Effect of temperature and salinity on substrate moisture measurements made with dielectric soil sensors

J. Ochoa, J. Miralles, D. Bañón, S. Bañón
The influence of substrate temperature on the output readings of the EC5 and GS3 dielectric soil sensors was studied. For this, an experiment with pots filled with coconut fiber and no plants was carried out in a growth chamber. Five levels of pore water electrical conductivity (ECp) (1.6, 5, 10, and 15 dS m‑1) and four volumetric water content (VWC) (13, 27, 41 and 51%) were investigated. The chamber was programmed to provide temperatures from 5 to 45°C. The outputs of the EC5 (voltage) and the GS3 (temperature and bulk dielectric permittivity, εb) were recorded every 5 min. Significant linear relationships between temperature and voltage, and between temperature and εb, were determined. The voltage increased linearly with the temperature at low salinity (1.6 dS m‑1) for the four VWC levels. This could cause an overestimation of the VWC when comparing measurements made above 25°C with respect to those made below this threshold. However, for GS3 temperature reduced the εb linearly, resulting in the opposite effect to that described for EC5. Under high moisture (51% VWC), the negative slope of the temperature-εb linear adjustment switched to positive due to salinity, while the effect of temperature on the voltage and εb was higher as the ECp increased. The latter could lead to larger VWC calculation errors depending on the temperature, particularly under high salinity; to minimize the error, voltage and εb could be corrected at a temperature of 25°C. Salinity increased both εb and voltage at any temperature. This effect was greater under high salinity, encouraging the overestimation of the VWC. Thus, water with an EC similar to the expected in our substrate will be needed to make an appropriate calibration equation.
Ochoa, J., Miralles, J., Bañón, D. and Bañón, S. (2020). Effect of temperature and salinity on substrate moisture measurements made with dielectric soil sensors. Acta Hortic. 1279, 125-130
DOI: 10.17660/ActaHortic.2020.1279.19
pot plant, irrigation, substrate humidity, soil probes

Acta Horticulturae