A simulation model for fate and transport of methyl bromide during fumigation in plastic-mulched vegetable soil beds

Abstract

A coupled water-heat and chemical transport model was used to describe the fate and transport of methyl bromide fumigant in low-density polyethylene plastic-mulched soil beds used for vegetable production. Methyl bromide transport was described by convective-dispersive processes including transformations through hydrolysis. Effects of non-isothermal conditions on chemical transport were considered through inclusion of temperature effects on transport parameters. An energy-balance approach was used to describe the plastic-mulched boundary condition that controls the thermal regime within the soil bed. Simulations were made for variable water-saturation regimes within the bed and for different depths of fumigant injection. Simulations for various scenarios revealed that large amounts (20-44% over a 7-day period) of applied methyl bromide are lost from the un-mulched furrows between the beds. Plastic mulching of the bed was found to be only partially effective (11-29% emission losses over a 7-day period) in reducing atmospheric emissions. Deep injection of fumigant and saturating the soil with water both led to increased retention of methyl bromide within the soil and less emission to the atmosphere. However, deep injection was unfavorable for effective sterilization of the crop root zone.