Research On Distributions Of Soil Water And Salt In Ningxia Yellow River Irrigation Area By Field Measurement And Numerical Simulation

Soil salinization problem is seriously threatening the sustainable development of agricultural production,and the problem is especially serious in the Yellow River Diversion irrigation area,where the harvest of many cultivated land is seriously reduced,and cultivate crops even can not be produced.Therefore,the scientific research on soil salinization is not only related to the national food security development strategy,but also of great significance to the healthy development of agriculture in Ningxia.In this thesis,taking the West Main Canal and the Tanglai Canal of Ningxia Yellow River irrigation area as the typical research area,we conducted field sampling for statistical analysis,established a soil unsaturated and saturated seepage mathematical model of analysis of one-dimensional and two-dimensional,set several typical case,and conducted numerical simulation research.The main research contents and relevant conclusions include the following aspects:(1)For the saturated and unsaturated soil moisture motion and solute movement,we established vertical one dimensional and vertical two dimensional mathematical models of unsaturated and saturated soil,and the numerical methods of the model are presented.(2)In the research area along the West Main Canal and Tanglai Canal in Ningxia Yellow River Irrigation area,165 sampling points were set for different soil layers.And the moisture content,salt ion concentration and p H values were measured,and the temporal and spatial distributions of soil salt,water and p H values were analyzed and studied.The spatial distribution of soil moisture content along the coast is uneven,and the West Main Canal is slightly higher than that of the Tanglai Canal.The time distribution of the soit moisture fluctuates greatly.The soil along the West Main Canal and Tanglai Canal is alkaline,and alkalization degree of the surface soil is higher than that of the deep soil.(3)Vertical one dimensional and vertical two dimensional mathematical models of soil water and salt transport are developed,and they are emloyed to simulate the soil transport in the study area.According to the characteristics of soil moisture and salt in the study area,several typical working conditions are designed to conduct the simulations.It can be found that soil structure has a great impact on soil water and salt movement.Different soil structure will affect the time needed for the model to achieve stability,and the change of soil properties will lead to obvious mutations in the soil curve.Continuous evaporation will lead to the upward movement of groundwater carrying salt,and water evaporation increases the surface salt content,showing serious "surface cohesion".Reducing the groundwater level can be used as an important entry point for the improvement of soil salinization.