Coupled Transport of Nitrate and Chloride in Soil Columns.

The excessive use of fertilizers containing nitrate and chloride is one of the causes for groundwater pollution. The purposes of this research are to: 1) study the fate and transport of nitrate and chloride in soil columns under different pore water velocities (0.1, 0.5, 1.0 and 1.5 cm/hr) and 2) study the anion exclusion process and compare the anion exclusion for nitrate and chloride. The behavior of nitrate and chloride was studied in 10 cm long-columns repacked with a sandy soil and loam soil. A pulse of 200 mL of 0.1 M Ca(NO₃)₂, 0.1 M CaCl₂ and 0.1 M Ca(NO₃)₂/CaCl₂ solutions was applied to the soil columns. The chloride and nitrate concentration in the effluent solution were measured and CXTFIT program was used to determine the equilibrium and non-equilibrium transport parameters including retardation factor (R), dispersion coefficient (D), anion exclusion volume (θ_ex) mobile and immobile fractions. Initial results have shown that sand has more adsorption for the solute than loam for the lowest pore water velocity. There was no significant difference in the behavior of chloride and nitrate with different pore water velocities. Further experiments are required to confirm the initial results and evaluate the effect of pore water velocity on the θ_ex. This research will provide information to understand the behavior of nitrate and chloride in the root zone. The results from this research may be applied to reduce the leaching of chloride and nitrate in soils with a texture similar to those used in this study.