Field Experiment And SWAP Model Simulation Of Soil Water And Salt Distribution In Farmland Under The Impact Of Subsurface Drains

Soil salinization and water shortage are main constraints to agricultural development in Hetao Irrigation District(HID)of Inner Mongolia,China.This study was conducted at a typical study area in the YongJi experimental station of China Agricultural University.The field experiment of sunflower growth under the condition of subsurface drainage was carried out.The processes of subsurface drainage,soil water content,salt content,groundwater level,groundwater salinity,crop growth indicators and yield were observed.Then,salt-water dynamic of groundwater and soil in the study area and their main influencing factors were analyzed.On this basis,the SWAP(Soil-water-atmosphere-plant)model is used to simulate the movement of soil water and salt under the condition of subsurface drainage.It provides a theoretical basis for the reasonable layout of local drainage pipe and the prevention and control of soil salinization.The main conclusions are as follows:(1)The water content and salt content of surface soil changed greatly with time.With the increase of soil depth,the water content of each treatment gradually increased and the salt content gradually decreased.During the growth period of 2020,the salt content of topsoil in A,B and C plots decreased by 34.8%,6.8%and 31.9%year on year.The results showed that leaching combined with subsurface drainage can effectively remove the salt in the surface soil,which is conducive to the early growth of crops.(2)According to the water balance analysis,the lateral leakage of the channel in the whole growth period of the experimental area in 2020 is as high as 84.5 mm,accounting for 38.6%of the total rainfall and irrigation.The lateral seepage of canal can not only recharge groundwater,but also affect the movement and distribution of soil water and salt.Therefore,if's necessary to pay attention to the influence of the seepage of canal on the whole experimental area.(3)The results showed that SWAP model can reflected well the change tendency of the measured values at the process of soil water-salt calibration and validation.Through different scenarios simulation,the results showed that under the current condition of the buried pipe layout,if the buried depth of the buried pipe increases by 0.5 m,the cumulative amount of water flux in the 40 cm soil profile increases by 48.2%,and the cumulative amount of salt flux in the 40 cm soil profile increases by 35.8%.Increasing the buried depth of underground pipe has more obvious effect on removing soil salt.Considering the effect of water drainage and salt drainage and crop yield under different buried depths and spacing of underground pipes,the depth of underground pipes is 2.0 m and the spacing of underground pipes is 45 m.(4)Under different irrigation treatments,the plant height,stem thickness,leaf area index and dry matter quality of sunflower was similar with time.Plant height,stem diameter and leaf area index grew faster at budding stage and dry matter weight increased faster at maturity stage.The output in 2020 is higher than that in 2019.The yield in area A,B and C increased by 5.3%,18.2%and 12.0%,respectively.The results showed that leaching combined with subsurface drainage can increase crop yield.