Study On Soil Water And Salt Migration Under Brackish Water Irrigation In The South Bank Of Laizhou Bay

The chain of seawater intrusion and soil salinization is actually the salt migration in the soil and water system.We investigated the ground water and soil in Changyi on the south shore of Laizhou Bay,collected the soil samples for the indoor soil column simulated experiments,and studied the relationships between the soil wetting front and the infiltration of water and time in brackish water under different salinities and different amounts of infiltrating water.Additionally,the distribution characteristics of the contents of soil moisture,ions,and salt were explored and the soil desalting efficiency under different irrigation orders were analyzed.Moreover,the fresh water and the brackish water prepared by the field experiments were employed to irrigate the soil by different irrigation methods with high-density electrical instrument.The differences of brackish water irrigation from fresh water irrigation on the transport of soil water and salt,as well as the transport characteristics of soil water and salt under different irrigation sequences were also studied.This work showed that:（1）The contents of Cl^-,SO₄^2-,and Na⁺in the ground water in Changyi aera were relatively high.The cation content decreases as follows Na⁺>Mg²⁺>Ca²⁺>K⁺,while the anion content decreases from C1^–to SO₄^2-and further to HCO₃^-,thus the ground water mainly contains Na Cl and belongs to 49-B type.（2）In the range of 0-90 cm,the soil samples demonstrate that the study aera mainly contains sulfate and chloride.The ion contents decrease with the increase of soil depth,which was consistent with the overall change of soil salt content previously reported.（3）Under different salinity,brackish water infiltrates.The higher the salinity of the infiltration water,the more progress of the wet front.With the change of salinity of the infiltration water,the soil as a whole is in the state of desalination,leading the desalination for the upper layer and the salt accumulation for the bottom.For the infiltration of brackish water at 3g/l under different irrigation rates,the wetting front has a linear relationship with the infiltration of brackish water and a power function with the infiltration time.The moisture content of soil gradually decreases from the surface to the wetting peak and increases with the progress of wetting front.（4）both freshwater irrigation and saltwater irrigation can desalinate the upper layer of the soil,but saltwater irrigation can increase the overall salinity of the soil while desalting,and both irrigation methods can increase the moisture content of the soil;Irrigation of salt water first and fresh water later will desalinate the soil surface and deposit salt in the bottom layer.Irrigating fresh water first and then salt water causes the soil to accumulate salt at the top and desalinate at the bottom.The leaching effect had the same effect on Cl^-and Na⁺in the soil.The results of this paper systematically described the groundwater chemical characteristics and soil salinization in the southern bank of Laizhou bay.Through indoor soil column simulated experiment and the field of high density resistivity method experiment explores the brackish water irrigation and irrigation under the soil water and salt movement characteristics,to explore different brackish water irrigation modes of soil water and salt migration distribution,research results will provide the Laizhou bay underground brine resources reasonable use,the science formulation to provide technical support of crop irrigation system.