Numerical Simulation of Soil Salinity Reduction Caused by Irrigation and Introduction of Sorbent

The soil salinity change caused by the effort of the input of external sorbent and irrigation is numerically investigated using the nonlinear non-stationary equations of filtration and kinetic equations of chemical reaction between the carbonate sodium and calcium sulfate. The numerical integration of the system of equation is realized by means of the Crank-Nicolson implicit numerical scheme for 1 month interval of time and with 1 cm and 1 min spatial and temporary steps, respectively. A method widely used in practice is thus modeled, when gypsum is introduced in the upper 20 cm layer of soil followed by irrigation. It is shown that dissolution of sodium sulfate in water and the infiltration of the obtained solution in the soil is the main mechanism of reduction of sodium in the upper layer of the soil. The obtained liquid phase of sodium sulfate is transferred to the lower layer of soil and the increase of concentration takes place. During a month the content of the solid and liquid phases of sodium sulfate in the upper 1 m layer decreases about 2.5 times and rises 2 times at the levels z > 1.7 m. The calculation shows that the use of gypsum is an additional mechanism for the reduction of the content of salt in the soil. The process of the reduction of salt by means of this procedure intensifies by 10%. The content of sodium sulfate obtained by means of the chemical reaction and infiltration increases more significantly in the upper 20 cm layer than in the lower part of the soil. At the same time, the obtained concentration of sodium sulfate is low and it cannot cause a noticeable degradation of the soil properties. In the upper 20 cm layer in 30 days calcium carbonate with volumetric content exceeds 10 times by the content of sodium sulfate. © 2013 Bull. Georg. Natl. Acad. Sci.