Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and...
Transcript of Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and...
![Page 1: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/1.jpg)
Soil Water Potential Measurement
Doug Cobos, Ph.D. Decagon Devices and Washington State
University
![Page 2: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/2.jpg)
Two Variables are Needed to Describe the State of Water
Water content and Quantity Extent
Related Measures
heat content and charge and
Water potential Quality Intensity temperature voltage
![Page 3: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/3.jpg)
Extensive vs. Intensive
Heat Content
Temperature
Energy flow?
620 J kg-1 K-1 X 100 Mg X 270 K = 16700 MJ 620 J kg-1 K-1 X 1kg X 1000 K = 0.62 MJ
270 K 1000 K
![Page 4: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/4.jpg)
Water Potential Predicts n Direction and rate of water flow in Soil,
Plant, Atmosphere Continuum n Soil “Field Capacity” n Soil “Permanent Wilting Point” n Seed dormancy and germination n Limits of microbial growth in soil and food
![Page 5: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/5.jpg)
Water Potential Energy required, per quantity of water, to
transport, an infinitesimal quantity of water from the sample to a reference pool of pure, free water
![Page 6: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/6.jpg)
Water Potential: important points n Energy per unit mass, volume, or weight of
water n We use units of pressure (Mpa, kPa, m H2O,
bars)
n Differential property n A reference must be specified (pure, free water
is the reference; its water potential is zero)
n The water potential in soil is almost always less than zero
![Page 7: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/7.jpg)
Water potential is influenced by:
n Binding of water to a surface n Position of water in a gravitational field n Solutes in the water n Pressure on the water (hydrostatic or pneumatic)
![Page 8: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/8.jpg)
Total water potential = sum of components
n ψT = ψm + ψg + ψo + ψp
n ψT – Total water potential n ψm – matric potential - adsorption to surfaces n ψg – gravitational potential - position n ψo – osmotic potential - solutes n ψp – pressure potential - hydrostatic or pneumatic
![Page 9: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/9.jpg)
Matric potential (Ψm) adsorptive forces
From Jensen and Salisbury, 1984
n Hydrogen bonding of water to surfaces n Always negative n Most important component in soil n Highly dependent on surface area of soil
![Page 10: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/10.jpg)
Soil Water Retention Curves
Matric potential (kPa)
Volu
met
ric w
ater
con
tent
(m3 /m
3 )
![Page 11: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/11.jpg)
Gravitational potential (Ψg)
10 m
Reference Height
Ψg = g * h * ρwater = 9.81 m s-2 * 10 m * 1 Mg m-3 = + 98.1 kPa
![Page 12: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/12.jpg)
Gravitational potential (Ψg)
1 m
Reference Height (soil surface)
Ψg = g*h = 9.81 m s-2 *1 m = - 9.81 kPa
Ψg = g * h * ρwater = 9.81 m s-2 * 1 m * 1 Mg m-3 = - 9.81 kPa
![Page 13: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/13.jpg)
Osmotic potential (Ψo) - solutes
n Arises from dilution effects of solutes dissolved in water n Always negative n Only affects system if semi-permeable barrier present
that lets water pass but blocks salts n Plant roots n Plant and animal cells n Air-water interface
![Page 14: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/14.jpg)
Osmotic potential (Ψo) - solutes
C = concentration of solute (mol/kg) φ = osmotic coefficient - 0.9 to 1 for most solutes ν = number of ions per mol (NaCl = 2, CaCl2 = 3, sucrose = 1) R = gas constant T = Kelvin temperature
Ψ0 = CφvRT
![Page 15: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/15.jpg)
Pressure potential (Ψp)
n Hydrostatic or pneumatic pressure (or vacuum) n Positive pressure
n Surface water n Groundwater n Leaf cells (turgor pressure) n Blood pressure in animals
n Negative n Plant xylem
![Page 16: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/16.jpg)
Water potential ranges and units Condition Water
Potential (MPa)
Water Potential (m H2O)
Relative Humidity (hr)
Freezing Point (oC)
Osmolality (mol/kg)
Pure, free water 0 0 1.00 0 0
Field Capacity -0.033 -3.4 0.9998 -0.025 0.013
-0.1 -10.2 0.9992 -0.076 0.041
-1 -102 0.993 -0.764 0.411
Permanent wilting point
-1.5 -153 0.989 -1.146 0.617
-10 -1020 0.929 -7.635 4.105
Air dry -100 -10204 0.478 -76.35 41.049
![Page 17: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/17.jpg)
