Soil and Environmental Physics
Soil and Environmental Physics SOIL 415
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a Urivezsitwrldaho Hydroloic Measurement Techniques 39 39 lune nu Measurement Techniques at the University of Idaho Do not distribute these notes Soil Bulk Density amp Compaction mu Demm Mgm vuuswxvxsu u Mm yiomug uywukum u Copyright Markus Tuller 20022006 gummtyarldam Dry Bulk Density Ratio of the mass of ovendry soil and total sample volume The dry bulk density is primarily affected by soil texture and structure including aggregation and particle size distribution lfthe pore space is half of the bulk volume the dry bulk density pb is about half of the particle density 35 1300 to 1350 kglm3 Fine textured soils commonly have lower bulk densities than coarse textured soils myqu M mm mm mums umessnymldam Determination of Bulk Density To determine bulk density we need to measure the dry mass and the total volume occupied by the soil sample A cylindrical metal sampler is driven into the soil to remove a known volume core l l l The core soil brass cylinder is ovendried at 105 C to remove nonstructural soil water until the mass remains constant usually after 24 48 hrs myqu M avkus mm mums umam iCore Method Dry Mass Sample Volume Cylinder VcVtr27zh QUmasmudaho Core Method Example r 3 cm h 12 cm M5 480 g ovendry mass K r2 41232 31412339cm3 M 480g 3 pb Vt g cm3 g Qummmm Excavation Methods Sand Funnel A quantity of soil is excavated in the eld dried at 105 C and weighed The volume is determined by lling the excavated hole with a well de ned standard sand ofwhich the volume per unit mass is known SAN DFUNN EL Method Standard Sand 1 x i quot39 Valve 1 I Base Plate Qumvasnymldam Excavation Methods Rubber Balloon In the RUBBER BALLOON Method the volume is l determined by inserting a balloon into the excavation and lling it with water or an other uid with known density Water Tower with Scalell Valve 39 V iquot Rubber Membrane a Untversltyoildaho Bulk pensity Clod Method CLOD METHOD Balance 0 7 Winona i V Q UrWeis yotldaho Bulk Density Gamma Rays GAMMA RAY TECHNIQUES Gamma ray techniques are based on attenuation and diffraction of gamma rays emitted from a 137Caesium or 2 Americium source due to collision with other atoms of the soil phases Attenuation and diffraction are dependent on bulk density and other soil properties eg water content 10 10 1 10 mquot inquotquot m 10 1a A aveiengm m centimeters Hmldings Human Humme human Prmnmans Awa 1h 5 1e 07quot lu nlnruics mums Arumir Nutlai Umatsnwldam Gamma Rays TRANSMISSION TECHNIQUE Two probes at a xed spacing are lowered into previously prepared openings in the soil One probe radiation transmitted through the soil from the gamma source located in the second Qumnymldam Gamma Rays SCATTERING TECHNIQUE A single probe contains placed in a hole dependent on design of the equipment Surface Probe Gamma Rev 919 Sam gum l l Tm Borehole Probe Souke 39quotAmlrldum or 39 mainn umatymldam Gamma Rays CaprM Maw Taller zuuzrzms a UrWasltyatldaho Soil Compaction Desired or Not O In agriculture and forestry soil compaction is undesirable 0 For many engineering applications a well compacted soil is crucial for safe foundations the Leaning Tower of Pisa is an example of building on soft soil Image Opera PH mazale Pisana Capwm Maw Tuuevzuuzrzms gummldaho isoil Compaction Low porosity n or high bulk density 3 are indicators for soil compaction Soil compaction results in mechanical impedance to plant root growth poor aeration and restrictions to water infiltration Forest ecos stems are extreme sensitive to soil compaction Compaction associated with timber harvest could disturb ecosystems for many years EnWHgMQMavkusTuHev 2nu22ms U vereilymldal39lo iAgricultural Soil Compaction Causes I 0 Operation of heavy vehicles eg harvesters construction machines on agricultural land can cause soil compaction EnWHgMQMavkus mm 2nu22ms ummam I Compaction alters soil hydraulic and gaseous