The Research On Surge Flow Border Irrigation Of Intermittent Infiltration And Simulation Of Water And Nitrogen Transport&Conversion In Aeration Zone Of Soil Under The Groundwater Condition

Comparing to other traditional irrigation,surface sealing is one of the main infiltration characteristics which is formed to reduce infiltration under Surge flow irrigation.Based on the research papers studied by foreign and domestic researchers,aiming at the characteristics of irrigation and fertilization in the Northern-Arid region of China,with the support of project of National Scientific Fund,this paper takes the integration of measures including theoretical investigation,numerical simulation,and laboratory test to investigate the regularity of intermittent infiltration and the law of water and nitrogen migration in layered soil.By improving the intermittent infiltration model,it has important theoretical significance and applied value to optimize the technical elements of surge irrigation,and the results of the research are listed as follow:(1)The study of upward capillary water movement characteristics of homogeneous soil and layered soilA theoretical model of capillary water rise based on Philip solution was built,and the curve linear relationship between the parameter of the model and soil moisture content belonged to quadratic polynomial functional relationship.Moreover,the law of water recharge and height of capillary water rising with time changing was revealed.It had been indicated the law of water recharge and capillary water rising height with time changing,the larger the buried depth was,the smaller the recharge and rising height of the nonlinear stage were,the larger the water recharge and capillary water rising height of the linear stage were,the greater the thickness of the sand layer was,the thickness of the sand layer and the depth of the sandy soil layer were independent of the time constant of the model,and the nonlinear stage had no effect on water recharge and capillary water rising height,linear stable supply rate and the capillary water rising rate were smaller.Moreover,water movement characteristic equation of capillary water rising capillary of layered soil has been built.Through correlation analysis pointed out that the thickness of sand layer and the depth of sand layer were independent of the time constant of the model,and there was a significant positive correlation between recharge constant and rising height constant and sand depth,an extremely remarkable negative relationship between the rate of steady groundwater recharge and steady rise of capillary water and the depth of sandy soil layer.In addition,there was a significant negative correlation between the thickness of the sandy soil layer and the stable rate of groundwater recharge and capillary water rising rate.The interaction among the initial soil moisture,the depth and the thickness of sandy soil layer has significant influence on capillary water rising change through multi-factor interaction analysis of layered soil.(2)The study of the intermittent infiltration model based on Combining models with Green-Ampt and Philip under unsaturated soil conditionsModified GA-P(Green-Ampt and Philip)infiltration model has been built;the parameters of model have been solved;the functional relationship between periodic soil moisture and changing time;the quantitative solution of soil moisture variance with time changing has been realized and which could be generalized to the ratio between the actual cumulative infiltration and the actual wetting front.The distribution of soil moisture in periodic infiltration with periodic number which was larger than two was divided into two infiltration areas during intermittent infiltration,including I water replenishment stage and II infiltration stage.And it was assumed that the outflow flux from zone I was equal to the influent flux of wetting front into zone II.The linear relationship between the soil moisture increase and the 0.5 power of infiltration time was obtained through graphical feature method.Finally,the calculated values of cumulative infiltration and wetting front migration distance were compared with the measured values through reversing KS and Sf.The results showed that the model had high fitting and good applicability.(3)The study of the layered soil model under intermittent infiltration under shallow groundwaterThrough the analysis of experimental data and theoretical study,the improved infiltration model of BC-GA(Brook-Corey and Green-Ampt)of layered soil under surge irrigation intermittent infiltration was established,and the function relationship between the water suction and the wetting depth of the wetting front of the layered soil was established,and the steady infiltration rate of the layered soil when the water entered the sand layer was determined.It was true that the saturated water conductivity and retention water content in the sandy soil,the intake suction,the conductivity,the shape coefficient and the depth were the main parameters for the change of the internal migration distance in the intermittent infiltration of layered soil,and the comparison of the soil intermission infiltration through the buried depth of different sand layers indicated that the cumulative infiltration of the sand layer was reduced under the same buried depth of sandy soil,the migration distance of the wetting front increased,the depth of the sand layer increases,the cumulative infiltration of the same water supply period increased,the wetting front increased with the increasing number of periodicity and the water supply cycle reached the maximum,and the buried depth of sandy soil affected the cumulative infiltration and the wetting front migration distance.(4)Effects of fertilizer concentration on water movement characteristics of intermittent infiltration under shallow groundwaterThrough the analysis of experimental data and model simulation,the infiltration quantity of soil intermittent infiltration and the change rule of soil moisture were revealed.The intermittent infiltration process was simulated by Hydrus-1D model,and the soil water movement parameters were determined by the intermittent infiltration of the fertilizer.The simulation results showed the soil water content,the soil saturated water content,intake suction value and saturated water conductivity were the main factors affecting the intermittent infiltration,but not with the soil retention water content and the soil shape coefficient,and the relationship between the fractal dimension and the soil pore type based on the V-G model was clearly defined.The fractal dimension had a very significant negative correlation with non-capillary porosity,capillary porosity and total porosity,and the contribution of non-capillary porosity to the intake suction reciprocal and the saturated water conductivity was the most important.The correlation analysis indicated that the number of cycles was increased,the concentration of fertilizer solution decreased,the fractal dimension increased,the bulk density of soil increased,and the conductivity of aeration decreased.(5)Effects of fertilizer concentration on nitrogen transport and transformation characteristics of intermittent infiltration under shallow groundwaterDistribution of ammonium nitrogen and nitrate nitrogen in soil under intermittent infiltration of fertilizer solution and the relationship between soil ammonium nitrogen and nitrate nitrogen and soil water content had been indicated in this paper.During the infiltration period,the greater the number of cycles which promoted the mineralization of urea and nitrification of NH4+-N and improved pore structure of soil;the accumulation of less than 250mg/l fertilizer was not conducive to the accumulation of both;more than 250mg/l fertilizer was beneficial to the accumulation of ammonium and nitrate in surface soil;the greater the concentration of fertilizer solution and the greater the concentration of ammonium nitrogen and nitrate nitrogen during redistribution stages,and the longer the redistribution time was,the higher the nitrate nitrogen was.The results showed that Ammonium nitrogen and nitrate nitrogen had two stages including the leaching stage which was the content of Ammonium nitrogen and nitrate nitrogen decreased with the increase of soil water content and the stage with the concentration increasing with the increase of water moisture.Moreover,the larger the cycle number was,the smaller the content of ammonium nitrogen decreased when the soil moisture changed.Ammonium nitrogen concentration no longer changed with soil moisture content during the second stage.The upper limit of nitrate nitrogen content decreased with the increase of the number of periodicity,the concentration of fertilizer liquid increased,and the content of the cumulative phase increased.The leaching loss of soil ammonium nitrogen and nitrate nitrogen decreased with time in the 5 day of leaching,and the content of ammonium nitrogen and nitrate nitrogen in the accumulated soil increased.The numerical simulation of nitrogen transport and transformation process in the intermittent infiltration soil under the condition of the concentration of fertilizer was carried out by Hydrus-1D model.The change law of the redistribution of the soil ammonium nitrogen and nitrate nitrogen concentration in the ground surface 5cm and the shallow groundwater was analyzed,and the dynamic function of the surface 5cm and the net mineralization amount and the net nitrate content in the shallow buried ground of the ground surface were clear.The effective transformation of nitrogen showed that the increase of the concentration of the fertilizer was beneficial to the rapid infiltration of nitrate nitrogen,the possibility of increasing the nitrate nitrogen leakage and the detrimental denitrification,which can provide a reference and theoretical basis for the establishment of the theory and model of soil solute transport.