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Soil and Microclimate Effects on Trifluralin Volatilization¹

ABSTRACT

A large fraction of many applied pesticides are lost to the air and dissipated. Microclimatological methods were used to determine the diurnal loss rates by volatilization of trifluralin applied and incorporated into the soil of a 1.26-ha upper Piedmont plateau watershed. Trifluralin flux decreased to very low levels during daytime when surface soil water content was low even though turbulence, soil temperature, and evaporative demand were high. During nighttime, when evaporative demand subsided and the surface soil water content increased, the trifluralin flux increased as the surface soil water content increased. Trifluralin and lindane flux on a limited plot-size study were compared and both pesticides reacted similarly to environmental conditions, except lindane volatilized more rapidly.

When the soil surface was not wet, trifluralin and lindane fluxes appeared to be controlled by surface soil water content and the water content's effect on pesticide adsorption to the soil particle. Apparently, adsorption to the soil particle upon soil drying is a reversible process since efflux of the pesticides was rapid when soil was rewetted by dew or rainfall to above the equivalent of three molecular layers of adsorbed soil water. Under controlled soil-water conditions, where the soil surface remained wetter than three molecular layers of adsorbed water, the pesticide fluxes responded to increased soil temperature and turbulence, and atmospheric stability conditions.

Key Words: pesticides • lindane • pesticide flux • aerial losses • micrometeorology • aerodynamic • energy balance • exchange coefficient • turbulent transfer

¹ Contribution from Southern Piedmont Conserv. Res. Center, Watkinsville, GA 30677, Athens, Georgia Area, Southern Region, Agric. Res. Serv., U. S. Dep. of Agric., in cooperation with the Georgia Agric. Exp. Stn.

² Soil Scientist, Soil Scientist, Soil Scientist, Agricultural Engineer, and Soil Scientist, USDA, Watkinsville, Ga., respectively.

Received for publication September 22, 1975.