Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/1998
Publication Date: N/A
Interpretive Summary: Loss of pesticides to the atmosphere in the form of vapor (volatilization) from agricultural fields is considered to be a significant portion of the amount applied to the field. Metolachlor is the active ingredient of a pre-emergent herbicide that is heavily used in the Northern cornbelt region of the United States. Little is known about metolachlor volatilization losses because measurement of these losses is difficult and not routinely done. Concentration profiles of metolachlor from two fields were combined with turbulence data (wind speed and temperature) to calculate metolachlor volatilization losses to the atmosphere. The effects of application methods and plant residue on the surface were shown to have significant impact on the volatilization losses of metolachlor. Banded herbicide application showed 9% cumulative loss over a 7-day period immediately after application compared to 22% loss using a broadcast application technique over a 7-day period. The impact of these results is a significant reduction in volatilization losses that can be attributed to application method and residue management, activities that can be easily transferred to the farmer/operator level.
Technical Abstract: Volatilization of pesticides has been considered to be a large part of the loss from fields after application, however there have been relatively few studies conducted to quantify the amount lost to the atmosphere. This study was designed to evaluate volatilization rates of a pre-emergent herbicide (metolachlor, (2-chloro-N-(2-ethyl-6- methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide) ) from two fields in central Iowa using banded and broadcast application techniques. Metolachlor vapor was trapped in polyurethane foam plugs (PUF) at six heights, with average concentrations calculated at each height every two hours for the first two days after application, then every four hours thereafter. Volatilization rates were calculated with a flux-gradient technique using data from Bowen ratio and eddy correlation measurements. Flux profile concentrations of metolachlor were large during the first 48 hours and quickly declined for the duration of the study. There was approximately a three-fold increase of cumulative metolachlor volatilization loss from the broadcast (22%) treatment relative to the banded treatment (6%) for the study period.