EFFECT OF SOIL FACTORS ON METHYL-BROMIDE VOLATILIZATION AFTER SOIL APPLICATION

Two current tasks regarding the use of methyl bromide (MeBr) as a soil fumigant are to accurately estimate its volatilization rate into the atmosphere from soil fumigation and to develop application and soil ma nagement techniques that minimize this volatilization. In this study, we established experimentally that a series of soil factors, e.g., soi l type, soil water content, and bulk density, affect MeBr behavior in the soil-water-air phases and its volatilization rate from the soil su rface. Methyl bromide volatilization was significantly decreased in an organic matter-rich soil due to enhanced degradation and in moist and dense soils due to reduced diffusion in the gas phase. These results imply that MeBr volatilization rate may vary from one geographic regio n to another or from one field to another in the same region due to ch anges in soil conditions or even from one site to another in the same field due to soil heterogeneity. To minimize MeBr volatilization from soil, MeBr should be injected at great depths in moist soil under tarp ed conditions, with the soil surface packed before or immediately afte r the application. Applying MeBr at a shallow depth into relatively dr y and loose soil under untarped conditions will result in maximum vola tilization and therefore should always be avoided.