exchange properties and increases mechanical impedance to plant roots umwmn Soil Compaction Effects I Compaction hampers plant growth and ecreases crop yield I The extent of soil egradation due to compaction exceeds an area of 68x10 kmz worldwide Oldeman otsamurban Soil Compaction Agriculture Potato yield on a clay loam in Minnesota o uhn l mlhf O i lralllc bull we a mm 24 Mgcha Yield rst Second Third Year sovwgme Markus mm 20922005 Mam Soil Compaction Effects on Pore Spaces sovwgme Markus mm 20922005 gummam Soil Compaction Ariculture Subsoiler umwm The tillage pan has been mechanically broken by a subsoiler The vertical slot allows roots to penetrate into the subsoil to access water and nutrients milling Soil Compaction Agriculture Root distribution of a cotton plant INTERROW TRAFFIC gum Soil Compaction Agriculture Soil compaction can be reduced by spreading the applied weigh I A id llm l E1 v W x t Soil Compaction uuu Characterization of the Liquid Phase Copyright Markus Tuller 20022006 Uriversltyarldaho Characterization of the Liquid Phase The two most important characteristics of the liquid phase are The amount of water in the soil soil water content 39 The forces by which water is held in the soil matrix matric potential These two soil attributes are related through a function known as the SOIL WATER CHARACTERISTIC SWC sorL WATER CHARACTERISTIC Mame P otrentlal an o 01 02 03 on 05 Volumetric Waher cement mlm3 Changes in soil water content and matric potential affect many soil transport and mechanical properties such as 1 ability to transfer liquid and gases 2 mechanical properties such as soil strength compactibility penetrability and bulk density in swelling soils EavyugMQ Mzrku my mum umersuymidaho Soil Water Content Measurement Methods GRAVIMETRIC WATER CONTENT Samples obtained by digging augering or coring are weighed moist sample and weighed again after oven drying 105 C 7 mass of water 7 mass wet soil 7 mass oven dIy soil mass of dIy soil mass oven dIy soil VOLUMETRIC WATER CONTENT Samples with known volume core samples may be processed the same way as in the gravimetric water content method mass of water volume of water 7 Kdensity of water V 7 bulk volume of soil 7 sample volume The conversion between gravimetric and volumetric water content requires knowing the dry bulk density 9V9mpb Pw UNvetstIyarldaho Soil Water Content Gravimetric Determination Gravimetric watcrcon 1t 7 J wet soil Oven 105 C 7 24 11 dry soil Umasllymldaho Soil Water Content Volumetric Determination Volumetric water content wet soil Oven 105 C 7 24 h dry soil Qummldam Nondestructive Methods Neutron Scattering N eutron Probe Neutron Scattering or Neutron probe is awidely used eld method for repetitive measurement of volumetric soil water content Sphere of In uence It is based on the propensity of water molecules to slow down thermalize a radio active source Americium241 Beryllium Thennalized neutrons are counted by a detector present in the access tube along with the source Qumawmdam Nondestructive Methods Neutron Scattering Fast neutrons are emitted radially into the soil and collide with various atomic nuclei Collisions with most nuclei are virtually elastic with only minor loss of kinetic energy Collisions with hydrogen nuclei causes signi cant loss 39 39 d slow down of the fast neutrons thermalization Urivers yovldaho Neutron Scattering Method 0 Calibration of the Neutron Probe is necessary to account fo background hydrogen sources and other local effects like bulk density Calibration is achieved by simultaneously measuring soil water content and count ratio CR ratio of slow neutrons to standard count obtained with the radiation source in the shield a VOWa g 6V 2 abCR gunmiyondam Limitations of Neutron Scattering Method 0 Radiation hazards o Requires site specific calibration 0 Variable volume of measurement 0 Not suitable for nearsurface measurements 0 Provides snap shots difficult to automate 0 Installation and measurements