DIURON AND SIMAZINE LOSSES TO RUNOFF WATER IN MEDITERRANEAN VINEYARDS

The Mediterranean climate is characterized by a hot and dry summer whe re occasional storm events induce erosion and runoff. The high leachin g potential of pesticides to surface waters under such climate conditi ons are not in relation to the main body of data that originated from summer-rain row-crop scenarios. In this 2-yr study we monitored runoff discharge and concentrations of the two soil applied herbicides diuro n [3-(3,4-dichlorphenyI)-1,1-dimethylurea] and simazine chloro-N-2,N-4 -diethyl-1,3,5-triazine-2,4-diamine] from two field sites-one tilled a nd one no-till-cropped with grapevine (Vitis vinifera L.; Cinsault and Aramon, respectively). Despite a time lag of 140 d in 1994 between ch emical application and first runoff event, diuron concentrations in ov erland flow exceeded 200 mu g L-1 at the no-till site. In 1995 the fir st strong rainfall-runoff event following application carried >87 and 60% of the respective seasonal simazine and diuron loss at both sites, although it accounted for <17 and 7% of the total runoff volume at th e no-till and tilled site, respectively. At the no-till site, seasonal diuron loss during 1995 was 1.71% of applied; the corresponding value for simazine was 1.25%. Only 0.68 and 0.79% of the respective applied diuron and simazine mass were washed from the tilled field, reflectin g differences in runoff volume between sites. Pesticide losses depende d primarily on runoff volume and intensity. Event average herbicide co ncentrations in surface runoff followed an exponential decay over time . Estimated first order rate coefficients were at least twice as large as those derived from soil samples using the alcoholic solvent extrac tion technique. The decreasing water availability with time compared w ith the herbicide content at the soil surface indicated an increasing adsorption with time.