Comparison of two sensors ECH₂O EC-5 and SM200 for measuring soil water content

Abstract

The goal of this study was calibration of the ECH<sub>2</sub>0 soil moisture sensor EC-5 and the sensor SM200 for selected soils of the Czech Republic. Based on the soil maps of the Czech Republic and various climatic conditions, five humic horizons of different soil types were selected: Stagnic Chernozem Siltic, Haplic Chernozem, Chernozem Arenic, Haplic Luvisol, and Haplic Cambisol. Soil properties (pH<sub>KCl</sub>, pH<sub>H2O</sub>, exchangeable acidity, cation exchange capacity, hydrolytic acidity, basic cation saturation, sorption complex saturation, oxidable organic carbon content, CaCO<sub>3</sub> content, salinity, sand, silt, and clay content, soil particle density, bulk density) were determined using the standard laboratory techniques. Six ECH<sub>2</sub>0 EC-5 sensors permanently installed in six 606 cm<sup>3</sup> repacked soil samples of each soil were calibrated. Four calibrated SM200 sensors were inserted into the same soil samples only when measuring sensor signal. Soil water contents were determined gravimetrically. Linear equation was used to find parameters of the calibration equations relating sensor signals or evaluated dielectric constants and soil water contents. The multiple linear analyses showed that the parameters of the calibration equations for the EC-5 depended on the bulk density, fraction of sand particles, and salinity. Parameters a and b of the SM200 depended on the initial soil salinity, sand fraction and CaCO<sub>3</sub> content, and on the sand fraction, respectively. The impact of KBr solute (concentrations of 0.01, 0.05 and 0.1M Br) on calibration equations was studied as well. It was found that ECH<sub>2</sub>0 EC-5 sensor measurements were more influenced by KBr solution than SM200 measurements. In the case of the ECH<sub>2</sub>0 EC-5 sensor, impact of KBr was lower in soils of higher initial salinity. SM200 measurements were noticeably influenced only when 0.1M Br solution was applied.

Influence of temperature on soil water content measured by ECH2O-TE sensors

“…A Similar effect of soil temperature fluctuations on measured soil water content near the soil surface was also described by Mead et al (1996). It should also be mentioned that the variable soil salinity may affect soil water content measurements (Kodešová et al, 2011b;Topp et al, 1980). However, in our case the soil salinity (Table 1) was low and no significant change during the studied periods was expected.…”

“…Sensors were first calibrated for surface A and subsurface C horizons under 20°C laboratory conditions using the same procedure as described by Kodešová et al (2011b). Six ECH 2 O-TE sensors and six plastic cylinders (volume of 606 cm 3 , height of 6 cm) were used for each soil horizon to calibrate sensors for distilled water.…”

“…Due to the fact that the dielectric of water is about 80, while other soil constituents are between 1 and 5, changes in soil dielectric permittivity are highly correlated with soil water content. However, the measurements may also be impacted by the other soil environmental factors, such as soil water salinity (Kodešová et al, 2011b) and temperature (Bogena et al, 2007;Evett et al, 2006;Kizito et al, 2008;Ruth and Munch, 2005;Verhoef et al, 2006), soil texture (Chandler et al, 2004;Guber et al, 2010;Kodešová et al, 2011b;Seyfried and Murdock, 2004;Wraith and Or, 1999), soil specific surface area (Skierucha, 2009), soil chemical composition and soil bulk density (Kodešová et al, 2011b;Verhoef et al, 2006) as well as other factors, such as measurement frequency which can range from 5-500 MHz (Chen and Or, 2006;Kizito et al, 2008;Seyfried and Murdock, 2004). Chandler et al (2004) refer to the need for calibration of each sensor to correct the inter-sensor variability.…”

Thermal properties of representative soils of the Czech Republic

“…deposited topsoil, which was removed before starting construction works, and redeposited subsoil material during and after construction mixed with construction waste) due to water loses when spraying water on the soil surface and/or homogenizing the soil sample. The applied method followed the procedure for calibrating soil water content sensors published by Kodešová et al (2011b). Mulch (bark chips) was also air dried and then carefully disintegrated into small fragments.…”

Evaluation of EC-5 Soil Moisture Sensorsfor Real-Time Determination of PoultryManure or Litter Moisture Content

“…It responds to the dielectric constant (ε) of a medium (soil, manure, or litter) affected by Ψ and has been tested for sensitivity to other properties such as bulk density (ρ), temperature, electrical conductivity, and pH of soils (Starr et al, 2000;Cobos, 2009;Casanova et al, 2012;Mittelbach et al, 2012;Ye et al, 2012;Qu et al, 2013). The change in ε is then reflected in electrical signal (mV) output of the sensor, which is correlated to soil Ψ through calibration procedures (Starr et al, 2000;Nemali et al, 2007;Cobos, 2009;Kodešová et al, 2011;Sakaki et al, 2011;Qu et al, 2013;Rowlandson et al, 2013). A typical calibration procedure for dielectric sensors used to measure soil Ψ has been described by Starr and Paltineanu (2002).…”