Dissolution and transport of gypsum were measured in columns of gypsiferous soil (25% gypsum). Gypsiferous soil material was treated with fuel oil (FO) and bentonite (Bt) and leached with river water. A model based on convection-dispersion solute transport, the continuity equation, and the first-order kinetic dissolution of gypsum was used to describe the rate of gypsum dissolution in soil in relation with solute transport parameters. Results showed that the application of FO and Bt reduced the solubility of gypsum as indicated by the reduction in dissolution rate coefficient (K). The model described very well the dissolution of gypsum. The reduction in K was associated with the reduction in mass transfer rate coefficient (α). When the value of α was fixed the value of K varied little, no matter what the variation in both dispersion coefficient (D) and average pore water velocity (v). It is concluded that the value of K depends mainly on the specific surface area and sorptivity of the soil.
"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"
Laboratory experiments were carried out to study the effect of biochar addition and gypsum content on some hydrophysical properties and soil quality index. Soil samples with gypsum content (G2) 100, (G3) 150, (G4) 200, (G5) 250 and (G6) 350 g kg-1, were prepared by mixing a surface soil sample for a depth of 0-10 cm with a gypsum content (G1) 60 g kg-1 and a subsurface soil sample from a depth of 60-100 cm with a gypsum content (G7) 443 g kg-1 at the research station of the College of Agriculture / Tikrit University. biochar was imported from the Plantonix company, boichar were mixed with the soil at a ratio of (B0) 0,(B1) 20, (B2) 40,(B3) 60,(B4) 80 g kg -1, then the prepared soil samples were moistened by spraying to within two-thirds of the field capacity, then incubated in open plastic containers with continuous stirring daily for two months for the purpose of homogenization. After the end of the incubation period, the soil samples were air dried and passed through a sieve with 2 mm openings. Mean Weight Diameter (MWD) gave highest values for biochar is 4.68,4.29,4.03,3.75 and 2.57 mm for gypsum levels, respectively. While it was less value for the comparison treatment. While the physical soil quality index gave the highest value when the treatment G4B3 reached 0.045 (good) while it was the lowest value when the treatment G1B2 reached 0.024 (weak or weak).and the results Infiltration were decreased at a content of 60 g kg-1 reaching 1.29 cm. Despite this, it was significantly superior to the comparison treatment, which amounted to 0.97 cm. Then increased significantly with increasing boichar content. They were 0.97, 1.64, 1.54, 1.29 and 1.98 cm for the biochar content of B4–B0, respectively.
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