Development Of Soil Hydraulic Property Model And The Character Of Nitrogen Distribution In A Typical Subtropical Catchment

Soil hydraulic properties are incrucial factors that have great impact on pollutant transportation in soil,and can quantificationally assess the risk of agricultural non-point pollution as well.For the application of hydraulic models, direct methods to get the parameters may be complicated,difficulty and costly,however,which could be solved by the indirect way called pedotransfer function.So we selected the typical catchment of jinjing in hunan province as the study location,and got50paddy and upland profiles in total.Finally,we developed pedotransfer functions for soil saturated hydraulic conductivity and soil water retention curve using the method of multiple linear stepwise regression with parameters of bulk density,organic matter and texture,respectively.In the meanwhile,we gave some description on nitrogen distribution in soil profile and the negative effect that might cause risk to underground water. The conclusions were listed as following:(1)Firstly, we had developed the soil Ks model for rice paddy with determined coefficient (R-Squared) of0.67,and in this Ks model influenced mostly by bulk density and organic matter,only including variables of soil bulk density,organic matter,sand content,clay content and GSD.In the process of prediction,our model got GMER value of0.68.Comparing with other famous models,such as Cosby,Vereecke,Wosten,Julia, Saxton and Aimrun model,the model we derived performed best in our location.Secondly,we also obtained the Ks function for upland soil with lower R-squared of0.52,surprisingly,which was mainly determined by soil bulk density and texture,and when predicted by two group datas,one of which used to develop the model and the other not,the correlative coefficients were0.74and0.71,respectively.(2)We utilized the Van Genuchten equation as the parameter equation,and selected its four parameters that were residual water content,saturated water content,a,n and other six parameters named soil air-dry water content,permanent wilt point,field capacity(-10Kpa and-33Kpa) and available water content to establish functions using soil properties.The result showed,for each function,the variable differed,and different precision as well.For all funcitons,the model for soil saturated water content predicted best with R-sqaured of0.85, worst for soil residual water content and the R-squared value of other funcitons were all beyond0.5.(3)The study of nitrogen distribution in soil profile suggested that the topsoil with depth of0-30cm had high concentration of nitrate nitrogen in paddy field,however,in upland soil the concentration changed slowly in different depths,which meaned that nitrate nitrogen in upland soil would transport more easily than in paddy soil,and that was to say,higer risk to underground water in upland.The ammonium nitrogen content in upland soil was higher than in paddy field.By analysing the relationship between different nitrogen formations,we found nitrate nitrogen was positive correlation(P<0.01)with total nitrogen in both landuses,which indicated that it might increase the content of soil nitrate nitrogen when soil total nitrogen content increased,and would boost the environmental risk of nitrogen pollution to groundwater.