Influence And Model Of Treated Waste Water Irrigation On Soil Infiltration Characteristics

With the global water shortage,treated waste water（TWW）irrigation has become an important way to solve the shortage of agricultural water.TWW irrigation has several advantages such as saving water resources,high guarantee rate,and increasing crop yield.However,a large amount of suspended solids,organic matter,salt and other substances contained in it enter the soil environment after irrigation,changing the physical and chemical properties and hydraulic properties of the soil.After long-term irrigation soil hydraulic conductivity decreased,and even water repellency appeared.In this study,one-dimensional vertical water head infiltration was used to irrigate hydrophilic and water-repellent soils with five different types of TWW and freshwater（FW）,and the cumulative infiltration,infiltration rate,the wetting front measured data were obtained.The HYDRUS-1D software,the improved Green-Ampt model,and the CTM algorithm were used to simulate the soil water migration process,exploring the applicability of each model to the simulation of soil infiltration process under TWW irrigation.After verification,the accuracies of each model were compared,and the optimal infiltration model under TWW irrigation was selected to provide theoretical support for TWW irrigation to relieve the pressure of agricultural water use.The main research contents of this study were as follows:（1）HYDRUS-1D software could be used to simulate the water movement of hydrophilic and water-repellent soils under TWW irrigation.The simulated values were verified by the measured cumulative infiltration and wetting front data,and the results showed good consistency.After correlation analysis between the simulated value and the measured value,the MAE of the cumulative infiltration of the hydrophilic soil were between0.3～1.9 cm and the R²were between 0.75～0.99.The MAE of the water-repellent soil were between 0.4～1.5 cm and the R²were between 0.75～0.97.The R²of the wetting front of the hydrophilic and water-repellent soils were both greater than 0.95,and the MAE were both less than 2 cm.The correlation analysis between the cumulative infiltration value and the irrigation water quality showed that the simulation effects of HYDRUS-1D under FW irrigation were better than that TWW irrigation.Due to the influence of a large amount of solute in the TWW,the less solute and the better the water quality index,the higher the simulation accuracy of HYDRUS-1D.（2）The improved Green-Ampt model was suitable for simulating water transport in hydrophilic and water-repellent soils under TWW irrigation.The measured infiltration rate and wetting front were used for verification,and the results showed that the simulated and measured values were in good agreement.After correlation analysis between the measured value and the simulated value,the RMSE of the infiltration rate of the hydrophilic soil were less than 0.09 cm min^-1and the MAE were less than 0.05 cm min^-1;the RMSE of the infiltration rate of the water-repellent soil were less than 0.08 cm min^-1except for the oxidation pool treatment,and MAE were all less than or equal to 0.05 cm min^-1;the hydrophilic soil wetting front were all less than 2.50 cm in RMSE and MAE were all less than or equal to 2.05 cm;water-repellent soil wetting front were all less than 1.00 cm in RMSE and MAE were all less than 0.90 cm except for oxidation pool treatment.The correlation analysis of the determined model parameters K_sand S_fwith the irrigation water quality showed that as the water quality deteriorated,the saturated hydraulic conductivity of hydrophilic and water-repellent soils increased.The effect of the increase of suspended solids on the saturated hydraulic conductivity was weaker than that of the organic matter content,salinity and EC on the saturated hydraulic conductivity;the matrix suction S_fwas affected by the soil intake suction and shape coefficient.（3）The characteristic time（CTM）concept had applicability for simulating water transport in hydrophilic and water-repellent soils under TWW irrigation.The measured cumulative infiltration and infiltration rate were used to verify the simulated value,and the results showed that the simulation effect was good.After correlation analysis between the measured value and the simulated value,the absolute value of CRM of the cumulative infiltration for the hydrophilic soil were less than 0.30 and the MAE were less than 1.90 cm;the absolute value of CRM of the cumulative infiltration for water-repellent soil were less than 0.20 and the MAE were less than 0.90 cm.The absolute value of CRM in the hydrophilic soil were all less than 0.45 and the MAE were all less than 0.07 cm min^-1.The absolute value of the CRM in the water-repellent soil were all less than 0.50 and the MAE were all less than or equal to 0.07 cm min^-1.The correlation analysis between the irrigation water quality and the parameter imbibition rate S showed that when the irrigation water quality was the same,the imbibition rate S of the water-repellent soil were all smaller than that of the hydrophilic soil.The rate S was basically lower than that of TWW irrigation.（4）Using the cumulative infiltration as the evaluation index,the simulation effects of the HYDRUS-1D software,the improved Green-Ampt model and the CTM algorithm were compared and analyzed.In general,for the hydrophilic and water-repellent soils,the improved Green-Ampt model had higher simulation accuracy,and the effect of simulating water transport under TWW irrigation was better.In this study,the optimal infiltration model under TWW irrigation was selected,which was beneficial to guide the production of TWW irrigation in water-deficient areas.