Water Characteristics Of Two Typical Soil Types In Desert Steppe And Their Influencing Factors

Desert steppe is located in arid and semi-arid climate zone,with less precipitation and uneven distribution,large plant evaporation,and very fragile ecological environment.Soil moisture is the link between precipitation,surface water,groundwater and biological earth circulation,the carrier of material transmission and transport,and is the most important part of the ecological hydrological process in water resources.The gradual increase in temperature and the implementation of enclosure measures have exacerbated the trend of soil water deficit.Precipitation is the main method of replenishing soil moisture in desert steppe areas,and whether precipitation can be converted into effective soil moisture is mainly related to water infiltration.Therefore,in this paper,the lime-calcareous soil and aeolian sand soil in the desert grassland area of Ningxia are taken as the objects,and the method of combining field observation and indoor experiments is adopted to explore the spatio-temporal dynamic characteristics of different types of soil moisture through in-situ monitoring for two consecutive years To explore the soil physical factors that affect the process of soil water migration,use orthogonal experiments to analyze the effects of bulk density,,salinity,particle grading,and water head height on homogeneous soil water transport,and use the texture layering to layer soil water transport process analysis.Grasp the migration laws of water infiltration and redistribution in different soil types,and analyze the laws of soil water infiltration in desert grassland in order to provide a theoretical basis for improving the soil structure and the efficiency of water resources utilization in desert grassland area.The main conclusions are as follows:(1)The corresponding precipitation years in 2017-2019 are:flat water year,partial water year and special water year.From 2017 to 2019,the frequency of precipitation in grades ? and ? is the highest,and the differences in annual precipitation patterns are mainly concentrated in the total precipitation in grades VI and VII.There is no significant pattern between rainfall and rainfall levels and precipitation times.(2)The seasonal dynamic law of soil moisture changes can be roughly divided into three stages:soil water compensation period(early May to early June),soil water consumption period(mid-June to end of September)and weak soil water balance period(9 End of month-beginning of November).The rapidly changing layers of gray-calcareous soil and aeolian sand in Tefeng Water Year are 0-20 cm,the active layer is 20-80 cm,and the secondary active layer is 80-100 cm.The sub-active layers of gray-calcareous soil in partial water years are 20-100 cm,and the relatively stable layers are 0-20 cm;the sub-active layers of sandy soil in partial water years are:0-10 cm,40-60 cm,and 80-100 cm,and the relatively stable layers are 10?40cm and 60?80cm;the secondary active layer of limestone in plain water years is 0?10cm and 60?100cm,the secondary active layer of sandy soil in plain water years is 0?10cm,and the relative stable layer is 10?100cm.The soil moisture content of lime-calcareous soil shows a "rising-falling-rising" change with the deepening of the soil layer.The soil moisture content of aeolian sand soil has a blowout increase in the 0-60 cm soil layer,and then increases slowly,but with the depth of the soil layer.Increasing the soil moisture content gradually increases.In 2017,the soil moisture of the lime-calcareous soil profile(0?100 cm)showed accumulation type,and the aeolian sand soil showed consumption type;in 2018,both types of soil moisture showed consumption type in the whole profile.In 2019,the two types of soil moisture are accumulative in all profiles.(3)The time stability of soil moisture of the two soil types increases with the increase of soil depth,and the soil moisture variability in the surface layer of 0-10 cm is the largest.The representative soil layers of the average soil moisture content of lime-calcareous soil and aeolian sandy soil are 80?100 and 40?60 cm,respectively.The two types of soils have different spatial and temporal distributions of soil moisture.Precipitation will increase the degree of soil moisture variability.Aeolian sand soil is more affected by precipitation than grey calcareous soil.(4)During the infiltration process of layered soil,the wetting front and infiltration rate gradually decrease with time,and the cumulative infiltration amount increases with time.During the whole infiltration stage,there was no significant difference between the lime-calcareous soil covered with aeolian sand soil 5cm,10cm,the wet front process,the infiltration rate and the cumulative infiltration amount.In the initial stage of infiltration,there is no significant difference between the wet front process,infiltration rate and cumulative infiltration amount of lime-calcite 5cm and 10cm on the sandy soil,but in the stable stage of infiltration,the sand-soil is covered with 5cm,10cm of gray calcium At 20 cm,the wet front process,infiltration rate,and cumulative infiltration volume were significantly different.The infiltration rate,cumulative infiltration volume and wetting front process of homogeneous aeolian soil are significantly higher than those of homogeneous lime-calcareous soil.Soil type and layer thickness have a significant effect on the soil infiltration process.The limestone soil covered with aeolian sand has a thickness of 20cm,and the permeability enhancement is the best,while the sandstone covered with lime-calcium soil has a thickness of 10cm.(5)Combining R2 value and model parameters to comprehensively compare the fitting effects of Kostiakov model,Philip model,and general empirical model on infiltration,and found that general empirical model has the best fitting effect on homogeneous soil,while Kostiakov model has good effect on layered soil The fitting effect of the infiltration process is the best.The simulation effects of the three models on the water infiltration process of different layered soils are:Kostiakov model,Philip model,and general empirical model.(6)During the infiltration process of homogeneous soil,the wet front and infiltration rate gradually decrease with time,and the cumulative infiltration amount increases with time.The migration process of humid front decreases with the increase of bulk density and clay powder content.The difference of salt content has no significant effect on the migration process of soil humid front.The infiltration rate decreases with the increase of the bulk density and the content of clay powder,and it changes with the increase of the salt content.From the initial period of soil infiltration to 30 minutes,the wet front process and infiltration rate increased significantly with the increase of pressure head,and when the soil infiltration reached a stable stage,it decreased with the increase of pressure head.When the bulk density is between 1.52 and 1.60(g/cm3),and the content of clay powder is between 5%and 10%,the cumulative infiltration decreases with the increase of bulk density and clay powder content.S "type changes.The influences of various factors on the process of homogeneous soil wetting front and infiltration rate are:bulk density>particle gradation>salinity>pressure head.The influence of various factors on the cumulative infiltration of homogeneous soil is:bulk density>particle gradation>pressure head>salt.(7)In the entire evaporation process,bulk density has the greatest influence on soil evaporation.In the early stage of evaporation(day 7),the influence of four factors on the cumulative evaporation is:bulk density>pressure head>salt>particulate gradation;in the middle stage of evaporation(day 21),the influence of four factors on the cumulative evaporation The order is:bulk density>salt>pressure head>particle gradation;in the later stage of evaporation(Day 35),the influence of 4 factors on the cumulative evaporation is:bulk density>pressure head>particle gradation>salt.