Real-Time Monitoring of Electroconductivity in Plants with Microscale Needle Probes

Abstract

In plant studies, electrical properties such as the conductivity and resistance are used for measuring the health of a plant or controlling the salinity of a nutrient solution. In recent years, continuous efforts have been undertaken to determine the state of a plant and establish an optimal growth environment by measuring the internal ion concentration of the sap, in plant horticulture. In this paper, we present a needle-shaped measurement sensor for measuring the internal electrical conductivity of a plant. The needle-sensor is targeted at horticultural plants such as cucumber, tomato, and paprika. As horticultural crops have small stem diameters and xylem areas, a minimally invasive measurement approach and measuring electrodes with small form factors are required. The proposed needle sensor has microscale width electrodes and a hundreds-of-microscale-width needle, enabling local measurement with minimal invasion. The interdigitated electrode was optimized to measure higher range of electrical conductivity (12.8 mS/cm) of horticultural plants through frequency sweeping analysis. The laboratory-proven sensors were applied to greenhouse-grown cucumbers and the ionic concentrations were monitored during the day and at night, in real time. Results indicate peculiar periodic pattern of electrical conductivity variation with respect to time occurring in the plant xylem.