Effects Of Typical Herbicides In Paddy On Tobacco Growth And Their Degradation Dynamics In Soil

Herbicides are used to reduce the labor force. Whereas, misuse of herbicides may often causeherbicide phytotoxicity.Tobacco is sensitive to herbicide. In recent years, the phenomenon of tobaccoaffected by herbicide phytotoxicity is increasing gradually. Particularly in rice and tobacco rotationarea, paddy herbicide phytotoxicity on tobacco severely affects its yield and quality. In this paper, theinfluence of paddy herbicide on tobacco growth and their degradation dynamics in different types ofsoil are studied. On this basis, quinclorac, which easily induces tobacco phytotoxicity, is studiedfurther. The influence of the soil moisture, soil organic matter, temperature and other environmentalfactors on quinclorac phytotoxicity on tobacco, and their degradation in the soil are analyzed. Theresults provide the theory basis for using scientificly and reasonablly of paddy herbicides in rice andtobacco rotation area, and have great significance for the tobacco production safety.Among the four typical paddy herbicides in this study, quinclorac has a most obvious effect ontobacco and the symptoms induced by quinclorac are most prominent. Its symptoms are mainlyshown as that tobacco leaves grow abnormally, leaf margin to roll back, tip bend down, uneven on theleaf, thick green leaf color, leaf thickening. Bensulfuron methyl and pyrazosulfuron-ethyl mainlyinhibit tobacco height, while cyhalofop-butyl has no effect on it. Quinclorac, bensulfuron methyl andpyrazosulfuron-ethyl have a suppressive effect on the tobacco root obviously. Within the experimentalconcentration range, the more suppressive effect was observed with the herbicide concentrationincreased. Quinclorac, bensulfuron methyl, pyrazosulfuron-ethyl and cyhalofop-butyl have no effecton the tobacco leaf chlorophyll content. The critical concentration of quinclorac, bensulfuron methyland pyrazosulfuron-ethyl leading to tobacco produce phytotoxicity are1.25a.i.g/hm~2、1a.i.g/hm~2、1a.i.g/hm~2, respectively.Using high performance liquid chromatography with ultraviolet detector (HPLC-UV), thedegradation dynamics of four typical paddy herbicides in the soil were detected. The results indicate:in brown loam soil in Shandong, moisture soil in Hunan, paddy soil in Sichuan and red loam inYunnan, the degradation half-lives of quinclorac were26.8,23.9,35.6and32.4days, respectively,average is29.7d; the degradation half-lives of bensulfuron methyl were17.8、11.8、17.2、9.3days,respectively, average is14.0d; the degradation half-lives of pyrazosulfuron-ethyl were10.7,8.0,10.2and7.2days, respectively, average is9.0d, the degradation half-lives of cyhalofop-butyl were6.9、4.8、7.9and5.9days, respectively, average is6.4d. In four different types of soil, the degradation ofquinclorac in the soil was the slowest, followed by bensulfuron methyl and pyrazosulfuron-ethyl, thedegradation of cyhalofop-butyl in the soil is fastest.Different environmental factors will affect tobacco phytotoxicity caused by quinclorac. Amongthem, temperature has the most influence. Tobacco plant became short significantly and leaf width wasnarrow at20℃and25℃, while quinclorac phytotoxicity had no significant effect on tobacco plantheight and leaf shape at35℃. Quinclorac phytotoxicity is the least in the soil which moisture ismoderate; Quinclorac phytotoxicity is middle under moist condition; Quinclorac phytotoxicity is thegreatest under droμght condition, and the inhibition rate of plant height is36.41%. Soil organic mattercan relieve quinclorac phytotoxicity influence on tobacco growth. With the organic matter contentincreased, the tobacco phytotoxicity decreased. When soil organic matter content is26.8g/kg, the inhibition rate of plant height was only1.99%.Various environmental factors can influence the degradation dynamics of quinclorac in the soil.Quinclorac degrade faster in alkaline condition than acidic conditions. Within the concentration range,the higher the soil humidity and temperature were, the faster degradation of quinclorac in the soil wouldbe.