Temperature Effect on Methyl Bromide Volatilization: Permeability of Plastic Cover Films

Conventional methods of applying methyl bromide (MeBr) for soil fumigation can result in significant losses to the atmosphere, potentially contributing to the depletion of stratospheric ozone. It has been found that one of the major factors controlling MeBr volatilization is the permeability of the plastic cover films. Since the most commonly used agricultural film (i.e., polyethylene or PE) is not effective in containing MeBr, one practical method of reducing MeBr volatilization is to replace the PE film with one that is less permeable to MeBr. In this study, we document the temperature‐dependent permeability of standard PE and a new plastic film (Hytibar) that is considered to be virtually impermeable to MeBr. Functional relationships between temperature and the film permeability to MeBr were obtained from a calibration experiment under controlled conditions. A field experiment was conducted to determine MeBr volatilization dynamics from plots covered with the two different plastic films. diffusion‐based transport model was used to simulate the fate and transport of MeBr gas in the soil and volatilization into the atmosphere. In both the calibration and field experiment, the Hytibar film was found to be nearly impermeable to MeBr. Volatilization of MeBr was affected directly by temperature changes of the PE or Hytibar film in the calibration experiment. Under field conditions, MeBr emission was less affected by temperature, especially at large times after application. Model simulation predicted MeBr volatilization reasonably well for the PE covered field plot, but overpredicted the emission for the Hytibar plot.