Use of Field Lysimeters to Determine ¹⁴C-Dicamba Persistence and Movement in Soil

Persistence and movement of ¹⁴C-dicamba was determined in the top 90 cm of a clay loam soil in 30 × 100 cm intact soil lysimeters in the field during a 16-mo period. All of the applied ¹⁴C was still in the profile 1 month after application (MAA). Although 97% was still in the top 20 cm depth, small amounts of ¹⁴C (<0.1% of applied) were found at the 80-90 cm depth. This was the only time during the study that ¹⁴C was found this deep. Of the 89% of the applied ¹⁴C remaining at 1 MAA in the top 10 cm of soil, 6% was dicamba and 27% was 3,6-dichloro-2-hydroxybenzoic acid. At 6 MAA, 50% of applied ¹⁴C was still present in the soil profile, 99% of which was in the top 20 cm of soil. Of the 54 % of the applied ¹⁴C remaining in the top 10 cm of soil, 11% was 3,6-dichloro-2-hydroxybenzoic acid, and we could not confirm any dicamba.