Flupyrsulfuron Soil Dissipation and Mobility in Winter Wheat Crops

Residues of the sulfonylurea herbicide flupyrsulfuron were extracted from cropping soils with 0.1 M NaHCO3. The soil extracts were cleaned up by partitioning and repeated thin-layer chromatography. Flupyrsulfuron was transformed by diazomethane into N-(4,6-dimethoxypyrimidine-2-yl)-N-(3-methoxycarbonyl-6-trifluoromethylpyridine-2-yl)methylamine (2), which was analyzed by gas−liquid chromatography with electron capture detection, and confirmation for several samples was made by gas chromatography combined with mass spectrometry. The sensitivity limit was 0.5 μg of flupyrsulfuron kg-1 of dry soil. Bioassays using sugar beet as test plant qualitatively confirmed the results of the chemical analyses. Flupyrsulfuron [10 g of active ingredient ha-1] was applied in autumn on plots in two winter wheat crops on a sandy loam soil, the first crop being made in 1996−1997 and the second one in 1997−1998. In the 0−8 cm surface soil layer of both crops, the flupyrsulfuron soil half-lives were 123 and 92 days, respectively. Flupyrsulfuron was also applied post-emergence in March to other plots in the same crops; the half-lives in the 0−8 cm surface soil layer were similar in both seasons, that is, ∼58 days. During all crop trials, flupyrsulfuron remained in the 0−8 cm surface soil layer and was not detected in the 8−10, 10−15, and 15−20 cm surface soil layers. The surface−2 cm soil layer contained the greatest flupyrsulfuron soil concentration, but the residues progressively moved down into the 2−4 and 4−6 cm soil layers. At the winter wheat harvest date for each trial, flupyrsulfuron was not detected in any of the soil layers (