are labor intensive 0 Limited accuracy gummmho Time Domain Reflectometry TDR SOIL 415 Soil and Environmental Physics Copyright Markus Tuller 20022006 Unvers yaildaho 7 Time Domain Reflectometry TDR TDR Cable Tester Tektronix 1502B BNC Connector Time Domain Reflectometry TDR is a relatively new technique for measurement of volumetric soil water content using electromagnetic waves propagating along embedded waveguides Eavvighm Mavxusruiiavzaazrzoaa umasmmldaho Time Domain Reflectometry TDR Advantages 0 Superior accuracy to within 12 of volumetric water content calibration requirements usually no soil speci c allbration necessary 0 No radiation hazard such as associated with neutron probe or amma ray attenuation techniques 0 Excellent spatial and temporal resolution 0 Continuous measurements through automation and multiplexing Limitations 0 Expensive typical system costs 4000 0 Limited performance in saline soils 0 Specialized no off the selfquot systems requires training Universityalldaho Time Domain Reflectometry TDR The propagation velocity v of an electromagnetic field along a transmission line waveguide of length L embedded in the soil is determined from the time response of the system to a pulse generated by the TDR cable tester opagation velocity v2Lt is a function of the soil bulk t nt The pr dielectric cons a V t travel ume nfthe wave amng me gums and back 2L Z c 2 ct Z c vemmty nfthe electromagnetic wave 5b m vacuum M n8 ms Coaxial Cable Stainless Steel Rods Ulivels yalldaho Time Domain Reflectometry TDR The dielectric constant a is the property of a material that determines the relative speed that an electrical signal will travel in that material 2 Lowe ft high signal propagation speed fastest 21 8 3 High 8 it slow signal propagation b The bulk soil dielectric constant 2 is governed by the dielectric of liquid water cw Water sw 81 Soil Minerals 5 3 to 5 Soil Air ea The large disparity between dielectric constant of water and other soil constituents results in dominance of soil bulk dielectric constant eb by the volume fraction of liquid water eW hence dielectric measurements are ideal for soil water content determination cavyllgMQ mm my mum umersuyalldaho 7 Time Domain Reflectometry TDR Table 14 Tabulated values ofthe dielectric constant for fluids and solids Material Dielectric Constant Material Dielectric Constant Fluid 2025quotC Solids 2025quotC Water 804785 Ice 12quotC 4137 Ethanol 243 Fused Quartz Si02 378 Ammonia 169 Sandy Soil dry 255 Benzene 229 Loamy Soil dry 251 Acetone 207 PVC 289 Air 10 Polyethylene 225 cm liquid 16 Te on 21 C02 gas 1001 Wood Douglas Fir 190195 Sources CRC Handbook of Chemistry and Physics 1993 vonHippel 1955 Urllversltyolldaho TDR Basic Principles The travel time of the electromagnetic wave to traverse the length of the apparem Ul 39 the probe 39 V k on the TDR output screen by diagnostic changes in the waveform The relationship between the locations oft e two g reflection points and bulk 39 die ectric constant is E 2 X i X 8b 2 1 vlo L H W M 3m aim in Distance cm VF is the relative propagation velocity often set at 099 a Universityalldaha TDR Basic Principles Re ection Distance cm 1 Reflection Coaxial Cable Epoxy handle 2 Transition Rods Epoxy Rods in Soil 3 Reflection end of rods Coaxial Cable Epoxy Stainless Steel Rods a Umersnymldaho TDR Basic Principles Ralenmn hoe lunl n 1 Re ection Coaxial Cable Epoxy handle As TDR signal leaves the shielded coaxial cable and enters the handle section formation of a blip ransition Rods Epoxy Rods in Soil As the signal leaves the handle the typically more efficient or lower impedance I A 1st 3 Re ection end of rods The end of 39 Urliveqsllymldaho TDR Basic Principles Different waveguide designs and associated electromagnetic fields o TDR sensor designs seek fewer conductors to reduce 39 39 disturbance o he porous e Ium o Measurement volume and sens ty vary with design Concentration of field lines near conductors emphasize y of 39 