J. Jpn. Soc. Soil Phys. No. 126, p (2014) ECH 2 O 1 2 Calibration of the capacitance type of ECH 2 O soil moisture sensors Shoichi MITSUISHI 1 a

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1 J. Jpn. Soc. Soil Phys. No. 126, p (2014) ECH 2 O 1 2 Calibration of the capacitance type of ECH 2 O soil moisture sensors Shoichi MITSUISHI 1 and Masaru MIZOGUCHI 1 Abstract: Volumetric water contents, θ, measured with various type of ECH 2 O soil moisture sensors (5TE, 5TM, EC-5, 10HS, ECH 2 O-TE, EC-TM) were evaluated for Toyoura sand, Andisol and Kanto Loam soils in Japan. The calculated value of ECH 2 O sensors reasonably estimated volumetric water contents for sand but underestimated for Andisol and Kanto Loam. It is necessary to independently calibrate the relationship between θ and ε obtained from each sensor for accurate measurements of θ for Japanese volcanic ash soils such as Andisol and Kanto Loam. The soil water content measurements could be improved by using the calibrated third regression equation with the determination coefficient more than Key Words : ECH 2 O soil moisture sensor (EC-5, 10HS, 5TE, 5TM, EC-TE, EC-TM), Toyoura Sand, Andisol, Kanto Loam, calibration 1. Decagon Devices, Inc. ECH 2 O Soil Moisture Sensor Decagon Em50 ECH 2 O ECH 2 O Decagon Topp Topp et al., 1980 ECH 2 O Topp, Decagon Decagon Topp, 1998;, 2000 Herkelrath et al., 1991 ECH 2 O 1 AINEX. Co., LTD. Minami Kamata , Ohta-ku, Tokyo, , Japan. Corresponding author 2 Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo , Japan ECH 2 O ECH 2 O ECH 2 O ECH 2 O Decagon Devices, Inc. 5TE, 5TM, EC-5, 10HS, ECH 2 O-TE EC-TE EC- TM Table 1 θ ε 5TE, 5TM Topp EC-5, 10HS, EC-TE, EC-TM Decagon EC 4 EC-TE 2 5TE T Em50 Decagon Devices, Inc. Em50 ECH 2 O Utility Ver.1.65, Decagon Devices, Inc , : cm : cm Table 2 JISA C 6 2 mm

2 (2014) Table 1 ECH 2 O Characteristic of ECH 2 O soil moisture sensors. Sensor cm 5TE θ C Topp EC-TE EC ds m 1 Decagon (Mineral) 5TM θ Topp C EC-TM Decagon (Mineral) EC Decagon (Mineral) 2 θ 10HS Decagon (Mineral) Table 2 Physical properties of sample soils. Soil Sand % Silt % Clay % % Sand Loam Clay Loam 12.5 Fig. 1 Experimental apparatus ECH 2 O ε ECH 2 O Cobos, 2008a Cobos, 2008b 3 EC cm 5TE, 5TM, EC-TE, EC-TM cm 10HS cm Fig. 1 1 mm 8 12 ECH 2 O 105 C C 24 3 θ s Mg m Mg m Mg m 3 θ Topp and Ferré, 2002 θ = ω ρ d ρ w (1) θ m 3 m 3 ω kg kg 1 ρ d Mg m 3 ρ w Mg m 3

3 ECH 2 O ECH 2 O Em50 ECH 2 O Utility θ ECH 2 O ε ECH 2 O 2.4 θ ECH 2 O RMSE Lu et al., 2004 RMSE = n i=0 (θ M θ ECH2 O) 2 θ M θ m 3 m 3 θ ECH2 O m 3 m 3 n n 3. (2) Fig. 2 5TE Relationship between the dielectric constant of 5TE and the volumetric water content of soil samples. Numbers in the figure mean the dry bulk density (Mg m 3 ) of the soil sample. 3.1 ECH 2 O Fig. 2 5TE ε θ θ ε θ > 0.7 m 3 m 3 θ ε 5TE ECH 2 O ε TDR 3.2 ECH 2 O ε θ Fig. 3 Fig. 4 ε ε ε TE, 5TM θ < 0.15 m 3 m 3 θ > 0.15 m 3 m 3 10HS EC-5, EC-TE, EC-TM θ < 0.40 m 3 m 3

4 (2014) Fig. 3 ECH 2 O 5TE 5TM EC-5 Infiltration Method Air dry Method Dielectric constant of 5TE, 5TM and EC-5 as a function of volumetric water content for all investigated soils. The open circle in the figure shows the measurement value of the saturated water content sample. The arrow in the figure of Loam and Andisol indicates that the moisture content adjustment method was different (Upper: Infiltration Method, Under: Air dry Method). θs 0.40 m 3 m 3 ECH 2 O θ < 0.10 m 3 m 3 θ > 0.10 m 3 m m 3 m 3 < θ < θs 5TE 5TM 0.60 EC HS 0.55 EC-TE EC-TM 0.75 RMSE m 3 m 3 Table m 3 m 3 Table m 3 m 3 Table 8 Topp 5TE 5TM θ Miyamoto et al., 2003 EC-5, 10HS, EC-TM θ = 0 EC-5,10HS θ < 0.10 m 3 m 3 EC-TM θ < 0.10 m 3 m 3 Decagon

