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The article presents the results of studies on the effect of fertilizers on the content of humus, the dynamics of nitrate nitrogen, and the amount of nitrogen fertilized with 15N, fixed in the soil during the cultivation of spring cereals in the conditions of the dry-steppe zone of the North. It was established that mineral fertilizers provided the content of humus at the level of the control variant or with a slight increase. When nitrogen fertilizers are applied against the background of presowing application of P60, the content of humus increases. The content of NNO3 increases depending on the use of nitrogen fertilizers. Against the background with the introduction of P60 before sowing, the content of N-NO3 is higher than in the absence of phosphorus fertilizers. Using the method of isotope indication, it was found that the proportion of fertilizer nitrogen that is fixed in the soil under wheat crops is lower than that of triticale. In the soil, 20-39% nitrogen fertilizer under spring wheat is fixed and 25.8-50.9% under spring triticale