In pot experiment, carried out according to the additive pattern on medium soil fertilized with standard and 50% higher dose of NPK, the effect of competitive interactions between spring wheat and spring barley was estimated on nitrogen accumulation in the above-ground mass, with the distinction of stems, leaves, and spikes. Studies included three series, which were carried out in years 2003-2004 in five periods set by the rhythm of development of barley in pure sowing, namely in phases: emergence (BBCH 10-13), tillering (23), straw shooting (32), earing (55), and ripening (87-89). In a mixture, both cereals accumulated less nitrogen in the above-ground mass than in pure sowing starting from the tillering phase until the end of growth. In wheat, the decrease to a similar degree included straws, leaves and spikes, and in barley during earing it was more clearly marked in straws and leaves, and during ripening in spikes. Doses of mineral fertilization with NPK had no effect on nitrogen accumulation by barely and wheat grown in pure and mixed sowing. Competition for nitrogen between cereals started in the tillering phase and grew until the earing phase, after which it decreased slightly. Almost in the entire period of common growth, barley demonstrated to be a stronger competitor than wheat in nitrogen gaining. On bedding richer in NPK, competitive interactions between barely and wheat were more intensive than on poorer one.

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