Use of field lysimeters to determine C-14-dicamba persistence and movementin soil

Persistence and movement of C-14-dicamba was determined in the top 90 cm of a clay loam soil in 30 x 100 cm intact soil lysimeters in the field during a 16-mo period. All of the applied C-14 was still in the profile 1 month a fter application (MAA). Although 97% was still in the top 20 cm depth, smal l amounts of C-14 (<0.1% of applied) were found at the 80-90 cm depth. This was the only time during the study that C-14 was found this deep. Of the 8 9% of the applied C-14 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 ap plied C-14 was still present in the soil profile, 99% of which was in the t op 20 cm of soil. Of the 54% of the applied C-14 remaining in the top 10 cm of soil, 11% was 3,6-dichloro-2-hydroxybenzoic acid, and we could not conf irm any dicamba.