cond ons in this region Qummmdaho TDR Of the Shelf Systems umzymldam Soil Bulk Dielectric Constant to Water Content No basic approaches are used to relate Soil bulk dielectric constant sh to o umetric water content 9V Empirical or calib ion relationships such as the 339quot order polynomial proposed by Topp et al 1980 that seems to t data for many mineral soils Topp s Equation 9V 753x1022924ng755x104a224r43X106g3 umwormm Physically Based Dielectric Mixing Models m r mp aquot mixingmuue 39 39 t39 39 suil 39 the mixture Roth et al 1990 1 5b 8V W lings n78v a g n is soil porosity and 1ltplt1 summarizes applied EM eld direction relative to medium axial direction of waveguide p 1 for an EM eld parallel to soil layering 1 for EM eld perpendicular to layering B 05 for an isotropic two phase mixed 39um a Umasltymldaha Dielectric Mixin Model he mixing model can be simpli ed using 305 and the dielectric constants of the constituents w 1 65439 d sa 1 5b BV gw lings n78v a g gb i inks inga 19V 5W 7 8 07 rue 5 as 5 Jab 7 2 7 n g mum vssu 9V gm 8 g m 17volcamcsamplas a Vngeleralnl 1595 20 an an sa Dmlmrl mm 0m Urivers ymldaho Mixing Model Example What is 3 of a soil having 0V 02 and bulk density of 1325 kglma What if the soil contained the same volume fraction of ethanol rather than water First we estimate the porosity for this soil as Then we use 5 05 and the dielectric constants of the constituents Law 81 as 4 and ea 1 to solve the mixing model for the bulk dielectric constant ab 1 8b 6v gw 1 ngs n t9vga g 1 gb 0281 5 1eo54 5 057021 505 961 EavyugMQ szku mum 2mm Uriversuyatldaho illIixing Model Example For ethanol and assuming 25 C we substitute the appropriate dielectric of 243 into the mixing model and receive 5b 02243051eo54 505eo21 5 E 5225 Note that because ethanol undergoes relaxation a change in dielectric constant within the TDR frequency bandwidth the apparent dielectric ammo as measured using TDR is closer to 16 This means that some caution is required in attempting to model the apparent bulk dielectric of soils or other complex mixtures based on tabular values of the component dielectric constants 25 a Umarsltymldaho Limitations of Empirical Relationships mama Rangem Wata Eontmt H me warm 5 covers the entire range ofinterest in most rrineral soils walel 39 high organic matter content nuweven mineral solls Mth a water wntem r z 1 Note that the soil s porosity needs to be known Urlive39sltymldaho Time Domain Reflectometry TDR DISADVANTAGES OF TDR o Relatively expensive equipment a Limited applicability under highly saline conditions due to signal attenuation 0 Soil speci c calibration may be required for soils having large amount of bound water or high organic matter content large surface area a Requires training and experience a No offthe sellquot systems yet UMs ymldalro Other Methods For Volumetric Water Content Capacitance Sensors Capacitance sensors use an oscillator to generate an AC field which is applied to the soil in order to detect changes in soil dielectric properties linked to variations in soil water content The sensors essentially consist ofa pair of electrodes either an array of parallel spikes or circular metal rings which form a capacitor with the soil acting as the dielectric in between This capacitor works with the oscillator to form a tuned circuit and changes in soil water content are detected by changes in the operating frequency EavyugMQ szku mum 2mm Urivars yarldal39n Other Methods For Volumetric Water Content 39 39 T Line Oscillator TLC The HydroSense probe has electronic components that generate high frequency electromagnetic energy along the length of the probe rods Ln Kldman and Taylors Flatssolls I WWquot HydroSense Callbmtlon Tavlurs REEressmn L v numonmaa Ru new Measured E HI 3 A Hydrosense Qummuam Other Methods For Volumetric Water Content ECHO PROBES e Echo probe measures the dielectric constant of a medium by nding the rate of change of voltage applied to the sensor once it is