AERODYNAMIC MEASUREMENTS OF METHYL-BROMIDE VOLATILIZATION FROM TARPEDAND NONTARPED FIELDS

Methyl bromide (MeBr) is used extensively in agriculture as a soil fum igant and there is growing concern over the role it may play in the de pletion of stratospheric ozone. Methyl bromide is applied using variou s techniques and very little is known about how much of the applied fu migant volatilizes into the atmosphere after the application. This hel d study was designed to estimate the post-application methyl bromide v olatilization loss rates from two different application practices. The fields were approximately 6 km apart in Monterey County, California, and were treated in conformity with local practices as of 1992. The Me Br was injected at a depth of 25 to 30 cm. One field was covered simul taneously with a high-barrier plastic film tarp during the application , and the other was left uncovered, but the furrows made by the inject ion shanks were bedded over. Volatilization fluxes were estimated usin g an aerodynamic-gradient technique immediately following the completi on of the application process and continued for 9 d for the tarped hel d and 6 d for the nontarped held. The cumulative volatilization losses from the tarped held were 22% of the nominal application within the f irst 5 d of the experiment and about 32% of the nominal application wi thin 9 d including the one day after the tarp was removed on Day 8 aft er application. In contrast, the nontarped field lost 89% of the nomin al application by volatilization in 5 d. The volatilization rate from the tarped field was shown to be significantly lower than the nontarpe d field at a 95% confidence level.