Modeling And Application Of Basin Surface Water Flow And Solute Transport With Two Fertilization Methods

Agricultural non-point source pollution has become increasingly prominent and irrigation with nitrogen fertilization is one of the major sources.Both experiment and numerical simulation for basin irrigation with fertilization have important theoretical significance and application value for saving water and fertilizer as well as reducing agricultural non-point source pollutionIn this study,the water and nitrogen distribution characteristic and performance of basin irrigation with different fertilization methods were analyzed based on the experimental data.Then,based on the results obtained from the complete hydrodynamic model for basin irrigation which is solved by a hybrid numerical method,the non-uniform velocity field along the basin length and vertical direction was re-constructed and the numerical model of surface water flow and solute transport for basin irrigation with conventional fertilization is proposed.Based on the scalar finite-volume method,the numerical coupled model of surface water flow and solute transport for basin irrigation with fertigation was proposed.Finally,non-uniform conventional fertilization was proposed.The proposed numerical models were used to evaluate the performance of basin irrigation with different non-uniform conventional fertilization and fertigation time,and the suitable stategies of different technical factors for basin irrigation with two fertilization methods were proposed.The innovation and conclusions obtained in this study are as follows.(1).In term of the performance comparison of basin irrigation with different fertilization methods,the performance comparison experiments of basin irrigation with conventional fertilization and fertigation was firstly carried out.The analyzed results show that the distribution uniformity of nitrogen within 1m soil layer along the basin length improves obviously one day later after irrigation for fertigation,but not for the conventional fertilization.The difference for indices,such as nitrogen distribution uniformity,nitrogen efficiency and nitrogen adequacy,between fertigation and conventional fertilization is significant,and fertigation is the suitable fertilization method.(2).In term of the numerical method,according to different mathematical and physical characteristic of different terms of the governing equation,the finite-volume,finite-element and finite-difference methods was use to respectively solve the governing equation.Then the hybrid numerical method was proposed.Based on the typical experimental data,by comparing the results obtained from Roe finite-volume method,the hybrid numerical method presents better numerical stability,convergence,accuracy and computational efficiency.(3).In term of the simulation of basin irrigation with conventional fertilization,the results obtained from the complete hydrodynamic model were used as the known and boundary conditions.By means of the vertical velocity distribution law and continuous equation of incompressible hydrodynamics,the non-uniform velocity field along the basin length and vertical direction was re-constructed.The turbulent diffusion coefficient was constructed by means of the non-uniform velocity and the numerical model for conventional fertilization was proposed.The validated results show that,the average relative errors between the simulated values and experimental data are from 5.91%to 11.92%,and the solute quantity balance error is smaller than 0.5%.(4).In term of the simulation of fertigation,a physical fact was used that the advection and gravity waves belong to different physical processes,and the shallow water and solute transport coupled equation was reformulated.Based on the case,the scalar finite-volume method was proposed.The validated results show that,the scalar finite volume method presents better stability and accuracy,and obtaines 3.5 times of computational efficiency than the Roe finite volume method.(5).In term of the performance evaluation and optimized design for conventional fertilization system,the non-uniform conventional fertilization was proposed and the corresponding measure index,USN,was constructed.The numerical analysis was carried out by means of the proposed model.The results show that under the condition of suitable USN,for small,middle and large inflow discharge,the standard derivation values of basin micro-topography should hold the condition of Sd?3.6,4.0cm,4.5cm,then the nitrogen distribution uniformity and nitrogen adequacy would are above 75%.(6).In term of the performance evaluation and optimized design for fertigation system,the proposed numerical model was used to analyze the performance of basin irrigation with different fertilization strategies.The results show that under the condition of suitable fertilization strategy,basin technique factor can impact the fertigation performance.The basin micro-topography is the major factor compared with basin length,soil type and inflow.Under the condition of suitable fertilization strategy,the basin micro-topography should meet the condition of Sd?3.5,3.7cm,4.3cm,then the nitrogen distribution uniformity and nitrogen adequacy would are above 75%.