Alternatives to MEBR for California Cropping Systems
Location: Water Management Research
Title: Fumigant degradation as affected by different application rate in five soils
Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: September 20, 2011
Publication Date: October 30, 2011
Citation: Qin, R., Gao, S., Ajwa, H. 2011. Fumigant degradation as affected by different application rate in five soils. International Conference on Methyl Bromide Alternatives and Emissions Reductions, San Diego, California, October 31-November 2, 2011. p. 79.1-79.3.
Interpretive Summary: Tarping fumigated fields with totally impermeable film (TIF) shows great potential in fumigant emission control and using reduced fumigation rates to achieve effective pest control. It is necessary to fill the knowledge gap on fumigant degradation rates as application rates vary because degradation determines fumigant residence time in soil and affects efficacy. Laboratory incubation experiments were conducted and determined the degradation rates of several important alternatives to methyl bromide, including 1,3-dichloropropene (1,3-D) isomers (cis- and trans-1,3-D), chloropicrin (CP), and dimethyl disulfide (DMDS) at different application rates in five different textured soils. The results show that fumigant degradation rate decreases significantly as the application rate increases. All fumigants demonstrated this inverse relationship and the degradation rate of CP and DMDS decreased faster than 1,3-D isomers with the increase in fumigant amount added to soil. This observation implies that to determine a reduced but effective fumigant application rate when using low permeability tarp to control emission in the field, the degradation rate affected by fumigant and soil properties need to be considered. The results are useful for optimizing soil fumigation technology and reducing environmental hazard from soil fumigation under field conditions.
Soil fumigation is critical in controlling soil-borne pests and diseases and ensuring high yields for many crops. The excellent performance of the totally impermeable film (TIF) on fumigant emission control and pest control efficacy made it possible to use reduced fumigation rates under the tarp to achieve satisfactory efficacy. However, there is a significant knowledge gap on fumigant degradation when different application rates are used. The objective of this study was to determine the degradation rate changes of several alternative fumigants to methyl bromide as a function of the amount applied to different soils. Three laboratory incubation experiments were conducted that included four fumigant compounds [cis-1,3-dichloropropene (1,3-D), trans-1,3-D, chloropicrin (CP), and dimethyl disulfide (DMDS)] and five soils from agricultural fields of California and Florida. The initial fumigant concentration added to soil ranged from 10 to 200 mg/kg for 1,3-D isomers and CP, and from 20 to 160 mg/kg for DMDS. The degradation for all fumigants followed pseudo first-order kinetics. As fumigant application rate increased, the degradation rate constant decreased (or half-life increased) significantly especially for CP and DMDS. When initial fumigant concentration in soil increased from 10 or 20 mg/kg to about 100 mg/kg for CP and DMDS, the half-life of CP and DMDS increased three time or higher. However, little changes were observed for both 1,3-D isomers when fumigant concentration increased from 10 to 200 mg/kg, These findings suggest that a proper fumigant application rate for ensuring good efficacy must be determined by considering the fumigant property and the soil type.