Study On The Effect And Key Parameters Of Water And Salt Discharge By Subsurface Pipe Under Drip Irrigation Farmland

The traditional subsurface pipe was buried below the groundwater level to control the groundwater level,adjust the soil moisture and reduce soil salinity.Most of soil water is unsaturated in the drip irrigation farmland,how to design the shallow subsurface pipe drainage design parameters lack of theoretical basis and experimental verification.In this paper,the relationship between drainage effect and soil moisture condition under unsaturated conditions was analyzed by soil column experiment.The dripper discharge and the subsurface pipe buried depth were selected as the main design parameters.The influence of the dripper discharge and the subsurface pipe buried depth on the drainage effect of the subsurface pipe was analyzed by the soil tank test.The soil water and salt transport mechanism and suitable design parameters were established.Two-dimensional soil water and salt transport model was established.In the different dripper discharge and buried depth,the soil moisture and salinity distribution of horizontal direction and vertical direction were simulated using HYDRUS-2D software.In this paper,a filter layer laying method for improving the drainage effect of drip irrigation in farmland was obtained,and the subsequent test was carried out on the basis of it.The main conclusions as follows:1.The subsurface pipe is the interface between the soil and the atmosphere,and the soil is affected by hysteresis when it is dehydrated.Subsurface drainage under drip irrigation is unsaturated soil drainage,and the soil moisture content is close to the field water holding capacity.2.When subsurface pipe is surrounded by the filter layer structure,there are continuous matrix potential gradient field in the filter layer,and the water will flow around the subsurface pipe,but not into them.When subsurface pipe is surrounded by the local filter layer structure,it can produce a partial saturation area in the upper part of the subsurface pipe,and the soil moisture flow into the subsurface pipe,realize drainage and salt discharge.3.Under the same amount of irrigation,the greater the dripper discharge,the better the desalination effect.And the larger the dripper discharge,the greater the total drainage salt discharge under the same buried pipe depth.4.In the process of subsurface pipe drainage and salt discharge,the partial saturation area of the filter layer is fluctuating.Pipe drainage when saturated,the water content of the filter layer and its upper soil layer decreases after drained,the displacement decreases,and then the saturated state appears again.