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Title: TEMPERATURE EFFECTS ON CAPACITANCE MEASUREMENTS OF SOIL-WATER CONTENT: THEORY AND FIELD APPLICATION

Author
item Green, Timothy
item SCHWANK, MIKE - ETHZ, TERRESTRIAL ECOLOGY
item FLUHLER, HANNES - ETHZ, TERRESTRIAL ECOLOGY

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/23/2004
Publication Date: 10/31/2004
Citation: Green, T.R., Schwank, M., Fluhler, H. 2004. Temperature effects on capacitance measurements of soil-water content: theory and field application. Agronomy Abstracts a04-5654. (CD-ROM) 2004.

Interpretive Summary: Apparent soil-water contents measured in the field display responses to atmospheric temperature fluctuations. Temperature effects on measured values need to be separated from real changes in water content that may be correlated with temperature fluctuations at time scales ranging from diurnal to weather events to seasonal or greater. Soil temperature and capacitance sensors have been collocated at depths of 30 and 60 cm in a farm field in Colorado under cropped and fallow conditions. Theoretical sensitivities of the bulk dielectric constant to temperature were derived and computed using a mixing model that accounts for the contributions of bound water, free water, solids and air. The resulting temperature corrections were applied to the field data to demonstrate the utility of this approach for removing temperature artifacts from capacitance-based, soil-water measurements ranging from diurnal to seasonal time scales. Direct measurement of temperature along with soil-water capacitance is recommended.

Technical Abstract: Apparent soil-water contents measured in the field display responses to atmospheric temperature fluctuations. Temperature effects on measured values need to be separated from real changes in water content that may be correlated with temperature fluctuations at time scales ranging from diurnal to weather events to seasonal or greater. Soil temperature and capacitance sensors have been collocated at depths of 30 and 60 cm in a farm field in Colorado under cropped and fallow conditions. Hourly measurements were recorded for over a year, and apparent values of the dielectric constant of the soil-water-air combination surrounding the access tubes at each depth were computed from measured frequencies (or raw counts). Theoretical sensitivities of the bulk dielectric constant to temperature were derived and computed using a mixing model that accounts for the contributions of bound water, free water, solids and air. The resulting temperature corrections were applied to the field data to demonstrate the utility of this approach for removing temperature artifacts from capacitance-based, soil-water measurements ranging from diurnal to seasonal time scales. Application to sites lacking in-situ soil temperature measurements will also be discussed, but direct measurement of temperature along with soil-water capacitance is recommended.