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Incubation Time Effects on Imazaquin Desorption as Determined by Nonequilibrium Thin-Soil Disc Flow

Department of Plant and Soil Sciences, Box 9555, 117 Dorman Hall, Mississippi State University, Mississippi State, MS 39762

View larger version (22K): [in a new window]   Fig. 1. Schematic of thin-soil disc flow system.

View larger version (20K): [in a new window]   Fig. 2. Influence of incubation time and fraction of effluent on desorption of imazaquin from soil. Initial imazaquin–soil concentration was 17.8 µmol kg–1. Flow rate for all treatments was 1.0 mL min–1.

View larger version (28K): [in a new window]   Fig. 3. Influence of incubation time and effluent on ratio of solution concentration to soil concentration (nonequilibrium Kd). Initial imazaquin–soil concentration was 17.8 µmol kg–1. Flow rate for all treatments was 1.0 mL min–1. The terms a and b denote initial event slopes that are different at the 0.05 level of significance; y and z denote second event slopes that are different at the 0.05 level of significance.

View larger version (20K): [in a new window]   Fig. 4. Influence of flow rate and fraction of effluent on desorption of imazaquin from soil. Initial imazaquin–soil concentration was 17.8 µmol kg–1. Incubation time for all treatments was 72 h.

View larger version (28K): [in a new window]   Fig. 5. Influence of flow rate and effluent on ratio of solution concentration to soil concentration (nonequilibrium Kd). Initial imazaquin–soil concentration was 17.8 µmol kg–1 in the 1.0 mL min–1 flow rate and 20.0 in the 0.67 and 0.33 mL min–1 flow rates. All treatments were incubated 72 h before desorption. Regression slopes were not different at the 0.05 level of significance.

View larger version (30K): [in a new window]   Fig. 6. Influence of kinetics type on accuracy of modeling imazaquin desorbing from soil, averaged over 24-, 72-, 168-h incubation times before desorption. Initial imazaquin–soil concentration was 17.8 µmol kg–1. Flow rate for all treatments was 1.0 mL min–1. Error bars equal ±1 standard deviation within each fraction of effluent.

View larger version (31K): [in a new window]   Fig. 7. Influence of empirical model and fraction of effluent on predicted leaching of imazaquin from soil. Initial imazaquin–soil concentration was 17.8 µmol kg–1. Error bars equal ±1 standard deviation within each fraction of effluent.

View larger version (24K): [in a new window]   Fig. 8. Influence of incubation time on (a) initial phase and (b) second phase of imazaquin desorption from soil as described by Elovich model. Initial imazaquin–soil concentration was 17.8 µmol kg–1. Flow rate for all treatments was 1.0 mL min–1. Initial phase volume was 50 mL, after which flow was stopped for 24 h. Second desorption phase included the subsequent 15 mL of effluent. Regression slopes are different at a 0.05 level of significance when indicated by a or b.

View larger version (27K): [in a new window]   Fig. 9. Influence of (a) time and (b) effluent volume on leaching of imazaquin from soil as described by Elovich kinetics. Initial imazaquin–soil concentration was 17.8 µmol kg–1 with the 1.0 mL min–1 flow rate and 20.0 µmol kg–1 in the 0.67 and 0.33 mL min–1 flow rates. All treatments were incubated for 72 h before desorption. Regression slopes are different at a 0.05 level of significance when indicated by a or b.

View larger version (26K): [in a new window]   Fig. 10. Influence of (a) time and (b) effluent volume on second phase leaching of imazaquin from soil as described by Elovich kinetics. Initial imazaquin–soil concentration was 17.8 µmol kg–1. All treatments were incubated for 72 h before desorption. Regression slopes are different at a 0.05 level of significance when indicated by a or b.