The studies were conducted on podzolic soil belonging to a good rye complex with good phosphorus availability, low potassium and magnesium. Humus content was maintained at 1.09% level. The experiment was carried out according to the split-block arrangement combined with a split-plot one. Throughout the experiment 22 species of short-term weeds and 3 perennial species appeared in a lentil canopy. The number of weed species proved to be higher in crop rotation (23) than in monoculture (22). Full soil tillage limited the biodiversity of the species occurring in both, crop rotation and monoculture. Cropping systems, soil tillage methods and the experiment length differentiated the weed number and the air dry mass in a lentil canopy individually in a significant way. Both, the weed number and mass were higher in crop rotation and at the objects with simplified soil tillage. The number and mass of weeds appearing in crop rotation was higher by around 60% comparing to monoculture. The number of weeds in the plots with simplified soil tillage turned out to be higher by 33%, while their mass by 45% as compared to the objects of full cultivation.