In a pot experiment, carried out in three series in years 2010-2012 at the greenhouse laboratory of the University of Warmia and Mazury in Olsztyn, the effect of Persian clover undersown and plant density on the morphological characteristics of spring wheat was evaluated. Experimental factors were as follows: I) spring wheat (Triticum aestivum ssp. vulgare L.) sowing method: pure sowing and with Persian clover (Trifolium resupinatum L.) undersown, II) density of both species in agreement with the recommendations of agrotechnics (called “higher” in the present work) and lowered by 20% (called “lower”). In the pots of 22 cm in diameter, the following plants were sown: in the pots with higher density, 19 spring wheat grains and 12 seeds of Persian clover, and in the pots with lower density, 12 wheat grains and nine clover seeds. Measurements were undertaken at the following developmental stages of wheat (the BBCH scale): leaf development (12-14), tillering (21-23), straw shooting (31-32), earing (54-56), and ripening (87-89). The studied factors were: plant height, root length, number of straws per plant, leaf parameters (area, length, and width), spike parameters (length, grain number, and mass), and grain yield per pot. The studies demonstrated that undersown diversified plant height and straw number in spring wheat. Its roots in the combination with clover were shorter than in pure sowing only during earing. In the presence of undersown, wheat developed fewer leaves (by nearly 10%), shorter spikes (by 10%) with fewer grains (by 15.7%) of lower mass (by 28.6%) and smaller yield (by 29.7%). Sowing method, depending on the developmental stage, differently affected leaf parameters. Plant density had no effect on the scope of the differences between pure and mixed sowings in the morphology of the vegetative above-ground parts and roots of spring wheat. In the pots with higher density, mixed sowing limited spike length and grain number and mass more than in the pots with lower density.

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