除草剂混用组合麦草畏+2，4-滴二甲胺盐能有效防除天然草原优势毒草黄帚橐吾等，施用除草剂后的安全放牧时间对确保家畜安全至关重要。为确定施用除草剂后的安全放牧时间和制定农药最大残留限量标准提供参考，利用超高效液相色谱串联质谱检测方法，对甘肃碌曲天然草原土壤和牧草中480 g/L麦草畏水剂和55% 2，4-滴二甲胺盐水剂的残留消解动态进行了研究。结果表明，480 g/L麦草畏水剂和55% 2，4-滴二甲胺盐水剂在天然草原土壤和牧草中的残留消解动态曲线均符合一级动力学方程，在土壤中的半衰期分别为1.8、4.7 d，在牧草中的半衰期分别为6.5、13.6 d。且480 g/L麦草畏水剂较55% 2，4-滴二甲胺盐水剂更易在土壤和牧草中快速消解，但二者均属于易降解除草剂。依据这2种除草剂在牧草中的残留量和国内外最大残留限量标准进行评价，认为在天然草原喷施除草剂组合480 g/L麦草畏水剂+55% 2，4-滴二甲胺盐水剂防除草原优势毒草黄帚橐吾等时，在施药后30~45 d放牧，对牛、羊等家畜安全。

Combination of decamba and 2,4-D dimethylamine salt can control many species of poisonous weeds including Ligularia virgaurea in natural grasslands. The safe grazing interval after herbicide application is crucial for livestock safety. In order to ensure safe grazing interval after herbicides application and provide reference for establishing the maximum residue limit (MRL) standards of pesticides, the degradation dynamics of 480 g/L dicamba aqueous solution and 55% 2,4-D dimethylamine salt aqueous solution in soil and forage of natural grassland in Luqu, Gansu, were investigated using ultra-high performance liquid chromatography-tandem mass spectrometry. Results showed that the dissipation dynamics of both 480 g/L dicamba aqueous solution and 55% 2,4-D dimethylamine salt aqueous solution in soil and forage followed the first-order kinetic equation. The half-lives in soil were 1.8 and 4.7 d, respectively, while those in forage were 6.5 and 13.6 d, respectively. Moreover, 480 g/L dicamba aqueous solution dissipated more rapidly in soil and forage than 55% 2,4-D dimethylamine salt aqueous solution, although both were easily degradable herbicides. Based on the residue levels of these two herbicides in forage and the evaluation against domestic and international MRL standards, it is suggested that grazing can be safely carried out 30 to 45 d after spraying the herbicide mixture of 480 g/L dicamba aqueous solution + 55% 2,4-D dimethylamine salt aqueous solution in natural grasslands to control dominant poisonous weeds such as Ligularia virgaurea.

S812.6

甘肃省2020年草原生态修复治理科技支撑项目；大熊猫祁连山国家公园(甘肃片区)科技创新联盟科技支撑项目(GYCX〔2020〕03-1)；国家现代农业产业技术体系(CARS-14-1-22)。