Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2009
Publication Date: 7/8/2009
Citation: Wang, D., G. Browne, S. Gao, B. Hanson, J. Gerik, R. Qin, N. Tharayil. 2009. Spot fumigation: fumigant gas dispersion and emission characteristics. Environ. Sci. Technol. 43:5783-5789. Interpretive Summary: The San Joaquin Valley (SJV) of California is a major agricultural area in the United States, where a significant portion of the farm lands are orchards of various fruit and nut trees, and they undergo replanting when an orchard reaches the end of economically productive life. Pre-plant soil fumigation is used widely to prevent replant problems of a complex of soil physical, chemical, and biological origin often dominated by soil-borne pests and diseases associated with the previous orchard. The air quality in SJV has also been among the worst because of the unique topography of the valley and large emissions of air pollutants from various sources including agricultural pesticides. A two-year replicated field study was conducted to develop and demonstrate site-specific application or drip spot application of soil fumigants only at tree sites with significantly reduced rates and treated areas per orchard. A significant contribution of the Spot Fumigation, as compared to the broadcast shank injection, is the dramatic reduction in total quantity of fumigant chemicals applied to an overall land area. A unique aspect about the low amount of fumigants needed is to help address the township cap limitations in SJV to protect and improve the regional air quality. The approach should be considered by regulators and growers as a practical and economical alternative, among other techniques such as plastic film cover, surface organic amendment, or applying water.
Technical Abstract: Reducing emissions of volatile organic compounds (VOCs) from fumigant pesticides is mandatory in California, especially in “nonattainment areas” that do not meet federal air quality standards such as in the San Joaquin Valley. A two-year field study was conducted to determine the feasibility of a site-specific application of fumigant chemicals only at tree sites with dramatically reduced rates for orchard replant. Soil gas distribution and atmospheric emission of 1,3-dichloropropene and chloropicrin were measured after “Spot Fumigation” with InLine® using subsurface drip irrigation. Based on soil concentration measurement and a concentration-time analysis, satisfactory pest control can be expected within 15 cm in radius from the injection point, and some degree of control from 15 to 51 cm radial distance of the fumigant source. Cumulative emission was 18-23% of applied active ingredient in a cover crop treatment and 2-6% in a no crop treatment. Considering the significantly small amount of fumigant used, the Spot Fumigation approach can achieve a 10-fold reduction in atmospheric VOCs load from fumigant pesticides.