buried in the soil TDR measures the dielectric constant by finding the travel time of an electromagnetic wave that traverses a wave guide I J I umzymdam Other Methods For Volumetric Water Content Advantages ofthe ECHO probe are the insensitivity for saline conditions and low expenses Only a Datalogger or Hand Read Out is required to send excitation voltage and record the rate of voltage change 28 G umwnllaam Other Methods For Volumetric Water Content RESISTANCE ELocKS gsum or Flherglass a porous matrlx gypsum or w A palr of electrodes ls embebbeb lh berglass that ls brought lh contact burleb th soll The porous materlal equlllhrates wlth the surrouhblhg soll so that the he matrlc potehtlal forces that hold the water ls the same T reslstahce between the electrodes ls measured and related to water content hlgh water contentlow reslstahce low water cohteht hlgh reslstahce mo callbratloh functlohs are regulre Matrlc potentlal versus reslstahce forthe block Volumetrlc water content versus matrlc potehtlal solL WATER CHARACTERISTIO forthe soll at Umrsmlnlldam Other Methods For Volumetric Water Content RESISTANCE ELocK Whine Potentla Julianne Whine pm llrcml um mm ml Volquotnun callbratloh Fuhctlohs MET comm 7 Man Pmenua mm Wan h h l gummm Other Methods For Volumetric Water Content OTHER METHODS XRay Computed Tomography CT Nuclear Magnetic Resonance NMR Ground Penetrating Radar GPR New CTFacility at WSU Qummlqam Other Methods For Volumetric Water Content Ground Penetrating Radar GPR Qummuam Other Methods For Volumetric Water Content Ground Penetrating Radar GPR suspended horn antenna umasuymldaho Other Methods For Volumetric Water Content Ground Penetrating Radar GPR measurements over wheat canopy wwwnemcanuwmmm mm W W Measurement of Soil Water Potential Components Copyright Markus Tuller 20022006 a Urwessllyatldal39n Measurement of Matric Potential Tensiometer Atensiometer consists of a porous cup usually made of ceramic having very fine pores that is connected to a vacuum gauge or other measuring device through a water filled tube After installing the tensiometer in the field the tube is filled with deaired water and sealed airtight In this initial stage water inside the tube is under atmospheric pressure If the potential in the surrounding soil is lower than atmospher39 pressure water will flow from the tensiometer through the porous cup into the soil until equilibrium is reac d m mm quotmum s mg This ow will lower the potential energy inside the V 62 we a suction that is sensed by the gauge or transducer When the soil is wetted ow can also occur in the reverse direction until a new equilibrium has been reached 32 Qummldam Tensiometer The gauge or transducer reading has to be corrected to account for the I at the point of interest in depth of the ceramic cup Measurement Range tie 415m hm Gauge m m head Tensiometer Equation Wm WWW 292m 2w Tensiometer Equation Wm WWW 29W 2cm W 1 2 02 435 05m 39P rou CUD gumasuymldaho Tensiometer Sketch showing tensiometers with vacuum gauges and electronic pressure transducers cm a Dahlnguor was Tmnsducnr Vacuum Diuiul E l mu mm mam H G Fresiwe vansduwr sou waxr maa I gt Pomus ceramic cup 0 UrWersltyarldaho Tensiometer amp Potential Diagrams Example The cups of tensiometers 1 and 2 are at a depth of 06 and 08 m below 39 quot 39 The gauge in tensiometer 1 indicates 1mm 09 m I u an 39 39 g 39 Assume static equilibrium conditions I Estimate the gage reading in tensiometer 2 u m First we set our reference level at the soil surface and calculatet e matric potential in 06 m depth using the tensiometer equation wm wgauge Zgauge Zcup Wm 709o27705 701 m Univeasltymldaho Tensiometer amp Potential Diagrams Example 39 at 06 m depth 1 soIl profile W Wm W1 Wp yh 701706 70 m throughout the profile tabulated values are in m head DET39EI h E l El 7 DD l i 39 calculated as U 1 El 1 El E E El 2 El 2 El 5 E El rm 7 rna rm nu V gauge El A El A El 3 E E El 5 El 5 El 2 E E U E El E El 1 E E El 7 El 7 E E E