Document Type : Research Paper
Ph.D. Student, Department of Irrigation and Drainage, Faculty of Water Sciences Engineering, Shahid Chamran University of Ahwaz
Associate Professor, Department of Irrigation and Drainage, College of Agriculture, Shahid Chamran University of Ahwaz.
Assistant Professor, Department of Irrigation and Drainage, College of Agriculture, Shahid Chamran University of Ahwaz
Associate Professor Department of Soil Sciences, College of Agriculture, Shahid Chamran University of Ahwaz.
Nitrogen (N) loss from irrigated cropland, especially in rice paddies, results in low N-use efficiency and groundwater contamination. Soil conditions that increase ammonium and nitrate ion retention alleviate these problems. Clinoptilolite, a naturally occurring zeolite with high ion-exchange capacity, may be used to adsorb ammonium and retard excess leaching of nitrate. The objectives of this research were to determine the effects of different rates of Na-zeolite application (0, 2, 4, 8 and 16 g/kg soil) on pore water velocity and leaching of ammonium and nitrate applied as ammonium nitrate fertilizer to a siltyloam soil at a rate of 350 kg N/ha under saturated conditions similar to that of a rice paddy. The results indicated that Na-zeolite applications of 2, 4 and 8 g/kg soil increase the pore water velocity by 5.0%, 19. 9, 68.0 and 58/6% compared with the control treatment, respectively. The maximum relative concentration (c/co) all treatments for the nitrate breakthrough curve(BTC) occurred at pore volume of about 0.5. When applying 39.1 cm of leaching water, leached nitrate by 86.9%, 66.00% and 48.5% of total applied nitrate at the soil surface with zeolite applications of 2, 4 and 8 g/kg soil, respectively. Although the ammonium discharged from all treatments was negligible(3.95, 3.48, 3.13 and 2.28 percent of total applied ammonium at the soil surface), the statistic analysis indicated significant differences among treatments that received zeolites. The relationship between the hydrodynamic dispersion coefficient (D) of nitrate and pore water velocity (v) was not linear and by increasing zeolite application to the soil, the value of D increased as well.