Water potentials in Soil-Plant-Atmosphere Continuum
Atmosphere -100
-3.0
-2.5
-1.7 -1.5
Soil
Root
Xylem
Leaf
Permanent wilt (MPa)
![Page 18: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/18.jpg)
Measuring Soil Water Potential n Solid equilibration methods
n Electrical resistance n Capacitance n Thermal conductivity
n Liquid equilibration methods n Tensiometer n Pressure chamber
n Vapor equilibration methods n Thermocouple psychrometer n Dew point potentiameter
![Page 19: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/19.jpg)
Electrical Resistance Methods for Measuring Water Potential
n Standard matrix equilibrates with soil
n Electrical resistance proportional to water content of matrix
n Inexpensive, but poor stability, accuracy and response
n Sensitive to salts in soil Sand
Gypsum capsule
![Page 20: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/20.jpg)
Heat Dissipation Sensor
n Robust (ceramic with embedded heater and temperature sensor)
n Large measurement range (-0.01 to -100 MPa)
n Stable (not subject to salts and dissolution
n Requires complex temperature correction
n Requires individual calibration Ceramic
Heater and thermocouple
![Page 21: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/21.jpg)
Capacitance Methods for Measuring Water Potential
n Standard matrix equilibrates with soil
n Water content of matrix is measured by capacitance
n Stable (not subject to salts and dissolution
n No calibration required n Range -0.01 MPa to air dry (-100
MPa) n Good accuracy from -0.01 to
-1.5 MPa, errors larger in dry end
![Page 22: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/22.jpg)
Liquid Equilibration: Tensiometer
n Equilibrates water under tension with soil water through a porous cup
n Measures tension of water n Highest accuracy of any sensor in
wet range n Limited to potentials from 0 to -0.09
MPa n Significant maintenance
requirements
![Page 23: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/23.jpg)
Liquid Equilibration: Pressure chamber
n Moist soil placed on saturated porous plate
n Plate and soil sealed in chamber and pressure applied, outflow at atmospheric pressure
n Ψsoil ≈ negative of pressure applied
n Common method for moisture characteristic curves
![Page 24: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/24.jpg)
Liquid Equilibration: Pressure chamber
n Equilibrium time n Hours at wet end n Months or more at dry end (maybe
never)
n Recent work shows that samples at -1.5 Mpa only reached -0.55 Mpa n Hydraulic contact between plate and
soil sample n Low Kunsat at low water potential
Gee et. al, 2002. The influence of hydraulic disequilibrium on pressure plate data. Vadose Zone Journal. 1: 172-178.
![Page 25: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/25.jpg)
Water Potential and Relative Humidity Relative humidity (hr) and water potential (Ψ)
related by the Kelvin equation:
rw
hMRT ln=Ψ
R is universal gas constant Mw is molecular mass of water T is temperature
Condition Water Potential (MPa) Relative Humidity (hr)
Pure, free water 0 1.000
Field Capacity -0.033 0.9998
Permanent wilting point -1.5 0.989
![Page 26: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/26.jpg)
Vapor Equilibrium Methods
n Thermocouple psychrometer n Measure wet bulb temperature depression of
head space in equilibrium with sample
n Dew point hygrometer n Measure dew point depression of head space in
equilibrium with sample
![Page 27: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/27.jpg)
Thermocouple Psychrometer
Chromel-constantan thermocouple
sample
Thermocouple output
Measures wet bulb temperature depression Water potential proportional to cooling of wet junction
![Page 28: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/28.jpg)
Sample Chamber Psychrometer
n Measures water potential of soils and plants
n Requires 0.001C temperature resolution
n 0 to – 6 MPa (1.0 to 0.96 RH) range
n 0.1 MPa accuracy (problems in wet soil)
![Page 29: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/29.jpg)
In Situ Soil Water Potential
Soil Psychrometer
Readout
![Page 30: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/30.jpg)
Chilled Mirror Dew Point
Infrared Sensor Mirror
Optical Sensor Fan
Sample
n Cool mirror until dew forms
n Detect dew optically
n Measure mirror temperature
n Measure sample temperature with IR thermometer
n Water potential is approximately linearly related to Ts - Td
![Page 31: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/31.jpg)
WP4 Dew Point Potentiameter
n Range is 0 to -300 MPa
n Accuracy is +/-0.05 MPa n Excellent in dry soil n Problems in wet soil
n Read time is 5 minutes or less
