title: Effect of application rate on fumigant degradation in five agricultural soils.
abstract: Soil fumigation is an important pest management tool for many high value crops. To address the knowledge gap of how fumigant concentration in soil impacts dissipation, and thereby efficacy, this research determined the degradation characteristics of four fumigants as affected by application rate. Laboratory incubation experiments were conducted to determine degradation rates of 1,3-dichloropropene (both cis- and trans isomers), chloropicrin (CP), dimethyl disulfide (DMDS), and methyl iodide (MeI) in five agricultural soils. Fitted to pseudo first-order kinetics, the degradation rate constant (k) of CP, DMDS, and MeI decreased significantly as application rate increased while the 1,3-D isomers were the least affected by rate. Half-lives increased 12, 17, and 6-fold for CP, DMDS, and MeI, respectively, from the lowest to the highest application rate. At low application rates, the degradation rate of all fumigants in the Hueneme sandy loam soil was reduced by 50-95% in sterilized soil compared to the biologically active controls. However, this difference became much smaller or disappeared at high application rates indicating that biodegradation dominates at low concentrations but chemical degradation is more important at high concentrations. When co-applied, CP degradation was enhanced with biodegradation remained above 50%, while 1,3-D degradation was either reduced or not changed. Among the fumigants tested, the relative importance of biodegradation was DMDS>CP>MeI>1,3-D. These results are useful for determining effective fumigation rates and for informing regulatory decisions on emission controls under different fumigation scenarios.
authors.affiliation: Department of Plant Sciences, University of California, Davis One Shields Ave., Davis, CA 95616, United States; USDA-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Ave., Parlier, CA 93648, United States. Electronic address: ruijun.qin@ars.usda.gov.
authors.forename: Ruijun
authors.initials: R
authors.lastname: Qin
authors.affiliation: USDA-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Ave., Parlier, CA 93648, United States.
authors.forename: Suduan
authors.initials: S
authors.lastname: Gao
authors.affiliation: Department of Plant Sciences, University of California, Davis, 1636 East Alisal Street, Salinas, CA 93905, United States.
authors.forename: Husein
authors.initials: H
authors.lastname: Ajwa
authors.affiliation: Department of Plant Sciences, University of California, Davis One Shields Ave., Davis, CA 95616, United States.
authors.forename: Bradley D
authors.initials: BD
authors.lastname: Hanson
mesh_terms: D000383:Agriculture; D001673:Biodegradation, Environmental; D004784:Environmental Monitoring; D005651:Fumigation / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D006207:Half-Life; D007700:Kinetics; D008956:Models, Chemical; D010571:Pest Control / Q000379:methods / Q000592:standards / Q000706:statistics & numerical data; D010573:Pesticide Residues / Q000032:analysis; D010575:Pesticides / Q000032:analysis*; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*
chemical_list: D010573:Pesticide Residues; D010575:Pesticides; D012987:Soil; D012989:Soil Pollutants
keywords: 1,3-Dichloropropene (1,3-D),; Chloropicrin (CP),; Dimethyl disulfide (DMDS),; Methyl bromide alternatives,; Methyl iodide (MeI); Soil fumigation,