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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Water Management Research » Research » Publications at this Location » Publication #310090
Title: Effect of application rate on fumigant degradation in five agricultural soils

Author
item QIN, RUIJUN - University Of California
item Gao, Suduan
item AJWA, HUSEIN - University Of California
item HANSON, B - University Of California

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2015
Publication Date: 10/28/2015
Citation: Qin, R., Gao, S., Ajwa, H., Hanson, B.D. 2016. Effect of application rate on fumigant degradation in five agricultural soils. Science of the Total Environment. 541:529-534.

Interpretive Summary: Soil fumigation continues to be critical for controlling soil-borne pathogens, nematodes, and weeds to ensure maximum yields for many high value crops. Efficient use of fumigants involves determination of the optimum rate for good pest control while reducing losses of fumigant to the environment, but there is a significant knowledge gap in fumigant degradation as a function of the amount in soil. This research determined degradation rates of several commonly used fumigants in laboratory incubation experiments. Fumigants studied include 1,3-dichloropropene, chloropicrin, dimethyl disulfide, and methyl iodide. While the degradation rates of 1,3-dichloropropene compounds showed little change, the remaining three fumigant degradation rates showed significant decreases as application rate increased. This study shows that the degradation behavior of fumigants is important to consider in determining an efficient rate in soil to achieve high fumigation efficiency while reducing chemical input to minimize negative impact on the environment.

Technical Abstract: Fumigants continue to be used in soil disinfestation for many high value crops. There is a significant knowledge gap on how fumigant concentration in soil impacts fumigant dissipation and determination of the most efficient rate. The aim of this study was to determine the degradation characteristics of several common fumigants as affected by application rate. Laboratory incubation experiments were conducted to collect degradation data of 1,3-dichloropropene isomers (cis- and trans-1,3-D), chloropicrin (CP), dimethyl disulfide (DMDS), and methyl iodide (MeI) ranging from 10 to 120 mg kg-1 in five soils. Fitted to pseudo first-order kinetics, the degradation rate constant (k) of CP, DMDS, and MeI decreased significantly while 1,3-D isomers were the least affected as application rate increased. Co-application of 1,3-D and CP did not alter their degradation rates compared to when applied separately. From the lowest (10 or 20 mg kg-1) to the highest application rate (100, 120, or 70 mg kg-1) for CP, DMDS, and MeI, their half-life increased up to 12, 17, and 6 times, respectively. The rate constant was dramatically reduced by sterilization of the soil at low application rates, while the impact was much smaller at high application rates. Although highly variable among soil types and amounts applied, the CP degradation was the fastest among all the fumigants. These results suggest that determination of an efficient rate for a specific fumigant should consider its degradation characteristics to achieve satisfactory pest control while reducing chemical input to minimize negative impact on the environment.