Field-scale metolachlor volatilization flux estimates from broadcast and banded application methods in central Iowa

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 stud y was designed to evaluate volatilization rates of a preemergent herbicide Dual [a.i. metolachlor 2.24 kg ha(-1) (2-chloro-N-(2-ethyl-6-methylphenyl)- N-(2-methoxy-1-methylethyl)acetamide)] from two fields (175 and 45 ha) in c entral Iowa under contrasting tillage operations and pesticide application scenarios. Metolachlor vapor was trapped using polyurethane foam plugs at s ix heights on a profile mast. Average concentrations were measured at each height every 2 h for the first 4 d after application, then every 4 h therea fter. Volatilization rates were calculated with a flux-gradient technique u sing data from Bowen ratio and eddy correlation measurements. Flux profile concentrations of metolachlor were large during the first 24 h and quickly declined for the duration of the study. There was approximately a threefold greater cumulative volatilization loss of applied metolachlor from the bro adcast (22%) treatment than from the banded treatment (6%) for the 10-d stu dy period. Metolachlor volatilization was affected by residue cover, spatia l concentration on the surface, and timing of precipitation.