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Effects of Soil Variability and Weather Conditions on Pesticide Leaching— A Farm-Level Evaluation

Laboratory of Soil Science and Geology, Wageningen University, P.O. Box 37, 6700 AA Wageningen, the Netherlands

View larger version (35K): [in a new window]   Fig. 1. Sampled soil profiles. Profile A combines heavy texture and high soil organic matter (SOM) percentage (relatively low risk for leaching), Profile B reflects average properties in the study area (average risk for leaching), and Profile C combines light texture and low SOM percentage (relatively high risk for leaching). Sand fractions are not included, but equal 100 minus the sum of clay and silt fractions.

View larger version (34K): [in a new window]   Fig. 2. Leaching (in percent) as a function of degradation time (DT50) and coefficient of sorption to organic matter (Kom). The DT50–Kom combinations of pesticides used in the study area are plotted as (leaching 0.1 µg L-1) or (leaching >0.1 µg L-1).

View larger version (20K): [in a new window]   Fig. 3. Degradation patterns of isoproturon recorded in incubated soil cores. Samples are coded according to their soil profile (A, B, or C) and sampling depth (1 for topsoil, 2 for subsoil). Sample B1 is excluded as pesticide concentrations failed to show a consistent decrease over time.

View larger version (20K): [in a new window]   Fig. 4. Simulated and measured isoproturon concentrations at 28 wk after application. Simulated concentrations for the higher dosage (1 kg ha-1) assume no initial losses, whereas the lower dosage (0.67 kg ha-1) accounts for interception losses during spraying.

View larger version (20K): [in a new window]   Fig. 5. Cumulative probability plots of isoproturon leaching from soil profiles (A, B, and C). Plotted data refer to simulated leaching fractions for 20 years of data.

View larger version (65K): [in a new window]   Fig. 6. Effects of soil variability on the leaching of isoproturon, metribuzin, and bentazon.