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.

The effect of different densities of Italian ryegrass (Lolium italicum L.: G₁- 5 kg/ha seeds, 60 cm row spacing; G₂- 5 kg/ha seeds, 20 cm row spacing; G₃- 20 kg/ha seeds, 60 cm row spacing, and G₄- 20 kg/ha seeds, 20 cm row spacing) and different rates of applied nitrogen fertilizer (N₁- 0 kg N/ha; N₂ - 50 kg N/ha; N₃- 100 kg N/ha and N₄-150 kg N/ha) on SPAD values under interaction between the crop and cleavers (Galium aparine L) was investigated.

In this experiment we used brown forest soil that has been used in long-term experiments, for 30 years, with increasing doses of introduced nitrogen fertilizer in variants. In order to determine the quantities of nitrogen fertilizer required for wheat, a calculation model has been applied.

Our research has been made on brown forest soil that is used in long-term experiments. The soil we used had a certain crop rotation (wheat-corn) and had been fertilized according to a certain system for 30 years. In the experiment, quantities of nitrogen fertilizers were gradually increased after which samples were taken from 0 to 30 cm depths in order to establish plant and soil parameters for assessing the applied methods. Two experiments were made: one in the field and one in a controlled environment.

In this paper investigations were carried out on two soil types (vertisol and brown forest soil) with different doses of applied N-fertilizer: diameter, N₆₀; N₉₀; N₁₂₀ and N₂₅₀. The potential ammonification in soil was obtained by arginine method. The following properties of soil were determined: pH value organic C, available NH₄-N and mobile-Al. The pH value in vertisol was 3.75-4.07; mobile-Al was 0.67-4.90 mg/100g; % organic C 1.38-1.46 and the content of available nitrogen was 4.4-11.2 ppm.