| In order to facilitate users to quickly evaluate the soil wetting pattern of horizontal moistube irrigation,solve the problem that the wetting body is not easy to observe,so as to design an economic and efficient moistube irrigation system.In this paper,based on soil hydrodynamics,the HYDRUS-2D software was used to simulate the soil water movement under different combinations of factors,and qualitative analysis was made on the law and influencing factors of soil wetting body size and the distribution of moisture content under horizontal moistube irrigation.Then,the size of soil wetting body and the relationship between the soil water content of wetting body and the moving distance of wetting front was quantified,and the relevant estimation model was established,and the estimation model was evaluated by the measured data.The main research results are as follows:(1)Origin 2018 is used to analyze the simulation data,and then the migration law of wetted body under different factors is summarized.The results show that the size of soil wetting body is mainly affected by soil texture,pressure head and matric potential,while the line source depth has little effect on it.When the wetting front reaches the surface,the shape of the wetting body in the upper part of the moistube changes from"semi ellipse"to"trapezoid",and the shape of the wetting body in the lower part of the moistube remains"semi ellipse".As irrigation time goes on,the size of wetting body increases,but the rate of outward expansion decreases.The characteristic value of wetted body size follows the rule of vertical downward>horizontal>vertical upward.(2)Based on the simulation data,the power function was used to fit the relationship between wetting body size and irrigation time.The results show that the power function index changed little in the horizontal,vertical upward and vertical downward directions of the moistube,which can be averaged 0.48,0.44 and 0.54,respectively.The power function coefficient and saturated hydraulic conductivity,specific discharge and matric potential conformed to the power function’s relationship.On this basis,the model based on multiple nonlinear regression analysis of soil wetting body size under moistube irrigation was established,which included irrigation time,saturated hydraulic conductivity,specific discharge and matric potential.Statistical indices of the built model were that the average absolute error is not more than 0.90 cm,the root mean square error is not more than 0.95 cm,and the Nash Sutcliffe efficiency is not less than 0.98.(3)Based on the simulation data,the model based on dimensional analysis which can estimate the size of soil wetting body moistube irrigation was established by dimensional analysis andπtheorem.The model was evaluated by experimental data and compared with the first model.The results show that the mean absolute error of the model is between 1.16 cm and 2.10 cm,the root mean square error is between 1.20 cm and 2.46 cm,and the Nash efficiency coefficient is between 0.83and 0.95.This shows that the estimation effect of the model based on dimensional analysis is worse than that of the model based on multiple nonlinear regression analysis.(4)Based on the simulation data,the distribution law of soil water content in wet body was summarized by Origin 2018 and Excel.The results show that,under the premise that the wetting front does not reach the surface,when the initial water content is low,the relationship between the soil water content and the moving distance of the wetting front in the vertical downward,45°downward,horizontal,45°upward and vertical upward directions conforms to quadratic function;when the initial water content is high,the relationship between the soil water content and the moving distance of the wetting front in the five directions conforms to linear function department.This rule is not affected by the irrigation time,but with the soil texture from fine to coarse,the relationship between the soil water content in all directions and the moving distance of the wetting front no longer strictly conforms to the quadratic function,and after the wetting front reaches the surface,the water content in the upward direction of the wetting body will redistribute,which is no longer applicable.Based on the summarized rules,the prediction model of soil water content distribution in horizontal moistube irrigation was established,and the model was evaluated with experimental data.The results show that the MAE,RMSE and NSE are 0.010～0.023 cm~3/cm~3,0.016～0.033 cm~3/cm~3and 0.90～0.99,respectively.The model has good estimation effect. |
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