Dimethenamid was applied on soil samples to determine the sorption, desorption, and leaching potential of this herbicide in different soils. After 24 hour shaking, the samples were centrifuged, and the supernatant filtered and analyzed by HPLC. Desorption periods were established by substituting the removed supernatant volume in each tube for a CaCl2 solution (0.01 M), shaking for 24 hours, and centrifuging it. The procedure was repeated three more times at 24, 48, and 72 h, when the supernatant was filtered and analyzed by HPLC. Dimethenamid sorption, described by Freundlich isotherm, was calculated by the differences between the applied concentrations and those measured by HPLC. Desorption percentages at 24, 48, and 72 h were calculated by the difference between the sorbed quantities and those measured in the HPLC. Pearson correlations were set up to determine the correlation between kf, kfoc, desorption, and the main soil properties, and GUS coefficient was used to estimate the leaching potential. The low dimethenamid kf values suggest that this herbicide is of low sorption in the studied soils. A significant and positive correlation between sorption and organic carbon content was established in the individual LVd-a profile analysis. The values for kfoc varied from 37.66 to 138.24, in surface samples of the studied soils. They presented a significant correlation with the organic carbon content only when the LVd-a soil profile was analyzed. Leaching potential evaluation showed that dimethenamid may be classified as a leaching agent only in the LVdf soil. Up to 72 hours after application, desorption was less intense than sorption. Dimethenamid desorption is greater in deeper LVd-a soil layers, where organic carbon contents are lower.
Freundlich isotherm; kf; kfoc; GUS; herbicide
