Study On Water And Nitrogen Transport Characteristics And Numerical Simulation Of Soil Fertilizer Infiltration Under Wide Ridge Furrow Irrigation

Wide ridge furrow irrigation is an advanced surface irrigation technology,which compared with traditional surface irrigation technology,wide ridge furrow irrigation has the advantage of saving water and fertilizer.In order to provide reasonable irrigation and fertilization management measures for wide ridge furrow irrigation,on the basis of consulting a large number of literatures about wide ridge furrow irrigation,the soil box fertilizer infiltration experiment was carried out in this paper.combined with the methods of software numerical simulation and analysis,the law of water and nitrogen transport and distribution in the process of wide ridge furrow irrigation was studied.The main conclusions are as follows:（1）The soil water movement model under the condition of different initial water content of wide ridge furrow irrigation was established by using HYDRUS-2D software,and the soil water movement model was solved by the observed data of laboratory experiment,and the model was used to simulate the water movement process of wide ridge and furrow irrigation.The model was verified by the experimental verification group,and the effect of different initial soil moisture content on water infiltration characteristics was analyzed.It was found that the HYDRUS2-D simulation results of cumulative infiltration and wetting front movement distance are in good agreement with the experimental results,which proves that the selected model can simulate the infiltration process of wide ridge and furrow irrigation.When the initial moisture content was 10%and 12%,the cumulative infiltration decreased by 2.13%and 4.38%,respectively,and the wetting front movement distance and wetting body range increased with the increase of water content.Among them,the wetting front transport distance is most significantly affected by the initial soil moisture content,but the effect of the initial water content on the vertical direction is more significant than that on the horizontal direction;The relationship between cumulative infiltration and infiltration time is fitted,the relationship between them with time is in accordance with the power function,and the relationship between fitting parameters and water content is linear,and the fitting results have high accuracy..（2）Combined with the measured water content in laboratory experiment,the parameters under different concentration of fertilizer solution（NH₄NO₃）were inversed by HYDRUS-2D software,and the water and fertilizer transport process of different combinations of wide ridge and furrow irrigation was simulated.The results show that comparing the simulated values with the measured values,it is found that the selected models and parameters are reliable to simulate the transport and distribution of water and fertilizer;the distribution law of nitrate nitrogen in soil is similar to that of water distribution,which decreases with the increase of soil depth,that is,nitrate nitrogen is easy to move with water;ammonium nitrogen mainly accumulates near the cross section of irrigation ditch,and the initial soil moisture content has no significant effect on the distribution of ammonium nitrogen.（3）Compared with wide ridge furrow irrigation solution（NH₄NO₃）infiltration and clear water infiltration,it was found that the coupling of water and fertilizer was more beneficial to the transport of water in the soil,and the transport distance of wetting front in both horizontal and vertical directions increased.The cumulative infiltration increased with the increase of fertilizer concentration.When the fertilizer concentration was 300mg·L^-1、600 mg·L^-1 and 900mg·L^-1,the cumulative infiltration increased by 14.03%,22.60%and 30.42%respectively compared with 0 mg·L^-1.A model for calculating the migration distance of the anisotropic wetting front and the cumulative infiltration amount per unit length under the coupled condition of water and fertilizer are established.The relationship between the two models and time can be calculated by the power function model,and the fitting parameters have a linear relationship with the concentration of fertilizer liquid（NH₄NO₃）,and the fitting results have high accuracy.With the increase of the concentration of fertilizer solution,the soil moisture content at the same observation point also increased,and the range with higher moisture content also increased.The law of nutrient redistribution in soil was simulated by HYDRUS-2D software,and it was found that the mass fraction of nitrate nitrogen in soil decreased in the upper layer and increased in the lower layer during the redistribution process,which proved that nitrate nitrogen was easy to lose with water,and there was a risk of deep leakage.