Experiment Study On Nitrate Transport Characteristics And NO₃^--N Distribution In Groundwater Under Intermittent Infiltration Of Surge Irrigation

On the basis of literature review on surge irrigation,nitrogen fertilizer transport and transformation in soils worldwides,considering irrigation and fertilization practice in China, this research involves laboratory studies and theoretical analyses.This dissertation covers researches on soil water and nitrogen transport characteristics,water and fertilizer coupling characteristics,the concentration of NO₃^--N in the ground water under surge infiltration with fertilization.Such research should provide the theoretical backgrounds for NO₃^--N pollution control of groundwater and improvement of nitrogen use efficiency.The main findings are as follows:(1)The capillary water ascending characteristics under in the uniform soil with different groundwater table are researched.The ascending rate of capillary water augments with the initial soil moisture;the height of the capillary water rise increases with time,the capillary water rise velocity decreases with time increasing;the more the initial soil moisture is,the less the time that capillary water reach to the same height is;the relationship between the height of the capillary and the time needed can be simulated by power functions.The little the initial soil moisture is,the more the underwater supply volume when soil water reach balance is and the longer the balance time is;there are power function relationship between the capillary water supply and time,and linear power function relationship between the capillary water rise velocity and the height of the capillary water rise.(2)The infiltration capacity,wetting front transport,soil water content distribution, NO₃^--N transport characteristics and the NO₃^--N concentration distribution of round water under intermittent and continuous infiltration with fertilizer solution are researched.Comparing with continuous infiltration,intermittent infiltration can decrease infiltration capacity and the reduction effects were more significant in the second cycle.Wetting front of the under intermittent infiltration with fertilizer solution moves slower than under continuous infiltration and the speed decreases with cycle number.Model for calculating transport distance of the wetting front under intermittent infiltration based on continuous infiltration data is proposed.The soil water content is more evenly distributed under intermittent infiltration than continuous infiltration.Soil NO₃^--N front under intermittent infiltration moves slowly than under continuous infiltration,which favors NO₃^--N conservation in shallow soil layer.The relationship curve between concentration NO₃^--N and soil water content is a "L" shape under intermittent and continuous infiltration effected by underwater.Comparing with continuous infiltration,the relationship curve is steeper under intermittent infiltration,and the NO₃^--N increment in the ground water is more under continuous infiltration.(3)The influences of technique factors on the infiltration capacity,wetting front transport, soil water content distribution,NO₃^--N transport characteristics and the NO₃^--N concentration under intermittent infiltration are researched.The infiltration quantity and wetting front transport models containing different affecting factors under intermittent infiltration with solution are established.In this experiment,the optimal cycle rate is 1/3,which leads to NO₃^--N being more easily stored in shallow soil layer and weakens the trend of NO₃^--N leaching and lightens groundwater NO₃^--N pollution;The infiltration rate,the concentration front transport distance of NO₃^--N and the increment of concentration of NO₃^--N in groundwater are least when the cycle number is 3.The wetting front and the concentration front transport distance and the NO₃^--N concentration increment in the groundwater increase with the irrigation water quota increasing.There is power function relationship between the increment of NO₃^--N concentration in the groundwater and the groundwater depth.(4)Coupled movement characteristics of soil water and nitrogen under intermittent infiltration with different fertilization concentration are researched.The infiltration capacity,the transport distance of NO₃^--N concentration front and the value of NO₃^--N front increases with the fertilizer solution concentration.After intermittent infiltration with fertilizer solution,the relationship curve between concentration NO₃^--N and soil water content is a "V" shape,in 0～72cm soil layer,NO₃^--N concentration and the soil water content are large.The NO₃^--N concentration decreases with soil water content decreasing.The more fertilization solution concentration is,the little the influence of soil water content on NO₃^--N concentration.The NO₃^--N concentration is close to initial value in 72cm～150cm,the "V" curve becomes more slipperier and the distribution of NO₃^--N concentration and soil water content are uniform. The NO₃^--N concentration decreases with soil water content increasing.In 0～76cm, NO₃^--N concentration increases more than after infiltration,the more solution concentration is,the more soil water content effect NO₃^--N concentration;NO₃^--N in underwater from irrigation water mainly distribute in the shallow groundwater,the more solution concentration is,the more NO₃^--N enters groundwater and the more seriously NO₃^--N pollutes,NO₃^--N entering groundwater is most after irrigation with different fertilization concentration and decreases gradually with redistribution time.The exponent function exists between the NO₃^--N increment of different concentration solution and groundwater depth.(5)The effect of fertilization applying manner on soil water content,nitrogen transport characteristic and NO₃^--N concentration in the groundwater are researched.The infiltration capacity of surface applying fertilization is more than chemigation and deep applying fertilization; in the same infiltration time,the order of wetting depth is surface applying fertilization＞deep applying fertilization＞chemigation＞no applying fertilization;the infiltration volume under intermittent infiltration with different fertilization applying manner is developed;in the same wetting depth,the order of soil water content is surface applying fertilization＞chemigation＞deep applying fertilization after redistribution for 1 day;the fertilization applying manner has great influence on NO₃^--N transport and distribution under intermittent infiltration.NO₃^--N in the wetting scope under chemigation infiltration distributes uniformly,while the NO₃^--N under surface applying fertilization and deep applying fertilization mainly distributes in the some depth and transports gradually to deeper soil with time;the NO₃^--N transports most fast with water under surface applying fertilization,comparing with surface applying fertilization and deep applying fertilization,intermittent infiltration with fertilizer solution favors the NO₃^--N conservation in shallow soil,and decreases effectively soil water and deep seepage of NO₃^--N; NO₃^--N concentration in the groundwater under intermittent infiltration with different fertilization applying manner increases with the underwater depth and infiltration time;the increase ration(the present of NO₃^--N concentration increase absolute value under different infiltration time to NO₃^--N increase gross under total infiltration time)of NO₃^--N concentration groundwater decreases with infiltration time,the increase ratio of NO₃^--N concentration is most after infiltration and least after redistribution for 5 days,the exponent function exists between the NO₃^--N concentration increment and groundwater depth under different fertilization applying manner,chemigation favors the improvement of the nitrogen use efficiency and mitigate the nitrogen pollution in groundwater.