Experiment And Simulation Study On The Law Of Soil Water Movement Under The Condition Of Membrane-Regulated Subsurface Drip Irrigation

Through the indoor experiment design and implementation of membrane-regulated subsurface drip irrigation,and the introduction of HYDRUS-2D software to study the numerical simulation of membrane-regulated subsurface drip irrigation,It is of great significance for the development and popularization of membrane-regulated subsurface drip irrigation in the later stage.In this paper,the movement of wetting front controlled by membrane in moist irrigation is analyzed through laboratory experiments,at the same time,various soil hydraulic characteristic parameters of HYDRUS-2D were calibrated and verified by indoor tests,and through the HYDRUS-2D software,the influence of membrane specifications and initial moisture content on the soil water movement of membrane-regulated subsurface drip irrigation was further explored..After experiments and numerical simulation experiments,the main results obtained are as follows:(1)The membrane-regulated subsurface drip irrigation migration stage is divided into the inter-film movement,the super-membrane movement phase,the sub-membrane movement phase and the intersection movement phase;In the second stage,the shape of the wetted body is an upper hemisphere,and the cross-sectional shape of the wetted body is the upper semicircle with the center of the circle at the boundary of the upper membrane,In the third stage,the cross section of the submembrane part will appear an irregular lower semicircle with the lower membrane boundary as the center,and the cochlear shape will appear after the irrigation is completed.In this experiment,the relationship between the migration distance of wetting front under membrane-regulated subsurface drip irrigation is vertical upward>horizontal right>vertical downward;For membrane-regulated irrigation,when the irrgation volume is the same,as the flow increases in the horizontal right and vertical downward directions,the migration rate of the wetting front and the final migration distance after the final irrigation show an increasing trend.,In the vertical upward direction,as the flow rate increases,the migration distance of the wet front shows a decreasing trend.(2)After calibrating and verifying the soil hydraulic characteristic parameters in HYDRUS-2D,the relative error between the simulated and measured moisture content of each observation point is basically within 10%,the root-mean-square error of the simulated value of the wetting front migration distance and the measured value is also within a reasonable range,which proves the feasibility of HYDRUS-2D for the simulation of membrane-controlled irrigation and irrigation.(3)In the same flow and irrigation time,water amount above the upper film was larger than that under the lower film in the four film treatments;when the upper film was the smallest,the vertical upward migration distance of the wet front was the largest,which was 29.04 cm,and the upper film water amount accounted for 79.57%,with the largest percentage in the four membrane treatments;and the vertical downward migration distance of the wet front was the smallest,and the water amount under the film was also the smallest;and when the upper film is at its maximum,the vertical migration distance of wetting front was the smallest,which was 23.03 cm,and the water amount on the film was also the smallest,with a percentage of 66.33%;but the vertical migration distance of wetting front was the largest,and the water amount under the film was also the largest.The results indicated that the change of membrane size could regulate the water content of the upper and lower membrane,and the decrease of the upper membrane could effectively reduce the water content of the submembrane leakage.In the process of the four film specifications processing from the distance of 0 cm,10 cm,20 cm and 30 cm from the dripper,the water content of the same observation points on the four membrane specifications within 20 cm is basically the membrane specification 40×20 cm>40×25 cm>40×30 cm>40×35 cm,and the opposite state will appear at 30 cm,membrane specifications are 40×35 cm>40×30 cm>40×25 cm>40×20 cm.There was an obvious power function relationship between the migration distance of wetting front and time in the vertically upward and horizontally to the right of the membrane-regulated subsurface drip irrigation,but an obvious linear relation between the migration distance of wetting front and time in the vertically downward.(4)In the same irrigation time,the water transport distance of the soil with high initial moisture content is greater than that of the soil with low initial moisture content in three directions;at the same irrigation time,the soil water wet front with high initial water content moves faster than the soil water with low initial water content,and the soil water with high initial water content must first move to the same location or the same section in the soil,it is consistent with the law of traditional underground drip irrigation.The water content of each observation point of membrane-regulated subsurface drip irrigation is greatly affected by the initial water content at the position far away from the emitter water surface,while the soil water content at the position near the emitter water surface will eventually approach the saturated water content,so the initial water content has little effect on the soil water content near the emitter water surface after irrigation.In the same flow rate and irrigation time,with the increase of initial water content,the percentage of water on the film showed a decreasing trend,while the percentage of water under the film showed an increasing trend.