我国土壤资源的现状及特点 (36).ppt

土壤水分常数和有效性5.3 Soil Water Constants and Availability 1.1 Hygroscopic Coefficient(Maximum Hygroscopicity)It refers to in the air with relative humidity close to saturation,the maximum amount of water vapor molecules that dry soil can adsorb.It can be used to roughly calculate wilting coefficient.Mainly depends on soil clay content and organic matter content.1.Soil water constants1.2 Maximum Molecular Water Holding CapacityIt refers to the soil water content when the membranous water reaches maximum thickness.Its water content is 2 to 4 times of Hygroscopic Coefficient,includes hygroscopic water and membranous water.1.3 Wilting Coefficient(Withering Coefficient)When the soil water content is too low,plants can not absorb water from the soil,they will wilt permanently.The soil water content(soil suction suffered maybe larger than 1.5 MPa)at this time is called the Wilting Coefficient.It is the lower limit of soil available water,includes hygroscopic water and unused membranous water,mainly influenced by soil texture,plant type and climate status.Soil textureCoarse sandy loamFine sandy soilSandy loam soilLoamClay loamWilting Coefficient 0.961.102.73.65.66.99.012.413.016.6Wilting Coefficient of different texture soils（m%）Lv&Li,20061.Soil water constants1.4 Field CapacityIt refers to the soil water content when the capillary hanging water reaches the largest.It is the maximum amount of water the soil can hold,is the irrigation maximum of dry land soil.Influencing factorsTexture,SOM content,soil structure,tillage status,etc.IncludesHygroscopic water,membranous water and capillary hanging water.1.Soil water constants 1.5 Saturated Water Content(Saturated Water Capacity)It refers to the water content when all soil pores are filled with water.It includes hygroscopic water,membranous water,capillary water and gravity water.If express with volumetric water content(v),it is equal to the total porosity.It is one important accordance for displacement calculation when drain and lower groundwater level.1.Soil water constantsPhysical classificationHygroscopic waterCapillarywater GravitywaterEcological classificationUnavailable waterAvailable waterSurplus water2.Soil water availabilityThe soil water that can be absorbed and used by plants is called available water,or is called unavailable water。Largest available water content=Field Capacity Wilting CoefficientActual available water content=Actual water content Wilting CoefficientInfluencing factorsSoil texture,structure,SOM content and plant type,etc.Hygroscopic Coefficient Wilting Coefficient Field CapacitySaturated Water Content 1000031150.10Soil suction(atm)Schematic diagram of soil moisture types.（Modified According to D.Stella）谢谢THANK YOU