| Agricultural non-point source pollution（ANPSP）has received more and more attention in recent years.It has become the primary task of agricultural environmental management in China at this stage.Compared with traditional flooded irrigated rice fields,water-saving irrigation affects soil physicochemical properties and nitrogen transport and transformation,and affects rice paddy water and fertilizer utilization and ecological environment.Therefore,the paddy fields under water-saving irrigation conditions are used in this study,and through the outdoor monitoring of meteorological data and field water level and indoor detection of soil physical and chemical properties and nitrogen concentration in paddy soil and water,the distribution of nitrogen concentration in soil profile and its variation with time are analyzed..According to the experimental data,the model parameters of water movement and nitrogen transformation process were determined,and the HYDRUS-1D model was established to simulate the process of water and nitrogen transport in paddy fields.The simulated and measured values and the balance of water and nitrogen in water-irrigated rice fields were analyzed to study the water movement and nitrogen transport and transformation characteristics in water-saving irrigated rice fields.The results show that the concentration of NH4+-N in the surface water of water-saving irrigated rice fields was greater than that of NO3--N.Therefore,the NH4+-N concentration value can be used as the main monitoring index for nitrogen loss in surface runoff water,and it is very important to prevent nitrogen loss in surface runoff water within 6 days after fertilization.The better fitting curve equation for NH4+-N over time is the power function and the quadratic polynomial.While the relationship between NO3--N and time is unstable,so there is no suitable fitting curve equation for NO3--N over time at present.In the fitting curve equation of NH4+-N with time,the amount of fertilization has a great impact on the coefficient of the fitting curve equation.In the power function equation,the larger the amount of fertilization,the larger the index and coefficient values.In the quadratic polynomial equation,the larger the amount of fertilizer applied,the larger the value of the quadratic coefficient.The simulation results of the HYDRUS-1D model established based on the monitored data show that the plow bottom layer has a small saturated hydraulic conductivity,which is a key area for rice field water study.The increases of groundwater capillary volume and soil preferential flow in the study of water-saving irrigated rice fields have great influence on water movement and nitrogen transport and transformation,which are important factors need to be considered in water-saving irrigated rice fields.According to the water balance analysis in the model,the overall water balance error is 0.135,and the relative balance error is 0.18%.In the nitrogen balance analysis,the nitrogen balance error was 2.22 kg/ha.These results suggests that the water movement and nitrogen transport simulation of paddy fields based on HYDRUS-1D model is an efficient way.This experiment mainly studies the water movement mechanism and nitrogen transport and transformation in water-saving irrigated rice fields,and provides important theoretical references for rice planting to save water resources,improve nitrogen fertilizer utilization rate and reduce ANPSP under the premise of ensuring yield. |
