Capacitance type sensors have been widely used to monitor soil water content and salinity, but little is known about their response to specific ions in soil solution. The goal of this laboratory study was to investigate the sensitivity of two capacitance probes, ECH2O EC-5 and EC-10, to NO3 concentration in soil solutions, as well as to understand the differences in sensor response to the presence of other ions in the solutions. Forty-five uniformly packed soil samples were prepared using a homogenized loam soil wetted to five volumetric water contents (VWC) with nine solutions containing different concentrations of NO3-, Cl-, or both. A two-stage analysis of the normalized data revealed that ion type and concentration had a significant effect (P ~ 0.01) only for the response of the EC-10 probes operating at a frequency of 5 MHz. The response of the EC-5 probes, operating at 70 MHz, was mainly explained by changes in VWC. Multiple linear regression models fitted to the EC-10 response to individual solutions showed that concentration had a statistically significant predictive value only for samples wetted with NO3 solutions when temperature was incorporated in the model. The study confirmed that capacitance probes operating at a relatively low frequency of 5 MHz are more sensitive to changes in NO3 concentration than in Cl. We attributed this effect to the difference in ion mass that manifests through an increase in conductivity at ion-specific frequency. Additional experimental work is needed, however, to accurately define optimal frequencies for measuring ion-induced effects on dielectric measurement and to quantify interrelations between them. [ABSTRACT FROM AUTHOR]