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Preferential Flow of Bromide, Bentazon, and Imidacloprid in a Dutch Clay Soil

^a Embrapa Agropecuária Oeste, Caixa Postal 661, CEP 79804-970 Dourados, MS, Brazil
^b Alterra, Wageningen University and Research Centre, PO Box 47, 6700 AA Wageningen, the Netherlands
^c Department of Environmental Sciences, Wageningen University and Research Centre, PO Box 8005, 6700 EC Wageningen, the Netherlands

View larger version (22K): [in a new window]   Fig. 1. (A) Map showing study site location in Andelst (the Netherlands) and (B) schematic diagram of the experimental field. In the diagram, the rectangles coded A to J are the 16 plots and the dashed lines indicate the six drain pipes.

View larger version (26K): [in a new window]   Fig. 2. Remaining mass of bentazon and imidacloprid as a function of time as measured in laboratory incubation studies at different temperatures using soil from the experimental field. (A) Bentazon in the 0- to 30-cm layer, (B) imidacloprid in the 0- to 30-cm layer, (C) bentazon in the 40- to 70-cm layer, (D) imidacloprid in the 40- to 70-cm layer, (E) bentazon at 10°C in the 80- to 120-cm layer, and (F) imidacloprid at 10°C in the 80- to 120-cm layer. The points are the measurements and the lines are fits assuming first-order kinetics. In the calculation of the fitted lines for 15 and 25°C in (B), all measurements later than 100 d were ignored.

View larger version (29K): [in a new window]   Fig. 3. Rainfall, ground water level, and drainflow as a function of time at the experimental field. (A) Daily rainfall and daily average ground water level; the shaded area is the range of the depths of the drain pipes. (B) Cumulative rainfall and cumulative drainflow. Time zero is 0000 h on 7 Apr. 1998.

View larger version (13K): [in a new window]   Fig. 4. Volume fraction of water as a function of depth as measured at the experimental field at 22, 69, and 125 d after bromide and bentazon application (Day 22 is 29 Apr. 1998, Day 69 is 15 June 1998, and Day 125 is 10 Aug. 1998). The thick line is the average of the 16 sampled soil columns and the thin lines are the average plus or minus one standard deviation of these columns.

View larger version (15K): [in a new window]   Fig. 5. (A) Ground water level, (B) rainfall, and (C) drain discharge in Drain Set 2 as a function of time on Days 18 to 21 (i.e., 25 to 28 Apr. 1998) as measured at the experimental field. The dashed lines in (A) indicate the range of the drain depth. Note that the scale of the vertical axes of (B) and (C) differ.

View larger version (15K): [in a new window]   Fig. 6. Amounts of (A) bromide, (B) bentazon, and (C) imidacloprid recovered from soil and the crop as a function of time as measured at the experimental field. Points are the averages and bars are the standard errors. Closed symbols are amounts recovered from the top 120 cm of soil and open symbols are amounts recovered from the crop (only for bromide). Time zero is 0000 h on 7 Apr. 1998. Note that the vertical axis of (B) is logarithmic and that imidacloprid was applied on Day 50. The arrow in (B) indicates that the point is an upper limit.

View larger version (29K): [in a new window]   Fig. 7. Concentration profiles of (A) bromide, (B) bentazon, and (C) imidacloprid in soil as measured at the experimental field at different sampling dates. The thick lines are average values and the thin lines are averages minus or plus one standard deviation of the four samples of each layer. Days indicate the period elapsed since the bromide and bentazon application on 7 Apr. 1998. Day 22 is 29 Apr. 1998, Day 69 is 15 June 1998, Day 125 is 10 Aug. 1998, Day 167 is 21 Sept. 1998, Day 239 is 2 Dec. 1998, and Day 378 is 20 Apr. 1999. Note that the horizontal axis of (A) is linear whereas the horizontal axes of (B) and (C) are logarithmic. The shaded area in (A) and the arrows in (B) indicate that the concentration is below the limit of quantification (LOQ).

View larger version (16K): [in a new window]   Fig. 8. Concentrations of (A) bromide, (B) bentazon, and (C) imidacloprid in drain water for both drain sets (closed symbols for Set 1 and open symbols for Set 2) as a function of time as measured at the experimental field. Time zero is 0000 h on 7 Apr. 1998 (i.e.. the application date of bromide and bentazon; imidacloprid was applied on Day 50). Note that vertical axes have different ranges and that in (B) the vertical axis has a break.

View larger version (16K): [in a new window]   Fig. 9. Concentrations of (A) bromide, (B) bentazon, and (C) imidacloprid in ground water collected from different filter depths as a function of time as measured at the experimental field. Time zero is 0000 h on 7 Apr. 1998 (i.e., the application date of bromide and bentazon; imidacloprid was applied on Day 50). Points are the averages and bars are the standard errors in (A) and (B). In (C) the points are individual values and the dashed line indicates the detection limit (points on this line indicate values below the detection limit).