The Influence Mechanism Of Particle Composition On Pore And Moisture Characteristics Of Coastal Clayey Saline Soil

Aiming at the problems of coastal clayey saline soil with heavy texture,poor structure,poor water infiltration,and difficulty in salt leaching,etc.,A combination of indoor simulation and field experiments was used to improve clayey saline soils to study on the influence mechanism of pore and moisture characteristics in the Yellow River Delta.This study focuses on the influence of particle composition changes on the pore distribution,soil water constant,saturated hydraulic conductivity,and soil moisture characteristic curve of clayey saline soil,and uses the ratio of soil very fine sand to clay content(sand viscosity ratio)as the characteristic index,to study the relationship between sand-viscosity ratio and soil moisture,saturated hydraulic conductivity and soil pores,and clarify the influence mechanism of soil particle composition changes on the pores and water characteristics of clayey saline soil.The main results are as follows:(1)There are obvious differences in the particle composition of the sediment from the Yellow River and the clayey saline soil.The sediment from the Yellow River is mainly composed of very fine sand grains of 0.1-0.05mm,and the clay saline soil is mainly composed of coarse powder grains of 0.05-0.01mm and fine clay grains of<0.002mm.In this study,the BP neural network prediction model was used to analyze the sensitivity of the soil particle size and the soil field water holding capacity.The results showed that very fine sand particles of 0.1-0.05 mm and fine clay particles of<0.002 mm affect the soil field water holding capacity.The key size.The soil sand viscosity ratio increased exponentially.(2)Using van Genuchten equation,Gardner equation and Rational equation to fit the soil moisture characteristic curve,the results show that the fitting errors of the three equations are small,the fitting degree of van Genuchten equation is higher,and the error of Rational equation is the smallest.With the change of soil particle composition,the soil moisture characteristic curve changes significantly.With the increase of the very fine sand particles in the soil,the fine clay particles decrease,and the soil water content decreases significantly under the same water suction,and the soil water holding capacity decreases.(3)With the change of soil particle composition,the content of very fine sand particles increases,the content of clay particles decreases,and the effective pores and ineffective pores of the soil decrease linearly.The macropores of the soil increase exponentially,and the ratio of macropores to ineffective pores is exponential.The exponential regression equation of very fine sand grains and soil macropores was established,and the correlation coefficient R~2 was greater than 0.96.A linear regression equation between fine clay particles and ineffective soil pores was established,and the correlation coefficient R~2 was greater than 0.96.A linear regression equation was established between the sand-v iscosity ratio and the volume ratio of macropores and voids,and the correlation coefficient R~2 was greater than 0.98.(4)With the change of soil particle composition,the content of very fine sand particles increases,the soil field water holding capacity and the ineffective water content decrease linearly,the soil gravity water content increases exponentially,and the ratio of soil gravity water to soil ineffective water content increases exponentially high.There is an obvious exponential relationship between the soil very fine sand content and the gravity water content,R2 is 0.94.Establish a linear regression equation for the ratio of soil sand viscosity to the ratio of gravity water and invalid water,and R2 is 0.97.(5)With the change of soil particle composition,the saturated hydraulic conductivity of the soil increases exponentially.The univariate nonlinear relationship equations between very fine soil sand particles and soil saturated hydraulic conductivity,soil fine clay particles and soil saturated hydraulic conductivity are established respectively,and the correlation coefficient R~2 is all greater than 0.97.A linear regression equation of soil-sand-viscosity ratio and saturated hydraulic conductivity was established,and the correlation coefficient R~2 was0.98.(6)Yellowing sediment can effectively change the particle composition of the 0-20cm soil layer of clayey saline soil.With the change of soil particle composition,the field soil saturated hydraulic conductivity shows an increasing trend.The yellowing sediment has a significant effect on reducing the soil water and salt in the 0-40cm soil layer,and has a significant impact on the increase of winter wheat yield.Among them,the yield of S2 and S3treatments increased the most,which increased by 27.40%and 23.51%respectively compared with the control.Using the relationship equation between the soil sand viscosity ratio and saturated hydraulic conductivity,the soil saturated hydraulic conductivity was estimated by the field test soil sand viscosity ratio.The predicted result and the measured value have R~2 of0.89 and RMSE of 0.088.The result is more accurate.Based on the above research results,it is shown that the sediment from the Yellow River can change the particle composition of clayey saline soil,improve soil porosity,increase soil water conductivity,reduce soil water content,effectively increase soil salt leaching capacity,and increase wheat yield.Very fine sand particles and fine clay particles in soil particles are the key to affecting soil physical and water properties.