Temperature and moisture effects on fumigant degradation in soil

Recent discovery of the contribution of methyl bromide fumigation to strato spheric ozone depletion has revealed our limited understanding of the envir onmental processes of fumigants. For instance, little is known about fumiga nt degradation in soil under high temperature or low moisture conditions th at prevail near the soil surface during fumigation. In this study we determ ined the interaction of soil temperature and moisture with degradation of 1 ,3-dichloropropene (1,3-D) and methyl isothiocyanate (MITC) for extended so il temperature and moisture ranges. Fumigant degradation increased 5 to 12 times when temperature increased from 20 to 50 degrees C. It was further sh own that chemical transformation of fumigants always increased with increas ing temperature, but temperature effects on microbial degradation were fumi gant dependent. The relative contribution of microbial degradation to the o verall fumigant degradation was highest for the soil with highest organic m atter content, and was greater for MITC than for 1,3-D isomers, When the te mperature was >30 degrees C, microbial degradation of 1,3-D was substantial ly suppressed, while that of MITC was greatly stimulated. As soil moisture content increased, 1,3-D degradation accelerated, but that of MITC decrease d. The specific responses of fumigant degradation to temperature and moistu re variations should be considered when describing their transport in the e nvironment, and also may be used for designing fumigation practices that al low reduced atmospheric emissions.