| Soil nitrogen is one of the main factors that affect crop yield and quality.Urea application as a source of soil nitrogen plays a key role in agricultural development.Because of the instability of urea and unreasonable fertilization and irrigation,the loss of nitrogen will be aggravated.Relying solely on increasing the amount of urea to increase crop yields may cause fertilizer loss,waste of resources,and pollution of land and groundwater.Therefore,the study of the migration and transformation of urea in soil is of great significance for the development of modern agriculture.The temporal and spatial distribution of soil moisture,ammonia nitrogen and nitrate concentration under different rainfall intensity and urea fertilizer amount were studied with soil column as the carrier and the theory of soil solute migration and transformation as a theoretical guide.Soil water and ammonia nitrogen and nitrate under the experimental conditions were constructed with the theory of soil capillary water and the theory of solute transport.The physical model of nitrogen migration and transformation was simulated by using the built-in function of MATLAB,PDEPE,to simulate the soil moisture,ammonia nitrogen concentration and nitrate nitrogen concentration in the transfer and transformation process of solute nitrogen.Finally,the numerical simulation results were compared with the data of physical experiment water content,ammonia nitrogen and nitrate nitrogen concentration.The reliability of the simulation results of soil moisture content,ammonia nitrogen and nitrate concentration in soil urea transfer and transformation under different rainfall intensity conditions was analyzed.The main conclusions are as follows:(1)the disturbed sand loam in Yichang area was selected as the experimental sample and the basic parameters were measured.At the same time,the saturated treatment of the sample with different nitrogen concentration was saturated.The soil moisture characteristic curve of the sample was measured by the centrifuge dehumidification method,and the empirical model of the soil moisture characteristic curve was used.The test results were fitted to get the physical indexes of the samples.Through the study,it can be seen that the concentration of urea fertilizer has a significant influence on the water characteristic curve,and with the increase of urea concentration,the water characteristic curve is obviously moving to the left,and the water holding capacity is weakened.The parameters of the VG classic model,and the increase of urea concentration,increase with the increase of urea;with the urea concentration,the urea concentration is increased.The total effective water area,field capacity,water holding capacity and the grading of the withered system decreased,and the water holding capacity decreased.(2)soil nitrogen migration and transformation under the influence of different rainfall intensity and urea fertilizer were simulated through laboratory experiments of soil urea transfer and transformation under different rainfall conditions.Through experimental data analysis,the distribution of soil water content,ammonia nitrogen and nitrate nitrogen under different conditions was studied,and the distribution rule in soil was studied.The results showed that the greater the rainfall intensity,the greater the soil water content,the more obvious the wetting front moving down;the soil moisture content increased rapidly in the rainfall period,and the rate of the increase gradually decreased;the soil moisture content gradually decreased and the rate decreased gradually,and the final water content reached a stable value in the redistribution stage.Under the same amount of fertilizer,the greater the rainfall intensity,the lower the concentration of ammonia nitrogen;the greater the amount of fertilizer,the higher the concentration of ammonia nitrogen under the same rainfall condition,and the ammonia nitrogen concentration gradually decreased with the time.Under the same rainfall condition,the greater the amount of fertilizer,the greater the concentration of nitrate nitrogen;the greater the rainfall intensity,the lower the concentration of nitrate nitrogen under the same fertilization condition;the concentration of nitrate and nitrogen gradually increased with the time.(3)to construct the physical model under the experimental conditions,and to embed the basic physical parameters of the soil,the VG model and the water flow equation into the nitrogen whole model,and use the PDEPE to solve the experimental process.The time and space distribution data of soil moisture content,ammonia nitrogen and nitrate nitrogen in soil urea transfer and transformation experiment under different rainfall intensity conditions were compared with the numerical simulation results,and the reliability of soil moisture,ammonia nitrogen and nitrate concentration was analyzed by the method.Through comparison,it is found that the method has a good effect on the simulation of soil moisture content distribution under different rainfall intensity conditions,and the simulation of soil ammonia nitrogen and nitrate concentration changes in accordance with the objective facts. |
