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2026 Vol.59, Issue 2 Preview Page

Original research article

Calibration of an FDR soil moisture sensor accounting for organic matter and andic properties in Jeju volcanic ash soils
Chol Jun Yang1†
,
Hosung Lee2†
,
Won-Pyo Park3*
1Researcher, Jeju Special Self-Governing Province Agricultural Research & Extension Service, Jeju 63556, Korea
2Master Student, Plant Resources and Environment Major, College of Applied Life Science, SARI, Jeju National University, Jeju 63243, Korea
3Associate Professor, Plant Resources and Environment Major, College of Applied Life Science, SARI, Jeju National University, Jeju 63243, Korea
*Corresponding Author
†These authors contributed equally to this work.
31 May 2026. pp. 172-183
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Abstract

Dielectric sensors are calibrated using soils of various types, but default factory calibration functions may not be valid under all conditions. Soils with high soil organic matter (SOM) content and volcanic ash soils often require soil-specific calibration to achieve acceptable accuracy. This study was aimed to developed and evaluated practical calibration methods for the TEROS 12 FDR (frequency domain reflectometry) soil moisture sensor using 39 soil samples from Jeju Island, covering a wide range of SOM (10 - 300 g kg-1) and contrasting andic properties. During controlled drying of repacked soils in containers at field bulk density, raw sensor counts were measured twice daily and paired with gravimetrically determined reference volumetric water content (θref). We compared the factory calibration equation (FCE) with the OM-group (OMCE) and integrated (ICE) calibration equations using bias and soil-level RMSE. The FCE exhibited moisture-dependent bias, overestimating θref under dry conditions and underestimating at medium to high moisture, with greater variability in high SOM soils and Andisols. Across all soils, RMSE decreased from 0.067 m3 m-3 (FCE) to 0.048 m3 m-3 (OMCE; 28.0% reduction) and 0.047 m3 m-3 (ICE; 29.8% reduction). OMCE performed best at low moisture, whereas ICE most effectively reduced errors in Andisols under high moisture. In Jeju volcanic soils, OMCE provides a practical option when SOM information is available, whereas ICE offers a robust general calibration for soils with mixed andic properties, improving the reliability of TEROS 12-based moisture monitoring.

OM-group and integrated calibration equations improved TEROS 12 soil moisture sensor accuracy in Jeju volcanic ash soils relative to the factory calibration.
Keywords
Andisols
Calibration equation
Sensor accuracy
Soil water sensor
Volumetric soil water content
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Information
  • Publisher :Korean Society of Soil Science and Fertilizer
  • Publisher(Ko) :한국토양비료학회
  • Journal Title :Korean Journal of Soil Science and Fertilizer
  • Journal Title(Ko) :한국토양비료학회 학회지
  • Volume : 59
  • No :2
  • Pages :172-183
  • Received Date : 2026-02-11
  • Revised Date : 2026-03-12
  • Accepted Date : 2026-03-13
  • DOI :https://doi.org/10.7745/KJSSF.2026.59.2.172
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