Numerical Simulation On Farmland Nitrogen Loss To Surface Runoff In A Raindrop Driven Process

In recent years,the losses of nitrogen,phosphorus and other nutrients to surface runoff by reason of soil erosion and fertilizer input have received widespread attention.It may cause direct damage to the farmland,not only reduce soil fertility and chemical fertilizer utilization,but also give rise to Agricultural Non-point Source Pollution(ANPSP)and then trigger eutrophication,since surface runoff caused by rainstorm may bring away particle and soluble state of nutrient.According to The first national pollution census bulletin,our country agricultural pollutant discharge total nitrogen2.7046 million t,total phosphorus 284700 t,accounting for the total national emissions of pollutants about 57.2% and 64.9%,agricultural pollution sources has become the main part of source of pollution.In order to study the loss character of nitrogen loss to surface runoff in a raindrop driven process and work out the reasonable project of chemical fertilizer use,we chose a bare land at the Irrigation Technology Extension Station of Qingpu District,Shanghai,China(31°12’N,121°08’E)and made the experimental scheme.There were three different tests made in the station,on August 13,August 22 and August 29,2014(hereinafter,named 0813 and 0829),respectively.Experimental procedures mainly include soil loosen,fertilization,artificial rainfall,runoff sampling,soil sampling and hydrochemical analyse.Based on the experiment,we finally establish the one-dimensional mathematical model of nitrogen transport through surface runoffThe model was based on the rainfall induced soil erosion and chemical loss model established by Gao et al.(2004).Which divided the soil into three aspect,that were surface runoff layer,exchange layer and soil layer.Nitrogen transport and transformation aspect were also included in our model,e.g.,urea hydrolysis,nitrification of ammonia nitrogen and denitrification of nitrate nitrogen.The established model was solved numerically through the modified Hydrus-1d source code in the form of FORTRAN language.Finite-difference method and Galerkinmethod were used in the dispersive process.Through trial and error method(i.e.the choose of some parameters should be repeatedly adjusted based on the original values),our model can better describe the nitrogen loss into surface runoff under raindrop driven process.And the results can provide references for rational application of fertilizer and preventing agricultural NPSP.