Exploration of the reasons for the large difference in hydraulic parameters of red soil in Yunnan Province
In order to explore the reasons for the large difference in the hydraulic parameters of red soil between Yunnan Province and the surrounding areas,the basic hydraulic parameters of red soil were measured by sampling in undisturbed soil farmland and farm-land after land leveling.At the same time,a two-hour field surface drip irrigation infiltration test was carried out.The soil profile was divided into four layers of 0～15 cm,15～25 cm,25～40 cm and 40～55 cm.Based on the Kosugi empirical model of HYDRUS-1D mod-el,different inversion models were constructed to analyze the effects of these methods on soil hydraulic parameters.In order to ensure the convergence of the inversion model under field conditions,the contact radius of the emitter was assumed to be in the range of(1.0±0.2)cm,which was calibrated by the trial and error method,and the conditions with the highest accuracy were selected for subse-quent analysis.The results showed that the simulation accuracy of the inversion model was the highest when the irrigation flow rate of 0.84 L/h was calibrated by the trial and error method,the contact radius of the emitter was 0.9 cm and the constant flux of the upper boundary was 2.75 cm/min,and the R2 was 0.926 18,the AIC value was-65.62,and BIC value was-62.04.The inversion method suitable for red soil in the field was that the fitting parameters were inverted by fixing the measured saturated water content,residual water content and saturated hydraulic conductivity of each layered soil.In view of the fact that the surface layer of red soil would form a water blocking layer during drip irrigation in the field,the saturated hydraulic conductivity of the surface soil also needed to be invert-ed.In addition,this study found that the undisturbed red soil in Yunnan Province had high water retention and strong water permeabili-ty due to factors such as geography,ultraviolet radiation,and dry and wet season climate.However,sampling of farmland after soil lev-eling or inversion based on inaccurate soil parameters through numerical models might lead to the conclusion that red soil had poor wa-ter retention and permeability.
red soilsoil hydraulic parametersparameter inversionsurface drip irrigationnumerical simulationYunnan Province
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