8/08/20151 solutions for soil, plant & environmental monitoring solutions for soil, plant &...

19/04/23 1

Solutions for soil, plant & environmental monitoring

www.ictinternational.comSolutions for soil, plant & environmental monitoring

www.ictinternational.com

Soil Water Potential

Peter Cull

ICT International

19/04/23 2




Water Content or Potential?

• Water Content:

– Total amount of water in the soil

– Does not indicate how much is available to a plant

• Water Potential:

– The amount of energy needed to extract water from soil

– Direct measure of how much water is available to a plant

19/04/23 3




Water Potential Units• Water Potential Units of Measurement:

J/kg MPa Bars RH

-1 -0.001 -0.01 0.999993

-10 -0.01 -0.1 0.999926

Field Capacity -33 -0.033 -0.33 0.999756

-100 -0.1 -1 0.999261

-1000 -1 -10 0.992638

Wilting Point -1500 -1.5 -15 0.988977

-10000 -10 -100 0.928772

Air Dry -100000 -100 -1000 0.477632

Oven Dry -1000000 -1000 -10000 0.000618

High Potential

Low Potential

19/04/23 4



Soil-Plant-Atmosphere Continuum

19/04/23 5



• Standard matrix equilibrates

with soil

• Electrical resistance proportional

to water content of matrix

• Inexpensive, but poor stability,

accuracy and response

• Sensitive to salts in soil

Gypsum Blocks

19/04/23 6



• Standard matrix equilibrates with soil

• Water content of matrix is measured

by capacitance

• Stable (not subject to salts and

dissolution)

• Good accuracy from -0.01 to -0.5 MPa

MPS-2 Capacitance Sensor

19/04/23 7



TM229 Thermal Matric Sensor

• Robust (ceramic with embedded heater and temperature sensor)

• Large measurement range (wet and dry end)

• Stable (not subject to salts and dissolution

• Requires complex temperature correction and calibration

19/04/23 8



• Equilibrates water under tension with soil water through a porous cup

• Measures tension of water

• Highest accuracy of any sensor in wet range

• Limited to potentials from 0 to -0.09 MPa

• Significant maintenance requirements

Tensiometers

19/04/23 9



Limitations of Field Techniques

• Gypsum Blocks:

– Inaccurate

– Requires individual calibration

– Limited range: 0 to -500kPa

• MPS-2 Capacitance Sensor:

– Inaccurate below -100kPa

– Requires individual calibration


• TM229 Thermal Matric Sensor:

– Calibration essential

– Relatively expensive

• Tensiometers:

– High maintenance


19/04/23 10



Lab Based Measurements

Pressure Extractor

WP4C Dewpoint Potentiameter

19/04/23 11



Pressure Extractors

• Apply known amount of pressure into asealed chamber and monitor outgoing moisture

• Long established, accepted technique

• Excellent accuracy between-0.03 and -1.5 MPa

19/04/23 12



WP4C Dewpoint Potentiameter

• Based on psychometric principle

• Dew forms on small mirror inside measurement chamber

• WP4C measures humidity and temperature when dew forms

• Poor results at wet end, excellent results at dry end

• Fast, accurate, easy maintenance

19/04/23 13



Limitations of Lab Techniques

• All Methods:

– Destructive

– Destroys soil structure

– Artificial result

– One-off, spot, measurement

– No continuous, in-situ data

• Pressure Extractors:

– Slow and expensive

– Limited range: -0.03 to -1.5 MPa

• WP4C:

– Small sample

– Limited range: -0.1 to -300 MPa

19/04/23 14



Lab & Field Technique

• Moisture Release Curves:

– Quantifying soil moisture content

Against soil water potential for

Varying Soil Textures

– Standard practice to measure

Between Field Capacity and

Plant Wilting Point: -0.03 to -1.5 MPa

19/04/23 15



19/04/23 16



SMM Soil Moisture Meter• Stand-alone data logging solution

• Up to 10 sensor capacity

• Wireless communication

• Low power requirement

• Real and virtual sensors

19/04/23 17



SMM Soil Moisture Meter

• Real and Virtual Channels:

– 5 channels to measure moisture content

– 5 virtual channels to measure soil water potential

19/04/23 18



SMM Soil Moisture Meter

• Calibration Feature:

– Individual channel calibration

– Precision measurement of soil moisture

parameters in any soil type

19/04/23 19



SMM – How it Works

• Step 1:

– Collect soils from field and air

dry for 2 weeks

• Step 2:

– Sieve soil through 2mm sieve

– Place in separate containers

19/04/23 20




• Step 3:

– 1st container, keep air dry

– 2nd container, 1 unit of water

– 3rd container, 2 units of water

– 4th container, 3 units of water

– and so on…

19/04/23 21




• Step 4:

– Measure soil with MP306

sensor in raw, millivolt format

in all of the containers

• Step 5:

– Measure water potential of

soil in each container with a

WP4C or pressure extractor

19/04/23 22




• Step 6:

– Once water potential is

known, determine volumetric

water content with a balance

and drying oven

19/04/23 23




• Step 7:

– Find equation from your

moisture release curve

Curve A Sandy Soil:

Soil Water Potential = 5343 x Soil Water Content-1.852

Curve B Clay Soil:

Soil Water Potential = 6x107 x Soil Water Content-4.228

19/04/23 24




• Step 8:

– Enter equation into the SMM

software as a script

19/04/23 25




• Step 9:

– Connect sensors to SMM and

install in the field. Start taking

measurements!

19/04/23 26



10

15

20

25

30

35

40

20

22

24

26

28

30

32

34

36

38

40

Content (%)

Potential (-kPa)

Simultaneous Content & Potential%

Vol

umet

ric W

ater

Con

tent

Soi

l Wat

er P

oten

tial (

kPa)

Day 1 Day 2 Day 3 Day 4 Day 5 Day 6

19/04/23 27



Virtual Channels = Flexibilty

• SMM Soil Moisture Meter can handle other equations:

– Hydraulic Conductivity; Degree of Saturation; Oxygen ContentWater Potential and Water Content Hydraulic Conductivity and Water Content

19/04/23 28



ICT International Pty LtdSolutions for soil, plant and environmental research

[email protected]: 61 2 6772 6770Fax: 61 2 6772 7616PO Box 503, Armidale, NSW, Australia, 2350 INTERNATIONAL

8/08/20151 solutions for soil, plant & environmental monitoring solutions for soil, plant &...

Documents

plant environmental

plant slide

plant water potential

soil water content of

soil gypsum blocks slide

soil direct measure

calibration slide

kpa slide