Numerical Simulations Of Soil Water Movement Under Indirect Subsurface Drip Irrigation Using HYDRUS-2D Software

Indirect subsurface drip irrigation is a new type of drip irrigation which can effectively reduce surface evaporation and improve water transport efficiency.Mathematical models have become an indispensable tool for studies on soil water movement and agricultural water management.Based on the measured data of soil water content from a lab experiment on indirect subsurface drip irrigation and HYDRUS-2D software,an attempt to infer the soil hydraulic parameters was first carried out,and the reliability of the inferred parameters on predicting soil wet distances was then assessed against a dataset from an independent experiment in this study.Furthermore,a systematic numerical investigation was performed to qualify the effects of different specifications of irrigation devices and soil textures on the distribution of soil water content after irrigation.The simulated soils included sandy loam,clay loam and sandy clay loam.The results from this study could form a scientific basis for designing indirect subsurface drip irrigation.Based on the results obtained from this study,the following conclusions could preliminarily be drawn.The software HYDRUS-2D could reliably be used for deduction of soil hydraulic parameters.The simulated values of soil water content and wetting distance based on the inferred parameters were in good agreement with the measured ones.The simulation results using three inferred parameters were similar with those from four inferred parameters.The calculated Nash-Sutcliffe efficiency coefficient of the model was all greater than 0.71.In the process of indirect subsurface drip irrigation,when the permeable height of the irrigation device was identical,the amount of inflow water of sandy loam was higher than that of clay loam which was in turn greater than that of sandy clay loam.Under the same soil condition,the higher the permeable height of the diversion device,the larger the amount of inflow water.With the increase in irrigation time,the ratios of inflow water of sandy loam to that of clayey loam and to that sandy clay loam increased accordingly.The diameter of water diversion devices had a little effect on the soil water content around the device under the same lateral permeable height.After the redistribution of soil water,the main differences in soil water content was at the edge of the wetting body,and no significant differences were simulated elsewhere.During the irrigation,water diversion devices with the same diameter and different lateral permeable boundary height influenced more greatly on soil water content around the devices and the upwards wetting distance.With the increase in the permeable height,water content in the upper part of the soil on the side of the device gradually increased,but decreased in the lower part of the soil obviously.In the process of soil water redistribution,the increase in the permeable boundary height could relatively increase the average water content in the upper part of the soil.The influence of the diameter of the diversion device on soil moisture content was greater near the bottom than that in other parts.Soil texture had a great influence on downwards wetting distance.The downwards wetting distance was clearly greater in sandy loam than that in other two soils.Under the same permeable boundary height,the ratio of the right wetting distance between different soil textures after irrigation was relatively fixed.