Soil Solute Transport Into Surface Runoff Along Loess Slope Land And Mathematical Model Simulation

In Loess Plateau,the phenomenon of soil erosion and nutrients loss is serious.Soil nutrients transport into surface runoff affected by various factors is a complex physical and chemical process.Thus,accurate predicting soil nutrients loss has a significant influence on watershed management and farming guidance.In this study,we adopted laboratory experiment,field experiment and combined with theoretical analysis to study the effect of rainfall,soil properties,topography,PAM,the way of fertilization patterns,and micro-topography et on soil solute transport along slope land.Furthermore,we proposed mathematical models to describe the transport of overland flow and nutrients,and also provide the way of parameters estimation.The obtained results as follows:(1)Surface runoff,sediment production rate,solute concentration in runoff increased with the increase of rainfall intensity,raindrop kinematic,slope,initial water content and slope length.However,surface runoff decreased as slope increased to 300.When surface covered with stones and applied PAM,surface runoff decreased,as well as sediment production rate and solute concentration in runoff.Same orders were observed in surface runoff and potassium concentration under different soil texture:silt clay soil>silt loam soil>silt sand soil.The order of potassium concentration under different way of fertilization patterns are:top application>mixed application>deep application.When micro-topography surface shaped as arch and trapezoid,the effect of retention of soil water and fertilizer is better.(2)Proposed a method of analytically solving the kinematic wave equation to describe overland flow along slope land under two different ways of water supply.Parameter c under rainfall condition power increased with rainfall intensity.And,we established relationship between Manning's roughness coefficient and stone coverage,stone cover area.Numerical solution was adopted to verify the accuracy of parameters,and performing so well.Results indicated that the proposed analytical model can be used to estimate infiltration parameters and Manning's roughness coefficient,as well as parameters characterizing hydraulic properties over slope land.(3)The effective mixing depth model and the equivalent mixing depth model can be applied to predict the process of nutrients transport and total loss.The incomplete mixing model performs better than complete mixing model.However,the complete mixing model is recommended to use influence factors.(4)Proposed solute transport model with the consideration of soil erosion under rainfall condition and ways of parameters estimation.Mixing depth is a function of rainfall intensity and time.And parameters m in the model only changed with nutrients type,while km can be expressed as a function of rainfall intensity,slope and nutrients type.(5)Proposed a solute transport model under water scouring condition,and the way of parameters determination.Mixing depth is a function of time and water flow depth.Simulation results of potassium concentration and mass in runoff fitted better with experimental data.Parameter k linear related to Re.