Based on a 3-year pot experiment carried out according to an additive design, the effect of competitive effect of red clover and water deficit was studied on morphological traits of spring barley (length of the root, shoot and ear, total and productive tillering, leaf number and grain number per ear). The experimental factors included: level of substrate moisture and sowing method. Two levels of moisture were used: the one which met plants’ requirements, and one reduced by 50%. The plants were sown in a pure stand (18 plants of spring barley per pot) and in a mixed stand (18 plants of spring barley with 8 plants of red clover per pot). Biometric measurements were conducted in five development stages determined by the growth rhythm of barley in pure sowing with a higher water dose, i.e. in the stages of (BBCH scale): leaf formation (10-13), tillering (22-25), shooting (33-37), ear formation (52-55) and maturation (87-91). It was indicated that common cultivation of spring barley with red clover had no effect on the analyzed morphological traits of this cereal throughout the whole growing season. On the other hand, water deficit in the substrate resulted in a reduction in cereal growth in tillering-maturation stages, in the formation of a lower number of leaves (tillering-shooting) and in a poorer total and productive tillering. Water stress also caused formation of shorter ears with a lower number of grains filling them. Competitive effect of red clover amplified with water deficit resulted in the reduction in the number of productive shoots in barley. No effect of experimental factors was found on the root length in the initial growth stages (leaf formation-tillering).

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