Sampling for zero-time hexazinone residues in forest soil dissipation study

Abstract

A new soil sampling method using glass jars to measure zero-time herbicide residues was compared with a conventional method using a soil corer under forest conditions in northern Alberta. A liquid formulation of hexazinone was diluted 20 times with water and applied with a four-nozzle overhead backpack sprayer. Use of the glass jar method resulted in 5 times more efficient recovery of hexazinone residues from soils (3.8 kg/ha) than the conventional corer method (0.8 kg/ha) at zero time. The corer method should be used following soil penetration of residues. Subsurface (0–30 cm) hexazinone levels sampled by this method were determined to be 2.0 and 0.35 kg/ha, respectively, 210 and 360 days after application. The combined use of glass jars for zero time and the soil corer for subsequent samplings produced the best result in estimating the dissipation rate of hexazinone in forest soils. Because of the late application in the fall and frozen ground in winter, the dissipation time for 50% of hexazinone was 206 days.