In a jar experiment, implemented according to the additive pattern on a medium soil with standard fertilization and NPK fertilization increased by 50%, the competitive influence occurring between spring wheat and spring barley was investigated. The influence was assessed on the basis of plant height, number of stems and leaves, length of heads, number of grains per head, and grain yield. The experiment was carried out in three cycles during the years 2003-2004, considering five periods determined by the development cycle of spring barley as pure crop, i.e. during the phases of seedling growth (according to Zadoks 10-13), tillering (25), stem elongation (37), inflorescence emergence (55) and ripening (87-91). It was shown that joint cultivation of both cereals had a negative influence on their morphological characteristics and grain yield. That situation was better visible in generative parts and less visible in vegetative ones. In the case of wheat, a larger reduction in the number of leaves and grains per head was recorded in the environment more abundant with NPK, while the head length in the less abundant one. In the case of the mix, the influence of soil abundance with NPK on the studied characteristics of barley was more ambivalent.