| Temperature is an important factor affecting soil moisture movement and retention,Based on the existing studies on soil moisture temperature effect and soil hydrothermal interaction,this paper deeply explores the influence of temperature change on soil hydraulic parameters and water movement,analyzes the influence mechanism,and discusses the soil hydrothermal change under natural conditions.The effects of temperature on the hydraulic parameters of different types of soil,especially the viscous red soil,were quantified by means of indoor simulation analysis;Combined with the traditional STVF theory,the main influencing factors and mechanism of temperature on soil moisture migration and retention are revealed from the perspective of soil structure and porosity.Based on the field monitoring data,the hydrothermal characteristics and hydrothermal interaction of undisturbed red soil upland under different treatment methods were studied.The research results show that:(1)The influence of temperature on the saturated water conductivity of soil is very significant,but the influence on different types of soil is very different.The saturated water conductivity of part of soil increases with the increase of temperature.The relation between saturated water conductivity(Ks)and temperature(T)can be roughly fitted by power function.The saturated water conductivity of some soils first increased and then decreased.The temperature effect of sandy light soil is more significant than that of clay heavy soil.(2)Soil water characteristic curve moves down and becomes gentle with the increase of temperature.The Van Genuehten model can be used to fit the soil water characteristic curve at medium-low temperature or at high water content stage.The effect of soil water potential temperature(Tw)increases with the decrease of soil moisture content,and the effect is more significant in the low temperature region.In the low water content stage,the temperature effect of soil water potential and its relationship with its own water content(θv)can be roughly fitted by power function.(3)The temperature effect of water movement and retention in lighter soil can be explained by STVF theory.For sandy light soil,the influence of temperature change on the surface tension and viscosity coefficient of soil moisture determines the temperature effect.For soils with high clay content,the effect of temperature on soil structure must be considered.Temperature rise causes soil matrix to expand thermally.The degree of soil thermal expansion mainly depends on soil texture,type of clay mineral and content of organic matter.Soil matrix of thermal expansion will change the internal structure and pore distribution,it not only makes the soil total porosity decreases,and will also change the soil equivalent aperture distribution,and is especially great for the impact of soil macropore and makes the aperture range of soil macropore decreased greatly,the ratio of large pore volume to total pore volume decreased,but the effect on small pore volume was not obvious..The influence of temperature change on soil water movement and retention is a complex process,which mainly occurs through three aspects:first,it affects soil water properties,including surface tension,viscosity coefficient and density of soil water;Second,the soil structure is affected by the temperature change,which will cause changes in the particle size of some particles in the soil,cause thermal expansion of the soil,and change the soil structure and porosity.In addition,in the process of soil temperature change,the change of soil moisture property and the change of soil structure will also have mutual influence.In fact,these two influence mechanisms exist simultaneously and restrict each other.(4)Under the condition of long-term temperature fluctuation(within a year),the overall change characteristics of soil temperature are consistent with air temperature.The change range of soil temperature within a year decreases with the increase of depth,and the change period of soil temperature has a lag period compared with atmospheric temperature.The Change of soil water is complex,it influences by air temperature and precipitation and presents a certain volatility.On the whole,soil moisture is mainly influenced by precipitation,soil moisture content and water potential changes are significantly positive correlation with precipitation,except 70cm soil layer,there was a significant negative correlation between soil temperature and soil moisture in each layer,and the correlation first increased,then decreased and then increased with the increase of soil depth.Under the condition of short period temperature fluctuation(within days),the soil temperature of 5cm and 10cm layer has a significant positive correlation with soil moisture,and the correlation decreases with the increase of soil depth,while the soil temperature of 5cm layer has a weak correlation with soil water potential.There was no significant correlation between soil moisture and soil temperature in soil layer below 10cm.(5)Without surface water recharge,the change of soil moisture content is related to the diurnal variation of ground temperature.The existence of soil temperature gradient causes the vertical thermal movement of soil moisture.The moisture in unsaturated soil will flow from the low suction point to the high suction point,that is,from the warm end to the cold end,thus affecting the vertical distribution of soil moisture.(6)External water input(precipitation event)has a significant impact on soil moisture change,which is reflected in the fact that the moisture content of each soil layer responds to the precipitation to a certain extent.The surface soil moisture content and water potential rise rapidly with the occurrence of precipitation,and the growth rate decreases with the increase of soil depth.There was a positive correlation between precipitation and soil temperature in the soil layer below 10cm,and the correlation first increased and then decreased. |
