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On the Accuracy of Factory-Calibrated Low-Cost Soil Water Content Sensors

1
Program of Efficient Use of Water in Agriculture, Institute of Agrifood Research and Technology (IRTA), Parc de Gardeny (PCiTAL), Fruitcentre, 25003 Lleida, Spain
2
Institute of Bio- and Geosciences, Agrosphere Institute (IBG-3), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
*
Author to whom correspondence should be addressed.
Sensors 2019, 19(14), 3101; https://doi.org/10.3390/s19143101
Received: 26 June 2019 / Revised: 10 July 2019 / Accepted: 11 July 2019 / Published: 13 July 2019
(This article belongs to the Collection Sensors in Agriculture and Forestry)
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Abstract

Soil water content (SWC) monitoring is often used to optimize agricultural irrigation. Commonly, capacitance sensors are used for this task. However, the factory calibrations have been often criticized for their limited accuracy. The aim of this paper is to test the degree of improvement of various sensor- and soil-specific calibration options compared to factory calibrations by taking the 10HS sensor as an example. To this end, a two-step sensor calibration was carried out. In the first step, the sensor response was related to dielectric permittivity using calibration in media with well-defined permittivity. The second step involved the establishment of a site-specific relationship between permittivity and soil water content using undisturbed soil samples and time domain reflectometry (TDR) measurements. Our results showed that a model, which considered the mean porosity and a fitted dielectric permittivity of the solid phase for each soil and depth, provided the best fit between bulk permittivity and SWC. Most importantly, it was found that the two-step calibration approach (RMSE: 1.03 vol.%) provided more accurate SWC estimates compared to the factory calibration (RMSE: 5.33 vol.%). Finally, we used these calibrations on data from drip-irrigated almond and apple orchards and compared the factory calibration with our two-step calibration approach. View Full-Text
Keywords: soil water content; 10HS sensor; calibration; sensor variability; specific calibration; CRIM model soil water content; 10HS sensor; calibration; sensor variability; specific calibration; CRIM model
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Domínguez-Niño, J.M.; Bogena, H.R.; Huisman, J.A.; Schilling, B.; Casadesús, J. On the Accuracy of Factory-Calibrated Low-Cost Soil Water Content Sensors. Sensors 2019, 19, 3101.

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