Table 1. Summary of Recent Experiments Measuring Methyl Bromide Volatilization Method Injection Surface Sampling Field MeBr Estimated Percent Mass Source Used Depth Cover Intervals Size Mass Volatile MeBr

There are many soil-chemical processes which affect the fate and transport of fumigants in agricultural soils. Generally, three factors must be controlled to reduce emissions while Maintaining adequate efficacy: containment, degradation and soil-gas distribution. Probably the most reliable method to reduce the amount of methyl bromide (MeBr) leaving the treated soil involves the use of virtually-impermeable plastic films. To demonstrate this, a recent field experiment was conducted using the traditional high-density polyethylene (HDPE) and a virtually-impermeable film (VIF), Hytibar (Klerks Plastic, Belgium), to cover triplicated field plots treated with MeBr at a rate of 280, 210 or 140 kg/ha. At the beginning of the experiment, 2 bags containing citrus nematodes (Tylenchulus semipenetrans), Yellow Nutsedge seeds (Cyperus esculentus) and fungi (Rhizoctonia solani) were placed 10-15 cm deep in each plot to determine the effectiveness of the fumigation. During the course of the experiment, the volatilization rate was continuously measured over 3 hour intervals using two or more flux chambers. After the experiment, soil bromide concentration was measured to provide information for a mass balance. It was found that MeBr emissions were reduced from approximately 60 % using current practices to less than 5 % when VIF together with an 210 kg/ha application rate and a 10-day cover period were used. VIF offer several advantages f6known in advance and films are more uniform in space and time compared to soil-based methods