Content Reflectometer Erin L. Bush Gerard J. Kluitenberg Nathan O. - - PowerPoint PPT Presentation

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Content Reflectometer Erin L. Bush Gerard J. Kluitenberg Nathan O. - - PowerPoint PPT Presentation

Jul 17, 2023 215 likes •375 views

Lab Calibration of a Water Content Reflectometer Erin L. Bush Gerard J. Kluitenberg Nathan O. Nelson Introduction Importance of accurate soil moisture measurements Monitor water use by cropping systems Assist with management

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SLIDE 1

Lab Calibration of a Water Content Reflectometer

Erin L. Bush Gerard J. Kluitenberg Nathan O. Nelson

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SLIDE 2

Introduction

  • Importance of accurate soil moisture measurements
  • Monitor water use by cropping systems
  • Assist with management decisions
  • Kansas Agricultural

Watershed Research Site

  • Smolan silty clay loam:

35% clay

  • Confirm calibration with

field measurements

  • Calibration necessary due to changes in soil

properties

  • Texture differentiation
  • Ranges of salinity
  • Bulk density
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SLIDE 3

Objective

Determine if CS655 water content reflectometers require soil-specific calibration prior to field use

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SLIDE 4

Methods

  • Soil Preparation
  • Air dried, 2mm sieve
  • Gravimetric water content

measured

  • Wetting Process
  • Soil wetted to target

gravimetric water content

  • 0.0005 M CaSO4
  • Bulk EC < 0.9 ds/m
  • Water content achieved
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SLIDE 5

Methods

  • Soil Packing
  • 4 - 20.3 cm (h) PVC columns
  • 6 layers, 3 cm each
  • Target bulk density: 1.25 g cm-3
  • Porosity at target bulk density: 0.53
  • 8 water contents: 0.03-0.40 cm3 cm-3
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SLIDE 6

Methods

  • Taking Readings
  • 4 probes
  • One probe per column
  • Volumetric water content,

EC, degrees Celsius, permittivity

  • Check permittivity
  • Measured gravimetric water

content

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SLIDE 7

Results

0.02 0.04 0.06 0.08 0.1

Volumetric Water Content (cm3/cm3)

0.38 0.40 0.42 0.44 0.46 0.48

0.38

Probe& 1 Probe& 2 Probe& 3 Probe& 4

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SLIDE 8

Calibration Correction

  • Linear Correction: Volumetric water content

comparison as a linear function

  • Permittivity Calibration 1: Permittivity vs known

volumetric water content as a quadratic function

  • Permittivity Calibration 2: Known volumetric water

content vs square root of permittivity

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SLIDE 9

Linear Correction

y = 1.27x

  • 0.042

R² = 0.99 0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.5

CS655 Volumetric Water Content (cm3/cm3) Known Volumetric Water Content (cm3/cm3 )

Probe 1 Probe 2 Probe 3 Probe 4 1:1 line

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SLIDE 10

Permittivity Calibration 1

y =

  • 0.0003x2 +

0.02x R² = 0.99

0.0 0.1 0.2 0.3 0.4 0.5

0.0 10.0 20.0 30.0 40.0

Known Volumetric Water Content (cm3/cm3) Permittivity

All Data Topp Equation

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SLIDE 11

Permittivity Calibration 2

y = 0.09x

  • 0.09

R² = 0.99 0.0 0.1 0.2 0.3 0.4 0.5 2 4 6

Known Volumetric Water Content (cm3/cm3) Square Root

  • f

Permittivity

All data

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SLIDE 12

Statistical Analysis

Root Mean Square Error Correction Method RMSE

CS655 Topp Equation 0.0330 Linear Correction 0.0109 Volumetric Water Content vs. Permittivity Calibration 0.0224 Volumetric Water Content vs. Square Root of Permittivity Calibration 0.0081

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SLIDE 13

Conclusion

  • No significant differences between the probes
  • Calibration necessary for accuracy:
  • - 4% to + 6%
  • Depends on soil moisture
  • Future research: Evaluate effects of soil

properties on calibration

  • Bulk density
  • Salinity
  • Different textures
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SLIDE 14

Acknowledgements

  • 4-R Research Fund
  • Kansas State Research and Extension
  • Kansas Soybean Commission
  • Kansas Corn Commission