Evaluation of a multi‐sensor for measuring solution electrical conductivity in coir

The simultaneous measurements of both volumetric water content (θ) and electrical conductivity of pore solutions (ECw) are essential for nutrient solution management within soilless culture systems. The present study was carried out in order to evaluate a capacitance sensor (METER 5TE) for the measurement θ and ECw within coir. Following the evaluation of the spatial sensitivity of the 5TE sensor, a calibration experiment was executed with six levels of θ (0.30, 0.35, 0.40, 0.45, 0.50, and 0.55 m3 m−3) and four levels of KCl solutions (1.0, 3.0, 5.0, and 7.0 dS m−1). The measured relationship between θ and dielectric permittivity (εa) for coir significantly deviated from Topp's equation for organic soil, but was similar to the calibration equation for growing media from the sensor manufacturer and for peat soils. The Hilhorst (2000) model recommended by the manufacturer overestimated ECw within coir. On the other hand, accounting for EC dependency on the real part of the complex dielectric permittivity of the solution within the Hilhorst model will greatly improve ECw prediction. In contrast, the Rhoades (1976) model was more capable of describing the dependence of the apparent soil electrical conductivity (ECa) on θ and ECw for the coir samples for ECa