Study On The Effect Of Soil And Water Environment And Optimization Of Key Technical Parameters Under Subsurface Drainage

Due to the unique hydrogeological conditions,soil salinization is more serious in Hetao Irrigation Area,How to prevent and control soil salinization is the key problem for healthy development of irrigated areas.As an effective engineering measure to improve and control salinization,subsurface drainage has been gradually introduced and applied in irrigated areas in recent years.The selection of subsurface pipe outsourcing materials is the key to ensure the long-term good operation,and the buried depth and distance of the subsurface drainage are important design parameters of the subsurface drainage engineering,which affect the drainage and salt removal efficiency of the subsurface drainage in the actual operation process.Based on the results of laboratory experiments,two kinds of buried pipe depth were set in the field:buried depth of 80 cm and 120 cm,(buried depth spacing is 20m),and five kinds of outsourced filter material processing:Sand filter material,68g/m~2geotextile,90g/m~2geotextile,68g/m~2geotextile+sand filter material and no outsourcing filter material,with local conventional open ditch drainage as the control.Field experiments were carried out to study the characteristics of soil and water environment and crop growth and change under the conditions of different buried depths of subsurface drainage and external filter materials.The practical application effect of different external filter materials of subsurface drainage was explored and optimized.Based on the field measured data,the layout parameters of subsurface drainage system were simulated and optimized using the HYDRUS-2D model.The specific research results are as follows:(1)Compared with the control treatment,the average soil moisture content of each buried pipe treatment decreased by 3.5%,and the average soil moisture content of 80 cm treatment decreased by 1.4%compared with 120 cm treatment.The buried drainage drainage system could significantly improve the soil desalinization effect,and the soil desalinization amount of buried drainage treatment was significantly higher than that of control treatment(P<0.05),and the soil desalinization effect of buried pipe 120 cm treatment was 17.8%higher than that of buried drainage 80 cm treatment on average.Different outsourcing filter material treatment had no significant effect on soil moisture content and salt content.Subsurface drainage treatment of soil organic matter,total nitrogen and phosphorus content than control treatment increased by 27.8%,11.0%and 13.2%on average,and available potassium content declined 11.7%,said subsurface drainage measures can promote improvement of soil fertility,but also causes in the process of water in soil nutrient loss,the late should establish reasonable system of irrigation fertilization.Subsurface drainage treatment average drop of 0.31 m for depth of embedment of groundwater,groundwater salinity by an average of 0.64 g/l,deal with significantly lower than control(P<0.05),indicating that embedded subsurface drainage system can regulate groundwater buried depth and reduce groundwater salinity,The buried depth of120 cm is better than that of 80 cm.(2)The maize plant height and leaf area index of buried subsurface drainage treatment were significantly higher than those of control treatment,with an average increase of 18.78%.Among the treatments of buried subsurface drainage,the growth condition of maize with buried depth of 120 cm was better than that with buried depth of 80 cm,with an average increase of 5.21%.In 2020 and 2021,the maize yield was increased by 15.72%and 20.33%,compared with control treatment.The buried depth of subsurface drainage was the main factor affecting maize yield compared with different outsourcing filter material treatment.(3)During the whole observation period,the drainage performance of each subsurface drainage system decreased with the increase of running time,and the drainage performance of the system without outsourcing filter material decreased most significantly.The overall drainage performance of the subsurface drainage system with laid outsourcing filter material was significantly better than that without filter material(P<0.05).When sand filter material was set around the subsurface drainage as the filter layer,the inlet resistance and drainage time of the subsurface drainage could be reduced,the infiltration water could be increased,and the drainage capacity of the subsurface drainage could be improved.The outsourcing filter material processing,sand filter material combined with 68g/m~2geotextile scheme is the best,when the conditions are not met,should also first choose sand filter material as outsourcing material.(4)Based on the simulation results of verified HYDRUS-2D model,considering the desalting rate of soil and the typical depth of the drain at the outlet of the subsurface pipe,the buried depth of the suitable soil in the test area(mainly silty soil and silty loam)should be between 1.5 m and 1.7 m,and the suitable buried distance of the subsurface drainage is 25 m.