Simulation Of Transport Of Nitrate-N And Leaching Loss Flux Of Aeration Zone In Luanjing Irrigation Area

Luanjing Irrigation Area is adjacent to the Tengri Desert in Inner Mongolia, where is the representative arid region in Northwest of China. The evaporation is large and precipitation is scarce, and shortage of water is severe. In consequence the agriculture development heavily relies on Yellow River irrigation. In recent years use of nitrogenous fertilizer in irrigated agriculture is at increase resulting in the increase of residual N in soil and leaching nitrate to the groundwater. The research was taken on the present irrigation and fertigation strategy and the transport the nitrate with wild flooding in the arid region to asses the flux of nitrate leaching from soil.First of all, the ku-pF Apparatus used to measure the soil pressure head and the weight of the soil samples can record the process of soil desorption and get the soil water characteristic curves(SWCC).Fit the SWCC with the van Genuchten Model and its revised Model and compare the fitting value to the measure value. Van Genuchten Model can simulate the different kinds of soil in Luanjing Irrigation Area better than the revised Model.The top sandy loam in Luanjing has the similar SWCC,which illustrates that the hydraulic parameters in Luanjing are typical.The bigger the ratio of clay is, the higher the residual water content raises.So does the sandy gravel.Secondly, undertake study to simulate the nitrate transport in the agricultural soil under current wild flooding system.The study involves the long term field experiment of monitoring soil hydraulic properties, to collect the soil samples and soil water to analysis the concentration of soil NO3--N,NO2--N and NH4+-N in different seasons for the solute transport model, the agricultural cultivation and fertigation system. According to the patterns of nitrogen transformation and loss, we can analysis the relative parameters and initial & boundary conditions about geological feature, the water flow,solute transport and meteorological data in the aeration zone.Then the the one-dimensional solute transport model HYDRUS-1D was applied to simulate the nitrogen leaching from various soils in Luanjing Area.Thirdly, the trend of value of model simulation responds to the measured value with time,which illustrates that the HYDRUS-1D Model can reflect the NO3--N transport dynamic in the aeration zone.The soil particle composition can influence the soil adsorbability of NO3--N.There is high ratio of clay in sandy loam with strong adsorbability,so the velocity slows down. Soil volume weight can affect the penetrate velocity.Therefore,the simulation value is smaller than the measured value,and the measured NO3--N concentration peak lags behind the simulated one in the aeration zone. For the macrovoid in the sand gravel, the preferential flow can affect the solute transport. As a result, the difference between measured and simulation value in the sand gravel is larger than it in the sandy loam.Fourthly, calculate the nitrate-N leaching loss flux with the HYDRUS-1D Model.The leaching loss flux is 67.5 kg/hm2 in KK2 and 24.1 kg/hm2 in K2. The results show that the nitrate-N leaching loss flux accounts for 8-23% of the total amount of N application throughout crop duration in Luanjing Area. The lower the available N in the soil mass is.the higher the loss rate of NO3--N is.The utilization rate of N is low in the perennial cultivation soil,and the very rate is higher in the soil with low N reserves.Finally, determine the best N application in the soil.Simulate the leaching loss of soil NO3--N with different split-application patterns.The more frequency is,the lower the leaching loss is. Suggestions are madeto enhance the utilization rate of N fertilizer with different measures such as deep tillage application combined with Phosphorus(P) and split-application.Then the N loss flux can be decreased and the influence can be avoided to the environment.