|Allen, Leon - Hartwell|
Submitted to: Archives of Environmental Contamination and Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2005
Publication Date: 8/1/2006
Citation: Ou, L., Thomas, J.E., Allen Jr, L.H., Vu, J.C., Dickson, D.W. 2006. Effects of application methods of metam sodium and plastic covers on horizontal and vertical distributions of methyl isothiocyanate in bedded field plots. Archives of Environmental Contamination and Toxicology. 51:164-173. Interpretive Summary: Methyl bromide use in vegetable production will be phased out since it has ozone depletion potential. Metam sodium (Vapam® and related formulations) is one possible replacement for methyl bromide as a preplant soil fumigant. Methyl isothiocyanate (MITC) is the active product in soil. USDA-ARS and University of Florida scientists compared effects of three application methods of metam sodium to bedded rows (broadcast spray and rototilling, single drip-tube, and double drip-tube) and two plastic covers (polyethylene, PE, and virtually impermeable film, VIF) on surface emissions and subsurface distributions of MITC in Florida sandy soil. Surface emissions of MITC lasted about 20 hours regardless of application method. The VIF was better than PE for reducing emissions and retaining MITC in soil. Downward movement of broadcast spray applications was limited to 12 inches and distributions were variable. Water penetrated to 24 inches in single drip-tube applications, but MITC was not transported to this depth. Horizontal distributions at 4 and 8 inch depths were more uniform in double than single drip-tube beds. More field research is needed to develop reliable methods of application of metam sodium in Florida sandy soils.
Technical Abstract: The preplant soil fumigant metam sodium is one potential replacement for methyl bromide. The objectives were to compare effects of three application methods (broadcast spray with rototiller incorporation, single drip tube delivery, and double drip tube delivery) and two plastic covers (polyethylene, PE, and virtually impermeable film, VIF) on surface emissions and subsurface distributions of the active product of metam sodium, methyl isothiocyanate (MITC), in bedded Florida sandy soil. Emission rates were measured by sampling air collected in inverted stainless steel pans at half-hour time intervals. Subsurface concentrations were measured from sampling probes placed at various depths and horizontal positions. Emissions of MITC lasted about 20 hours regardless of application method. The VIF was better than PE in reducing emissions. Downward movement of broadcast spray applications was limited to 30 cm and distributions were variable. Water penetrated to 60-cm in single drip tape applications, but MITC was not transported to this depth. Horizontal distributions at 10 and 20 cm were more uniform in double than single drip tube beds. More MITC was retained for longer periods in the VIF than PE treatments.