SORPTION-DESORPTION HYSTERESIS OF THE DIKETONITRILE METABOLITE (DKN) OF ISOXAFLUTOLE (IFT)

摘要

Isoxaflutole [4-(2-methanesulphonyl-4-trifluoromethylbenzoyl)-5-cyclopropyl isoxazole] (IFT), is a systemic, pre-emergence herbicide which belongs to the isoxazole class of herbicides. IFT is chemically benzoyl isoxazole and it rapidly converts to a diketonitrile metabolite [2-cyano-3-cyclopropyl-1-(2-methylsulphonyl-4-trifluoro methyl phenyl) propan-1, 3-dione] (DKN), by opening of the isoxazole ring. The conversion to DKN takes place in both plants and soil. The half-life of isoxaflutole is very short but, the half-life of DKN is much longer and hence, DKN remains in soil for for an extended period of time. Sorption-desorption studies were conducted with five soils varying in physical and chemical properties. The soils were collected from different parts of the United States of America (South Deerfield, MA; East Monroe, CO; Moorehead, MN; Amherst, MA; and Chelsea, MI). The soils had a wide variation in their soil texture, pH, organic matter, and cation exchange capacity (CEC). Batch equilibration technique was used for the sorption experiments, while completely-mixed batch reactor systems with decant and refill method was used for the desorption experiments. Four subsequent desorptions were examined after the sorption process in each soil with an equilibration period of 7 days. An apparent sorption-desorption hysteresis was observed in all the five soils. Organic matter content along with the clay content of the soils were the two determining factors for hysteresis. In soils with high organic matter content, the sorption-desorption hysteresis was mainly governed by organic matter content, but in soils with low organic matter, clay content played an important role. Except the soil with a very high organic matter content (57.4%), all the other soils exhibited a high correlation between the clay content and HI values calculated at 0.75 (r~2 = 0.960), 25 (r~2 = 0.934), and 150 mg L~(-1) (r~2 = 0.928). In conclusion, the potential for leaching through soil and crop injury due to isoxaflutole and its metabolite would decrease as soil organic matter and clay content increase.