The electrical conductivity of several rock meal based fertilizers with expressed ISR activity, measured as voltage dropping when their distilled water solution was affected with low – voltage electric currents of 5 volts (DC and AC) was examined. For comparison, hard and soft tap water (with 196 and 65 ppm CaCO3 hardness), 1% distilled water solutions of NaCL and CuSO4.5H2O solution and 0.1% solution of organosilicone surfactant were also tested in the conducted trials. The result shows that hard water, solutions of NaCL and CuSO4.5H2O and solutions of fertilizers with fulvic acids content can cause drops in the voltage of electric currents. The same results were received for the fertilizer on the basis of K2O, SiO2, Cu, although other products with similar content do not cause a voltage decrease. There were no differences in the conducted tests between the DC and AC electric currents.
Keywords: fertilizers, ISR, electricity, voltage, water hardness