The loss of pendimethalin (N-(ethylpropyl)-2,6-dinitro-3,4-xylidine), a selective herbicide in runoff water was determined on sandy-clay-loam soil plots cultivated with tobacco in relation with the use of ammonium nitrate limestone as fertelizer, for a period of two years, 1990 and 1991. The surface slope of plots was 11 and the use of fertilizer decreased the soil erosion from a value 617 g/m2to 320 g/m2. The runoff of surface waters were between 16-24 of the rainfall amounts. Reduction in pendimethalin in waterways results from water loss by infiltration, sediment loss, and by attachment adsorption on vegetative and organic matter. Surface runoff levels were highest for the first runoff event after herbicide application, 1.5 g/10 m2and initial concentrations were related to the time lapse between herbicide application and the date of the first run-off event. Maximum concentrations were 5.95 and 8.54 #x3BC;g/L in 1990 and 1991 respectively. Persistence studies showed that pendimethalin concentration in runoff of 0.5 cm soil layer decreased by 88.2, from 2.46 to 0.29 #x3BC;g/g within 233 days, in 1990 and by 87.6, from 2.42 to 0.30 #x3BC;g/g within 235 days in 1991. After 310 day the concentration of pendimethalin was only 0.1 #x3BC;g/g.
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