This study estimated the amount of nitrogen taken up by spring triticale from different sources depending on varied nitrogen fertilization and the development phase when the previous crop – yellow lupine was harvested. Lupine was cultivated in three fertilization variants: without nitrogen fertilization and after the application of rates 30 kg·ha^-1 N and 150 kg·ha^-1 N. Lupine harvest was performed in full flowering and full maturity phases. At the first harvest time, the whole biomass was introduced into soil. At the second time, seeds were collected and the other parts of lupine were introduced into soil. Spring triticale as a successive crop was cultivated without additional fertilization with nitrogen and harvested in the full maturity phase. Ammonium sulfite enriched in nitrogen ¹⁵N isotope was used in the study as well as the method of isotopic dilution. The highest yield of grain and the whole biomass as well as the total amount of nitrogen taken up by triticale were obtained after the application under lupine of 150 kg·ha^-1 N. Yields and nitrogen uptake by triticale were higher when the previous crop was harvested in flowering than in full maturity. Nitrogen content in triticale grain and biomass was not dependent on the harvest phase and nitrogen fertilization of the previous crop. Proportion of nitrogen taken up by triticale from soil resources, from parts of lupine introduced into soil and from mineral fertilizer applied under lupine amounted to 71,0; 17,2 i 11,8%, respectively, of the total amount of this macroelement accumulated in the biomass. Triticale took up on average 20.9% of biologically reduced nitrogen introduced into soil with the lupine biomass.

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