METHYL-BROMIDE DIFFUSION AND EMISSION THROUGH SOIL COLUMNS UNDER VARIOUS MANAGEMENT-TECHNIQUES

The proposed phaseout of methyl bromide (MeBr) in 2001, while undertaken for environmental reasons, has important economic implications. At the present time, very Little is known about how much MeBr escapes from fumigated soils into the atmosphere, or about methods for reducing this loss in an economically feasible manner. In this study we report the results of a series of experiments on MeBr diffusion and emission through soil columns under various management techniques. Column experiments were conducted to evaluate the effectiveness of commonly used polyethylene films in preventing MeBr emission into the atmosphere, and were analyzed with a mathematical model to estimate the soil gas diffusion coefficient (D-g(s)) and the mass transfer coefficients (h) for different polyethylene films. Additional experiments were then conducted to evaluate the effect of adding various amounts of irrigation water after injection and tarping on total MeBr emission into the atmosphere. The films were found to be only marginally effective in preventing MeBr emission from fumigated soils, while irrigating and then covering the soil with the film was much more effective in reducing MeBr loss.