Different Application Rate On the Degradation of Several Important Soil Fumigants.

Low permeability tarp can effectively retain soil fumigant and increase concentration time exposure indices in soil. As a result, there is a potential to use reduced fumigant application rate that are efficacious to control soil pests. However, information on the effect of varying fumigant amount on fumigant degradation is very limited. A series of laboratory incubation experiments were conducted to study the degradation characteristics of several fumigants including 1,3-dichloropropene isomers (cis- and trans-1,3-D), chloropicrin (CP), and dimethyl disulfide (DMDS) at application rates ranging from 10 to 200 mg kg-1 in five soils. Results showed that the degradation of these fumigants over time following a pseudo first-order kinetics. Generally, the half-life of fumigant degradation increased with the increase of application rates, but this change depends highly on the type of soil and the compound, more profound changes for CP and DMDS than 1,3-D. When the application rate increased from 10 to 200 mg kg-1, the half-life of 1,3-D isomers slightly increased, while that of CP increased 9-16 times. The half-life of DMDS increased 3-17 times when its application rate increased from 20 to 120 mg kg-1. Autoclave sterilization significantly slowed the degradation of CP and DMDS but had no impact on 1,3-D in a sandy loam, implying that the biodegradation was an important factor impacting the fate CP and DMDS in the soil. These data suggest that fumigant degradation can be important to determine a proper fumigant rate for ensuring satisfactory pest control with the use of low permeability tarp.