LOSS OF METHYL-BROMIDE TO THE ATMOSPHERE DURING SOIL FUMIGATION

Models of soil vapor transport were developed and applied to the prediction of atmospheric emissions of methyl bromide during soil fumigation. With effective cover placement and good injection depth control estimated cumulative methyl bromide losses to the atmosphere after 14 days ranged from 26% to 65% of that originally injected under a variety of injection conditions. The rate of emission after 14 days is small and was neglected. The best estimate of cumulative methyl bromide losses to the atmosphere under current emission practices is about half of that injected, in good agreement with estimates by Watson et al. [1] based on global concentrations of methyl bromide. The model suggests that deep injection with surface porosity control by moisture addition or use of low permeability covers could be an effective means of minimizing losses to the atmosphere during soil fumigation. Emissions would also be the smallest for high organic carbon content soils which tend to increase both reactivity and retardation due to sorption.