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Abstract
Residues and dissipation of the herbicide hexazinone in soil leachate were determined under a 3‐year‐old clear‐cut forest after a 1986 fall application of PRONONE 10G at 0, 2, and 1 kg ai/ha over a 448‐day period. Soil leachates were collected at depths of 30, 55, and 80 cm and were individually analyzed for hexazinone (ai) residues. There was no soil leachate collected up to 112 days after application and before ground freeze. Leaching of hexazinone was triggered by the snow melt in spring 1987 and continued until the end of November 1987. Detected amounts of residues were the highest in the first postwinter collection 227 days after treatment, reaching 205 and 61 ug at 30 cm depth in the 4 and 2 kg ai/ha treatment plots, respectively and reaching 89 and 39 ug at 80 cm depth; at the 55 cm depth, the peaks were 178 ug after 264 days and 28 ug after 351 days in the 4 and 2 kg ai/ha treatment plots. Hexazinone residues declined to less than 17 ug after 448 days in all depths and in both herbicide treated plots. There were no hexazinone residues detected in the 0‐treatment plot. The concentration of hexazinone in soil leachates was inversely related to the volume of leachate. The sample collected from the 4 kg ai/ha plot at a depth of 30 cm had the highest concentration (492 ppb) but the lowest volume (152 mL) 277 days after application, compared to samples collected at the same depth but at different times. In all cases the total amount of hexazinone residues (ug) in soil leachates increased with the rate of soil water percolation but declined over time.