Managing Soil Moisture Using a Portable Soil Moisture Probe If you - - PowerPoint PPT Presentation

Managing Soil Moisture Using a Portable Soil Moisture Probe

If you don’t measure it, you can’t manage it

U.S. Golf Course Water Consumption

• Water is an increasingly valuable resource
• Amount used
• 2.1 billion gallons of water per day.
• 149 million gallons per course annually in southwest U.S.
• Cost
• High - Southwest ($107,880/year)
• Low – North-Central ($4,700/year)

GC Environmental Profile 2007 – GCSAA & EIFG

Drought Conditions – Jul 2012

Drought Conditions – Oct 2012

U.S. Golf Course Water Consumption

• ~16% of courses have been

subject to stringent water restrictions

• Cost of water higher
• Expectations not lower

Why Is Water Important?

• Plant tissue is ~80% water
• Too much
• No oxygen in soil
• Soils susceptible to compaction
• Reduced microbial activity
• Movement of nutrients out of root zone
• Disease susceptibility increases
• Too little
• Less transpiration
• Reduced photosynthesis
• Decrease in turf density (decreased tillering and fewer leaves)
• Reduced nutrient uptake

Why Measure?

• Optimally time inputs
• Identify and solve turf problems
• Conserve water and energy
• Improve turf quality and consistency
• Minimize input losses of fertilizer
• Maximize return on investment
• Develop optimal irrigation programs
• Reduce labor costs

Methods of Soil Moisture Measurement

The Old Methods

• Historically, soil moisture was monitored…
• By feel
• Visually
• Disadvantage
• Subjective and not highly accurate
• Can lead to too much/too little water

Common Devices for Tracking Soil Moisture

• Weather Stations with rain collectors and/or

evapotranspiration (ET) capability

• Not site specific
• Need crop coefficient specific to your turf species
• In-ground sensors
• Limited site specificity
• Has to be wireless ($$)
• Advantage
• Can monitor over time

Common Devices for Tracking Soil Moisture

Portable Probes

• What if you want to know soil moisture everywhere?

Use a portable probe!

Basics of the FieldScout TDR 300 Soil Moisture Meter

TDR Meter

• Main Components
• Block / Rods
• Digital display / Keypad
• Built-in data logger
• GPS compatibility
• Advantage
• Can monitor many

different sites quickly

• Irrigation scheduling
• Hand watering

Applications

Volumetric Water Content (VWC)

• Measurement of the percent of soil

profile comprised of liquid water

• Measurement unit is percent (%) or

decimal (mwater / msoil) water content

• Useful tool for water budgeting
• Especially powerful when used in

conjunction with evapotranspiration (ET) data

• Irrigation generally recommended

when half of plant-available water has been depleted

Air Water Soil

Water Holding Capacity by Soil Type

• Wave guide composed of two rods
• Acts like an antenna which carries the

EM Wave

• Speed of the wave is dependent on the

Dielectric Permittivity ( )

• Water has high
• Both soil and air have low
• Wave partially reflects back to probe when it reaches ends of

rods (impedance discontinuity)

• Output signal is calibrated to average VWC
• Probe response is influenced by: EC, OM and Clay content

Time Domain Reflectometry (TDR)

Collecting / Analyzing Data from the TDR 300

Meter Operation

• Select probe length that best

matches depth of root zone

• Insert rods fully in ground
• Proper insertion is important for

accurate readings

• Ensure good soil / rod contact
• Take enough measurements to

properly characterize the variability

• f the site
• Compaction / Traffic
• Undulations
• Shade
• Irrigation uniformity

How to Sample

• Divide the area to be measured

into a simple grid

• Make as many quadrants as you feel

you have time to complete

• Take one reading within each

square

• Follow the same ‘pattern’ each day

when monitoring

How to Sample

• Ground truthing
• Spend a few weeks sampling

and determining what is your ‘baseline’ threshold for moisture

• Threshold may change with

event schedule and/or time of year

How to Sample

• The goal is to have consistent

moisture values throughout the entire surface

• Accomplished by hand

watering only necessary ‘quadrants’

