Chloride and atrazine transport through saturated soil columns

Abstract

A possible contamination of water resources by the application of pesticides is a problem confronting many irrigated areas in arid and semi-arid areas. The best management practices have to be adopted to minimize pesticide transport and leaching under irrigated conditions. Atrazine dissipation in loam and sandy loam soils has been tested in the laboratory using disturbed soil columns under saturated flooding conditions. All the experiments were performed in replicates. The chloride transport was also studied to test its behavior as an inert tracer in both the soils. Atrazine and chloride breakthrough curves were analyzed with the parameter optimization program CXTFIT to determine transport parameters including pore-water velocity (v), retardation coefficient (R), hydrodynamic dispersion coefficient (D), and pulse duration (t o ). The pore-water velocity and pulse duration of the solute were estimated from the experimental conditions and kept constant during the optimization procedure. The results indicated that the R of chloride was not significantly different from 1, indicating that chloride is an inert tracer for the types of soil tested in this study. The average R of atrazine was 4.56 and 3.15 for sandy loam and loam soils, respectively. Results also showed that the hydrodynamic dispersion coefficient was much higher in the case of sandy loam soil compared to the loam soil for the two solutes, thus indicating non-equilibrium transport conditions. In the case of chloride, D increased from 0.4 for the loam soil to 16.2 cm2/min for the sandy loam soil. Similar results were observed in the case of atrazine in which D for the sandy loam soil was 60% higher than that for the loam soil. More atrazine leaching is expected under field conditions due to the presence of soil cracks and macropores.