Research On Simulation Of Soil Infiltration During Vertical Line Source Irrigation And Its Prediction Model

The western regions of China have abundant land resources and adequate lighting conditions,which are suitable for the development of the forestry and fruit industry.Vertical line source irrigation is a kind of irrigation method suitable for deep-rooted systems.As a newly developed irrigation technology,the design and management of vertical line source irrigation lack a complete theoretical basis.It is necessary to systematically study soil infiltration characteristics and wetting pattern characteristics of vertical line source irrigation in order to realize the theoretical innovation of efficient use of water in deep-rooted plants.In this paper,the vertical line source irrigation was taken as the research object,and the combination of simulation analysis and experimental verification was used to explore the characteristics of soil infiltration and wetting pattern under two kinds of?sufficient and non-sufficient?water supply methods.The dominant influencing factors were sought,and the cumulative infiltration and the wetting front migration distance were calculated.A simplified model for predicting cumulative infiltration and wetting front migration distance was proposed and verified.The preliminary results are as follows:?1?The moistube characteristics of vertical moistube-irrigation were investigated by laboratory tests.Based on Darcy's law,a moistube specific discharge calculation formula including water pressure,pressure head and water suction was established.Based on the Richards equation,the mathematical models of soil water movement under vertical irrigation were established for two kinds of water supply methods and solved by HYDRUS-2 D software.The data of cumulative infiltration,wetting front migration distance and water content distribution at the end of irrigation were selected to verify.The MAE and RMSE of the simulated and measured values are close to 0,PBIAS<±10,and NSE?0.946.It is proved that it is feasible to use HYDRUS-2 D to simulate soil water movement during the vertical line source irrigation.The mathematical model and its solution method are reliable.?2?The effects of different soil characteristics,emitter specifications and design parameters on the soil water movement law in vertical line source irrigation were simulated by HYDRUS-2 D.Under the two kinds of water supply methods,the wetting pattern and water content contour are approximately"ellipsoid"around the line source,and the wetting front migration distance in each direction increases with time.In the initial stage of irrigation,the wetting front migration distance moves in line with the pattern of horizontal>vertical downward>vertical upward,which is conducive to the extension and deep-rooting of the plant roots,and meets the requirements for efficient irrigation of deep-rooted plants.With the continuation of the irrigation time,the wetting front migration distance for coarse soil gradually shows the law of vertical downward>horizontal>vertical upward.Under the condition of sufficient water supply,the infiltration rate and cumulative infiltration of soil are mainly affected by the soil texture and the seepage area.The soil initial water content and line source buried depth have little effect on it.The wetting front migration distance is mainly affected by the soil texture,and the soil initial water content,line source diameter,line source length,and line source buried depth have relatively little effect on it.At a same irrigation quota,the soil wetting pattern volume is mainly affected by the soil texture,the line soure length,and the line source buried depth,and the initial water content and the line source diameter have little effect on it.Under the condition of non-sufficient water supply?vertical moistube-irrigation?,the wetting parttern characteristics are mainly affected by the soil texture and the water infiltration rate of moistube,and the initial water content has a relatively small influence on it;the water infiltration rate of moistube is mainly affected by the pressure head,line source length and line source buried depth.?3?The relationship between the cumulative infiltration I and the irrigation time t from the vertical line source irrigation under sufficient water supply can be expressed by the Philip infiltration formula(I=St^0.5+At).At a same soil texture,the soil water sorptivity?S?and the line source seepage area?S_a?have a good linear relationship?S=aS_a+b?,and the steady infiltration rate?A?and S_a have a good power function relationship?A=cS_a^d?.The coefficients a and c have a power function relationship with the saturated hydraulic conductivity K_s,and the coefficients b and d have little change.Based on this,a simplified prediction model for cumulative infiltration of the same soil texture S_a was established.The model contains two parameters to be determined.The experimental data of one group can be inferred and the precision is high.It can be used to predict the soil cumulative infiltration from a vertical line source irrigation under sufficient water supply.A simplified prediction model for cumulative infiltration of different soils containing S_a and K_s was proposed.The error between the predicted value and the measured value is slightly larger,but the model is simple.It is preliminarily realized that the soil parameters?K_s?can predict the possible cumulative infiltration of the vertical line source irrigation of different soil quality.?4?Under the condition of sufficient water supply,the wetting front migration distance F and irrigation time t can be described by the power function?F=at^b?.The coefficient a increases with the increase of the saturated hydraulic conductivity,and The index b changes little in the horizontal direction and the vertical downward direction,and increases with the increase of the saturated hydraulic conductivity in the vertical downward direction.A simplified prediction model of the wetting front migration distance for different soil texture was established.It is in good agreement with the measured value;the only parameter required in the model is K_s,which can facilitate the end user to perform quick on-site assessment.?5?The relationship between the wetting front migration distance F and the irrigation time t in the vertical moistube-irrigation can be expressed by the power function?F=at^b?.The coefficient a increases with the increase of the saturated hydraulic conductivity in the vertical upward and horizontal directions,but the coefficient a decreases with the increase of the saturated hydraulic conductivity in the vertical downward direction.The index b changes little in the vertical upward and horizontal directions,but increases in the vertical downward direction with the increase of the saturated hydraulic conductivity;A simplified prediction models of soil wetting front migration distances for different soil texture during vertical moistube-irrigation,including saturated hydraulic conductivity and moistube seepage rate was established.The error between the predicted value and the experimental value is small;the model includes the parameters?length and specific discharge?.The flow rate allows the designer to determine reasonable irrigation parameters for different soil textures.