Modeling of NO3 transport in gypsiferous soil under unsaturated flow

"This study was conducted to determine the effect of gypsum content and depth of water head on displacement and transport of nitrate in gypsiferous soil under unsaturated flow conditions. Also, to predict the concentration of nitrate using convection dispersion model (CDE). Soil columns with 63, 97, 142, 180, and 236 g kg-1 of gypsum were prepared. 200 mg L-1 of potassium nitrate were added to the surface of each soil column. The soil columns were leached by intermittent ponding in 2 pore volumes of water. A constant head depth of 0.005, 0.01, and 0.015 m of water was kept on the top of soil column. Samples of effluent were collected for measuring nitrate concentration. The CDE model was analyzed to estimate the best fitting between measured and predicted nitrate concentration, and to calculate dispersion coefficient (D), the retardation factor (R), and Peclet number (P). Results showed that CDE can be used to predict nitrate concentration in soil. Good fit was observed to describe breakthrough curves (BTC's), and predict the transport of nitrates in the leachate of gypsum soil columns. D values increased with the increase in the content of soil gypsum and decrease with increase the water head. Its values ranged between 6.59-9.87 m 2h-1. P and pore water velocity (v) decreased with the increase in soil gypsum content. The R values were less than 1 for all treatments"