In this study, the NH 4 + removal and release from clinoptilolite (Cp) and nitrate removal and release from surfactant-modified zeolite (SMZ) were evaluated. The feasibility of using SMZ in comparison with Cp application to reduce nitrate leaching and enhance crop growth was also investigated. Then LEACHN parameters that would describe the field observations in two treatments of unamended soil lysimeter (control) and Cp-amended lysimeter were determined using SUFI-2 procedure. Millimeter- and nanometer-sized Cp showed 8.16% to 88.42% and 8.44% to 91.5% NH 4 + removal efficiency, respectively, over a wide range of initial NH 4 + concentrations and different Na + concentrations. Nitrate removal efficiency by millimeter- and nanometer-sized SMZ were 26.67% to 82.26% and 37.84% to 85.49%, respectively, over a wide range of initial nitrate concentrations and different Cl - concentrations. Using lysimeters, it was determined that the amount of NO 3 -N leached from SMZ- and Cp-amended lysimeters at the higher application rate (60 gr kg -1 ) was approximately 26 and 22% lower, respectively, than that from the control system. N uptake was significantly greater in Cp-amended than SMZ-amended lysimeters. The estimated values for denitrification rate, distribution coefficient, and soil/solution NO 3 -N nitrification rate were greater in Cp-amended lysimeter compared to control. Key Words: Nitrate leaching, Clinoptilolite zeolite, Surfactant-modified zeolite, Ammonium removal, LEACHN, SUFI-2.
