In a vegetation pot experiment with non-inoculated seed stock of narrow-leaf lupine (Lupinus angustifolius, L.), we investigated the effect of NH₄NO₃ applied at different times and in various doses on changes in the level of yield-forming elements, seed yields and the content of crude protein in seeds. The experiment included four application procedures and control treatment with no nitrogen fertiliser. In the other treatments we applied nitrogen either in a single dose before sowing or in three split doses. In the latter case nitrogen was applied before sowing, after emergence and during flowering. The treatments resulted in a significant increase in the number of pods per plant (40 %), number of seeds in pods (78.6 %), the 1000-seed weight (55.9 %) and, therefore, higher seed yields per plant (286.3 %) compared with the control treatment. With increasing nitrogen doses, its content in plants during flowering increased to 3.00–3.26 %. The content of crude proteins in seeds during harvest increased linearly from 20.75 % to 42.18 %, thus increasing their nutritional quality.