Leaching of soil‐active herbicides in acid, low base saturated sands: Worst‐case conditions

Abstract

AbstractEffects of litter‐humus treatments and precipitation acidity on the mobility of the soil‐active herbicides hexazinone, tebuthiuron, and sulfometuron methyl were determined in 15‐ × 150‐cm lysimeters with intact soil columns collected from six sites across the northern Lake states. Each column had received a cap of litter‐humus from either a jack pine or mixed hardwood stand, or a quartz sand (control) and was preconditioned by treatment with rainwater acidified to pH 5.4 or 4.2, applied weekly throughout the growing season for four years. 14C‐labeled material was added to the commercial formulation of each product and applied at 2.24 kg (active ingredient [a.i.])/ha of hexazinone and tebuthiuron and 42.5 g (a.i.)/ha of sulfometuron methyl. Acidified rainwater was applied weekly to approximate ambient precipitation; additional water was applied on three occasions. Soil water was sampled once at 10, 20, and 40 cm, and 10 times at the 150‐cm level over the 130‐d post‐treatment. Sulfometuron methyl apparently had dissipated by 80 d post‐treatment and was not detected below 20 cm. At the 150‐cm level, hexazinone and tebuthiuron were detected in leachate beginning 52 and 66 d post‐treatment, respectively. Leaching of both products was affected significantly by litter‐humus treatment; by amount of applied rainwater, and for tebuthiuron, by site. The lack of a humus cover increased the amount of hexazinone at 150 cm by nearly threefold and tebuthiuron by nearly fivefold. The greatest leaching occurred after high applications of water and on the four sites with the lowest pH and base saturation. The combination of soil characteristics, litter‐humus treatments, and applied precipitation provides reference values for worst‐case conditions likely to be encountered in the Lake states region.