The researches were performed on brown forest soil used within stationary experiment with a certain fertilizing system for more than 40 years. Researches were made on experiment variants where the increasing dosage of nitrogen fertilizer was applied. The aim of the research was to establish which plant and soil parameters (pots and/or field) might be considered reliable to evaluate values of applied chemical methods (hot water method and easily hydrolyzing nitrogen), being methods used to evaluate potentially mineralized nitrogen in soil.