![Page 32: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/32.jpg)
Some applications of soil water potential n Soil Moisture Characteristic
n Plant Available Water n Surface Area n Soil Swelling
n Hydropedology
n Water flow and contaminant transport
n Irrigation management
![Page 33: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/33.jpg)
Soil Moisture Characteristic
n Relates water content to water potential in a soil
n Different for each soil n Used to determine - plant available water - surface area - soil swelling
![Page 34: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/34.jpg)
Plant Available Water
n Two measurement methods needed for full range n Hyprop, tensiometer, pressure plate
in wet end n Dew point hygrometer or
thermocouple psychrometer in dry end
n Field capacity (-0.033 Mpa) n Upper end of plant available water
n Permanent wilting point (-1.5 Mpa) n Lower end of plant available water n Plants begin water stress much lower
![Page 35: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/35.jpg)
Surface Area from a Moisture Characteristic
y = 1231.3x2 + 406.15xR2 = 0.9961
0
50
100
150
200
250
0 0.05 0.1 0.15 0.2 0.25 0.3
Slope of Semilog plot
EG
ME
Surf
ace
Are
a (m
2/g)
![Page 36: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/36.jpg)
pF Plot to get Soil Swelling
y = -17.02x + 7.0381R2 = 0.9889
y = -29.803x + 7.0452R2 = 0.9874
y = -97.468x + 6.8504R2 = 0.96883
3.54
4.55
5.56
6.57
7.5
0 0.05 0.1 0.15 0.2
Water Content (g/g)
Suct
ion
(pF)
L-soilPalousePalouse B
![Page 37: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/37.jpg)
Expansive Soil Classification from McKeen(1992)
Class Slope Expansion
I > -6 special case
II -6 to -10 high
III -10 to -13 medium
IV -13 to -20 low
V < -20 non-expansive
![Page 38: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/38.jpg)
Hydropedology n Requirements:
n Year around monitoring; wet and dry n Potentials from saturation to air dry
n Possible solutions: n Soil psychrometers (problems with
temperature sensitivity) n Capacitance matric potential sensor
(limited to -0.5 MPa on dry end) n Heat dissipation sensors (wide range,
need individual calibration)
![Page 39: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/39.jpg)
Water Flow and Contaminant Transport
n Requirements: n Accurate potentials and gradients
during recharge (wet conditions) n Continuous monitoring
n Possible solutions: n Capacitance matric potential sensor n Pressure transducer tensiometer
(limited to -0.09 MPa on dry end)
![Page 40: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/40.jpg)
Irrigation Management
n Requirements: n Continuous during growing season n Range 0 to -0.1 Mpa
n Possible solutions: n Tensiometer (soil may get too dry) n Electrical resistance (poor accuracy) n Heat dissipation or capacitance
![Page 41: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/41.jpg)
Measuring water content to get water potential
n Requires moisture characteristic curve for converting field measurements from θ to ψ
n Conventional wisdom: time consuming n Most moisture release curve have been done on
pressure plates n Long equilibrium times, labor intensive
n New techniques n Fast (<24 hours) n Automated
![Page 42: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/42.jpg)
Bridging the gap
10%
20%
30%
40%
50%
60%
70%
Volu
met
ric W
ater
Con
tent
Volumetric water content at various depths over over the growing season of wheat grown in a Palouse Silt Loam (Location: Cook's Farm, Palouse, WA)
30 cm
60 cm
90 cm
120 cm
150 cm
![Page 43: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/43.jpg)
Summary n Knowledge of water potential is important
for n Predicting direction of water flow n Estimating plant available water n Assessing water status of living organisms
(plants and microbes)
![Page 44: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/44.jpg)
Summary n Water potential is measured by equilibrating a
solid, liquid, or gas phase with soil water
n Solid phase sensors n Heat dissipation n Capacitance n Granular matrix
n Liquid equilibrium n Tensiometers n Pressure plates
![Page 45: Soil Water Potential Measurementlibrary.metergroup.com/Retired and Discontinued/Slicks and content... · Extensive vs. Intensive Heat Content Temperature Energy flow? 620 J kg-1 K-1](https://reader033.fdocuments.in/reader033/viewer/2022060404/5f0eda0f7e708231d4414025/html5/thumbnails/45.jpg)
Summary
n Vapor equilibration n Thermocouple psychrometers n Dew point potentiameters
n No ideal water potential measurement solution exists n Maintenance and stability n Accuracy and calibration n Ease of use n Range of operation