Level of harvest of agricultural crops in sod-podzolic soil determines the nitrogen. Thus, the aim of our research was to study the influence of nitrogen fertilizer on soil mineral nitrogen supply in plow layer when cultivating spring barley аnd its yield. To achieve the aim, it was necessary to solve the following tasks: to determine dynamics of mineral nitrogen in plow layer; to reveal dependence of soil mineral nitrogen supply on the dose of nitrogen fertilizer; to determine the ability of sod-podzolic soil to mineralize nitrogen and to establish a relationship of spring barley yields of nitrogen nutrition conditions. The following research was carried out in the Republic of Mari El with the help of field trial method and laboratory analyses in accordance with standard and recommended procedures. Conditions of nitrogen nutrition were studied in connection with phosphate-potassium fertilizer and were determined by doses and times of nitrogen fertilizer application. Nitrogen fertilizer was used in the doses of 30–120 kg/ha, with the interval of 30 kg/ha of active material. The fertilizer was applied fully and in parts. As a result, it is stated that soil mineral nitrogen supply when cultivating spring barley in taiga-forest zone depends on the dose of mineral nitrogen fertilizer and does not depend on time of application, it is redundant to use fertilizing of 30 kg/ha of active material at the tillering phase. Increasing doses of nitrogen fertilizer at the tillering phase increase supplies of nitrogen in plow layer from 7,5 to 73,7 kg/ha, by the end of vegetation these supplies decrease to 7,4 … 30,0 kg/ha. The quantity of mineralized soil nitrogen is 49,9 kg/ha when cultivating barley after winter rye in sod-podzolic soil in the layer 0–40 cm. Stated dependence of soil mineral nitrogen on the dose of nitrogen fertilizer allows to forecast provision of spring barley with this nutrient during vegetation period. A positive effect of increasing doses of nitrogen fertilizer on the feeding conditions of spring barley plants and its yield has been established. Increasing doses of nitrogen fertilizer up to N90 contribute to an increase of barley grain yield (increase of 1. 38 t / ha). Further increase in the dose does not increase the yield. Crushing dose of nitrogen fertilizer reduces its return on grain. The most effective dose is the N60, since its application to get the maximum payment (19,7 kg per 1 kg of nitrogen).