E U E El E E E El 1 El 9 El 9 E E El 2 1 El 1 E E E El 3 envmwu um mum12m Urivers yarldaho Tensiometer amp Potential Diagrams Example As the final step we can draw the potential diagram for equilibrium conditions 00 20 cm 1 2 EllllElllll HHEIHUE EavyugMQ mm my mum umersuymidaho Measurement of Matric Potential Heat Dissipation The rate of heat dissipation in a porous medium is dependent on the medium s speci c heat capacity the thermal conductivity and the density The thermal conductivity and heat capacity of a porous matrix is affected by its water content matric potential The measurement is based on application ofa heat pulse through a heating element and analysis of the temperature response measured with a thermocouple The measured magnitude of temperature change during a given heating period is linearly related to the natural logarithm of the matric potential measured AT AT a1nlm 3 11quot eXp a from calibration The linearity coefficient a has to be determined through calibration of the heat dissipation sensor 35 a Unvessilymldaho Heat Qissipation A typical line source heat dissipation sensor consists of a fine wire heating element that is axially centered in a cylindrical ceramic matrix having a diameter of about 15 cm and a length of 32 cm The thermocouple is located adjacent to the heating element at mid length Both the thermocouple and the heating element are placed in the shaft portion of a hypodermic needle LineSource Heat Dissipation Sensor 39 Measurement Range Porous MW 10 to 1000 kPa 01lo 10 bar 1 lo 100 m head Heating Element Q Thermocouple umveusnymidam Measurement of Matric Potential Psychrometer In cases where the solute potential is considered to be negligible matric potential can be inferred from psychrometer measurements The potential energy of soil water is in thermodynamic equilibrium with the potential energy of water vapor in the ambient air A psychrometer measures the relative humidity in the ambient air vapor pressure in the soil air relative to the saturation va or pressure of air at the same temperature that is related to potential energy WV of water vapor RH exp MwlV 80 prT Mw Molecular weight of water 0018 kgmol R Ideal gas constant 831 J K391 moiquot T Absolute temperature K pw Density ofwater 1000 kgm3 at 20 C 36 Urivers ymldaho Psychrometer Rearranging and logtransformation yields RT sz pwln 3 MW 80 w w n0 salts Matric Potential WV WW Wm 15 salts present Water Potential This equation can be further simplified for RH close to 1 a value often encountered in agricultural soils entire range of plant available water is between RH 098 and RH 10 Foriml Agni i71 462T 171 60 M 60 60 w e e e If ml gt 1n W 71 Note 60 K60 CO cavyugMQ szku mum 2mm Urlversltyatldaho Psychrometer Measurement Principle A psychrometer infers relative humidity from the difference in temperature between a dry non evaporating surface called dry bulb I and the I of an I quot I surface called wet bulb temperature The wet bulb temperature is usually below the dry bulb temperature because of the latent heat loss that is associated with the evaporation process The rate of evaporation from a wet surface depends on the relative humidity or vapor pressure of the ambient air Low humidity high evaporation rate High humidity lower evaporation rate The higher the evaporation rate the larger is the temperature depression of the wet bulb below the dry bulb temperature 37 a Uriversltyatldaho Eychrometer A thermocouple psychrometer consists of a fine wire chromel constantan or other standard bimetallic thermocouple A thermocouple is a double junction of two dissimilar metals When the twojunctions are subjected to different temperatures they generate a voltage difference explained as the SEEBECK effect Conversely when an electric current is applied through the junctions it creates a temperature difference between the junctions by heating one and cooling the other dependent on the current s direction For typical soil use onejunction