Research On The Transport Of Soil Water And Salt Under The Condition Of One Dimensional And Three Dimensional Infiltration Based On HYDRUS Model

Drip irrigation is a new water-thrift irrigation technique, which has characteristics such as obvious water saving and production. The distribution rule of water and salt in drip irrigation soil is the basis of drip irrigation system design and establishment of irrigation system. And ponding water and infiltration migration regularity is the basis of the point source drip irrigation soil water and salt migration. Usually the studies of soil water and salt migration are outdoor experiments. The outdoor experiment is not only time-consuming, but manpower and financial resources. And the process of the test is easily affected by natural and artificial factors, so as to produce a large error. In recent years, computer science is developing rapidly. Many experts domestic and overseas start to use the theory of unsaturated water movement and solute transport to build a mathematical model, which simulating soil water and salt migration rule. This method is simple, rapid and less disturbed. HYDRUS is the computer software, which simulating water and solute transport and applied more widely. Therefore, this article is to study and simulate water and salt migration regularity in clay loam soil by using HYDRUS software. To obtain and verify the model parameters of the soil water and solute transport on the basis of laboratory tests. To simulate and analyze the effect of soil water and salt migration of one-dimension water ponding infiltration by soil bulk density, seeper depth, and initial water content through the model, as well as the effect of water and salt migration of point source drip irrigation by soil bulk density and dripper discharge. There are the following main conclusions through the analysis of soil water and salt migration rule under different test conditions.(1) Soil moist sharp point of one-dimension water ponding infiltration, cumulative infiltration and moist sharp point on horizontal and vertical direction of the point source drip irrigation all have a power function relationship with the time.(2) One-dimension water ponding infiltration is effected by soil bulk density, seeper depth, and initial water content. Soil infiltration rate and moist sharp point decrease with the increase of density. The greater the soil bulk density, the smaller the average moisture content of the profile. Soil infiltration rate and moist sharp point increase with the increase of seeper depth. The greater the seeper depth, the greater the average moisture content of the profile. The greater the initial water content, the greater moist sharp point and the average moisture content of the profile, but the smaller the soil infiltration rate.(3) Soil bulk density has a significant influence on the distribution of soil salinity in one-dimension water ponding infiltration. In the same initial conditions and boundary conditions, the bulk density is 1.4g/cm3,1.45g/cm3 and 1.5g/cm3,1.55g/cm3. With the increase of bulk density, desalination index, surface desalination rate and maximum salification decreases, and coefficient of salification increases. As the largest bulk salification rate are 210.64%, 156.55%, 110.04%, 156.55%, the largest salification location is 36 cm, 30 cm and26cm, 22 cm.(4) Seeper depth has a smaller influence on the distribution of soil salinity in one-dimension water ponding infiltration, but a great effect when seeper depth is large. In the same initial conditions, with the increase of seeper depth, desalination index, coefficient of salification, surface desalination rate and maximum salification are smaller. As the seeper depth are1 cm, 4cm, 7cm and 10 cm, maximum salification and its depth are 156.55%, 160.95%, 165.09%, 160.95% and 32 cm, 30 cm, 31 cm, 33 cm.(5) Initial water content has a significant influence on the distribution of soil salinity in one-dimension water ponding infiltration. In the same seeper depth of 1cm and bulk density of 1.45g/cm3, initial water content are 0.05cm3/cm3, 0.1cm3/cm3, 0.15cm3/cm3, 0.2cm3/cm3. With the increase of initial water content, coefficient of salification increases and desalination index, surface desalination rate and maximum salification rate decreases. Maximum salification rate and its depth are 132.15%, 100.00%, 73.92%, 100.00% and 43 cm, 46 cm, 48 cm, 49 cm.(6) Soil bulk density and dripper discharge have remarkable effect on the distribution of soil water and salt of three-dimensional point source drip irrigation. The greater the bulk density, the smaller the vertical wetting front and the bigger the horizontal wetting front. The greater the dripper discharge, vertical wetting front is smaller, and the greater the horizontal. The greater the bulk density, the salts in wetted soil volume distributed more uniform. The smaller the coefficient of desalination index, the larger coefficient of salification, and the smaller the maximum salt deposition. The greater the dripper discharge, the smaller the desalination coefficient and the greater the coefficient of salification in the vertical direction. The horizontal direction is in contrast.(7) HYDRUS model can reflect the rule of water and salt movement in the clay loam soil under the condition of drip irrigation well. By the analysis of the sensitivity of model parameters, n had the greatest influence on the simulation results and the residual moisture content of θr had minimal impact. Saturated moisture content θs, α, Ks and αL have some impact on the results of the simulation. HYDRUS software is a simple and effective method to backstep soil hydraulic parameters and solute transport parameters. The estimation data and the measured data can be matched well.