The Experiment Research On The Soil Moisture Dynamic Change Of Soil Water Movement Under Subsurface Drip Irrigation

Research on soil moisture movement of underground drip irrigation is the premise of the underground drip irrigation design, which means accurate management of practical guidance for drip irrigation. Through laboratory tests on free infiltration of a single-point source and interfered infiltration of double-point source, the paper analyses the influence about soil moisture content, shape and range of wetting , in connection with the different drip discharge, irrigation, spacing and other factors. The main conclusions is followed:(1) Water Infiltration can be divided into two stages: The first is the stage of matric suction, the wetting soil is regular ellipsoid; the second is the stage of water gravity, the wetting body irregular; The wetting front on all directions with time follows the exponential function equation.(2) Under the same wetted radius, the moisture content of vertical downwards is bigger than horizontal direction, the moisture content of vertical upwards is smallest; The relation between wetted radius and infiltration duration conforms well power function. The isoline of soil moisture content is similarity to the shape of wetted soil, take the dripper as circle center, soil moisture decreases with distance; under the same irrigation quantity, the soil moisture decreases faster under small drip discharge.(3) When the drip discharge are in low rate, the relation between wetted volume and irrigation quantity conforms well linear function; the average volume of moisture content maintain a certain value increment during Infiltration; when the drip discharge is 0.8L/h, the average volume of moisture content becomes disturbance at this inflection point, and the vertical depth of wetting can be up to 50cm, the width of the level of moisture up to 60cm, the aspect ratio of 5:6 and the water content increment can reach to 39%, so 0.7L/h can be used as guidance for drip irrigation.(4) Interfered infiltration can be divided into two stages: the first is free infiltration stage, there is no interfered infiltration; the second is interfered infiltration stage, two wetted soil combined into one wetted soil, the wetted volume become bigger; the wetting front of vertical downwards is bigger than vertical upwards at the Interference interface, and which has no relation with drip discharge.(5) The redistribution of wetted soil made the increase of wetted volume and decreased of average volume; which has possibility effect on corps; when the irrigation quantity was increased to 16L and drip discharge over 1L/h,the wet range exceed 40cm.(6) At the same dripper spacing, the drip discharge is bigger and the interfered occurred earlier; when the interfered occurred, the volume of soil wetting front changed obviously, the average volume of moisture content increased bigger, but it also a constant value.(7) After redistribution of interfered infiltration, the shape of wetting is irregular ellipsoid, and become bigger with the drip discharge. At the end of 24h after Irrigation, the wetted volume increased with dripper spacing increase; when dripper spacing is big, the volumetric water content is small; then it become smaller obviously after distribution, especially a smaller dripper spacing. In case of a same dripper spacing, drip discharge bigger and the decrease rate faster.