Effect of soil water content at the time of application on herbicide content in soil solution extracted in a pressure membrane apparatus

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Abstract
Summary: Wettable powder formulations of simazine, metribuzin and linuron and a suspension concentrate of simazine were sprayed on to soil particles which were either at a water content equivalent to pF 2·5 or air dry. Air dry samples were then wetted to pF 2·5 immediately or after 24 h. Soil solutions were removed using a pressure membrane apparatus at intervals up to 96 h after wetting. In each case the concentration in soil solutions expressed after 96 h following application to wet soil, or dry soil wetted immediately, were close to those predicted on the basis of Freundlich adsorption isotherm data obtained in slurry equilibrium conditions. There were, however, some differences after shorter periods.Concentrations were always lower in solutions obtained from air dry soil that was not wetted for 24 h. After 96 h simazine and metribuzin concentrations were about 50% of those obtained following application to wet soil, while that of linuron was about 25%. Differences of this size may be large enough to affect mass transfer phenomena and phytotoxicity. It seems likely that suspension of these herbicides sprayed in formulations on to wet soil dissolved in soil water at least as fast as would be predicted theoretically.