• Should lead to reduced water

usage over time

Why Consistent Moisture Is Important

• Reduced disease pressure
• Healthier turf
• Better conditions for the golfer
• Aesthetics

• Ability to achieve firm and fast conditions

Why Consistent Moisture Is Important

Meter Operation / Output

• Digital display screen will show the most current reading

along with a running average

• Hit “READ button – readings are instantaneous

“Normal” soil conditions VWC altered by high Salts

Meter Calibration

• Calibration can be done with air and distilled water
• Good for customers with multiple meters

What Do the Readings Mean?

• Threshold values will be unique for each course
• Forest Akers CC (E. Lansing, MI)
• Sampled every green over 2-week period
• Compared to visual assessments
• Determined that VWC = 18% was appropriate threshold for spring

Further…

• Initial threshold will not necessarily apply for the entire

season

• Increased demand during the summer
• Reduced root depth
• Tournament play

NOT a Magic Black Box

• Other Important Factors
• Weather
• Visual assessments
• Crop growth stage

Calibration

Calibration

• Only direct way to measure volumetric water content (VWC) is with a

gravimetric measurement

• Used to calibrate indirect methods (capacitance, TDR)
• Sample of saturated soil of known volume is allowed to dry (Lab), or wet

samples are extracted from ground (Field)

• Raw sensor reading is taken
• VWC calculated from wet and

dry weights

V W C M M V

w e t d r y w a t e r t

• t

a l

( % ) * * 1

Developing the Calibration Curve

10 20 30 40 50 60 2000 2500 3000 3500 4000

Period ( s) VWC (%)

Data Linear Fit Period < 2800 s VWC = 0.0193*Period - 37.9 Period > 2800 s VWC = 0.0326*Period - 75.3

VWC = (mwet - mdry) / volume

Gravimetric Soil-specific Calibrations

• 1. Create sites with different water contents
• 2. Insert TDR 300 probe and take Period reading
• 3. Pull soil cores of known volume from each site
• 4. Measure wet weight of soil
• 5. Weigh again after oven-drying soil
• 6. Calculate volumetric water content
• 7. Do regression analysis to create calibration curve

Mapping of Soil Moisture Data

Soil Moisture Maps

• Geo-Referenced Soil Moisture Measurement

Name: Test Serial #: 3 Datum: WGS 84 Longitude,Latitude,No.,% Water,Type ,,Logger Started: 7:39:58

• 88.358170,41.311000,N=1,40,Standard VWC,3.0in
• 88.358170,41.311000,N=2,40,Standard VWC,3.0in
• 88.358512,41.311340,N=3,16,Standard VWC,3.0in
• 88.358510,41.311342,N=4,14,Standard VWC,3.0in
• 88.359667,41.311340,N=5,20,Standard VWC,3.0in
• 88.359515,41.311340,N=6,18,Standard VWC,3.0in
• 88.360500,41.311337,N=7,14,Standard VWC,3.0in
• 88.360500,41.311338,N=8,20,Standard VWC,3.0in
• 88.361343,41.311340,N=9,13,Standard VWC,3.0in
• 88.361343,41.311342,N=10,12,Standard VWC,3.0in
• 88.361343,41.311342,N=11,12,Standard VWC,3.0in

SpecMaps

SpecMaps

• Uses Inverse Distance

Weighting (IDW) to create contours

• Charts are .jpg files that

customer can capture and manipulate or distribute

SpecMaps

Chart Statistical information Available Meters User Login Histogram

SpecMaps

Before Irrigation After Irrigation Catch Can Results

SpecMaps

Visual Inspection Area receiving most water

Affordable Plant Monitoring Technology to Help You Grow

If you don’t measure it, you can’t manage it

Appendix

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