Study On The Effect Of Salt Control In The Subsurface Drainage Project Along The Yellow River Irrigation Area In Inner Mongolia

The irrigation area along the Yellow River in Inner Mongolia is an important commercial grain base in my country.Soil salinization is a key factor restricting the discharge technology is an important means to prevent salinization.Due to the serious slope collapse of the open ditch in the irrigation area,resulting in poor drainage,the application of concealed drainage technology has become a trend.In addition,concealed pipe drainage is one of the important means for the autonomous region to implement the strategy of "reform salt,increase grass,and promote grazing".However,the natural conditions and production conditions in different salinization areas are not the same,and the soil improvement effect after the arrangement of the concealed pipe is unknown.Therefore,this paper conducted a two-year monitoring of the drainage and salt control effect in four typical subsurface drainage project deployment areas in the upper reaches of the Yellow River Irrigation District in Inner Mongolia,Wuyuan County in the middle reaches,Wuyuan County,Wulateqian Banner,and Dalate Banner in the lower reaches.The correlation analysis of the main factors affecting soil EC was made through field experiments and Pearson and Spearman analysis methods.The main research results are as follows:(1)The moisture content of the surface soil is affected by irrigation,rainfall and evaporation,and changes drastically;the soil moisture content of the cultivated layer and the deep layer is relatively stable.With the arrival of the rainy season and the irrigation period,the soil moisture content is positively correlated with the irrigation volume and rainfall.The soil moisture content increases with the depth of the soil layer in the vertical direction.Affected by factors such as soil texture and irrigation system in the monitoring area,the electrical conductivity of the surface soil has a large variation.With the arrival of the irrigation period and the rainy season,the electrical conductivity of the soil surface has a significant downward trend.From a vertical perspective,after the concealed pipe discharges the salinity of the irrigation and rainfall in time,the soil electrical conductivity decreases with the increase of the soil depth.(2)Concealed pipe drainage can effectively control the buried depth of groundwater.In 2020,the buried depth of young,moderate and severe saline-alkali soils in Zone B has increased by 9.85,8.32 and 7cm respectively compared with 2019.Monitoring shows that the buried depth of groundwater has a linear relationship with soil conductivity.The greater the buried depth of groundwater,the lower the conductivity of soil.Controlling the buried depth of groundwater through concealed pipe drainage plays an important role in improving salinized soil and growing crops.(3)The amount of irrigation water has a significant impact on the salt control effect of subsurface pipe drainage.In 2019,the average desalination rate of young,moderate and severe B area saline-alkali land was 63.1%,64.5% and 38.4%respectively,and in 2020 it was 36.7%,55.7% and 41.2%,the desalination rate of mild and moderate saline-alkali land decreased compared with 2019,and the desalination rate of severe saline-alkali land was increased in 2020 compared with 2019 due to the serious salt accumulation.The salt content of irrigation is limited,but the desalination rate is reduced.After irrigation,the overall trend of the cumulative drainage of the concealed pipe is the same.Take the cumulative drainage of the spring irrigation in the young saline-alkali soil in 2019 as an example.After irrigation,the drainage rate of the concealed pipe is 1mm/d.Ten days after irrigation,the maximum drainage rate of the concealed pipe is 5mm/d.The final stage is 1mm/d,showing a rapid rise first,then a slow rise,and finally maintain the same pattern.The overall trend of concealed pipe drainage salinity in the monitoring area first rises and then declines.Taking the spring irrigation of the young saline-alkali soil in 2019 as an example,the drainage salinity first increases from 5.5g/L to then decreases with the passage of irrigation time 3.2g/L.(4)Using Pearson correlation analysis and Spearman correlation analysis to analyze the soil physical and chemical properties,concealed pipe parameters,groundwater depth and other data and soil conductivity in monitoring areas with more influencing factors,and found that Spearman correlation analysis is more suitable for analysis The main influencing factors of soil EC in the monitoring area.