Study On Characteristics Of Soil Water And Salt Transport In Typical Depressions Of Degraded Grassland In Western Jilin

Soil salinization is a hot issue in the world today.The Songnen Plain is one of the three major soda saline-alkali soils in the world.In recent years,due to the superimposition of natural factors and human irrational development and utilization factors,the originally fragile ecosystem The stability and resistance to adversity have become worse,grassland degradation,soil desertification,salinization,and production capacity decline,restricting the sustainable development of regional agriculture and animal husbandry,and also endangering the food production and safety of large granaries in Northeast China.It has been proved that the salt movement in saline-alkaline soil follows the law of"the salt follows the water,and the water leaves the salt and stays".The study of water and salt transport in soda saline-alkaline soil has attracted much attention.Generally,in a large terrain,the water movement on the surface flows from highlands to depressions,and salt also accumulates with water to low-lying places,but in the microscopic scale,the height difference is small.Changes,the intensity of sunlight and the influence of wind will also affect the intensity of water evaporation on the surface of the soil,resulting in changes in the amount of salt accumulation.This paper takes a typical depression on the degraded grassland in Xishilipu,Lesheng Township,Anguang Town,Da’an City,West Jilin Province as the research object,and studies the bulk density,texture,p H,EC,and soluble salt of soil profiles at different heights in the micro-topography.The characteristics of water and salt transport in different seasons in the same year and the water characteristic curve,combined with the Van-Genuchten（VG）model to fit the measured data and model simulation data of the soil moisture in each layer of the profile.The study of salt transport provides basic reference materials,and provides a scientific basis for the development and utilization of saline-alkali degraded grasslands.The main findings are as follows:（1）Through field investigation,soil sample collection and indoor experiment,the soil particle composition,bulk density,p H,EC,water content,soluble salt and main salt segregants(K⁺,Na⁺,HCO₃^-,CO₃^2-)and other indicators were analyzed and determined.According to the international system classification,the types of soil texture are divided.The depressions are dominated by silty loam,accounting for more than 85%of the total number of samples.In terms of spatial distribution in the micro-domain,with the increase of terrain height,the change trend of soil bulk density and soil water content is similar,the variation coefficient of soil bulk density is small,and the variability decreases with the deepening of soil depth;research More than 80%of the sampling points in the area have soil p H>9.0,which is a strong alkaline soil;the spatial distribution of soil p H,EC and soluble salt content are similar,showing a trend of first decreasing and then increasing,and the phenomenon of surface accumulation of soluble salt is significant.（2）On the time scale,the change of soil water content and soluble salt content in depressions was higher in September than in October and higher in June,and the changes in major salt segregants were similar.The higher the terrain and the greater the slope,the soluble salt content of the soil increases and the water content decreases.From June to September,K⁺,Na⁺,CO₃^2-,HCO₃^-increased by 48.41%,20.95%,84.21%,68.34%.Salt comes with water,and the salt shifts upwards during the salt-returning season.The surface accumulation of salt is strong,and the surface layer of the soil increases by 52.51%compared with the lower part of the soil.There was a negative correlation between soil water and salt（P<0.05）.（3）In the longitudinal section,soil water content,p H,EC,and soluble salt content change in the same trend with soil depth,showing a trend of first increasing and then decreasing.The salinization of the soil profile from 0～40 cm is relatively serious;the soil bulk density is in the soil Increase in the lower part.The linear relationship between soil p H and EC is more obvious（4）The pressure film meter method was used to measure the soil water content under different soil water suction,and combined with the soil physical and chemical properties,the parameters of the soil water characteristic curve were obtained.The saturated water content and residual water content of different soil depths in different sections are different.Changes in topographical factors have a greater impact on residual water content.The maximum values of residual water content and saturated water content of different sections of soil basically appear in the section 40～80 cm.The residual water content first increases and then decreases as the soil deepens,and the saturated water content is in the soil.The lower part is relatively stable.The flatter the terrain,the greater the gap between the scale parametersαof the soil layers that reflect the soil aeration index,but the higher the terrain of the same soil layer,the more stableαis.As the water suction increases,the soil moisture characteristic curve has a changing trend from a sharp decrease to a slow decrease and then to stabilize.（5）From the coefficient of determination R²and the root mean square error RMSE of the Van-Genuchten（VG）model,it can be seen that the Van-Genuchten（VG）model fits the measured moisture data and the calculated data well,it can more accurately indicate the relationship between soil moisture content and soil matrix potential,and is suitable for analyzing the moisture characteristic curve of lowland profile and determining the distribution of pores in the soil layer.However,the upper part of the soil profile will be affected by meteorological factors,and there will be a certain deviation,The lower part of the soil has a better fitting effect.