Experimental And Numerical Simulations On The Hydraulic Properties Of Salinized Soils In Ningxia Yellow River Irrigation Area Under The Action Of Different Improvers

The sustainable development of agricultural production is severely restricted by soil salinization.And the degree of soil salinization in the Ningxia Yellow River Diversion Irrigation Area is relatively higher.For this reason,improve of the soil salinization problem has been the focus of research in agricultural production in irrigation areas.Aiming at the soil salinization problem in the studied area,four typical areas are chosen and then soil improvement tests and indoor soil column experiments have been conducted by using some organic soil improvers,such as cow dung and furfural residue,and inorganic soil improvers,such as desulfurization gypsum and fly ash.One-dimensional(1D)mathematical model of water movement and salt transport and three-dimensional(3D)mathematical model of water movement are developed to simulate the water movement and salt transport in the studied area,and the finite difference method is employed to discrete the control equations.Based on the soil hydraulic parameters of the soil column experiments,numerical simulations are carried out for the water movement and salt transport under different cases.Under different improve schemes,the effect of different factors on water movement and salt tranport in the soil column is investigated.The studied results provide a theoretical and technical basis for preventing soil salinization and secondary salinization in irrigation areas and achieving the purpose of improving saline soils.The main contents are as follows:(1)The analysis of soil bulk density,soil water characteristic curve(SWCC)and saturation permeability coefficient showed that the water holding capacity of the soil after the application of different amendments is better than that of the control group,while the water holding capacity of the organic improvers(cow dung and furfural residue)treatment group is better than that of the inorganic improvers(fly ash and desulfurization gypsum)treatment group.(2)The Van Genuchten(VG)model is used to fit the SWCC,and it is found that the model could well fit the SWCC in this region.Moreover,the soil hydraulic parameters required for simulation are obtained through parameter inversion.(3)For the five improved homogeneous soils,the soil hydraulic gradient is constant,the infiltration line at infiltration of the soil column descends at a conatant speed,and the soil column gradually tended to become wet from the upper and lower parts towards the middle.Under the same infiltration time,the infiltration line advancing rate of furfural slag and cow dung amelioration group is the fastest,fly ash and desulfurized gypsum amelioration group is the faster,and the change rate of blank control group without amendment is the slowest.(4)In the three-dimensional point source infiltration simulation,for two-point source infiltration,the soil amended with the furfural residue and cow dung is more infiltrated than the unamended soil at the same time;for two or three point sources infiltration with different number of point sources,the water intersection surface appeared earlier for three-point source infiltration.