Simulation Of Nitrogen Migration And Transformation In Typical Agricultural Region Based On HYDRUS-1D Model

Agricultural non-point source is the main source for nitrogen pollution in water bodies.The vadose zone,as a link between surface water and groundwater,is the only way of vertical infiltration for nitrogen pollution.A series of complex physical,chemical and biological reactions will happen during vertical infiltration of nitrogen,such as nitrification,denitrification and adsorption.Research on the nitrogen transformation and leaching under different natural and artificial conditions in soil-vadose zone can promote deeply understanding the nitrogen cycle and its flux process in agricultural areas,as a guide for control the nitrogen pollution of shallow groundwater.The study area is located in dry farming region of Huaihe grain industry association,Anhui Province.A field experiment station was set up for observation of soil water movement and solute transport process.According to the results of experiment,a model which based on HYDRUS-1D was built to simulate soil water and nitrogen transport.The actual observation data were used to calibrated and validated the model parameters,and ensure the accuracy of the model.Different agricultural production conditions,such as fertilization measures,precipitation and soil type,were designed to analysis the water balance in unsaturated zone and nitrogen distribution,and to quantitatively evaluate the nitrate leaching rate.The major results were as follows:1.The results of field observation show that the range of soil moisture content in experimental area of Lime concretion black soil is 0.252～0.455,and the average concentration of nitrate and ammonia nitrogen is 77.60 and 1.28 mg·L-1 for collected soil solution samples.However,the range of soil moisture content in experimental area of Alluvial soil is 0.203～0.416,and the average concentration of nitrate and ammonia nitrogen is 29.27 and 1.02 mg·L-1 for collected soil solution samples.2.Good performances were obtained for nitrate concentration simulations with R2>0.75 and RE<20%in Lime concretion black soil,R2>0.60 and RE<10%in Alluvial soil.It was showed the soil water movement and nitrogen transport process can be described appropriately by HYDRUS-1D model in the study area.3.According to the different nitrogen application scenario in Lime concretion black soil,normal-using N(100%),abnormal-using N(75%、50%),the simulate nitrogen leaching losses were 146 kg·hm-2.Moreover,according to the different rainfall condition in Lime concretion black soil,50%,75%and 90%of assurance rate in different years.the nitrogen leaching losses were 253.7,166.49 and 66.59 kg·hm-2 calculated by HYDRUS-1D model.The simulation results show that the rainfall is the main effect factor which affect nitrogen leaching under the design conditions.4.The nitrogen has a larger leaching in Alluvial soil(205.98 kg·hm-2)than Lime concretion black soil(166.49 kg·hm-2)in based on the present condition simulation and design condition simulation of normal-using N(100%)and 75%rainfall assurance rate.