中的残留情况，采用超高效液相色谱-串联质谱仪（LC-MS/MS），建立了甲咪唑烟酸、咪唑乙烟酸、唑草酮和特草定在紫花苜蓿中的残留检测方法，于2023年春季和夏季分别开展田间试验，研究了4种除草剂在紫花苜蓿中的降解动态及最终残留情况。结果表明，甲咪唑烟酸、咪唑乙烟酸、唑草酮、特草定在紫花苜蓿中的最低检出限为0.01~0.1 mg/kg，添加回收率为83.8%~113.2%，相对标准偏差均小于4.81%，所建残留检测方法的准确度和精密度符合农药残留检测方法的要求，具有可行性。甲咪唑烟酸、咪唑乙烟酸、唑草酮、特草定在紫花苜蓿中降解符合一级动力学反应，半衰期分别为1.37~1.62、2.57~2.86、2.09~3.18、8.66~9.36 d；紫花苜蓿收获时，仅在夏季试验中检测到咪唑乙烟酸150 g/hm²（推荐高剂量的1.5倍）和特草定432 g/hm²（推荐高剂量的1.5倍）剂量处理紫花苜蓿中有残留量，但均低于美国最高残留限量（MRL值）。可见，甲咪唑烟酸、咪唑乙烟酸、唑草酮、特草定在紫花苜蓿体中属于易分解农药，正常施用是安全的。

关键词: 紫花苜蓿, 除草剂, 降解动态, 残留量, 甲咪唑烟酸, 咪唑乙烟酸, 唑草酮, 特草定