of the thermocouple is suspended in a thin wall ceramic or stainless steel cup that is buried in the soil while the other one is embedded in an insulated plug to measure the ambient temperature at the same location Fleld Psychrometer Finewire ceoiagginslgsild Thermocouple Steel Screen CopperConstanian Junc iOquot Junction Urivasltyarldaho Psychrometer In psychrometric mode the suspended thermocouple is cooled below the dew point so that a droplet of water forms on the junction this is called Peltier cooling Then the cooling stops and water evaporates from the junction drawing heat and depressing the temperature below that of the ambient air The difference in temperature between the wet bulb suspended junction and the dry bulb insulated junction is measured and used to infer the relative vapor pressure using the psychrometer equation measured RH i 1 Hy AT 60 60 SSlope of the saturation water vapor curve yPsychrometer constant about 0067 kPa K1 at 20 C 38 a UrINersltyaIldaho Psych rometer The slope of the water vapor curve is temperature dependent and can be approximated according to Brutsaert 1982 s 133185739SZLR 719335tR2 705196tR3 Where tR1373151T The saturation vapor pressure e is also temperature dependent and can be approximated by integrating the previous equation 2 z 4 so 1013258Xp 3 3185LR 19760LR 06445LR 01299LR TL 39 A39 m vapul plessule e 39 A39 L 394quot R and temperature T is uniquely defined That means knowledge of any two of them leads automatically to the third one Uriveasllymldaho Psych rometer A good Psychrometer can measure tempera ure depressions on the order of 0000085 quotC per kPa Any error in measuring wet 60 bulb depression introduces to n m za an m39sn 4 1 40 Vapor Pressure kPa G THERMODYNAMIC 2 EQUILIBRIUM BETWEEN SAMPLE AND AMBIENT AIR Is REQUIRED To ACHIEVE ACCURATE MEASUREMENTS 0 0 10 20 30 40 50 Temperature C Umasnymdam Laboratory Psychrometer Psychrometer Mounting Plate Processpr 5m ox Plns T ber er I hermocouple t Thermist Thermocouple Soll Sample Sample Cup Measurement Range 800 to 10000 kPa 80 to 1000 m head Cowgth Markus Tuner 2oozzoos Worm Psychrometer Laboratory Psychrometer sovwgme Markus my 2oozzoos 4O Qummmldaho Psych rometer second procedure inferring water potential using thermocouple psychrometers is called the DEWPOINT METHOD In AL 4 3 new and kept at exactly this temperature using a monitoring system and electronic circuitry State of the art equipment eg WP4 Potentiameter uses a chille mirror dewpoint t 39 39 39 39 system to keep the su ace of a mirror at dewpoint tem erature Ambient temperature at the sample surface is measured with an infrared thermometer WP4 Potentiameter The Soil Water Characteristic Introduction and Measurement 1 u n u as Volumnnc Wauv comm m39lm y Copyright Markus Tuller 20022006 UrllVeI sltyolldahO The Soil Water Characteristic Curve 0 The Soil water 39 quot r w content 01 or am rium conditions under eq 0 The SWC is a primary hydraulic property required for modeling water flow in porous ateri als rook L my mama o Moznunmans N nonlinear and relatively dif cult to obtain iLEvs lanumr at accurately m n 2 n a n t n 5 Volumetric Snli Watanonlunl im m a Umasltymldaho The Soil Water Characteristic Curve Typical suit Wale 39 39 for soils u Matric Potential m 00 01 02 03 04 05 06 Volumetric Water Content mum3 a Universityolldaho The Soil Water Characteristic Curve 0 Early conceptual models for the SWC curve and liquid distribution in partially saturated porous media are based on the quotbundle of cylindrical capillariesquot BCC representation of pore space geometry Nillington and Quirk 1961 Mualem 1976 0 The BCC representation postulates that at a given matric potential a portion of interconnected cylindrical pores is completely liquid lled whereas larger pores are completely empty Soil Sample Actual Equivalent Pore Capillary ummmldam The Soil Water Characteristic Curve capillary rise equration
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