5 ECH 2 O 67 Fig. 4 ECH 2 O 10HS EC-TE EC-TM Infiltration Method Air dry Method Dielectric constant of 10HS, EC-TE and EC-TM as a function of volumetric water content for all investigated soils. The open circle in the figure shows the measurement value of the saturated water content sample. The arrow in the figure of Loam and Andisol indicates that the moisture content adjustment method was different (Upper: Infiltration Method, Under: Air dry Method). θ θ 3.3 ε θ Topp 3 Fig. 3 Fig. 4 R 2 Table 3, Table 4, Table 5 θ s 0.95 RMSE m 3 m m 3 m 3 Table m 3 m m 3 m 3 Table m 3 m m 3 m 3 Table ECH 2 O Fig. 5 ECH 2 O 3 ε EC-TE EC-TM θ > 0.2 m 3 m 3 θ < 0.3 m 3 m 3 θ > 0.5 m 3 m 3 θ < 0.3

6 (2014) Table 3 Regression coefficient of Sand. θ= a ε 3 b ε 2 c ε d Sensor a b c d R 2 5TE TM EC HS EC-TE EC-TM Table 4 Regression coefficient of Andisol. θ= a ε 3 b ε 2 c ε d Sensor a b c d R 2 5TE TM EC HS EC-TE EC-TM Table 5 Regression coefficient of Kanto Loam. θ= a ε 3 b ε 2 c ε d Sensor a b c d R 2 5TE TM EC HS EC-TE EC-TM m 3 m 3 θ > 0.5 m 3 m 3 ε ε ECH 2 O ε 4. Decagon 6 ECH 2 O 5TE, 5TM, EC-5, 10HS, EC-TE, EC-TM ε θ ECH 2 O θ θ ε θ ECH 2 O ε ECH 2 O ε θ

7 ECH 2 O 69 Table 6 (θ) (RMSE) Accuracy (RMSE) of the calculated value of the Standard and Regression equation in comparison with volumetric water content of Sand. RMSE (m 3 m 3 ) Sensor Standard Eq. Regression Eq. 5TE TM EC HS EC-TE EC-TM Table 7 (θ) (RMSE) Accuracy (RMSE) of the calculated value of the Standard and Regression equation in comparison with volumetric water content of Andisol. RMSE (m 3 m 3 ) Sensor Standard Eq. Regression Eq. 5TE TM EC HS EC-TE EC-TM Table 8 (θ) (RMSE) Accuracy (RMSE) of the calculated value of the Standard and Regression equation in comparison with volumetric water content of Kanto Loam. RMSE (m 3 m 3 ) Sensor Standard Eq. Regression Eq. 5TE TM EC HS EC-TE EC-TM Fig. 5 ECH 2 O 5TE, 5TM, EC-5, 10HS, EC-TE, EC-TM Regression curve of ECH 2 O soil moisture sensors (5TE, 5TM, EC-5, 10HS EC-TE, EC-TM) by soil sample.

8 (2014) Cobos, D. (2008a): EC-5 Volume of Sensitivity. decagon.com/education/ec-5-volume-of-sensitivity an/ (accessed: 20/08/2013). Cobos, D. (2008b): 10HS Volume of Sensitivity. decagon.com/education/10hs-volume-of-sensitivity an/ (accessed: 20/08/2013). Decagon Devices, Inc. (2012): 5TE Water content, EC and Temperature Sensors Operator s Manual Version 8. decagon.com/education/5te-manual/ (accessed: 20/08/2013). Decagon Devices, Inc. (2010): 5TM Water content and Temperature Sensors Operator s Manual Version 0. com/education/5tm-manual/ (accessed: 20/08/2013). Decagon Devices, Inc. (2012): EC-5 Soil Moisture Sensor Operator s Manual Version 2. manual/ (accessed: 20/08/2013). Decagon Devices, Inc. (2010): 10HS Soil Moisture Sensor Operator s Manual Version 3. (accessed: 20/08/2013). Decagon Devices, Inc. (2008): ECH 2 O-TE/EC-TM Water content, EC and Temperature Sensors Operator s Manual Version O-te-and-ec-tmmanual/ (accessed: 20/08/2013). Herkelrath, W.N., Hamburg, S.P. and Murphy, F. (1991): Automatic, real-time monitoring of soil moisture in a remote field area with time domain reflectometry. Water Resour. Res., 27: Topp, G.C., David, J.L. and Annan, A.P. (1980): Electromagnetic determination of soil water content: Measurement in coaxial transmission lines. Water Resour. Res., 16(3), Topp, G.C. and Ferré, P.A. (TY) (2002): 3.1 Water content: General information. Method of Soil Analysis. Part 4. Physical Methods. p.417. Soil Science Society of America, Madison, WI., (1998) :., 194: , (2000) :., 206: Miyamoto, T., Annnaka, T. and Chikushi, J. (2003): Soil aggregate structure effects on dielectric permittivity of an Andisol measured by time domain reflectmetry. Vadose Zone J., 2: Lu, D., Shao, M., Horton, R. and Liu, C. (2004): Effect of changing bulk density during water desorption measurement on soil hydraulic properties. Soil Sci., 169: Decagon Devices, Inc. 6 ECH 2 O 5TE 5TM EC-5 10HS ECH 2 O-TE EC-TM θ ECH 2 O θ θ θ ε m 3 m m 3 m m 3 m m 3 m m 3 m m 3 m 3 ECH 2 O θ θ ε θ ECH 2 O 5TE, 5TM, EC-5, 10HS, ECH 2 O-TE, EC-TM

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