Study On Characteristics Of Soil Hydrodynamic Parameters And Spatial Variability In Gravel-Mulched Fields

Soil water characteristic curve and soil hydraulic conductivity as important soil hydrodynamic parameters,characterizing soil water infiltration performance and solute transport speed,is the foundation of interdisciplinary subjects such as soil hydrodynamics,hydrology and water resources,ecological hydrology.In view of this,this study takes the gravel-mulched fields of Jingtai county in the northwest arid region as the research object.Through field sampling and interior design experiments,the effects of different planting years on the soil hydrodynamic parameters of the gravel-mulched fields were studied.On this basis,the spatial variability of soil water characteristic curve was analyzed by classical statistics and geostatistics,and the soil water characteristic curve was predicted by regression model and fractal theory.The main contents are as follows:(1)In order to investigate the effect of different planting years on the soil hydrodynamic parameters,laboratory experiments were used to stud y the effects of different planting years on soil water holding capacity,and the variation of soil unsaturated hydraulic conductivity curves in different planting years was analyzed in the gravel-mulched fields.The results showed that the soil water content of different planting years showed a trend of decreasing with the increase of suction.The change trend of soil unsaturated hydraulic conductivity in the gravel-mulched fields is faster than that in bare land,and the change trend of new gravel-mulched field is the fastest.In the 0-20 cm and 20-40 cm soil layers,when the unsaturated hydraulic conductivity is the same,the water content is expressed as new gravel-mulched field>middle gravel-mulched field>old gravel-mulched field>bare land.This result can provide important theoretical guidance for the quantitative discussion of soil water holding capacity in the gravel-mulched fields.(2)Using RETC software,van Genuchten(VG)model and Brooks Corey(BC)model were used to fit the soil water characteristic curve of different planting years of gravel-mulched fields,and the measured value of soil water content under each suction was compared with the fitted value and the error analysis was carried out.The results showed that both the VG model and the BC model can fit the soil water characteristic curves of gravel-mulched fields with different planting years.The correlation coefficients are both greater than 0.98,and the relative error is small,and the fitting accuracy is high.Compared with BC model,VG model has higher precision,which shows that VG model is more suitable for fitting soil water characteristic curve of different planting years than BC model.The results provide a necessary basis for the analysis and calculation of the law of soil water movement in gravel-mulched fields.(3)The spatial variability of soil water characteristic curve under different planting years was studied based on classical statistics,geostatistics,Kriging interpolation and other methods.The results showed that?_s and n were weak variation and?was medium variation,and the parameters?_s,?,and n have strong autocorrelation.?_s is scattered in space,and it is much larger than the bare land in the high value area of the new gravel-mulched field,middle gravel-mulched field and old gravel-mulched field.The parameters of the parameters?_s???n of different planting years all show the distribution of"unevenness".The degree of"unevenness"of the parameters of the new gravel-mulched field is the least obvious,while the old gravel-mulched field and bare land have an obvious"concave-convex"trend.This result is helpful to further understand the spatial variability pattern of the soil water characteristic curve of gravel-mulched fields in arid regions.(4)Taking the new gravel-mulched field in Jingtai County for less than 10 years as an example,use the fractal theory to study the relationship between the soil particle size distribution and the fractal characteristics of the soil water characteristic curve and predict the soil water characteristic curve.The results showed that the fractal dimension of the soil particle size and the fractal dimension of the soil water characteristic curve in the gravel-mulched fields are closely related to the soil particle size distribution.The correlation between the fractal dimension of the particle size of different soil layers and the fractal dimension of the soil water characteristic curve is significant at 0.01 level,and the coefficient of deter mination is higher than 0.983.The fractal dimension of soil particle size can be used to accurately predict the fractal dimension of soil water characteristic curve.This result can provide a simple method for determining the soil water characteristic curve of gravel-mulched fields.