| Infiltration was a process in which water penetrates the soil surface into the soil.The infiltration performance determines the water quantity and distribution of water entering the soil profile from the surface and affects the migration process of solute.The infiltration characteristics of soil water in sierozem soil were studied,and the variation rules of hydraulic parameters of sierozem soil were deduced.It could provide reference for clarifying the law of water transport of sierozem soil in Yinchuan farmland and formulating reasonable farmland development strategy.In production and life,improving and enhancing the quality and potential of cultivated land was an important method and way to solve soil leakage and fertilizer leakage,water holding capacity is weak,humic acid as a commonly used soil amendment,widely exist in soil and water,with hydrophilicity,cation exchange capacity,complexation and adsorption and dispersion capacity,affecting the hydraulic characteristics of soil.Therefore,it is necessary to conduct a series of studies on the water infiltration characteristics and the variation rule of hydraulic parameters of the sierozem soil with humic acid sddition.Based on this,this paper used the method of combining laboratory simulation experiment and mathematical model to study the determination experiment of one-dimensional vertical infiltration,one-dimensional horizontal absorption,water characteristic curve and solute transport penetration curve under the treatment of humic acid addition ratios of CK,1%,2%,3%and 4%.(1)Through the laboratory one-dimensional vertical infiltration test,soil water infiltration characteristics under different humic acid addition were compared.With the increased of humic acid additions,soil wetting front process,cumulative infiltration and infiltration rate gradually decreased.When the infiltration time is 90min,the wetting front of 1%,2%,3%and 4%is reduced by 6.5%,10%,15%and 21%compared with CK,respectively,and the cumulative infiltration is reduced by 4.5%,11.14%,18.42%and 23.6%compared with CK.The fitting results of Phillip model,Horton model and Kostiakov model were analyzed and compared.It was concluded that Kostiakov model(R2>0.95)could more accurately describe the soil water infiltration in the study area.Using Hydrus-1D inversion of soil hydraulic parameters,it was found that humic acid additions affected the hydraulic parameters.The humic acid additions was positively correlated with the retained water content θr and saturated water content θs,and negatively correlated with the reciprocal intake suction a and the saturated water conductivity Ks,which fully explained the permeability reducing and water holding performance of humic acid.(2)A one-dimensional horizontal soil column absorption test was carried out using the indoor simulation method.The results showed that humic acid additions to sierozem soil could slow down the water absorption process.With the increase of humic acid addition ratios,the saturated water conductivity of soil gradually decreased,the saturated water content gradually increased,and the soil water holding capacity increased Under the same water content,with the increase of humic acid content,the soil water suction increased while the unsaturated water conductivity decreased,which enhanced the water holding capacity and soil water availability of sierozem soil.In the Brooks-Corey model,humic acid additions had an obvious effect on the hydraulic parameters of the field sierozem soil.(3)The tensimeter method was used to measure the soil water characteristic curve of sierozem soil under different humic acid additions.Five models,VGM(m,n),VGM(m,1/n),VGB(m,2/n),BCM and BCB,were used to fit the measured data of water characteristic of sierozem soil under different humic acid additions,combined with statistical analysis.Compared with Brooks-Corey model,van Genuchten model has better applicability.On this basis,VGB(m,1/n)model has the best fitting effect,which is the optimal model for soil moisture characteristic curve of sierozem soil in Yinchuan Plain.Soil water characteristic curves showed obvious differences with different humic acid additions,especially in the low suction section(S<10kPa).The curves under different additions showed obvious morphological differences.(4)In laboratory simulation experiments,CDE and TRM models were used to simulate the solute transport process of the sierozem soil in Yinchuan plain under different humic acid additions.Humic acid additions had a certain delay effect on the process of solute penetration into the soil.Both CDE equation and TRM model could describe and simulate solute transport conditions under different humic acid additions,but TRM model has higher fitting accuracy.According to the analysis of the dispersion coefficient D,the β value decreased gradually from 0.497 to 0.196 with the increase of the proportion of humic acid,indicating that the mechanical dispersion of water in sierozem soil was small.Humic acid prevents the leaching of nitrate nitrogen downward,which has positive significance for farmland soil. |
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