Soil Water And Salt Transport And Numerical Simulation Of Saline Soil And Brackish Water Infiltration

China is facing problems of water scarcity and soil salinization,which seriously hinder crop growth and sustainable agricultural development,and developing brackish water irrigation and saline soil cultivation has gradually become effective agricultural measures.The salt in agricultural soil can be divided into irrigation water（brackish water/saline water irrigation）and the soil itself（saline soil）.The impact of brackish water and saline soil on soil physical properties,water movement and the similarity of their influencing mechanisms,has become a problem to explore.The study set up irrigation water sources and saline soils with different solutes and concentrations,and used centrifuge method to measure soil water characteristic curve and shrinkage characteristic curve.The study used one-dimensional constant water head infiltration test to observe soil water and salt transportation and redistribution characteristics,and then used Hydrus-1D model to simulate water transportation and salt distribution.The study aimed to explore the effects of brackish water irrigation and saline soil infiltration in saline areas on soil water characteristic curves and water-salt movement,and to provide measured data and theoretical basis for formulating scientific irrigation plans in saline areas.The main research results are obtained as follows:（1）The soil water characteristic curve indicates that within a certain range of suction and concentration,salt could improve soil’s water holding capacity,and the conductive pores of saline soil or brackish water samples are higher than those of no-saline soil.Under the same suction conditions,the linear shrinkage of brackish water samples is lower than that of no-saline soil samples,indicating that brackish water has an inhibitory effect on soil shrinkage.（2）The one-dimensional constant water head infiltration test of salt water infiltration（brackish water group）shows that the power function is suitable for describing the change relationship of wetting front movement with time.Kostiakov model is more suitable than Philip model for describing the cumulative infiltration curve with time.Infiltration solutions containing Mg Cl₂ could hinder soil water infiltration and reduce cumulative infiltration.At the end of infiltration,the surface soil water content in the soil profile is significantly higher than which in the deep.The deep soil water content reduced in wave with the increase in the soil depth,while the deep soil water content changes less and the water distribution is relatively uniform.The infiltration solution concentration higher,the soil salt accumulation more serious.The soil salt content is decreased with the increase in the soil depth,and cation is more easily leached than anion.（3）The one-dimensional constant water head infiltration test of saline soil（saline soil group）shows that the power function is suitable for describing the variation of wetting front movement with time.Kostiakov model is more suitable than Philip model for describing the cumulative infiltration curve with time.At the end of infiltration,the surface water content of the soil profile is the highest,and the soil water content decreases with the increase of the soil depth.The initial salt content of the soil higher,the salt accumulation more serious.After the infiltration of distilled water into saline soil,the result shows that the surface salt content is low,the salt concentration inside the soil continuously increases with the soil depth,and cation is more easily leached than anion.The infiltration rate of saline soil is faster than that no-saline soil.Compared with Mg²⁺,the desalination effect of Na⁺saline soil after being washed with distilled water is more significant.（4）Using Hydrus-1D to simulate one-dimensional constant water head infiltration tests has high simulation accuracy and relatively accurate results.For water transport simulation,R²>0.89 for salt water infiltration treatment and R²>0.86 for saline soil infiltration treatment;For concentration transport simulation,both salt water infiltration treatment and saline soil infiltration treatment showed R²>0.78.From this,it can be seen that the Hydrus-1D model is more accurate in water transport simulation than in salt transport,simulation,and the simulation of saline infiltration is more accurate than that of saline soil infiltration.