Empirical Temperature Calibration of Capacitance Probes to Measure Soil Water

Abstract

Dielectric sensors have been widely used for nondestructive determination of volumetric soil water content (θ, m3 m−3). Since the output of such sensors is affected by soil temperature (T, °C), the calibration for the effect is indispensable for accurate determination of θ. The objectives of this paper were (i) evaluation of the temperature effects on outputs of the commercial capacitance probes called ECH2O probes for various types of soils, and (ii) to include temperature in empirical calibration equations. Laboratory experiments were performed to obtain probe outputs at various T (5– 35°C) and θ (air‐dry– near‐saturation), using four soils and four probe models with different oscillation frequencies (5 and 70 MHz). The results showed that the outputs linearly responded to T at constant θ for all tested soil–probe combinations. The slope values of the linear responses to T depended on θ. The curves of the output–θ functions at a reference temperature (25°C) varied among the soils and probe models. A calibration equation describing the probe output as a function of θ and T was derived for each soil–probe combination by combining the output–θ function at the reference temperature and the slope–θ function. The derived calibration equations substantially reduced the temperature effects on the probe outputs for all soil–probe combinations. We also briefly considered the theoretical background of temperature effects on the probe outputs based on the results from the experiments and the properties of the soils tested. To demonstrate the importance of temperature calibration, the derived calibration equations were applied to two field observations from arid reasons.

Soil moisture sensor calibration for organic soil surface layers

“…In addition, the probe also provides temperature and electrical conductivity measurements. The Decagon 5TE sensor as well as its predecessor TE have been tested in several studies (e.g., Kizito et al, 2008;Saito et al, 2009;Assouline et al, 2010;Rosenbaum et al, 2010Rosenbaum et al, , 2011Sakaki et al, 2011;Varble and Chavez, 2011;Ganjegunte et al, 2012;Vaz et al, 2013). To our knowledge, only one calibration curve for organic material has previously been reported.…”

“…The latter are generally considered more accurate with less signal contribution of ε and hence, reduced sensitivity to salinity (electrical conductivity), temperature, and soil type effects (e.g., Blonquist et al, 2005;Kelleners et al, 2005;Saito et al, 2009). However, the former are often cheaper and power consumption is lower.…”

Advanced Monitoring and Management Systems for Improving Sustainability in Precision Irrigation

“…In addition, for capacitance type probes, it is essential that the probe access tubes are fitted correctly without air gaps to ensure robust soil water measurements. For a detailed technical description of factors affecting the performance of dielectric sensors, readers are referred to [58,59].…”

Investigation of Rainfall-Runoff Processes and Soil Moisture Dynamics in Grassland Plots under Simulated Rainfall Conditions

“…The type of soil moisture sensor was EC-5, with the measurement accuracy of soil volumetric water content reaching ±1%-2% (as given by the manufacturer). The moisture sensors were calibrated before installation [21][22][23]. The soil moisture data acquisition was conducted with soil moisture sensors externally linked with an EM50 data collector, for which the acquisition time interval can be set to 1-1440 min.…”