Soil Water And Nitrogen Distribution Characteristics And Simulation Under Double-point Intersection Of Drip Fertilization

With the increasing widespread use of the technology of drip fertilization in domestic agricultural production.It is of great significance to study the distribution of water and fertilizer in soil under different operating conditions of drip fertilization system,optimize the operation mode of drip fertilization system and improve the utilization ratio of water and fertilizer.In this paper,laboratory test and numerical simulation were both applied to investigate the impact of different double-point-source drip parameters on the distribution of soil water and nitrate nitrogen.The work mainly adopted the indoor soil-bin test,and the chemical pure potassium nitrate was selected as the test fertilizer to configure the fertilizer solution.There were two independent variables,in the irrigation tests,namely dripper discharge and irrigation amount.The former was set individually at three levels of 0.4 L/h,0.8L/h and 1.2 L/h,and the later at three levels of 1.5 L,2 L and 2.5 L.Likewise,the fertilization tests had fertilizer solution concentration and the fertilization time sequences as independent variables.The first was set at three levels of 300 mg/L,600 mg/L and 900 mg/L,and the second was set at three levels of1/2N-1/2W,1/4W-1/2N-1/4W,3/8W-1/2N-1/8W.By observing the wetting front,and the water and nitrate nitrogen were measured,furthermore analyzed the distribution characteristics of soil water and nitrate nitrogen.The numerical simulation used the Hydrus-3D for modeling and calculation.The parameters of the model were calibrated by the test data,then validated by model,and carried out in application finally.The test results are obtained as follows:(1)The point sources interference is intersected in the middle of the two emitters under the double-point-source drip tests.The wetting front,water content and nitrate nitrogen content are symmetric distribution on either side of the interference section.(2)With the same dripper spacing,the moving distance of vertical wetting front decrease and the moving distance of horizontal wetting front increase with the increasing of dripper discharge.However,with the increasing of irrigation amount,the moving distance of vertical wetting front and horizontal wetting front can increase together.The time of wetting front intersection is mainly related to the dripper discharge.which are 20 min,50 min and 100 min under the treatment of 1.2 L/h,0.8 L/h and 0.4L/h respectively.Resulting from the interaction of the wetting front,the vertical wetting front moved faster.(3)Under the condition of drip fertilization,the soil water is uniformly distributed in the wetting body,and the water content decrease from 30% ~ 35% of the soil surface layer to 16% ~ 20% of the edge of the wetting body in the intersection area.The smaller the dripper discharge is,the lower the soil water content in the same position of shallow soil becomes.Moreover,the greater the irrigation amount is,the deeper the water movement in the vertical direction is and the greater the soil water content becomes in the same position of the wetting body.(4)The content of nitrate nitrogen in the shallow soil layer is generally between 10 mg/kg and 30mg/kg,which is slightly less than the initial nitrate nitrogen content in the soil.However,the content ofnitrate nitrogen accumulated at the edge of the wetting body in the intersection area is much more than the shallow nitrate nitrogen content.The nitrate nitrogen content in the inside of wetting body and the edge of the wetting body increase with the increasing of the fertilizer solution concentration and irrigation amount,but is not affected significantly by the dripper discharge.(5)It is dominant to conduct comprehensive consideration of the leaching and distribution routine of nitrate nitrogen.When under the condition of point-source interference,and compare with the strategy of fertilizer-water,it is suitable to use the strategy of water-fertilizer-water(1/4W-1/2N-1/4W,3/8W-1/2N-1/8W).(6)In the numerical simulation results of Hydrus-3D,there is a great agreement between the simulated value and the measured value of water content within the average relative error of MRE of10%,but the simulated value of nitrate nitrogen and measured value shows a mediocre agreement,with the average relative error of MRE not beyond 20%.The experiment can basically reflect the distribution characteristics of water and nitrogen in the intersection area,but the distribution law of nitrate nitrogen concentration at the edge of the wetting body needs further researches.