Measurements described in this paper were realized in order to find out whether there is some relationship between mass flow of plant material passing through a parallel plate capacitive sensor and its output signal. This possibility of mass flow determination could be useful for the aim of forage crops or sugar beet yield maps creation. A parallel plate capacitive throughput sensor was designed for that purpose. The capacitive sensor and the whole oscillating circuit were driven at 27 MHz frequency. The laboratory set-up consisted of a conveyer belt, carrying a measured quantity of material into sensor, equipped with an electronic measurement apparatus. Material passed through the sensor between its plates. Laboratory tests were carried out with forage crops and with sugar beet. Resulting coefficients of determination ranged from R2=0.95 to 0.97 for forage crops and around R2=0.98 for sugar beet. It was possible to conclude from our measurement that forage and sugar beet mass flow determination by means of the parallel plate capacitive sensor is a promising way. The results showed a strong linear relationship between the feed rates of plant material passing through the sensor and tested measuring capacitive sensor circuit output signal.