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. We also wanted to establish the most favorable time to evaluate the values of applied methods (March, July and October). On the basis of established correlation dependences, the plant and soil parameters, either from pots or fields should be used to evaluate the reliability of the hot water method and the reliability of mentioned methods can be estimated in March, July and October. As for the evaluation of easily hydrolyzing nitrogen, we can use both plant and soil parameters in controlled conditions and in the field and the most suitable time is in spring (March) and in fall (October).