The Numerical Simulation For Farmland Soil Water And Salt Migration With Vertical Well Drainage

Soil salinization has been a worldwide problem.With the continuous increase of the world's population,the improvement and prevention of saline-alkali land becomes more and more important as a reserve farmland.In China,the area of saline-alkali land in Xinjiang accounts for 22.01%,and the area of salinealkali land in southern Xinjiang is more extensive than that in northern Xinjiang.The wide distribution of saline-alkali land in southern Xinjiang is caused by the salt content of the parent soil,high groundwater level and unreasonable irrigation methods.Water conservancy project improvement measures is the key of salinealkali land management measures,including shaft drainage measures can reduce the underground water level,a wide range applicable to high underground water level and wide distribution area of saline-alkali areas.In this paper,we carried out an experimental study in the 224 regiment of Hotan District,Xinjiang.The 224 regiment is located in the northern part of the Kunlun Mountains,and the Ackland dry area on the junction of PI Shan county and Moyu county is located at the southern edge of the Taklimakan Desert.In the 224 regiment,the groundwater level is high and the soil back to salt is serious.The farmland is arranged in the shaft to drain the salt.However,because the shaft layout is not reasonable,the groundwater level can not be reduced effectively for a long time,causing the groundwater level to return and the soil surface area salt is serious.In this paper,the soil salt content in 1m soil was measured at different distances in the vertical well drainage area,and the soil salinity distribution characteristics and desalination efficiency were analyzed on the basis of field measured data.In this paper,the soil salt content in 1m soil was measured at different distances in the vertical well drainage area,and the soil salinity distribution characteristics and desalination efficiency were analyzed on the basis of field measured data.Based on the above research ideas,we get the following conclusions through research.(1)In the early stage of irrigation,the salt accumulation of soil surface(0~20cm)was obvious in 1m soil.After the irrigation,the salintiy of the surface soil decreased obviously,and the accumulation of salt appeared in the soil layer of 40~60cm and 60~80cm.(2)Drainage shaft can effectively reduce soil salinity,and soil salinity is desalinated in full section,and salinity in 1m soil decreases.During the irrigation period,the decrease of soil salinity is faster and the distance from the drainage shaft is closer.The faster the soil desalination rate is,the farther away from the drainage shaft,the slower the soil desalination rate is.In the early period of irrigation,the soil desalination rate in April 2017 was 27%,22%,17%,10%,5%,3%,3% and 2% compared with the April 2016 sampling period.After the irrigation,the soil desalination rate was 33%,36%,36%,22%,15%,5%,September 2017,and September 2017 compared with September 2016.The results showed that the total salt content of the whole soil increased significantly with the increase of drainage time of the shaft,and the effect of saline alkali soil improvement was obvious.(3)The distance of desalination at 20,40,60 and 80 m of vertical shaft is larger than that of 100 m.It shows that the nearer the drainage shaft is,the greater the desalination degree is,the faster the desalination rate is,the farther from the drainage shaft,the less the desalination degree is,the slower the desalination rate is.(4)Based on the physical parameters of soil sampling,the HYDRUS model,which is constructed after the calibration and test of parameters,can reasonably reflect the water and salt migration in the soil section layer of the vertical well drainage condition.(5)The drainage shaft can effectively reduce the groundwater level,and the deeper water level descending funnel can be formed in the influence range of the water well.The closer the vertical shaft is,the greater the depth of the groundwater level is.(6)With the growth of the life of the shaft,the soil salt content in the soil of the test area is also decreasing year by year,but the effect of soil desalting is different from the distance from the well distance.The soil salinity in the 20,40,60 and 80 m of the well was reduced significantly,and the soil desalination was slow at the distance from the well to the well 100 m,and the soil did not desalination or even the salt accumulation after more than 100 m.