The sensors for determination of potassium in soil are examined: i) medium-size ion-selective electrodes with plasticized PVC-based ion-selective membranes, hydroxyethylenecelulose-based gel as inner electrolyte and silver/ silver chloride inner electrode and ii) back-side contact miniaturized sensors with gold inner electrode, polyacrylate-based ionselective membrane and redox-active Self-Assembled Monolayer as an intermediate phase. The selectivity of sensors to potassium ion was achieved by introduction of valinomycin as ionophore into the membrane phase. Preliminary potentiometric characterization of the examined sensors confirmed their good working parameters. The sensors were applied for the analysis of soil extracts. Results revealed good reproducibility and accuracy of proposed sensors, indicating their successful usage for this purpose.