Leaching of bentazon in Swedish soils using field lysimeters
1992
Bergstroem, L. (Sveriges Lantbruksuniv., Uppsala (Sweden). Inst. foer Markvetenskap)
Leaching of the herbicide bentazon (3-isopropyl-(1H)-benzo-2,1,3-thiadiazin-4-one-2,2-dioxide) was studied for 325 days in field lysimeters filled with an intact clay or sandy soil. The herbicide was applied at two rates on each soil type, either 0.6 or 1.2 kg active ingredient/ha. The weather during the experimental period was relatively warm (mean air temperature 7.5 deg C) and dry (444 mm of precipitation). Therefore, all lysimeters received 145 mm supplemental watering in addition to natural precipitation. The accumulated leachate volumes were larger in the sand than in the clay lysimeters, i.e. on average, 253 and 206 mm respectively. Leachate from the sand lysimeters had also considerably larger bentazon concentrations than leachate from the corresponding clay lysimeters. Bentazon concentrations in leachate from the clay lysimeters (both herbicide application rates) reached nondetectable concentrations (0.1 microgram/l) within ca. 10 months or less, whereas the corresponding sand lysimeters still had concentrations just above the detection limit. Overall peak concentrations (ca. 4 microgram/l in the sand) occurred 105 days after spraying, by which time ca. 4 mm of leachate had been collected. Converted to loads over the 11-month period, a maximum of 0.15 and 0.03% of the active substance applied on the sand and clay soils, respectively, appeared in leachate.
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