A four-electrode conductivity sensor and associated electronics were designed and applied to the continuous monitoring of conductivity and the rate of K+ and NO-3 uptake in a hydroponic system. The new device was successfully used to monitor continuously the depletion rate of K+ and NO-3 in a hydroponic solution in which tomato plants (Lycopersicon esculentum cultivar 'Naama') were cultivated. A model is proposed for estimating the rate of K+ and NO-3 uptake by the plant, and their total concentration, from conductivity measurements. Experimental results verify the proposed mathematical criterion for choosing the initial concentrations of K+ and NO-3, and validate the underlying assumption of the proposed model.
- four-electrode conductivity system