The aim of the research conducted on mixed rendzina soil (belonging to bonitation class IIIb and to defective wheat complex) in the Experimental Farm Bezek located near Chełm (51°19’ N; 23°25’ E) was to study the influence of 3-year crop rotation with the part of winter rape being 33, 66 and 100%, as well as of its different row spacing (25 and 33 cm) on the number, mass and species composition of weeds. Air dry mass of weeds in a winter rape canopy was not significantly modified by the part of rape in the crop rotation. However, significantly higher number of monocotyledonous weeds and weeds in total was noted in the rape grown at wider row spacing (33 cm). Papaver rhoeas L. was the predominant taxon constituting major mass of the weed infestation. The number of plants of this species was the greatest in the rape grown in monoculture as well as on plots with wider row spacing.

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