Monitoring And Benefit Evaluation Of The Improvement Effect Of Downstream Underground Subsurface Pipe Drainage Project In Hetao Irrigation Area,Inner Mongolia

Soil salinization is an important bottleneck restricting the high-quality development of agriculture in Hetao Irrigation Areas,In order to promote the high-quality,sustainable and healthy development of agriculture in the Hetao Irrigation area.In this paper,the field experiment area of the subsurface pipe drainage in the Hongwei Field Water-saving Irrigation Experimental Demonstration Park in Wulateqian Banner,the westernmost Sanhu River Irrigation Basin of the Hetao Irrigation Area is taken as the research object.According to the distribution of drainage ditches and roads in the field and the degree of soil salinization,the subsurface pipe control area is divided into mild,moderate and severe salinized soil areas,At the same time,set no subsurface pipe area as a control.Monitoring the soil and water environment,economic and social benefits of farmland under the condition of subsurface pipe drainage.And use the combination weighting method and the TOPSIS model to calculate the comprehensive benefit evaluation score of the subsurface pipe drainage project,To clarify the comprehensive benefit effects of the subsurface pipe drainage project on different degrees of salinized soil,it aims to provide a certain reference for the popularization,application and benefit evaluation of the subsurface pipe drainage project in the Hetao Irrigation Area.The main research results obtained are as follows:(1)The soil moisture content of the 0～100cm profile shows that it gradually increases with the depth of the soil layer,and the variation range is between 13.78% and32.26%.The soil moisture content of each area controlled by the subsurface pipe is lower than that of the area without the subsurface pipe.The reduction range of soil salinity in the 0～40cm soil layer in each area controlled by the subsurface pipe is more than 1.5g/kg,and the reduction range of the soil salinity in the 40～100cm soil layer is between0.84g/kg～2.74g/kg.Among them,the decrease of soil salinity in the severely salinized area is greater than that in other areas,indicating that the subsurface pipe drainage project can reduce the soil salinity and the greater the degree of salinization,the greater the decrease.(2)The salinity of groundwater in the subsurface pipe control area shows a decreasing trend,and the reduction range is between 0.37g/kg and 1.13g/kg.Among them,the salinity reduction effect of groundwater in the heavily salinized area is the best,while the salinity of groundwater in the area without subsurface pipe increases slightly.The subsurface drainage project has a certain promotion effect on soil nutrients,However,some nutrients are lost with irrigation water,lead to the decrease of nutrient content in the soil plough layer in the subsurface pipe control area,the increase of soil nutrient content in the area without subsurface pipe concentrated between 3% and 8%.(3)The increase in yield in all areas controlled by subsurface pipes is higher than that in areas without subsurface pipes,with an increase of more than 4.59% in corn production and more than 1.71% in sunflower production.Affected by market price fluctuations,in 2021,compared with 2020,some areas will increase production but not increase income;Due to the different factors such as the area and construction conditions of each area controlled by the subsurface pipe,there are also certain differences in the investment per unit area.(4)The area of arable land can be increased after the implementation of the subsurface pipe drainage project,The newly added cultivated land accounts for about8.46% of the total area of the study area.It is expected that the whole area of the study area will be cultivated within two years.In 2020 and 2021,the satisfaction score of residents in the subsurface pipe control area is more than 1.2 higher than that in the no subsurface pipe area,In 2021,it will increase by 5.06%～11.11% compared with 2020.(5)The comprehensive benefit evaluation results of the subsurface pipe drainage project based on the combined weighting method and the TOPSIS model show that,in2020 and 2021,the trend of comprehensive benefit evaluation scores in each district is consistent,Severe salinization area > mild salinization area > moderate salinization area >no subsurface pipe area.Compared with the areas without subsurface pipe,the comprehensive benefit score increases of all areas under the control of subsurface pipe are all above 0.167.And the heavier the soil salinization degree,the higher the comprehensive benefit score.