Effects Of HPMC On Soil Erosion And Solute Transport Characteristics On Loess Slope

Soil nutrient loss in loess region directly aggravated soil quality degradation and agricultural non-point source pollution.In this paper,the effect mechanism of hydroxypropyl methyl cellulose(HPMC)on soil erosion and nutrient lossed on loess slope under rainfall conditions was studied by combining indoor analysis test,field artificial rainfall test and model simulation analysis,and the mathematical model describing nutrient transport law was further explored.The research results are as follows:(1)After the application of HPMC,the soil structure tends to be more stable,and its ability to resist damage and erosion is enhanced.As the content of HPMC increases,the percentage of water-stable aggregates increases,the fractal dimension of soil decreases,and the average weight diameter increases.A certain amount of HPMC in soil can significantly reduce soil infiltration capacity and saturated water conductivity,significantly delay the initial and complete penetration time of solute,and extend the total penetration duration.The fitting curves of the two models are in good agreement with the measured curves,but the simulation accuracy of the two-zone model is higher.Based on the parameter fitting results of the two-zone model,with the increase of the HPMC content,the average pore water velocity and the water content ratio of the soil moving water become smaller,and the hydrodynamic dispersion coefficient,dispersion degree and mass exchange coefficient increase,which have a significant impact.(2)HPMC with different viscosity in soil can significantly reduce the infiltration ability of soil,and the infiltration process fitted by Philip equation and Kostiakov formula is of high significance.HPMC with different viscosity in soil can reduce the transport speed of soil solute.CDE equation and two-zone model can well simulate the transport status of solute when HPMC with different viscosity is applied in soil,but the two-zone model has higher fitting accuracy.With the increase of HPMC viscosity,the average pore water velocity and the ratio of water content in immovable water are smaller,and the hydrodynamic dispersion coefficient,dispersion degree and mass exchange coefficient increase.(3)HPMC was applied to each group,and the initial flow time was generally prolonged compared with the control group.With the same viscosity,the single-width flow rate and cumulative runoff rate increase with the increase of HPMC application amount.When the same amount is applied,the higher the HPMC viscosity is,the single-width flow rate and cumulative runoff rate first increase and then decrease with the increase of HPMC viscosity.Compared with CK group,the cumulative sediment amount of each group with HPMC was reduced to different degrees.The overall performance was that the larger the applied amount and viscosity,the smaller the effective sediment loss.Under the same viscosity condition,with the increase of HPMC content,the slope velocity decreases gradually,and the average runoff depth,flow shear force and thin layer flow resistance coefficient increase.Under the same applied amount,with the increase of HPMC viscosity,the average runoff depth and flow shear force increase gradually,and the unit of flow section can decrease.Froude number is negatively correlated with HPMC content and viscosity.Reynolds number and runoff power are positively correlated with it.Through the comparative analysis of section water content,the application of HPMC increased the section water content of soil surface layer by 15cm.Generally speaking,the more the application,the higher the viscosity,and the more the soil water content increased.(4)The cumulative nitrate nitrogen loss in runoff was negatively correlated with the viscosity and application of HPMC,and the profile nutrients presented a unimodal distribution.Both the fully mixed depth model and the equivalent mixed depth model can be used to predict the nitrate-nitrogen loss process of slope runoff under the action of HPMC,but the power function based equivalent mixed depth model has better fitting effect.With the increase of HPMC viscosity and application amount,the mixing layer depth hm and HO both showed an increasing trend.